ELECTROSTATIC AND ELECTROMAGNETIC
EFFECTS OF OVERHEAD TRANSMISSION LINES
-
RURAL ELECTRIFICATION ADMINISTRATION
N
0
UNITED STATES DEPARTMENT OF AGRICULTURE
TABLE OF CONTENTS
I
-.
CHAPTE.S
.
I
PAGE
SUMMARY OF OBJECT GROUND 1NG RECOMMENDATIONS
I NTRODUCT I ON
A,
1
1
C, RECOMMENDATIONS
1, LINES 230 KV AND BELOW
2, LINES 345 KV AND ABOVE
II, GENERAL DISCUSSION OF ELECTROSTATIC AND
ELECTROMAGNET1C EFFECTS
GENERAL
1, CAPACITIVE COUPLING-ELECTROSTATIC
(E/s) INDUCTION
2, INDUCTIVE COUPLING-ELECTROMAGNET I C
(E/M) INDUCTION
3. RESISTIVE COUPLING
A.
EFFECTS OF ELECTRIC CURRENTS ON THE HUMAN BODY
1. STEADY-STATE LET-GO CURRENT
2, VENTRICULAR F IBRI LLATION CURRENT
B,
III. DETAILED ANALYSIS OF ELECTROSTATIC INDUCTION
A.
'
B.
c.
-
GENERAL
1, MEDICALAND BIOLOGICAL
2. INDUCED VOLTAGE
ELECTROSTATIC EFFECTS
1. STATIONARY STRUCTURES
2, VEHICLES
- 3. PARKING LOTS AND SERVICESTATIONS
8
8
8
8
8
9
9
11
14
14
14
14
16
16
16
17
C.
D.
THEORETICAL A N A L Y S I S (E/s)
1,
2,
A N A L Y T I C A L E/S C 1 RCU IT MODEL
3
NON-ELECTRIC
4.
E L E C T R I C FENCES
NON-ELECTRIC
BUILDINGS,
ROOFS AND GUTTERS
VEHICLES
T R A N S I E N T ELECTROSTATIC I N D U C T I O N
1,
2,
Fn
FENCE CALCULATIONS
ELECTROSTATIC F I E L D TESTS
1,
FENCES
2,
3,
E,
GENERAL R E L A T I O N S H I P S
THEORETICAL ANALYS IS
F l E L D TESTS
MEASURES TO REDUCE ELECTROSTATICALLYINDUCED VOLTAGES
1,
2.
3,
IV,
M O D I F Y L I N E DESIGN
STATIONARY STRUCTURES
VEHICLES
DETAILED ANALYSIS OF ELECTROF!AGNETIC INDUCTION
A,
GENERAL
In
E/M COUPLING PARAMETERS
2 , F A U L T CURRENT LEVELS
3, S O I L R E S I S T I V I T Y
B,
THEORETICAL A N A L Y S I S ( E/M)
1,
2,
ANALYTICAL E/M CIRCUIT
MODEL
FENCE IMPEDANCE CALCULATIONS
3,
S I M P L I F I E D THEVENIN MODEL
SHOCK CURRENT CALCULATIONS
FENCE GROUNDING CALCULATIONS
4,
5,
APPENDIX A - MATHEPMTICAL SYMBOLS
APPENDIX B - REFERENCES
x-
-
CHAPTER I
SUMMARY OF OBJECT GROUNDING RECOP!MENDATIONS
A.
INTRODUCTION
AS t r a n s m i s s i o n l i n e v o l t a g e s and c u r r e n t s i n c r e a s e , p o s s i b l e problems
a s s o c i a t e d w i t h e l e c t r o s t a t i c (E/S) and e l e c t r o m a g n e t i c (E/M) c o u p l i n g
between overhead a l t e r n a t i n g c u r r e n t t r a n s m i s s i o n l i n e s and conductive
objects increase.
E l e c t r o s t a t i c a l l y - i n d u c e d v o l t a g e s a r e p o s s i b l e when
a conductive o b j e c t i n s u l a t e d from ground is i n t h e v i c i n i t y of overhead l i n e s . S i m i l a r l y , e l e c t r o m a g n e t i c i n d u c t i o n e f f e c t s a r e p o s s i b l e
when t r a n s m i s s i o n l i n e phase conductors c a r r y i n g f a u l t c u r r e n t s cause
induced v o l t a g e s a t t h e open ends of an i n s u f f i c i e n t l y grounded conductive object,
I f t h e conductive o b j e c t i s n o t a d e q u a t e l y grounded when a person o r
animal comes i n c o n t a c t w i t h i t , a c u r r e n t flows i n t h e . c o n n e c t i o n t o
ground through t h e e l e c t r i c a l body r e s i s t a n c e . O b j e c t ground i n t e r v a l s
t h a t w i l l reduce t h e E / S and E/M i n d u c t i o n e f f e c t s a r e based on t h e
maximum a l l o w a b l e shock c u r r e n t p a s s i n g through a person o r animal
when touching t h e conductive o b j e c t .
For t h e E / S c a s e , a s t e a d y s t a t e
shock c u r r e n t magnitude of f i v e milliamperes i s b e i n g c o n s i d e r e d a s
t h e maximum " l e t r g o " l e v e l i n t h e proposed r e v i s i o n of P a r t 2 of t h e
National E l e c t r i c a l S a f e t y Code. Other p r a c t i c a l c o n s i d e r a t i o n s may
d i c t a t e t h a t t h e shock c u r r e n t magnitude be k e p t below t h e one milliamp e r e " t h r e s h o l d o f p e r c e p t i o n " l e v e l . For t h e E/M c a s e , recommended
o b j e c t grounding i n t e r v a l s a r e based on a 50 k i l o g r a m (110 pound)
person e x p e r i e n c i n g no more than a 0.5 p e r c e n t p r o b a b i l i t y of "vent r i c u l a r f i b r i l l a t i o n " ( s e e Chapter 11). D e t a i l e d a n a l y t i c a l methods
i n Chapters 11, I11 and I V a r e employed i n d e t e r m i n i n g t h e e f f e c t s of
E/S and E/M i n d u c t i o n on conductive o b j e c t s . F i e l d t e s t d a t a of seve r a l i n v e s t i g a t o r s a r e a l s o included t o v e r i f y t h e t h e o r e t i c a l calculations.
B.
PURPOSE
The purpose of t h i s b u l l e t i n i s t o provide guidance, s u g g e s t i o n s and
recornendations f o r minimizing t h e e l e c t r o s t a t i c and e l e c t r o m a g n e t i c
i n d u c t i o n e f f e c t s on conductive o b j e c t s i n t h e v i c i n i t y of overhead
transmission l i n e s .
C.
RECOMMENDATIONS
The recommendations o u t l i n e d below a r e c o n s e r v a t i v e and adequately
minimize t h e e l e c t r o s t a t i c and electromagnetic e f f e c t s on conductive
o b j e c t s i n t h e v i c i n i t y of overhead t r a n s m i s s i o n l i n e s .
1.
Lines 2 3 0 kV and Below
(a)
E l e c t r o s t a t i c (E/S)
Case
A s a g e n e r a l r u l e , E / S e f f e c t s should n o t b e a problem on
t y p i c a l r u r a l system t r a n s m i s s i o n l i n e s .
(b)
E l e c t r o m a g n e t i c (E/M) Case
I f c o n d u c t i v e o b j e c t s such a s f e n c e s i n t h e v i c i n i t y of
- t r a n s m i s s i o n l i n e s 230 kV and below a r e completely i n s u l a t e d
from ground, a s i n g l e point-of-contact such a s a body touch
w i l l p r e s e n t no problems s i n c e a complete c i r c u i t w i l l n o t
exist.
T h e r e f o r e , one s o l u t i o n t o minimize e l e c t r o m a g n e t i c
e f f e c t s on conductive o b j e c t s is t o e l i m i n a t e a l l p o s s i b l e
p a t h s t o ground on the conductive o b j e c t i n q u e s t i o n . Howe v e r , i f c o n d i t i o n s e x i s t i n which o b j e c t grounding can be
c o n s i d e r e d inadequate f o r t h e s p e c i f i c c a s e i n v o l v e d , a
p o t e n t i a l l y u n d e s i r a b l e s i t u a t i o n could e x i s t . I n p r a c t i c e ,
i n a d e q u a t e grounding could be t h e r e s u l t of an i n s u f f i c i e n t
number of a c t u a l p h y s i c a l grounds, p a t c h e s of t a l l g r a s s ,
bushes, branches, o r even m u l t i p l e i n s t a n t a n e o u s body c o n t a c t s .
C o n s i d e r a t i o n should t h e r e f o r e b e given t o a l l c o n d u c t i v e
o b j e c t s i n t h e v i c i n i t y of t r a n s m i s s i o n l i n e s and a d e c i s i o n
made t o d e t e r m i n e which approach w i l l b e followed e i t h e r adeq u a t e l y grounded o r completely i n s u l a t e d .
I n t h o s e c a s e s where a d e t e r m i n a t i o n i s made t h a t i n a d e q u a t e
grounding e x i s t s and t h e o b j e c t must be a d e q u a t e l y grounded,
recommended grounding i n t e r v a l s (Gf) v e r s u s f a u l t c u r r e n t s
( I f ) f o r s i n g l e line-to-ground f a u l t s a r e s p e c i f i e d i n Table
1-1 f o r f e n c e s p a r a l l e l t o t r a n s m i s s i o n l i n e s 2 3 0 kV and
below.*
For f e n c e s t h a t c r o s s t h e t r a n s m i s s i o n l i n e r i g h t of-way (ROW) a t r i g h t o r o b l i q u e a n g l e s , i t i s recommended
t h a t t h e f e n c e b e grounded a t t h e edges of t h e ROW.
2.
Lines 345 kV and Above
A s a g e n e r a l r u l e , E/S and/or E/M e f f e c t s must be c o n s i d e r e d and
minimized. While each s p e c i f i c c a s e may b e e v a l u a t e d on t h e b a s i s
of m a t e r i a l i n c l u d e d i n Chapters I1 through I V of t h i s b u l l e t i n
t h e following g e n e r a l recommendations should be adequate i n r e ducing E/S and E/M e f f e c t s of t r a n s m i s s i o n l i n e s 3 4 5 kV and above
t o acceptable l e v e l s .
*For balanced t h r e e phase f a u l t s , the induced v o l t a g e on an o b j e c t i s
minimal s i n c e t h e v e c t o r r e l a t i o n s h i p s of t h e symmetrical phase f a u l t
c u r r e n t s cancel t h e n e t E/M e f f e c t .
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(a)
E l e c t r o s t a t i c (E/S) Case
Fences, Non-Electric - Recommended grounding i n t e r v a l s f o r
non-eiectric fences p a r a l l e l t o transmission l i n e s a r e
s p e c i f i e d i n T a b l e 1-2 f o r l i n e v o l t a g e s o f 345,500 and
765 kV. For n o n - e l e c t r i c f e n c e s t h a t c r o s s t h e t r a n s m i s s i o n
l i n e right-of-way (ROU) a t r i g h t o r o b l i q u e a n g l e s , i t i s
recommended t h a t - t h e f e n c e be grounded a t t h e e d g e s of t h e
ROW.
Fences, E l e c t r i c - I n c o n j u n c t i o n w i t h t h e g r o u n d i n g i n t e r v a l s
s p e c i f i e d i n T a b l e 1-2, i t i s recommended t h a t t h e e l e c t r i c
f e n c e c h a r g e r be an U n d e r w r i t e r ' s L a b o r a t o r y approved capaci t i v e discharge type, coupled with t h e i n s t a l l a t i o n o f s e p a r a t e
60 Hz s e r i e s f i l t e r s a t t h e g r o u n d i n g l o c a t i o n s . T h i s p r o c e dure permits proper o p e r a t i o n of t h e e l e c t r i c f e n c e w h i l e
r e d u c i n g t h e 60 Hz E/S i n d u c e d v o l t a g e s from overhead t r a n s mission l i n e s t o acceptable l e v e l s . For e l e c t r i c fences t h a t
c r o s s t h e t r a n s m i s s i o n l i n e ROW a t r i g h t o r o b l i q u e a n g l e s ,
i t is recommended t h a t t h e f e n c e b e grounded and 6 0 Hz s e r i e s
f i l t e r s be l o c a t e d a t t h e e d g e s of t h e ROW.
-
B u i l d i n g s , Roofs and G u t t e r s
The grounding c r i t e r i a i n T a b l e
1-3 i s recommended f o r m e t a l l i c s u r f a c e s n e a r 345,500 and 765
kV t r a n s m i s s i o n l i n e s . T h i s g r o u n d i n g also p e r t a i n s t o a l l
b u i l d i n g s w i t h m e t a l components i n c l u d i n g r o o f s , g u t t e r s , and
downspouts
.
V e h i c l e s - It i s recommended t h a t t h e E/S e f f e c t s between
overhead t r a n s m i s s i o n l i n e s and i n s u l a t e d v e h i c l e s be minimized t o r e d u c e t h e p o t e n t i a l s h o c k c u r r e n t t o a maximum of
f i v e m i l l i a m p e r e s t h r o u g h a p e r s o n s t a n d i n g on t h e ground and
t o u c h i n g t h e v e h i c l e ( s e e C h a p t e r 111, S e c t i o n s D and F ) .
(b)
E l e c t r o m a g n e t i c (E/M) Case
A s a g e n e r a l r u l e , g r o u n d i n g f o r E/S e f f e c t : s a t i s f y t h e E/M
grounding r e q u i r e m e n t s .
However, t o minimize E/M e f f e c t s on
c o n d u c t i v e f e n c e s t h a t are i n a d e q u a t e l y grounded*, recommended
f e n c e grounding i n t e r v a l s (Gf) v e r s u s f a u l t c u r r e n t s ( I f ) f o r
s i n g l e line-to-ground f a u l t s a r e s p e c i f i e d i n T a b l e 1-4 f o r
f e n c e s p a r a l l e l t o 345 kV t r a n s m i s s i o n l i n e s . F o r f e n c e s t h a t
c r o s s t h e t r a n s m i s s i o n l i n e right-of-way (ROW) a t r i g h t o r
o b l i q u e a n g l e s , i t i s recommended t h a t t h e f e n c e b e grounded
a t t h e edges o f t h e ROW.
* I f c o n d u c t i v e f e n c e s i n t h e v i c i n i t y of 345 kV t r a n s m i s s i o n l i n e s a r e
c o m p l e t e l y i n s u l a t e d from ground, a s i n g l e p o i n t - o f - c o n t a c t s u c h as a
body t o u c h w i l l p r e s e n t no problems s i n c e a c o m p l e t e c i r c u i t w i l l n o t
e x i s t . For f u r t h e r d i s c u s s i o n s r e f e r t o C h a p t e r I , -Section C 1 (b) , and
Chapt%r I V ,
@
TABLE 1-2 NON-ELECTRIC FENCE GROUNDING INTERVALS
FOR LINE VOLTAGES 345 KV AND ABOVE (E/S CASE)
L I?lE VOLTAGE
( KV)
FENCE LATERAL DISTANCE
FROM CENTER OF ROW
(FEET)
345
500
500
765
WITIIIN 75
WITHIN 125
BETWEEN 125
WITHIN 175
765
BETWEEN 175 A N D 375 (MINI
AND
250 (MINI 1
FENCE GROUNDING
INTERVAL FOR
= 1 MA*
ISHOCK
(FEET)
FENCE GROUND] NG
INTERVAL FOR
I
= 5 MA"*
SHofl~~~)
200
150
ZOO
1,000
750
1,000
125
200
62 5
1,000
"
=
PERCEPTION THRESHOLD CURRENT LEVEL FLOWING THROUGH A PERSON
YY
=
LET-GO THRESHOLD CURRENT LEVEL FLOWING THROUGH A PERSON
TABLE 1-3 METALLIC OBJECT GROUIiDING CRITERIA
FOR L I N E VOLTAGES 345 KV AND ABOVE (E/S CASE)
L l iJE VOLTAGE
( KV)
-345
34 5
500
500
765
765
"
OBJECT tiORI ZONTAL
DISTANCE FROM OUTS IDE
PHASE CONDUCTOR (FEET)
-
MINIMUM AREA OF
METALL IC SURFACE
REQUIRING GROUNDING
(SQUARE FEET)
WITHIN 75
BETWEEN 75 AND 100 ([IN, 1
WITHIN 100
2,000
(MIM , >
2,000
BETWEEN 1 0 0 AND 150
WITHIN 130
1NSULAI'ED METALLI C OBJECT
3
i+
it
BETWEEN 130 AND 215 (MIN,)
= NO, PlINIr4UMS ARE SPECIFIED,
MINIMUM LENGTH OF
GUTTER REQUIRING
GROUNDING (FEET)
2,000
CONSIDERATION SH0I)LD BE GIVEN TO GROUNDIIVG OF ANY
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CHAPTER I 1
GENERAL DISCUSSION OF ELECTROSTATIC
AND ELECTROMAGNET1C EFFECTS
A.
GENERAL
The v o l t a g e i n d u c t i o n e f f e c t s of overhead t r a n s m i s s i o n l i n e s on
i n s u l a t e d o r i n a d e q u a t e l y grounded c o n d u c t i v e o b j e c t s a r e governed
by t h e amount of c a p a c i t i v e c o u p l i n g , i n d u c t i v e c o u p l i n g and r e s i s t i v e
c o u p l i n g from t h e l i n e t o t h e o b j e c t .
1.
C a p a c i t i v e Coupling
- E l e c t r o s t a t i c (E/s) I n d u c t i o n
E / S i n d u c t i o n e f f e c t s a r e p o s s i b l e when any o b j e c t p o s s e s s i n g
c o n d u c t i v e c h a r a c t e r i s t i c s and i n s u l a t e d from ground i s n e a r an
e l e c t r i c a l l y energized t r a n s m i s s i o n l i n e . An i n c r e a s e i n l i n e
v o l t a g e g e n e r a l l y i n c r e a s e s t h e E/S induced v o l t a g e .
2.
I n d u c t i v e Coupling
-
E l e c t r o m a g n e t i c (E/M) I n d u c t i o n
E/M i n d u c t i o n e f f e c t s may o c c u r when t r a n s m i s s i o n l i n e p h a s e
c o n d u c t o r s c a r r y i n g f a u l t c u r r e n t s c a u s e induced v o l t a g e s a t t h e
open ends of i n a d e q u a t e l y grounded conductive o b j e c t s ,
In t h i s
c a s e an i n c r e a s e i n l i n e v o l t a g e d o e s not a p p r e c i a b l y change t h e
E/M induced v o l t a g e i f t h e f a u l t c u r r e n t remains e s s e n t i a l l y t h e
same. E/M i n d u c t i o n g e n e r a l l y i n c r e a s e s a s t h e f a u l t c u r r e n t
increases.
3.
R e s i s t i v e Coupling
V o l t a g e s may a l s o e x i s t on i n s u l a t e d conductive o b j e c t s v i a
r e s i s t i v e c o u p l i n g d u r i n g f a u l t c o n d i t i o n s on power l i n e s .
R e s i s t i v e c o u p l i n g o c c u r s when a c o n d u c t i v e o b j e c t i s i n c l o s e
proximity t o a s t e e l tower f o u n d a t i o n , a s w i t c h i n g s t a t i o n o r any
o t h e r e l e c t r i c f a c i l i t y t h a t h a s an e x t e n s i v e grounding network.
If t h e o b j e c t i s n o t connected t o t h e grounding network, t h e n
when a phase-to-ground f a u l t o c c u r s on t h e e l e c t r i c a l s y s t e m , t h e
p o t e n t i a l of t h e e a r t h , a d j a c e n t t o t h e grounding network, may
i n c r e a s e considerably with r e s p e c t t o the o b j e c t ' s p o t e n t i a l .
Various s u b s t a t i o n and e l e c t r i c f a c i l i t y grounding t e c h n i q u e s
a r e e x t e n s i v e l y r e p o r t e d i n r e f e r e n c e s 11, 25, 2 8 and 32.
B.
EFFECTS OF ELECTRIC CURRENTS ON THE HZMAN BODY
When a c o n d u c t i v e o b j e c t is c o n n e c t e d t o ground t h r o u g h a p e r s o n ' s
body r e s i s t a n c e , a s h o c k c u r r e n t f l o w s t h r o u g h t h e c o n n e c t i o n i f s n
i n d u c e d v o l t a g e e x i s t s between t h e p o i n t o f c o n t a c t and ground. The
s e r i o u s n e s s o f t h i s e l e c t r i c s h o c k i s d e t e r m i n e d by t h e magnitude of
c u r r e n t f l o w i n g t h r o u g h t h e body.
C u r r e n t s o f 1 m i l l i a m p e r e (mA) o r
more, b u t less t h a n 6 mA, a r e o f t e n termed s e c o n d a r y s h o c k c u r r e n t s .
C u r r e n t s w i t h m a g n i t u d e s of 6 rnA o r more a r e c o n s i d e r e d p r i m a r y s h o c k
c u r r e n t s . A p o s s i b l e c o n s e q u e n c e o f p r i m a r y s h o c k c u r r e n t is v e n t r i c u l a r f i b r i l l a t i o n o f t h e h e a r t w h i c h r e s u l t s i n a n immediate a r r e s t o f
b l o o d c i r c u l a t i o n . T a b l e 11-1 summarizes t y p i c a l e f f e c t s o f e l e c t r i c
c u r r e n t s on a n a v e r a g e s i z e man (150 p o u n d s ) ( r e f e r e n c e 1 0 ) .
T A B L E I I-1
E L E C T R I C CURRENT E F F E C T S ON AN AVERAGE S I Z E MAN
60
HZ RMS CURRENT
(MILLIAMPERES)
<
0.7
0,7
NO APPRECIABLE EFFECT
TO
1
PERCEPTION THRESHOLD
1 TO 3
M I L D SENSATION
3 T O 10
10 TO 16
PAINFUL SENSATION
30
(APPROXIMATELY)
RESPIRATORY PARALYSIS
75
TO
250
4000
>
1.
EFFECT
5000
S t e a d y - S t a t e "Let-Go"
LET-GO THRESHOLD
VENTRICULAR FIBRILLATION
HEART PARALYSIS,
NO FIBRILLATION
TISSUE BURNING
Current
The s t e a d y - s t a t e "let-go" c u r r e n t , a s d e f i n e d by D a l z i e l and Lee
( r e f e r e n c e s 1 4 and 22) "is t h e maximum c u r r e n t l e v e l a t which a
human h o l d i n g a n e n e r g i z e d c o n d u c t o r c a n c o n t r o l h i s m u s c l e s
enough t o r e l e a s e t h e c o n d u c t o r . "
"Let-go" c u r r e n t s o b s e r v e d i n
1 3 4 men and 28 women a r e shown i n F i g u r e 11-1. While t h e c u r v e s
i n t h i s f i g u r e i n d i c a t e a v e r a g e ( 5 0 p e r c e n t i l e ) 60 Hz "let-go"
WOMEN
MEN
10
14
18
22
LET-GO CURRENT (mA-RMS)
FIGURE TI-1 LET-GO CURRENT DISTRIBUTION
FOR 134 MEN AND 28 WOMEN
c u r r e n t s of 1 6 IIIA f o r men and 10.5 mA f o r women. 99.5% of a l l
men and women t e s t e d were a b l e t o w i t h s t a n d " l e t - g o " c u r r e n t
magnitudes of 9 mA and 6 mt4 r e s p e c t i v e l y .
Based on t h i s d a t a ,
5 mA i s b e i n g c o n s i d e r e d a s t h e maximum "let-go" c u r r e n t i n t h e
proposed r e v i s i o n of P a r t 2 of t h e N a t i o n a l E l e c t r i c a l S a f e t y
Code.
Numerical examples i n Chapter I11 i n c l u d e o b j e c t grounding
5 mA s t e a d y - s t a t e "let-go" l e v e l
c a l c u l a t i o n s f o r both t h e and t h e 1 mA p e r c e p t i o n t h r e s h o l d l e v e l .
E f f e c t s of f r e q u e n c y on "let-go" c u r r e n t i s shown i n F i g u r e 11-2.
The change i n c u r r e n t l e v e l i s due t o t h e body impedance b e i n g
e s s e n t i a l l y r e s i s t i v e a t low f r e q u e n c i e s and a n o n l i n e a r r e s i s t o r - c a p a c i t o r c o m b i n a t i o n a t h i g h f r e q u e n c i e s . A 60 Hz metal-tom e t a l c o n t a c t r e s i s t a n c e i n t h e o r d e r of 1500-1600 ohms i s u s u a l l y
used t o r e p r e s e n t t h e e l e c t r i c a l body c i r c u i t r e s i s t a n c e between
normal p e r s p i r i n g hands i n e s t i m a t i n g s h o c k c u r r e n t s ( r e f e r e n c e 22).
2.
V e n t r i c u l a r F i b r i l l a t i o n Current
Another e f f e c t produced on t h e h e a r t by e l e c t r i c shock c u r r e n t s i s
m e d i c a l l y known a s v e n t r i c u l a r f i b r i l l a t i o n . Once t h e h e a r t goes
i n t o f i b r i l l a t i o n , i t r a r e l y r e c o v e r s s p o n t a n e o u s l y . Here t h e
i m p o r t a n t problem i s t o e s t a b l i s h t h e maximum c u r r e n t n o t l i k e l y
t o exceed a s a f e v e n t r i c u l a r f i b r i l l a t i o n t h r e s h o l d .
D a l z i e l ' s s t a t i s t i c a l s t u d i e s ( r e f e r e n c e 14) r e s u l t e d i n t h e
f o l l o w i n g v e n t r i c u l a r f i b r i l l a t i o n c u r r e n t v e r s u s time r e l a t i o n ship:
where i f i b ( t )
= Current l e v e l corresponding t o a p a r t i c u l a r
p r o b a b i l i t y of v e n t r i c u l a r f i b r i l l a t i o n . i n
amperes.
t = Shock d u r a t i o n , i n s e c o n d s .
kfib = F i b r i l l a t i o n c o n s t a n t d e p e n d i n g on t h e s t a t i s t i c a l
weight d i s t r i b u t i o n . *
The p a r a m e t e r s i n f l u e n c i n g v e n t r i c u l a r f i b r i l l a t i o n a r e w e i g h t ,
c u r r e n t magnitude and shock d u r a t i o n . R e l a t i v e l y l i t t l e is known
r e g a r d i n g t h e e f f e c t of frequency on f i b r i l l a t i o n c u r r e n t s .
*
D a l z i e l ' s e x p e r i m e n t s i n d i c a t e d t h a t t h e minimum f i b r i l l a t i o n c u r r e n t
f o r f u l l grown a n i m a l s was i n d i r e c t p r o p o r t i o n t o t h e i r body and h e a r t
weights.
C
-
1.
80 --
60
--
40
--
99 PERCENTILE
50 PERCENTILE
-
0.5 PERCENTILE
20
-I
I
_j
0
II
10
I
I
60 100
I
I
1
I
B
't
10,000
FREQUENCY (HZ)
FIGURE IT-2 "LET-GO" CURRENT VS FREQUENCY
(134 MEN)
4
Results of Dalziel's experiments on animals have been extrapolated
to provide effective parameter data for man. The fibrillation
constants for a 50 kilogram (110 pound) person based on 0.5 and
99.5 percent probabilities of ventricular fibrillation were determined to be the following:
Kfib = 0.185 (99.5% probability)
The expression for fibrillation current used in the E/M calculations
(Chapter IV) for a 50 kilogram (110 pound) person experiencing a
0.5% probability of ventricular fibrillation is:
ifib(t) = Jt (seconds
0.116 )
amperes
CHAPTER I I I
DETAILED ANALYSIS OF ELECTROSTATIC INDUCTION
A.
GENERAL
The d i s c u s s i o n of e l e c t r i c f i e l d e f f e c t s a s s o c i a t e d w i t h h i g h v o i t a g e
t r a n s m i s s i o n l i n e s c a n be d i v i d e d i n t o two c a t e g o r i e s :
1.
1.
D i r e c t m e d i c a l and b i o l o g i c a l e f f e c t s o f s c r o n g e l e c t r i :
fields.
2.
E l e c t r o s t a t i c i n d u c t i o n e f f e c t s on c o n d u c t i v e o b j e c t s i n
t h e v i c i n i t y of t r a n s m i s s i o n l i n e s ,
H e d i c a l and B i o l o g i c a l
T h i s c a t e g o r y d e a l s w i t h t h e d i r e c t p h y s i o l o g i c a l e f f e c t s on humans,
a n i m a l s and p l a n t s s u b j e c t e d t o s t r o n g e l e c t r i c f i e l d s . The magnit u d e o f e l e c t r i c f i e l d s t r e n g t h ( o r v o l t a g e g r a d i e n t ) a t ground
l e v e l i s u s u a l l y used i n m e d i c a l s t u d i e s t o d e t e r m i n e t h e permiss i b l e f i e l d s t r e n g t h l i m i t f o r p e o p l e and a n i m a l s n e a r e n e r g i z e d
transmission lines.
There are s e v e r a l s t u d i e s on humans and a n i m a l s t h a t i n v o l v e
e l e c t r i c a l shocks i n t h e v i c i n i t y of h i g h v o l t a g e t r a n s m i s s i o n
l i n e s . Two o f t h e s e s t u d i e s a r e P r o j e c t UHV and t h e Waltz X i 1 1
P l a n t P r o j e c t ( r e f e r e n c e s 4 and 1 0 ) . To d a t e no l o n g r a n g e
c o n c l u s i o n s have been r e a c h e d .
2.
Induced V o l t a g e
The second c a t e g o r y d e a l s w i t h c a s e s where e l e c t r o s t a t i c .:cjl:agss
a r e induced on c o n d u c t i v e o b j e c t s s u c h as f e n c e s , v e h i c l e s s n d
o t h e r m e t a l s t r u c t u r e s i n s u l a t e d from ground.
If t h e i n s c l z ~ e d
o b j e c t is c o n n e c t e d t o ground t h r o u g h a p e r s o n c o u c h i n g t n e o u j e c t .
c u r r e n t flows i n t h e connection.
As w i t h t h e m e d i c a l s t u d i e s of t h e p r e v i o u s s e c t i c n , cbe e l e c t r i c
f i e l d e f f e c t s on c o n d u c t i v e o b j e c t s i n s u l a t e d from g r ~ a n c ?cari ' 2 s c
be c o r r e l a t e d i n terms of t h e v o l t a g e g r a d i e n t e x i s t i n g 3 : grsun5
level. This voltage gradient i s d i f f i c u l t t o e v a i u a t e i f t h e t e r r z i n
i s i r r e g u l a r . T y p i c a l E / S ground g r a d i e n t p r o f i l e s 2s 3 f u n c t i o n o f
l a t e r a l d i s t a n c e f r o m t h e c e n t e r o f t h e r i g h t - o f - w a y (QOW! a r ? s h w n
i n F i g u r e 111-1 f o r 345,525 and 765 i V lines.::
.An apprc?xin!ace i : i : ~ -
*
F i g u r e 111-1 d o e s n o t i n c l u d e t h e e f f e c t s of o v e r h e a d ground wlrec whicS
r e d u c e t h e v o l t a g e g r a d i e n t s a t ground l s v e l i n t h e o r d c r of 1 =a 2?;-
i
14 --
765 kV
I
/
I
12 --
I
10 --
I
I
I
8 --
525 kV
J
I
6 -4-
-
-
.
2 120
.
I
I
IL
1
.
1
I
I
I
Ir
I
I
I
I
I
40
0
40
80
120
LATERAL DISTANCE FROM CENTER OF R.O.W. (FT)
80
FIGURE III-1 ELEICTROSTATIC GROUND
GRADIENT PROFILES
(REFERENCE 8)
thumb f o r m o s t s i n a l e - c i r c u i t l i n e s i s t h a t a maximum v o l t a g e
g r a d i e n t a t ground l e v e l of 1.6 kV/M (0.5 kiJ/ft.) is experienced
Eor each l i n e - t o - l i n e v o l t a g e increment of 100 kV.
of
F a c t o r s which determine t h e magnitude o f t h e induced E/S v o l t a g e
on a conductive o b j e c t and t h e r e s u l t i n g object-ro-ground shock
c u r r e n t a r e l i s t e d below:
B.
(a)
Line-to-ground v o l t a g e of t h e energized t r a n s m i s s i o n l i n e
(as l i n e v o l t a g e s i n c r e a s e , e l e c t r o s t a t i c e f f e c t s on conduct i v e objects increase).
(b)
P o s i t i o n of t h e t r a n s m i s s i o n l i n e phase conductors r e l a t i v e
t o ground ( v e r t i c a l c l e a r a n c e ) and t o each o t h e r (phase
separation).
(c)
P o s i t i o n of t h e o b j e c t r e l a t i v e t o t h e t r a n s m i s s i o n l i n e
phase conductors.
(d)
Dimensions of t h e o b j e c t .
(e)
Capacitances between t h e t r a n s m i s s i o n l i n e phase c o n d u c t o r s ,
o b j e c t and ground.
(f)
Q u a l i t y of i n s u l a t i o n between t h e o b j e c t and e a r t h ( l e a k a g e
impedance-to-ground of o b j e c t )
.
ELECTROSTATIC EFFECTS
Conductive o b j e c t s i n s u l a t e d from ground which could r e s u l t i n
u n d e s i r a b l e e l e c t r o s t a t i c e f f e c t s a r e p r e s e n t e d below f o r s t a t i o n a r y
s t r u c t u r e s , v e h i c l e s and parking l o t s .
1.
2.
Stationarv Structures
(a)
I n s u l a t e d Fences ( b o t h n o n - e l e c t r i c
(b)
Metal b u i l d i n g s , r o o f s and g u t t e r s .
(c)
Storage t a n k s .
and e l e c t r i c ) .
Vehicles
Vehicles n e a r high v o l t a g e t r a n s m i s s i o n l i n e s may c a u s e two p o s s i b l e
problems :
(a)
E l e c t r i c a l shock
(b)
I g n i t i o n of hydrocarbon f u e l v a p o r s
3.
P a r k i n g Lots and S e r v i c e S t a t i o n s
Right-of-way agreements u s u a l l y c o n t r o l a c c e s s of p a r k i n g l o t s ,
p l a y g r o u n d s and s e r v i c e s t a t i o n s . However, p r e c a u t i o n s s h o u l d
be t a k e n when t r a n s m i s s i o n l i n e s c r o s s t h e s e a r e a s t o minimize
u n d e s i r a b l e E/S e f f e c t s .
THEORETICAL ANALYSIS (E/S)
The f o l l o w i n g d i s c u s s i o n p r e s e n t s a g e n e r a l a n a l y t i c a l method f o r
c a l c u l a t i n g t h e amount of s h o c k c u r r e n t p a s s i n g t h r o u g h a p e r s o n ' s
body when c o n t a c t i n g a c o n d u c t i v e o b j e c t i n s u l a t e d from ground. A s
a r e s u l t of t h i s a n a l y s i s , o b j e c t g r o u n d i n g c r i t e r i a may b e d e t e r m i n e d
f o r a s p e c i f i e d t r a n s m i s s i o n l i n e v o l t a g e and c o n f i g u r a t i o n .
1.
A n a l y t i c a l E/S C i r c u i t Model
The amount of shock c u r r e n t p a s s i n g t h r o u g h a p e r s o n ' s body c a n
b e d e t e r m i n e d u s i n g t h e t h r e e p h a s e t r a n s m i s s i o n s y s t e m model i n
F i g u r e 111-2* w i t h t h e p a r a m e t e r s d e f i n e d a s f o l l o w s :
Cac, Cbc = Mutual c a p a c i t a n c e s between p h a s e s ( a ) and ( b ) ,
( a ) and ( c ) , and ( b ) and ( c ) , i n f a r a d s p e r u n i t
length.
Cab,
C,,
Cy,
C, = E f f e c t i v e m u t u a l c a p a c i t a n c e s between t h e phase
c o n d u c t o r s and a p e r s o n t o u c h i n g t h e o b j e c t a t
P o i n t P, i n f a r a d s p e r u n i t l e n g t h .
R
= P e r s o n ' s body p l u s c o n t a c t r e s i s t a n c e t o ground,
i n ohms.
C
=
C a p a c i t a n c e between t h e o b j e c t and ground a t t h e
p o i n t of c o n t a c t ( P ) , i n f a r a d s p e r u n i t l e n g t h .
RQ = Leakage r e s i s t a n c e of o b j e c t and ground a t P o i n t P,
Re).
i n ohms ( g e n e r a l l y Rp
D' = V e r t i c a l d i s t a n c e between t h e p h a s e c o n d u c t o r s and
ground, i n f e e t .
D = V e r t i c a l d i s t a n c e between t h e p h a s e c o n d u c t o r s and
t o p of o b j e c t , i n f e e t .
d = D i s t a n c e between p h a s e s ( a ) and ( b ) and between
p h a s e s ( a ) and ( c ) , i n f e e t .
h = O b j e c t h e i g h t above ground = D '
Va,
*
FI
Vb,
Vc = Line-to-ground
-
D, i n f e e t .
v o l t a g e s of p h a s e s ( a ) , (b) and ( c ) .
T h i s m o d d d o e s n o t i n c l u d e overhead ground w i r e s .
The p r e s e n c e of t h e s e
w i r e s r e d u c e s t h e v o l t a g e g r a d i e n t a t ground l e v e l by a p p r o x i m a t e l y 1 t o 2%.
FIGURE III-2 ANALYTICAL MODEL FOR THE
STUDY OF ELECTROSTATIC INDUCTION
C a p a c i t a n c e s C x , C and C can be e x p r e s s e d i n terms of t h e s e l f
c a p a c i t a n c e s , Ca, ,'ebb an2 Ccc and t h e m u t u a l c a p a c i t a n c e s Cab,
Cac and Cbc of t h e phase c o n d u c t o r s a s f o l l o w s :
Cat
( ~ q .111-la)
- Cbc
(Eq. 111-lc)
Cx = Caa - Cab -
C,
2.
= Ccc
-
General Relationships
To c a l c u l a t e t h e amount of shock c u r r e n t t h r o u g h a p e r s o n when
c o n t a c t i n g an insulated object i t i s necessary t o f i r s t determine
t h e ground v o l t a g e g r a d i e n t and t h e o b j e c t - t o - g r o u n d c a p a c i t a n c e
p e r u n i t l e n g t h ( r e f e r e n c e 1 ) . Thus,
I 'shock 1
( E q . 111-2)
= wEgradhCp
where :
[
~
=
~
~
~
~
~
l
Magnitude of shock c u r r e n t , i n amperes p e r u n i t l e n g t h .
w = Transmission l i n e radian frequency,
i n r a d i a n s per second.
Egrad = V o l t a g e g r a d i e n t between t h e o b j e c t and ground a t p o i n t
of c o n t a c t , i n v o l t s p e r u n i t l e n g t h .
h = O b j e c t h e i g h t above ground a t p o i n t of c o n t a c t .
Cp = Object-to-ground c a p a c i t a n c e a t p o i n t of c o n t a c t , i n
f a r a d s per u n i t length.
Once t h e ground v o l t a g e g r a d i e n t and o b j e c t - t o - g r o u n d c a p a c i t a n c e
a r e s p e c i f i e d , t h e w o r s t c a s e shock c u r r e n t magnitude can b e
d e t e r m i n e d ( i f t h e r e is l e a k a g e r e s i s t a n c e from t h e o b j e c t t o
ground t h e n t h e amount of shock c u r r e n t p a s s i n g t h r o u g h t h e body
w i l l b e l e s s ) . The main problem i n c a l c u l a t i n g t h e o b j e c t - t o ground c a p a c i t a n c e i s t h a t o b j e c t s u s u a l l y h a v e g e o m e t r i e s t h a t
a r e d i f f i c u l t t o model f o r a c c u r a t e c o m p u t a t i o n s . T h e o r e t i c a l
c a l c u l a t i o n s - f o r simple conductive o b j e c t s such a s a fence p a r a l l e l
t o a h i g h v o l t a g e t r a n s m i s s i o n l i n e c a n p r o v i d e some i n d i c a t i o n o f
t h e p o s s i b l e shock c u r r e n t s t h a t may be e n c o u n t e r e d . I f t h e f e n c e
i s b u i l t i n d i f f e r e n t s e c t i o n s o r i f i t is n o t p a r a l l e l t o t h e
t r a n s m i s s i o n l i n e , computations s h o u l d b e made f o r each s e c i t o n .
The r e s u l t i n g shock c u r r e n t s w i l l b e t h e v e c t o r summation of e a c h
section.
3.
Non-Electric
Fence C a l c u l a t i o n s
For t h e s i m p l e g e o m e t r i c a l c a s e where t h e o b j e c t i s a l o n g none l e % t r i E f e n c e (and is p a r a l l e l t o t h e p h a s e c o n d u c t o r s a s shown i n
F i g u r e 111-2) t h e amount of shock c u r r e n t p a s s i n g t h r o u g h a p e r s o n
coming i n c o n t a c t w i t h a s i n g l e * f e n c e w i r e i s e x p r e s s e d as
( r e f e r e n c e 9) :
I I ~ h o c k l=
amperes
meter
grad
where c O = D i e l e c t r i c c o n s t a n t of a i r
=
-12 f a r a d s
8.85 x 1 0
meters
and GMR = Geometric mean r a d i u s of a s i n g l e f e n c e w i r e , i n m e t e r s .
For t y p i c a l f e n c e v a l u e s , h = 4 f e e t (1.22 m e t e r s ) , GMR = 0.125
i n c h e s (3.2 x
m e t e r s ) and a ground v o l t a g e g r a d i e n t of 4 kV/M
(maximum g r a d i e n t f o r a l a t e r a l d i s t a n c e of 38 f e e t from t h e c e n t e r
l i n e of t h e 345 kV t r a n s m i s s i o n l i n e , F i g u r e 111-1, and a p h a s e
conductor v e r t i c a l c l e a r a n c e of 29 f e e t , r e f e r e n c e 1 2 ) t h e n from
Equation 111-3 t h e magnitude of e l e c t r i c shock c u r r e n t is:
I lshock 1
= 15.4
10-6
amperes or 25 m i l l i a m p e r e s
meter
mile
C o n s i d e r i n g a maximum "let-go" c u r r e n t l e v e l of 5 mA, then t h e
f e n c e s h o u l d be grounded*" approximately every:
mA
= 0.2 m i l e s o r 1,050 f e e t
25 m A / m i l e
For a 1 mA p e r c e p t i o n t h r e s h o l d c u r r e n t l e v e l , t h e f e n c e grounding
i n t e r v a l s are reduced t o approximately 210 f e e t . A s shown from t h e
e x p e r i m e n t a l c u r v e s of F i g u r e 111-1, t h e w o r s t c a s e v o l t a g e g r a d i e n t
i s when t h e f e n c e i s l o c a t e d o u t s i d e t h e c e n t e r p h a s e c o n d u c t o r a t
a l a t e r a l d i s t a n c e o f approximately 38 f e e t f o r a 345 kV l i n e
v o l t a g e . F i g u r e 111-3 i l l u s t r a t e s where t h e f e n c e grounds s h o u l d
b e placed i f t h e f e n c e i s p a r a l l e l t o t h e t r a n s m i s s i o n l i n e b u t
l o c a t e d a t v a r i o u s l a t e r a l d i s t a n c e s from t h e c e n t e r o f t h e t r a n s m i s s i o n l i n e right-of-way (ROW) f o r l i n e v o l t a g e s of 345, 525 and
765 kV.
*
When a person t o u c h e s a s i n g l e w i r e of a m u l t i w i r e f e n c e , t h i s w i l l be
d e f i n e d as t h e s i n g l e w i r e f e n c e touch. I f t h e p e r s o n comes i n c o n t a c t
w i t h two w i r e s s i m u l t a n e o u s l y , then t h e amount of s h o c k c u r r e n t i s
a p p r o x i m a t e l y doubled. T h i s is o n l y an approximation s i n c e t h e amount
of shock c u r r e n t i s n o t e x a c t l y doubled d u e t o t h e v o l t a g e g r a d i e n t s
b e i n g s l i g h t l y d i f f e r e n t a t each f e n c e w i r e h e i g h t .
**Actual f e n c e grounding i n t e r v a l s i n c r e a s e as t h e l e a k a g e r e s i s t a n c e from
t h e f e n c e t o ground d e c r e a s e s s i n c e t h e amount of shock c u r r e n t p a s s i n g
t h r o u g h t h e p e r s o n i s less.
2500Y
W
U-
W
0
7
a
I0
a
i
0
.
20
I
t
I
40
I
I
60
I
a
80
t
LATERAL DISTANCE FROM d OF R.O.W. (FT)
(Single Wire Fence Touch)
FIGURE III-3 FENCE GROUNDING CRITERIA
VS FENCE LOCATION FROM CENTER OF
R.O.W. (5mA "LET-GO" CURRENT)
Advanced Systems Technology (AST) T h e o r e t i c a l Study
A t h e o r e t i c a l study was conducted by AST t o determine t h e amount
of shock c u r r e n t per u n i t l e n g t h t h a t would pass through a person
touching a four f o o t high i n s u l a t e d f e n c e t h a t was i n f i n i t e l y long.
The f e n c e was p a r a l l e l t o t h e t r a n s m i s s i o n l i n e . Curves i n
F i g u r e 111-4* show t h e r e s u l t s f o r t r a n s m i s s i o n l i n e v o l t a g e s of
230, 345, 500, 765 and 1100 kV f o r corresponding conductor h e i g h t s
of 23, 27, 32, 41 and 49 f e e t .
It can be seen from t h e 345 kV
curve t h a t t h e maximum shock c u r r e n t f o r a 38 f o o t fence l a t e r a l
d i s t a n c e from t h e c e n t e r of ROW was approximately 30 mA/mile f o r
a conductor h e i g h t of 27 f e e t . T h i s compared f a v o r a b l y w i t h t h e
25 mA/mile v a l u e c a l c u l a t e d p r e v i o u s l y f o r a l i n e v o l t a g e and
conductor h e i g h t of 345 kV and 29 f e e t r e s p e c t i v e l y .
4.
E l e c t r i c Fences
The v o l t a g e on an e l e c t r i c f e n c e is t h e combination of t h e f e n c e
c h a r g e r o u t p u t v o l t a g e and t h e induced v o l t a g e on t h e f e n c e due
t o t h e E/S coupling from t h e overhead transmission l i n e . The
r e s u l t a n t combination of t h e E/S induced v o l t a g e and t h a t of t h e
f e n c e c h a r g e r o u t p u t may b e c o n s i d e r a b l y higher than t h e f e n c e
c h a r g e r o u t p u t by i t s e l f .
S e v e r a l e l e c t r i c f e n c e c h a r g e r s a r e designed t o produce o n l y
t r a n s i e n t shocks. Some s t a t e s r e q u i r e a l l fence c h a r g e r s s o l d
w i t h i n t h e i r borders t o be of t h i s type f o r s a f e t y reasons.
For
example, t h e Underwriters' L a b o r a t o r i e s (U.L.) r e q u i r e t h a t t h e
f e n c e c h a r g e r o u t p u t l a s t no more than 0.2 seconds and t o be o f f
n o t l e s s than 0.75 seconds ( r e f e r e n c e 15).
The 60 Hz impedance of t h e e l e c t r i c fence d i f f e r s from t h e l e a k a g e
impedance of t h e n o n - e l e c t r i c f e n c e s i n c e t h e e l e c t r i c fence p a t h
t o ground i s provided by t h e secondary winding of t h e f e n c e c h a r g e r
o u t p u t transformer.
T h i s winding impedance i s i n t h e o r d e r o f
10,000 t o 50,000 ohms, which i s high enough n o t t o reduce apprec i a b l y t h e r e s u l t a n t E/S induced c u r r e n t flowing through a p e r s o n
o r animal touching t h e e l e c t r i c fence.
E/S induced v o l t a g e s on t h e e l e c t r i c f e n c e may be t h e d i f f e r e n c e
between a s a f e and u n d e s i r a b l e s i t u a t i o n . For fence c h a r g e r s which
d e l i v e r 60 Hz v o l t a g e s , a p a r t i a l s o l u t i o n t o e l i m i n a t e t h e 6 0 Hz
E/S induced v o l t a g e component i s t o i n s e r t a s e r i e s d r a i n c o i l
between t h e fence c h a r g e r o u t p u t and ground. This does n o t complet e l y a l l e v i a t e t h e problem and could reduce t h e fence charger o u t p u t
v o l t a g e . However, many U.L. approved chargers a r e c a p a c i t i v e d i s charge types. Such models do n o t have a 60 Hz component. Thus a
*
References 6 and 13.
LATERAL DISTANCE FROM
OF R.O.W.
(FT)
FIGURE lI-4 SHOCK CURRENT VS FENCE
LOCATION FROM CENTER OF R.O.W.
(AST THEORETICAL STUDY)
60 H z s e r i e s r e s o n a n t c i r c u i t ( f i l t e r ) composed of an i n d u c t o r
and c a p a c i t o r can b e i n s t a l l e d between t h e e i e c t r i c f e n c e and
ground t o minimize t h e e f f e c t s of t h e E/S v o l t a g e w i t h o u t r e d u c i n ~
t h e f e n c e c h a r g e r oucput voltage."
The series f i l t e r i s s u b j e c t e d t o t h e h i g h v ~ l t a g eo u t p u t of t h e
f e n c e c h a r g e r and s h o u l d b e w e l l i n s u l a t e d . T h i s e n t a i l s an
i n d u c t o r w i t h an i n s u l a t i o n breakdown v o l t a g e i n t h e o r d e r of
3,000 v o l t s r.rn.s. a t a 5 t o 8 h e n r y r a t i n g . The c a p a c i t o r c a n
be a n o n - e l e c t r o l y t i c type i n t h e 1 t o 2 microfarad range having
These 6 0 Hz
a d c w o r k i n g v o l t a g e i n t h e o r d e r of 500 v o l t s .
f i l t e r s are commercially a v a i l a b l e -
I n c o n j u n c t i o n w i t h t h e g r o u n d i n g i n t e r v a l s s p e c i f i e d i n F i g u r e 111-3
and T a b l e 1-2, i t i s recommended t h a t t h e e l e c t r i c f e n c e c h a r g e r b e
a n Underwriters' Laboratory approved c a p a c i t i v e d i s c h a r g e type
c o u p l e d w i t h t h e i n s t a l l a t i o n of 60 Hz s e r i e s f i l t e r s a t t h e
grounding l o c a t i o n s .
D.
ELECTROSTATIC FIELD TESTS
1.
Non-Electric
Fences
T h i s s e c t i o n summarizes f i v e e x p e r i m e n t a l f i e l d test r e s u l t s and
t h e two t h e o r e t i c a l r e s u l t s of t h e p r e v i o u s s e c t i o n i n e v a l u a t i n g
t h e e l e c t r o s t a t i c e f f e c t s when a p e r s o n t o u c h e s a n i n s u l a t e d none l e c t r i c f e n c e under a high v o l t a g e t r a n s m i s s i o n l i n e ( r e f e r e n c e s
3 , 6, 7 , 8, 9 , 1 0 , 13 and 1 5 ) .
(a)
A l l e g h e n y Power System (APS)
I n 1 9 6 8 , APS conducted a s e r i e s of e l e c t r o s t a t i c i n d u c t i o n
t e s t s o n n o n - e l e c t r i c i n s u l a t e d f e n c e s p a r a l l e l t o a 500 kV
t r a n s m i s s i o n l i n e . S e v e r a l f e n c e s were t e s t e d a t v a r i o u s
l a t e r a l positions i n r e l a t i o n t o the transmission l i n e .
These f e n c e s were t h r e e f e e t h i g h and 500 f e e t l o n g . A 1500
ohm r e s i s t o r was c o n n e c t e d between t h e fe-nce and ground t o
s i m u l a t e t h e body p l u s c o n t a c t e l e c t r i c a l r e s i s t a n c e . The
maximum s h o c k c u r r e n t m a g n i t u d e r e c o r d e d was 1.1 mA f o r a
f e n c e l o c a t i o n of 35 f e e t from t h e c e n t e r of t h e t r a n s m i s s i o n
l i n e ROW.
(b)
N o r t h e a s t U t i l i t i e s S e r v i c e (NUS)
N U S c o n d u c t e d e l e c t r o s t a t i c t e s t s on a 300 f o o t l o n g - 6 f o o t
h i g h n o n - e l e c t r i c f e n c e p l a c e d under t h e o u t s i d e phase of a
*
A low impedance p a t h from t h e f e n c e t o ground i s p r e s e n t e d by t h e 60 Hz
s e r i e s f i l t e r t o minimize t h e 60 Hz E / S i n d u c e d v o l t a g e from t h e o v e r head t r a n s m i s s i o n l i n e .
345 kV l i n e .
T h e i r s z u d i e s conciuded t h e following f o r
m e t a l l i c f e n c e s mounted o n wood o r o t h e r insulated p o s t s :
(c)
(i)
"When f e n c e s r u n p a r a l l e l t o o r d i a g o n a i l ~t o t h e 3 4 5 kV
l i n e , f e n c e g r o u n d i n g s h o u l d b e i n s t a l l e d e v e r y 200 f e e t
i E t h e f e n c e i s w i t h i n t h e ROW."
(ii)
"When f e n c e s r u n p e r p e n d i c u l a r t o t h e 345 kV l i n e , f e n c e
g r o u n d i n g s h o u l d be i n s t a l l e d a t e a c h e d g e c f t h e ROW."
N o r t h e r n S t a t e s Power (NSP)
T e s t s w e r e r u n a t NSP on a s i m u l a t e d man (1500 ohms body p l u s
c o n t a c t r e s i s t a n c e ) touching an i n s u l a t e d n o n - e l e c t r i c f e n c e
4 f e e t h i g h a n d 1100 f e e t l o n g . The f e n c e was p a r a l l e l t o a
345 kV l i n e . A maximum s h o c k c u r r e n t m a g n i t u d e of 3 . 9 mA was
o b s e r v e d p a s s i n g t h r o u g h t h e 1 5 0 0 ohm s i m u l a t e d body p l u s
contact r e s i s t a n c e .
(d)
B o n n e v i l l e Power A d m i n i s t r a t i o n (BPA)
BPA c o n d u c t e d t e s t s o n a n o n - e l e c t r i c i n s u l a t e d f e n c e 3 . 5
f e e t h i g h a n d 1 0 0 0 f e e t l o n g l o c a t e d p a r a l l e l t o a 5 0 0 kV
l i n e . A t t h e p o i n t o f maximum i n d u c e d v o l t a g e p i c k u p ( 5 t o
1 5 f e e t beyond t h e o u t s i d e p h a s e c o n d u c t o r ) , r e s u l t s showed
t h a t a maximum s h o c k c u r r e n t m a g n i t u d e o f 3 a4 p a s s e d t h r o u g h
a 1500 ohm s i m u l a t e d body p l u s c o n t a c t r e s i s t a n c e .
(el
P r o j e c t UHV ( G e n e r a l E l e c t r i c )
T e s t s w e r e p e r f o r m e d on a n i n s u l a t e d n o n - e l e c t r i c f e n c e 1
m e t e r ( 3 . 3 E e e t ) h i g h and 1 5 0 m e t e r s ( 4 9 0 f e e t ) l o n g and
which w a s l o c a t e d p a r a l l e l t o a t r a n s m i s s i o n l i n e . The
A maximum
r e c o r d e d v o l t a g e g r a d i e n t was 5000 v o l t s / m e t e r .
s h o c k c u r r e n t m a g n i t u d e o f 2.225 mA was f o u n d p a s s i n g
t h r o u g h a s i m u l a t e d 1500 ohm body p l u s c o n t a c t r e s i s t a n c e .
Shown i n T a b l e 111-1 i s a summary o f t h e e l e c t r o s t a t i c r e s u l t s of
t h e previous s e c t i o n s .
The n o n - e l e c t r i c f e n c e i s assumed t o b e
p a r a l l e l t o t h e t r a n s m i s s i o n l i n e and l o c a t e d w i t h i n t h e t r a n s m i s s i o n l i n e ROW.
Worst case shock c u r r e n t magnitudes p a s s i n g
t h r o u g h a s i m u l a t e d 1500-1600 ohm body p l u s c o n t a c t r e s i s t a n c e
a r e presented.
A l s o shown a r e optimum f e n c e g r o u n d i n g i n t e r v a l s
i f a person i s r e q u i r e d t o w i t h s t a n d a s t e a d y s t a t e "let-gu"
c u r r e n t of 5 mA o r a p e r c e p t i o n t h r e s h o l d c u r r e n t of 1 mA.
2.
Buildings, Roofs and G u t t e r s
The amount o f s h o c k c u r r e n t p a s s i n g t h r o u g h a p e r s o n when c o n t a c t i n g
a m e t a l b u i l d i n g , r o o f o r g u t t e r t h a t i s i n s u l a t e d f r o m ground i s
g i v e n by E q u a t i o n 111-2.
Due t o t h e complex g e o m e t r y of b u i l d i n g s ,
rnsthod? t o d e t e r m i n e t h e o b j e c t - t o - g r o u n d c a p a c i t a n c e , C p , a r e
d i f f i c u l t t o formulate.
B o n n e v i l l e Power A d m i n i s t r a t i o n (BPA),
r e f e r e n c e 1 5 , d e r i v e d t h e f o l l o w i n g shock c u r r e n t r e l a t i o n from
f i e l d t e s t d a t a b a s e d on a 500 kV d e l t a t r a n s m i s s i o n l i n e
configuration:
Where :
(
~= Magnitude
~
~
~of shock
~
(c u r r e n t , i n milliamperes.
I
A = Area of m e t a l l i c s u r f a c e , i n s q u a r e f e e t .
Hc
=
Average h e i g h t o f o u t s i d e p h a s e c o n d u c t o r above
ground, i n f e e t .
Hob = Average h e i g h t of m e t a l l i c s u r f a c e above ground,
i n feet.
R = H o r i z o n t a l d i s t a n c e from t h e m e t a l l i c o b j e c t t o
t h e o u t s i d e phase c o n d u c t o r , i n f e e t .
VLL = L i n e - t o - l i n e
voltage, i n k i l o v o l t s .
Based on BPA f i e l d t e s t s , t h e grounding c r i t e r i a i n T a b l e 1-3 i s
recommended f o r m e t a l l i c s u r f a c e s n e a r 345, 500 and 765 kV t r a n s m i s s i o n l i n e s . T h i s grounding c r i t e r i a p e r t a i n s t o o b j e c t s w i t h
m e t a l components s u c h a; b u i l d i n g s , r o o f s , g u t t e r s and downspouts.
3.
Vehicles
When an i n s u l a t e d v e h i c l e of complex geometry i s parked under t h e
t r a n s m i s s i o n l i n e , t h e e l e c t r o s t a t i c a l l y i n d u c e d v o l t a g e and
r e s u l t a n t s h o c k c u r r e n t through a p e r s o n s t a n d i n g on t h e ground
and t o u c h i n g t h e v e h i c l e depend on v e h i c l e s i z e and t i r e r e s i s t a n c e .
The amount o f s h o c k c u r r e n t depends on t h e r e l a t i v e e l e c t r i c a l
r e s i s t a n c e p a t h of t h e tires t o t h e r e s i s t a n c e p a t h p r o v i d e d by
t h e p e r s o n . Use o f low r e s i s t i v e t i r e s may l e s s e n t h e p o s s i b i l i t y
o f shock c u r r e n t through a person. The v e h i c l e c a p a c i t a n c e t o
ground i s d i r e c t l y r e l a t e d t o i t s s i z e . O t h e r f a c t o r s t h a t i n fluence v e h i c l e capacitance a r e the following:
(a)
I r r e g u l a r s h a p e under t h e v e h i c l e .
(b)
Grass which d e c r e a s e s t h e s p a c i n g and t h e r e f o r e r a i s e s t h e
capacitance.
(c)
Pavement t y p e .
Thus, due t o t h e compiex geometry o r v e n i c l e s , rhe v e h i c l e - t o i n t h e sbock c u r r e n c e x p r e s s i o n (Equation
ground c a p a c i t a n c e , C
P'
111-2) i s d i f f i c u l t t o compute a c c u r a c e l v .
Shown i n Table ILI-2 a r e minimum t r a n s m i s s i o n l i n e c o n d u c t o r
c l e a r a n c e s a s determined by severa: f i e l d t e s t i n v e s t i g a t o r s
when a person t o u c h e s an i n s u l a t e d v e h i c l e l o c a t e d d i r e c t l y
under t h e l i n e and a 5 mA "let-go" c u r r e n t flows through a
s i m u l a t e d body p l u s c o n t a c t r e s i s t a n c e of 1500 ohms. V e h i c l e
s i z e i s i n d i c a t e d by l e n g t h (i), width (W) and h e i g h t ( H ) .
The f i e l d t e s t i n v e s t i g a t o r s a r e P r o j e c t URV, B o n n e v i l l e Power
A d m i n i s t r a t i o n (BPA) and Rene and Comsa ( r e f e r e n c e s 1, 9 , 1 6 ,
23 and 2 4 ) .
F i g u r e 111-5 i l l u s t r a t e s t h e t y p i c a l t r a n s m i s s i o n l i n e conductor.
to-ground c l e a r a n c e s a s a f u n c t i o n of l i n e v o l t a g e and v e h i c l e
s i z e . The 5 rnA "let-go" c u r r e n t v a l u e p a s s i n g through a person
touching t h e v e h i c l e i s used a s t h e shock c u r r e n t c r i t e r i a t o
o b t a i n t h e c l e a r a n c e v a l u e s . T y p i c a l phase s p a c i n g s f o r l i n e
v o l t a g e s of 345, 500 and 765 kV a r e 28, 34 and 50 f e e t r e s p e c tively (reference 5 ) .
E.
TRANSIENT ELECTROSTATIC INDUCTION
E l e c t r o s t a t i c i n d u c t i o n e f f e c t s on i n s u l a t e d o b j e c t s r e s u l t i n g from
t r a n s i e n t o v e r v o l t a g e s on t r a n s m i s s i o n l i n e s such a s t h o s e caused by
s w i t c h i n g s u r g e s and l i g h t n i n g impulses should a l s o be c o n s i d e r e d .
Because of t h e r e l a t i v e l y small p r o b a b i l i t y t h a t a r e s u l t a n t t r a n s i e n t c u r r e n t i s induced i n t h e human body, t h i s i s p r e s e n t l y n o t
considered t o b e a primary problem.
However, a t r a n s i e n t v o l t a g e
produced on t h e overhead t r a n s m i s s i o n l i n e could induce u n d e s i r a b l e
induced v o l t a g e p u l s e s on an i n s u l a t e d fence. A p e r s o n s t a n d i n g on
t h e ground and t o u c h i n g t h e i n s u l a t e d f e n c e may r e c e i v e a t r a n s i e n t
c u r r e n t , t h e peak v a l u e depending on t h e shape of t h e primary s u r g e
and t h e e l e c t r i c a l r e s i s t a n c e of t h e p a t h o f f e r e d by t h e human body.
The p h y s i o l o g i c a l e f f e c t o f very s h o r t e l e c t r i c shock i s n o t s u f f i c i e n t l y known. However, i n o r d e r t o produce v e n t r i c u l a r f i b r i l l a t i o n
t h e shock must o c c u r a t a p r e c i s e time i n t h e h e a r t c y c l e ( s e e
Equation 11-1)
.
1.
Theoretical Analysis
The induced t r a n s i e n t v o l t a g e on a human, w i t h e l e c t r i c a l body
p l u s c o n t a c t r e s i s t a n c e , Rp, t o u c h i n g a n i n s u l a t e d f e n c e can be
expressed a s f o l l o w s :
Consider only phase ( a ) of F i g u r e 111-2
The v o l t a g e
w i t h an e q u i v a l e n t c i r c u i t d e f i n e d by Cx,
and C
s u r g e , u s ( t ) , a s a f u n c t i o n of t h e shock duration,';,
on p h a s e
( a ) i s of t h e form:
%
(Eq.
111-5)
LlNE VOLTAGE (kV)
FIGURE III-5 MINIMUM CONDUCTOR-TOGROUND CLEARANCE VS. LlNE VOLTAGE
FOR INSULATED VEHICLES (5mA "LET-GO"
CURRENT CRITERIA)
TABLE II1-2 MINIMUM TRANSMISSION LINE CONDUCTOR
CLEARANCES TO GROUND (E/S CASE-VEH ICLES)
3
?
L I KE
VOLTAGE
W
a
F I E U I TEST
VEHICLE SIZE
TYPICAL CONDUCTOR
TO GROUND
345
PROJECT UHV
25' x 7' x 7'
18
345
PROJECT UHV
BPA
25'
50'
25'
25'
50'
39'
25'
25'
19,7
29
27
30,2
345
525
52 5
x 8 ' x 13,5'
x 8' x 13,5'
PROJECT UHV
x 7' x 7'
PROJECT UHV
x 8 ' x 13,5'
x 8' x 13,5'
40
BPA
RENE 8 COMSA
x 8 ' x 13,5'
54
PROJECT UHV
x 1' x 7'
37
PROJECT UHV
x 8 ' x 13,5'
42,7
*A 5 MA "LET-GON LEVEL I S USED AS THE SHOCK CURRENT CRITERIA PASSING THROUGH A
SIMULATED 1 5 0 0 OHM ELECTRICAL BODY PLUS CONTACT RESISTANCE TO OBTAIN THESE
CLEARANCE VALUES,
w h e r e T1 and T2 a r e t h e t i m e c o n s t a n t s i n s e c o n d s w h i c h f i x t h e
d u r a t i o n of t h e f r o n t a n d t a i l o f t h e s u r g e r e s p e c t i v e l y and V
is t h e v o l t a g e m a g n i t u d e of t h e s u r g e , i n v o l t s .
The i n d u c e d t r a n s i e n t v o l t a g e , u ~ ~ ( t i)n, v o l t s , a c r o s s t h e
e l e c t r i c a l body r e s i s t a n c e , Rp, and r e s u l t i n g t r a n s i e n t c u r r e n t .
ishock(t) through
can be expressed a s :
I
(Eq. 111-6)
w h e r e T = (Cx
+
C ) R seconds
P
P
and i s h o c k ( t ) = " x p ( t ) / R p a m p e r e s
Thus t h e m a g n i t u d e a f t h e i n d u c e d t r a n s i e n t v o l t a g e and r e s u l t i n g
i n d u c e d s h o c k c u r r e n t i s g o v e r n e d by t h e d u r a t i o n o f t h e s w i t c h i n g
s u r g e . These q u a n t i t i e s c a n r e a c h v e r y h i g h m a g n i t u d e s f o r s h o r t
durations.
2.
Field Tests
T e s t s w e r e p e r f o r m e d b y Hydro-Quebec on a 735 kV t r a n s m i s s i o n l i n e
t o d e t e r m i n e t h e amount of i n d u c e d t r a n s i e n t s h o c k c u r r e n t p a s s i n g
t h r o u g h a human d u e t o s w i t c h i n g s u r g e s and l i g h t n i n g s t r o k e s
( r e f e r e n c e s 1 0 and 21).
R e s u l t s a r e shown i n F i g u r e s I l I - 6 a n d
111-7 f o r o b j e c t h e i g h t s o f 1 . 0 6 , 2 . 4 7 , and 3.87 f e e t f o r a s w i t c h i n g
s u r g e waveform o f 1 x 2000 m i c r o s e c o n d s and a l i g h t n i n g s t r o k e wavefrom of 1.5 x 40 m i c r o s e c o n d s . C u r v e s y i e l d t h e p e a k s h o c k c u r r e n t
magnitude,
v e r s u s body p l u s c o n t a c t r e s i s t a n c s , Rp*.
I I ~ ~ ~ ~ ~ ( ,
F.
MEASURES TO REDUCE ELECTROSTATICALLY INDUCED VOLTAGES
The f o l l o w i n g a r e m e a s u r e s f o r r e d u c i n g E/S i n d u c e d v o l t a g e s on c o n d u c t i v e
o b j e c t s i n s u l a t e d from g r o u n d :
1.
Modify i i n e D e s i g n
I n c r e a s e t h e c o n d u c t o r - t o - g r o u n d c l e a r a n c e ( s e e T a b l e 111-2 f o r
t y p i c a l conductor c l e a r a n c e s w i t h r e g a r d t o i n s u l a t e d v e h i c l e s ) .
2.
S t a t i o n a r y S t r u c t u r e s (Fences, B u i l d i n g s , Roofs)
- (a)
*
Permanent s t r u c t u r e s s h o u l d have m e t a l p a r t s bonded t o g e t h e r
and grounded n e a r h i g h v o l t a g e t r a n s m i s s i o n l i n e s ( s e e T a b l e s
1-2 and 1-3 f o r t y p i c a l f e n c e and b u i l d i n g g r o u n d i n g i n t e r v a l s ) .
With r e f e r e n c e t o F i g u r e s 111-6 and 111-7, a s t h e body p l u s c o n t a c t
r e s i s t ~ n c eS n c r e a s e s , - t h e m a g n i t u d z of s h o c k c u r r e n t d e c r e a s e s ( 5 . ~ 1 ,
. for
R = 1500 ohms and h = 1106 f e e t , c h e m a g n i t u d e of s h o c k c u r r e n t i s i n t h e
P
o r d e r of 1 0 amperes i n F i g u r e 111-6).
h = Object Height Above Ground
h =1.06 ft.
BODY RESISTANCE, Rp (OHMS)
FIGURE m-6 PEAK SHOCK CURRENT VS
BODY RESISTANCE FOR A SWITCHING
SURGE OF 1.0 X 2000 ps (735kv LINE)
800--
A
ld
h = Object Height Above Ground
600"-
\
4
L
i
Ii
h = 1.06 ft.
c
h
e 400-2
es
bi
8
I
ZOO--
V)
H
#
I
0
I
f
I
I
I
I
100
200
300
400
BODY RESISTANCE, Rp (OHMS)
I
#
.
t
500
FIGURE III-7 PEAK SHOCK CURRENT VS BODY
RESISTANCE FOR A LIGHTNING STROKE
OF 1.5 X 4 0 1 ~ s(735kv LINE)
(b)
3.
S a f e t y procedures should b e s t r i c t l y enforced when c o n s t r u c t i n g
t o w e r s , fences or s t r i n g i n g t r a n s m i s s i o n l i n e s p a r a l l e l t o
energized c i r c u i t s .
Vehicles
(a)
U s e t i r e s w i t h low e l e c t r i c a l r e s i s t a n c e p r o p e r t i e s .
(b)
Employ grounding s t r a p s o r drag c h a i n s t o reduce E/S f i e l d
hazards.
CHAPTER I V
DETA ILED ANALYS IS OF ELECTROPIAGNETIC INDUCT I O N
A.
GENERAL
E l e c t r o m a g n e t i c (E/M) i n d u c t i o n o c c u r s when t r a n s m i s s i o n l i n e phase
c o n d u c t o r s c a r r y i n g f a u l t c u r r e n t s a r e l o c a t e d i n t h e v i c i n i t y and
p a r a l l e l t o c o n d u c t i v e o b j e c t s such a s f e n c e s . The c h a n g i n g
m a g n e t i c f i e l d s c a u s e d by s t e a d y - s t a t e l o a d c u r r e n t s * o r t r a n s i e n t
f a u l t c u r r e n t s on t h e p h a s e c o n d u c t o r s i n d u c e v o l t a g e s a t t h e open
e n d s of n e a r b y c o n d u c t i v e o b j e c t s . When a p e r s o n t o u c h e s one open
end of a grounded o b j e c t , s h o c k c u r r e n t f l o w s t h r o u g h t h e e l e c t r i c a l
body p l u s c o n t a c t r e s i s t a n c e (Rp) t o ground. I f t h e o b j e c t i s
c o m p l e t e l y i n s u l a t e d from ground, o t h e r t h a n a t t h e s i n g l e v o i n t - o f c o n t a c t , no s h o c k c u r r e n t w i l l flow s i n c e t h e r e i s no c o m p l e t e
c i r c u i t f o r t h i s s i n g l e p o i n t - o f - c o n t a c t c o n d i t i o n . However, a s a
p r a c t i c a l c o n s i d e r a t i o n , t h e r e can be s e v e r a l o t h e r c o n d u c t i v e p a t h s
from t h e o b j e c t t o ground v i a a n i n a d e q u a t e number of g r o u n d s , p a t c h e s
of t a l l g r a s s , b u s h e s o r o t h e r body o r o b j e c t c o n t a c t s .
The unbalanced c o n d i t i o n s t h a t e x i s t when t h e r e i s a f a u l t on a t r a n s m i s s i o n l i n e may p r o d u c e u n d e s i r a b l e induced v o l t a g e s a t t h e open ends
of t h e grounded c o n d u c t i v e o b j e c t t h a t i s s u f f i c i e n t l y l o n g and p a r a l l e l s
t h e t r a n s m i s s i o n l i n e . For t h i s t y p e of f a u l t , t h e f a u l t e d p h a s e cond u c t o r s and i t s e a r t h r e t u r n c a n be c o n s i d e r e d a s t h e p r i m a r y of a
s i n g l e - t u r n t r a n s f o r m e r i n which s h o r t c i r c u i t c u r r e n t c i r c u l a t e s . The
c o n d u c t i v e o b j e c t grounded a t one o r more p o i n t s c a n be c o n s i d e r e d a s
t h e secondary of t h e t r a n s f o r m e r .
An e x a c t t r e a t m e n t of t h e g e n e r a l problem of mutual c o u p l i n g between
two e a r t h - r e t u r n c i r c u i t s i s e x t r e m e l y c o m p l i c a t e d and a s i m p l e
s o l u t i o n e x p r e s s i n g t h e induced v o l t a g e a s a f u n c t i o n of t h e shock
c u r r e n t f o r a l l t y p e s of s t e a d y - s t a t e and t r a n s i e n t c o n d i t i o n s i s
d i f f i c u l t . I n g e n e r a l , t h e s t e a d y - s t a t e * * a n a l y s i s a p p r o a c h i s used
f o r t h e s o l u t i o n of s u c h problems. Employing t h i s t y p e of a n a l y s i s ,
t h e mutual impedances between t h e f a u l t e d p h a s e c o n d u c t o r s and t h e
grounded o b j e c t , b o t h h a v i n g a common e a r t h r e t u r n , c a n be c a l c u l a t e d
u t i l i z i n g C a r s o n ' s m u t u a l impedance r e l a t i o n s ( r e f e r e n c e 3 4 ) .
*
For normal l o a d c u r r e n t s , t h e amount of i n d u c t i v e c o u p l i n g between t h e
p h a s e c o n d u c t o r s and t h e o b j e c t i s c o n s i d e r e d minimal on b a l a n c e d l i n e s .
**
S t e a d y - s t a t e a n a l y s i s assumes t h a t t h e magnitude of f a u l t c u r r e n t i s
e s s e n t i a l l y c o n s t a n t o v e r a s p e c i f i e d number of c y c l e s b e f o r e t h e f a u l t
is cleared.- -
1.
E/M C o u ~ l i n eParameters
To a n a l y z e t h e e f f e c t s of i n d u c t i v e c o u p l i n g d u r i n g f a u l t c o n d i t i o n s ,
t h e f o l l o w i n g f a c t o r s should be c o n s i d e r e d :
(a)
P r o b a b i l i t y of a f a u l t o c c u r r i n g
(b)
Type of f a u l t
(c)
Magnitude and d u r a t i o n of f a u l t c u r r e n t
(dl
Mutual impedances between t h e t r a n s m i s s i o n l i n e phase
c o n d u c t o r s and o b j e c t
(el
Length of l i n e t h a t p a r a l l e l s t h e o b j e c t *
(f)
Earth r e s i s t i v i t y surrounding t h e o b j e c t
(g)
S i z e and c o n f i g u r a t i o n of o b j e c t
(h)
Transmission l i n e c o n f i g u r a t i o n
(i)
V e r t i c a l c l e a r a n c e between t h e t r a n s m i s s i o n l i n e and ground
(j) S e p a r a t i o n between t r a n s m i s s i o n l i n e p h a s e c o n d u c t o r s
2.
(k)
Leakage impedance of t h e o b j e c t t o ground
(1)
H o r i z o n t a l p o s i t i o n of o b j e c t r e l a t i v e t o t h e t r a n s m i s s i o n
l i n e ( l a t e r a l distance)
(m)
T r a n s m i s s i o n l i n e frequency (normally 60 Hz)
F a u l t C u r r e n t Levels
A line-to-ground
f a u l t on a t r a n s m i s s i o n l i n e w i l l cause a f a u l t
c u r r e n t flow i n t h e e a r t h . While f o r s e c t i o n s of s m a l l e r systems
t h i s c u r r e n t may be a few hundred amperes, f o r l a r g e r i n t e g r a t e d
networks t h e a v a i l a b l e f a u l t c u r r e n t a t a g i v e n l o c a t i o n may
approach 50 o r 60 thousand amperes.** The amount of shock c u r r e n t
t h a t f l o w s through a person w i t h o u t producing v e n t r i c u l a r
f i b r i l l a t i o n i s g i v e n by t h e c u r r e n t - t i m e r e l a t i o n of Equation 11-1.
Thus, t h e f a s t e r a f a u l t i s c l e a r e d t h e g r e a t e r t h e c u r r e n t t h a t
can be t o l e r a t e d b e f o r e r e a c h i n g t h e v e n t r i c u l a r f i b r i l l a t i o n
current threshold.
*
I f t h e t r a n s m i s s i o n l i n e i s not p a r a l l e l t o t h e o b j e c t , t h e t o t a l l e n g t h
is d i v i d e d i n t o s e c t i o n s and t h e mutual impedance between t h e l i n e and
o b j e c t i s determined f o r each s e c t i o n . The v e c t o r sum of t h e s e mutual
impedances i s e q u a l t o t h e t o t a l mutual impedance.
**
F a u l t c u r r e n t s tend t o i n c r e a s e a s t h e l o a d i n c r e a s e s . T h i s is due t o
t h e a d d i t i o n a l s u b s t a t i o n c a p a c i t y needed t o h a n d l e new l o a d s ( r e f e r e n c e s
11 and 28).
3.
Soil Resistivitv
The mutual impedance between t h e t r a n s m i s s i o n l i n e and a p a r t i a l l y
grounded o b j e c t i s a f u n c t i o n of t h e s o i l r e s i s t i v i t y ( p ) . T y p i c a l
s o i l r e s i s t i t r i t y q u a n t i - t i e s used i n t h e c a l c u l a t i o n s a r e 1 0 (wet
o r g a n i c s o i l ) , 100' (moist s o i l ) and 1 , 0 0 0 ( d r y s o i l ) ohm-meters.
B.
THEORETICAL ANALYSIS (E/M)
1. A n a l v t i c a l E/M C i r c u i t Model
The f o l l o w i n g i s a g e n e r a l a n a l y t i c a l method f o r c a l c u l a t i n g t h e
amount of s h o c k c u r r e n t p a s s i n g t h r o u g h a p e r s o n when c o n t a c t i n g
a f e n c e grounded a t a s i n g l e p o i n t and p a r a l l e l t o a t r a n s m i s s i o n
l i n e . A s a r e s u l t o f t h i s a n a l y s i s , optimum f e n c e g r o u n d i n g
i n t e r v a l s (Gf) a r e d e t e r m i n e d based on t h e f o l l o w i n g p a r a m e t e r s :
(a)
Type and d u r a t i o n ( t ) of f a u l t
(b)
Magnitude of f a u l t c u r r e n t ( I f )
(c)
Leakage r e s i s t a n c e o f f e n c e t o ground (RR)
(d)
P e r s o n ' s body p l u s c o n t a c t r e s i s t a n c e t o ground (Rp)
(e)
S e l f impedance of f e n c e ( Z f f )
(f)
Mutual impedances between p h a s e c o n d u c t o r s ( a ) , ( b ) and ( c )
and t h e f e n c e i f ) , ( Z a f , Zbf and Zcf)
Note t h a t t h e mutual impedance between any p h a s e c o n d u c t o r and t h e
f e n c e a s shown i n F i g u r e s I V - 1 and IV-2 i s a f u n c t i o n of s e v e r a l
complex f a c t o r s a s d e f i n e d below:
(a)
Radian f r e q u e n c y o f t h e l i n e ( w w h e r e w = 21Tf)
(b)
Diagonal s p a c i n g between any phase c o n d u c t o r and t o p of f e n c e
(x).* T h i s s p a c i n g i s a f u n c t i o n of t h e p h a s e s e p a r a t i o n ( d ) ,
t h e v e r t i c a l d i s t a n c e ( D l ) between t h e p h a s e c o n d u c t o r s and
ground, t h e f e n c e h e i g h t (h) above ground and t h e l a t e r a l o r
h o r i z o n t a l d i s t a n c e ( s ) between t h e c e n t e r l i n e , p h a s e c o n d u c t o r
( a ) , and t h e f e n c e .
(c)
S o i l r e s i s t i v i t y (P)
* T h e d i a g o n a l s p a c i n g between p h a s e c o n d u c t o r s ( a ) , ( b ) and ( c ) and t h e t o p
of f e n c e a r e d e n o t e d by xa, xb and x c , r e s p e c t i v e l y .
FIGURE IF-1TRANSMISSION LINEFENCE POSITION (ELECTROMAGNETlC INDUCTION ANALYSIS)
Fence (f) Parallel
To Line at
Point P
FIGURE E - 2 EQUIVALENT MODEL FOR THE STUDY OF
ELECTROMAGNETIC INDUCTION
U t i l i z i n g C a r s o n ' s mutual impedance r e l a t i o n ( r e f e r e n c e 34) between
phase c o n d u c t o r s ( a ) , (b) and ( c ) and t h e f e n c e y i e l d s :
Zaf = Raf
+
j.Xaf
ohms/mile
(Eq. IV-la)
Zbf
= Rbf
+
jXbf
ohms/mile
(Eq. IV-lb)
Zcf = Rcf
+
j X C f ohmsimile
(Eq. IV-lc)
The r e a l o r r e s i s t i v e p o r t i o n s of t h e mutual impedances, Raf, Rbf
and Ref, a r e e q u a l and a r e given by t h e f o l l o w i n g e x p r e s s i o n :
Raf
= Rbf
= Rcf
= 1 0 - ~ ~ ( 0 . 2 5 2 8 )ohms/mile
S i m i l a r i l y , t h e imaginary o r r e a c t i v e p a r t s , X a f ,
d e f i n e d below:
*af = ~ o - ~ u ( 74113
o.
Xbf
(Eq. IV-2)
Xbf and X c f ,
loglO<E+
are
2.47) ohms/mile
(Eq. IV-3a)
= 10-~w(0.74113 l o g l O L ~ + 2.47) ohms/mile
(Eq. IV-3b)
*b
where :
x,
=
xb
=
Jm
feet
J(~'-h)2
+
(s
xc = J ( D I - ~ ) +
~ (s
D'
=
+ dl2
feet
-
feet
dl2
V e r t i c a l d i s t a n c e between t h e phase c o n d u c t o r s and ground,
i n feet.
d = D i s t a n c e between phase c o n d u c t o r s (a) and ( b ) , and between
phase c o n d u c t o r s (a) and ( c ) , i n f e e t .
s = L a t e r a l d i s t a n c e between t h e c e n t e r phase c o n d u c t o r ( a ) and
the object, i n feet.
h = Object h e i g h t above ground, i n f e e t .
w = Transmission l i n e frequency, i n r a d i a n s p e r second.
9 = S o i l r e s i s t i v i t y , i n ohm-meters.
2.
Fence Impedance C a l c u l a t i o n s
To c a l c u l a t e t h e optimum f e n c e grounding i n t e r v a l when a person
touches a f e n c e g r o u n d e d . a t one p o i n t , t h e fence s e l f impedance
must be known o r be determinedFrom r e f e r e n c e 1 9 , t h e s e l f impedance of t h e f e n c e ( Z f f ) * can b e
expressed a s :
Z f f = ZTH = (Re
+
R1)
+
j(Xe
+
X1)
ohms/mile
(Eq. IV-4)
where :
R1
=
R e s i s t a n c e of t h e f e n c e conductor, i n ohms/mile (from
conductor m a n u f a c t u r e r s ' s p e c i f i c a t i o n s , r e f e r e n c e 31).
X1 = I n d u c t i v e r e a c t a n c e of t h e f e n c e conductor, i n ohms/mile
(from conductor m a n u f a c t u r e r s ' s p e c i f i c a t i o n , r e f e r e n c e 31).
f = Transmission l i n e frequency, i n Hz.
P = Soil r e s i s t i v i t y ,
i n ohm-meters.
Exampl e
For a t y p i c a l s o i l r e s i s t i v i t y of 100 ohm-meters (moist s o i l ) and
a frequency of 60 Hz, Re = 0.095 ohms/mile and Xe = 0.96 ohms/mile.
The e f f e c t i v e f e n c e r e s i s t a n c e , R1, and t h e i n d u c t i v e f e n c e r e a c t a n c e ,
X1, can be determined from a given f e n c e c o n f i g u r a t i o n . For example,
i f a wood p o s t f e n c e i s f o u r f e e t high and h a s t h r e e il6 BWG w i r e
conductors a s shown i n F i g u r e IV-3, then R1 = 10.5 ohms/mile and
X1 = 1 . 7 ohms/mile.
S u b s t i t u t i n g t h e known v a l u e s of Re,
IV-4 y i e l d s :
R1,
Xe and X1,
where t h e magnitude of t h e f eoce s e l f impedance i s
11 ohms/mile and t h e p h a s e a n g l e i s 14.1 d e g r e e s .
*
The s e l f impedance, Z f f ,
Z~~
-
m.
r
i n t o Equation
/ Zff1
=
1 ZTH 1
=
i s t h e same a s t h e e q u i v a l e n t Thevenin impedance,
-
No. 6 BWG Wire
-i
Wooden Post
t
1 ft.
t.
1 ft.
h=4 ft.
I
I
FIGURE IF-3 FENCE MODEL
3,
.\
S i m p l i f i e d Thevenin Model
A s o l i d l y grounded f e n c e p a r a l l e l t o t h e t r a n s m i s s i o n l i n e ( F i g u r e
IV-1) h a v i n g a n E/M induced v o l t a g e a t an open end ( P o i n t P) may be
a n a l y z e d i n terms of t h e Thevenin e q u i v a l e n t c i r c u i t of F i g u r e IV-4.*
The Thevenin impedance (ZTH) i s t h e s e l f impedance of t h e f e n c e ( Z f f )
a s d e t e r m i n e d i n S e c t i o n 2. For d i f f e r e n t t y p e s of f a u l t s , t h e
Thevenin v o l t a g e s (VTH) a r e d e f i n e d by E q u a t i o n s IV-5, IV-6 and IV-7
below.
:I
(a)
S i n g l e Line-to-Ground
F a u l t on Phase ( a )
VTH(a) = Ifa Zaf v o l t s / m i l e
(Eq. IV-5)
where If, = F a u l t c u r r e n t on p h a s e (a), i n amperes.
and Zaf
(b)
= M u t u a l impedance between p h a s e ( a ) and t o p of f e n c e
a s d e f i n e d by Equation IV-la, i n ohms p e r m i l e .
Double Line-to-Ground
F a u l t o n P h a s e s ( a ) and ( b )
where :
I f a , I f b = F a u l t c u r r e n t s on p h a s e s ( a ) and ( b ) , i n amperes
and
Zaf,
(c)
Zbf
=
Mutual impedances between p h a s e s ( a ) , ( b ) and t o p of
f e n c e a s d e f i n e d by E q u a t i o n s I V - l a and IV-lb, i n
ohms p e r mile.
Three Phase F a u l t
VTH(a,b,c) = I f a Zaf
+
I f b Zbf
+
I f c Zcf
v o l t s / m i l e (Eq. IV-7)
where :
I f a , I f b , I f c = F a u l t c u r r e n t s on p h a s e s ( a ) , (b) and ( c ) , i n
amperes
and
Zaf,
*
Zbf,
Zcf = Mutual impedances between p h a s e s ( a ) , ( b ) , ( c )
and top of f e n c e as d e f i n e d by Equations IV-la,
I V - l b , and IV-lc, i n ohms p e r m i l e .
I f t h e f e n c e i s n o t s o l i d l y grounded, a r e s i s t a n c e i n s e r i e s w i t h t h e
Thevenin impedance should be i n c l u d e d . T h i s s e r i e s r e s i s t a n c e r e d u c e s
t h e shock c u r r e n t through t h e person.
4.
Shock Current C a l c u l a t i o n s
With r e f e r e n c e t o Figure TV-4 and f o r R <RZ, t h e maximum shock
P
c u r r e n t magnitude p a s s i n g through a person t o u c h i n g a s i n g l e
fence w i r e a t P o i n t P is*:
( E q . IV-8)
S u b s t i t u t i n g t h e g e n e r a l t h r e e phase f a u l t r e l a t i o n (Equation IV-7)
i n t o Equation IV-8 y i e l d s t h e f o l l o w i n g e x p r e s s i o n :
llfazaf+lfbzbf+lfczcf
I'shock1
5.
=
IRp
+
1
amperes/mile (Eq. IV-9)
ZTHI
Fence Grounding C a l c u l a t i o n s
The amount of shock c u r r e n t t h a t can p a s s through a 50 kilogram
(110 pound) person e x p e r i e n c i n g a 0.5 p e r c e n t p r o b a b i l i t y of
v e n t r i c u l a r f i b r i l l a t i o n i s given by Equation 11-2.
When t h i s
v a l u e i s equated w i t h Equation IV-9, t h e r e s u l t a n t f e n c e grounding
i n t e r v a l (Gf) r e l a t i o n f o l l o w s :
(Eq. IV-10)
where :
Gf = Fence grounding i n t e r v a l t o produce a 0.5 p e r c e n t
p r o b a b i l i t y of v e n t r i c u l a r f i b r i l l a t i o n i n a 5 0
kilogram (110 pound) p e r s o n , i n m i l e s .
Rp = P e r s o n ' s body p l u s c o n t a c t r e s i s t a n c e , i n ohms.
ZTH=Zff
=
S e l f impedance o f f e n c e , i n ohms.
t = F a u l t d u r a t i o n , i n seconds ( t h e number o f c y c l e s n t o
c l e a r a f a u l t i n a 60 Hz system is n = t x 6 0 ) .
'fa"fb'lfc
'af
*
"bf
"cf
= F a u l t c u r r e n t s on phases ( a ) ,
amperes.
=
(b) and ( c ) , i n
Mutual impedances between p h a s e s ( a ) , (b) and
( c ) and t o p of f e n c e , i n ohms p e r m i l e .
This e q u a t i o n is based on t h e l e a k a g e r e s i s t a n c e of t h e f e n c e t o ground
( R f ) being v e r y l a r g e compared w i t h t h e p e r s o n ' s body p l u s c o n t a c t
r e s i s t a n c e (R ).
P
Q
FIGURE E-4 THEVENIN EQUIVALENT
CIRCUIT (EIM INDUCTION)
Curves of fence grounding i n t e r v a l s (Equation IV-10) v e r s u s f a u l t
c u r r e n t ( I f ) and s o i l r e s i s t i v i t y (P) a r e shown i n F i g u r e s IV-5
and IV-6 f o r a person t o u c h i n g a s i n g l e f e n c e w i r e . *
These c u r v e s
a r e c o n s e r v a t i v e fence grounding i n t e r v a l s f o r a s i n g l e l i n e - t o ground f a u l t . For balanced t h r e e phase f a u l t s , t h e induced v o l t a g e
on t h e f e n c e is minimal s i n c e t h e v e c t o r r e l a t i o n s h i p s of t h e symm e t r i c a l phase f a u l t c u r r e n t s c a n c e l t h e n e t E/M e f f e c t - The
f o l l o w i n g 69 and 345 kV p a r a m e t e r s a r e used i n t h e c a l c u l a t i o n s :
Rp
1600 ohms (body p l u s c o n t a c t r e s i s t a n c e ) .
=
lzf 1
=
IzTH1
= 11 ohms/mile (fence s e l f -impedance)
.
h = 4 f e e t (fence h e i g h t ) .
f = 60 Hz ( t r a n s m i s s i o n l i n e frequency).
= 10 (wet s o i l ) , 100 (moist s o i l ) and 1,000 (dry s o i l )
ohm-meters ( s o i l r e s i s t i v i t y ) .
s = 7 5 f e e t (345 kV l i n e ) and 30 f e e t (69 kV l i n e ) ( f e n c e
h o r i z o n t a l l a t e r a l d i s t a n c e from c e n t e r phase).
d = 2 5 f e e t (345 kV l i n e ) and 1 0 f e e t (69 kV l i n e ) (phase
separation)
.
D f = 29 f e e t (345 kV l i n e ) and 20 f e e t (69 kV l i n e ) ( v e r t i c a l
d i s t a n c e between phase conductor and ground).
n = 3 c y c l e s (345 kV l i n e ) and 8 c y c l e s (69 kV l i n e ) ( n i s t h e
number of c y c l e s t o c l e a r a f a u l t )
.
Shown i n Table I V - 1 is a summary of t h e f e n c e grounding i n t e r v a l s
t h a t w i l l reduce t h e E/M i n d u c t i o n e f f e c t s when a p e r s o n t o u c h e s
a s i n g l e w i r e of a four-foot h i g h f e n c e t h a t i s p a r a l l e l t o a
t r a n s m i s s i o n l i n e . The l i n e v o l t a g e s a r e 69, 115, 138, 161, 230
and 345 kV. Parameters used i n t h e c a l c u l a t i o n s a r e shown i n
Table IV-2.
--
*When a p e r s o n touches two w i r e s s i m u l t a n e o u s l y , t h e f e n c e grounding
i n t e r v a l d e c r e a s e s by approximately two. Fence grounding i n t e r v a l s
a r e based on a 50 kilogram (110 pound) person e x p e r i e n c i n g a 0 . 5
p e r c e n t p r o b a b i l i t y of v e n t r i c u l a r f i b r i l l a t i o n .
p = SOIL RESISTIVITY
FAULT CURRENT (KILOAMPERES)
FIGURE m-5 FENCE GROUNDING CRITERIA VS
SINGLE PHASE-TO-GROUND FAULT CURRENT
(Rp:1600 OHMS, n- 3 CYCLES, s - 75 FT., 345
KV LINE)
P = SOIL RESISTIVITY
FAULT CURRENT (KILOAMPERES1
FIGURE IX-6 FENCE GROUNDING CRITERIA VS
SINGLE PHASE-TO-GROUND FAULT CURRENT
(Rp=1600 OHMS, n=8CYCLES, s-30 m,
69 KV LINE)
Liqe Voltage
(kV)
Vertical Clearance*
D', (Feet)
P =
Soil Resistivity
h
=
Fence Height
(
= Fence Impedance = 11 ohms per mile
(Zff
R
*
Typical Phase
Separation, d,
(Feet)
P
=
=
Typical
Fence Lateral
Distance, s,
(Feet)
Typical Number
of Cycles to
Clear A
Fault (n)
100 ohm-meters (moist soil)
4 feet
= Body plus contact resistance = 1600 ohms
These are the minimum phase conductor-to-ground vertical clearances as listed in reference 12.
E f f e c t o f Body R e s i s t a n c e on Fence Grounding I n t e r v a l s
Fence g r o u n d i n g i n t e r v a l s f o r a nominal e l e c t r i c a l body p l u s
o f 1600 ohms a r e g i v e n i n T a b l e IV-1.*
contact resistance,
U t i l i z i n g E q u a t i o n IV-10, f o r a s p e c i f i e d f a u l t c u r r e n t , t h e
f e n c e g r o u n d i n g i n t e r v a l d e c r e a s e s by 37 p e r c e n t a s
decreases
from 1600 t o 1000 ohms. S i m i l a r l y , t h e i n t e r v a l i n c r e a s e s by
25 p e r c e n t a s Rp i n c r e a s e s from 1600 t o 2000 ohms.
%,
%
(b)
E f f e c t of V a r y i n g T r a n s m i s s i o n Line P a r a m e t e r s on Fence
Grounding I n t e r v a l s
T a b l e s I V - 3 d e p i c t s p e r c e n t changes i n t h e f e n c e g r o u n d i n g
i n t e r v a l (Gf) a s t h e f e n c e l a t e r a l d i s t a n c e from t h e c e n t e r
o f t h e ROW ( s ) and t h e phase s e p a r a t i o n (d) a r e v a r i e d from
t h e nominal v a l u e s i n T a b l e I V - I . * *
3
Attachments :
Appendix A - M a t h e m a t i c a l Symbols
Appendix B - R e f e r e n c e
Index :
CONSTRUCTION
TRANSMISSION FACILITIES
*
**
A nominal body p l u s c o n t a c t r e s i s t a n c e of 1600 ohms i s c o n s i d e r e d
c o n s e r v a t i v e when c a l c u l a t i n g t y p i c a l f e n c e g r o u n d i n g i n t e r v a l s .
A l l o t h e r p a r a m e t e r s i n T a b l e IV-2 a r e assumed t o be c o n s t a n t .
m-
-
TABLE
-----1'1-3 - FENCE GROUNDING
INTERVAL
-----VERSUS LATERAL DISTANCE
L I N E VOLTAGE
( KV)
S
(FEET >
CHANGE IN
"THE PERCENT CHANGES I N GF FOR A L I N E VOLTAGE OF
69 KV ARE FOR A REFERENCE FENCE LATERAL POSITION
( s ) OF 30 FEET (SEE TABLE I V - 2 > ,
""THE PERCENT CHAIdSES I N GF FOR A L I N E VOLTAGE OF
345 KV ARE FOR A REFERENCE FERCE LATERAL POSITION
OF 7 5 FEET (SEE TA:BLE I V - 2 ) .
Gc
APPENDIX A
E.Ll'IXEbL4TICAL SYMBOLS
A = Area o f m e t a l l i c s u r f a c e , i n sq.
Ft.
Cab,
Cat,
Cbc = Mutual c a p a c i t a n c e s between p h a s e s (a) and ( b ) , ( a ) and (c),
and (b) and (c-), i n f a r a d s l u n i t l e n g t h .
'aa,
'bb,
'cc
= S e l f c a p a c i t a n c e s of p h a s e s (a), ( b ) and ( c ) , i n f a r a d s l u n i t
length.
Cp = Object-to-ground
unit length.
C,,C
Y ,C,
=
c a p a c i t a n c e a t p o i n t of c o n t a c t , i n f a r a d s /
E f f e c t i v e mutual c a p a c i t a n c e s between p h a s e s ( a ) , (b) and ( c )
and o b j e c t , i n f a r a d s l u n i t l e n g t h .
D = V e r t i c a l . d i s t a n c e between t h e p h a s e c o n d u c t o r s and t o p of f e n c e ,
i n feet.
D' = V e r t i c a l d i s t a n c e between t h e p h a s e c o n d u c t o r s and ground, i n
feet.
d = D i s t a n c e between p h a s e c o n d u c t o r s (a) and ( b ) , and between
p h a s e c o n d u c t o r s ( a ) and ( c ) , i n f e e t .
Egrad = V o l t a g e g r a d i a n t between o b j e c t and ground a t p o i n t of c o n t a c t ,
i n voltslmeter.
co = D i e l e c t r i c c c n s t a n t o f a i r , i n f a r a d s / m e t e r .
f
=
T r a n s m i s s i o n l i n e f r e q u e c c y , i n Hz.
Gf = Optimum f e n c e ground i n t e r v a l ( e l e c t r o m a g n e t i c i n d u c t i o n
analysis), i n feet .
GMR = Geometric mean r z d i u s of a s i n g l e f e n c e w i r e , i n f e e t .
h = O b j e c t h e i g h t above ground, i n f e e t .
Hc = Average h e i g h t of o u t s i d e phase c o n d u c t o r above ground, i n
feet.
Hob = Average h e i g h t of m e t a l l i c s u r f a c e above ground, i n f e e t .
I f = F a u l t c u r r e n t magnitude, i n amperes.
= F a u l t c u r r e n t magnitudes on p h a s e s ( a ) , ( b ) and ( c ) , i n amperes.
'fa'Ifby1fc
i f i b ( t ) = V e n t r i c u l a r f i b r i l l a t i o n c u r r e n t a s a f u n c t i o n of time, i n
amperes.
(Ishockl= Magnitude of shock c u r r e n t p a s s i n g through a person o r animal,
i n amperes.
i s h o c k ( t ) = Shock c u r r e n t p a s s i n g through a person o r animal a s a f u n c t i o n
o f t i m e , i n amperes.
kfib = F i b r i l l a t i o n c o n s t a n t .
L
=
H o r i z o n t a l d i s t a n c e from m e t a l l i c o b j e c t t o o u t s i d e phase
conductor, i n f e e t .
n = Number of c y c l e s t o c l e a r a f a u l t , i n c y c l e s
p =
S o i l r e s i s t i v i t y , i n ohm-meters
r = O u t s i d e r a d i u s of a s i n g l e phase c o n d u c t o r , i n f e e t .
R1 = R e s i s t a n c e of t h e f e n c e c o n d u c t o r , i n ohms/mile
Re = Real p a r t o f fence impedance t h a t is dependent on l i n e
f r e q u e n c y , i n ohms/mile.
R R = Leakage r e s i s t a n c e of f e n c e t o ground, i n ohms.
..
I..
Rp = Sum of p e r s o n ' s body and c o n t a c t r e s i s t a n c e t o g r o u n d , i n ohms.
Raf ,Rbf ,Rcf
=
Real p a r t of mutual impedances between p h a s e s ( a ) , (b) and ( c )
and t o p of f e n c e , i n ohms/mile.
s = L a t e r a l d i s t a n c e between t h e c e n t e r p h a s e ( a ) ' and o b j e c t , i n f e e t .
P
t = Shock d u r a t i o n o r f a u l t c l e a r i n g t i m e , i n seconds.
T = Time c o n s t a n t a s s o c i a t e d w i t h an induced t r a n s i e n t s u r g e v o l t a g e ,
i n seconds.
T1,T2 = Time c o n s t a n t s a s s o c i a t e d w i t h t h e f r o n t and t a i l of a t r a n s i e n t
s u r g e v o l t a g e r e s p e c t i v e l y , i n seconds.
Va,Vb,Vc
=
Line-to-ground
v o l t a g e of phases ( a ) , ( b ) and ( c ) , i n v o l t s .
VLL = Nominal l i n e - t o - l i n e
transmission voltage, i n v o l t s .
VTH = Thevenin v o l t a g e s o u r c e , i n v o l t s .
v ~ p ( t )= Induced t r a n s i e n t v o l t a g e a c r o s s a body r e s i s t a n c e d u e t o a
transient surge voltage. i n v o l t s .
l j s ( t ) = T r a n s i e n t s u r g e v o l t a g e a s a f u n c t i o n of t i m e , i n v o l t s .
x
x,,xb,xc
=
Diagonal s p a c i n g between any phase c o n d u c t o r and t o p of
fence, i n f e e t .
= Diagonal s p a c i n g s between p h a s e s ( a ) ,
(b) and ( c ) and t o p
of f e n c e , i n f e e t .
Xaf,Xbf,Xcf
=
R e a c t i v e p a r t o f m u t u a l impedances between p h a s e s ( a ) , ( b )
and ( c ) and t o p of f e n c e , i n ohms/mile
X1 = I n d u c t i v e r e a c t a n c e o f f e n c e c o n d u c t o r , i n ohms/mile
Xe = I n d u c t i v e r e a c t a n c e o f f e n c e t h a t is dependent on f r e q u e n c y
and s o i l r e s i s t i v i t y , i n ohms/mile.
Zaf , Z b f , Z c f
= Mutual impedances between p h a s e s ( a ) ,
of f e n c e , i n ohms/mile
Zff
.
= S e l f impedance of f e n c e , i n ohms.
ZTH = Thevenin impedance, i n ohms.
( b ) and ( c ) and t o p
APPENDIX B
REFERENCES
L.
"Transmission Line Reference Book 345 kV and Above" by E l e c t r i c Power
Research I n s t i t u t e , Chapter 8, 1975.
2.
IEEE T r a n s a c t i o n s on Pbwer Apparatus and Systems, "EHV and UHV E l e c t r o s t a t i c ~ f f e c t s " , by T. M. McCauley, November/December 1975.
3.
"Transmission Design Standard C o n s t r u c t i o n S p e c i f i c a t i o n s " , Bonneville
Power Administration, 1975.
4.
EPRI Report 129 "Ecological I n f l u e n c e of E l e c t r i c F i e l d s " , May 1975.
5.
E l e c t r i c a l World, "Induced C u r r e n t s I n f l u e n c e Transmission L i n e Design",
L. E. B u r n e t t , N. R. Prasad, e t c . , November 1, 1974.
6.
IEEE Midwest Power Symposium, Volume 1, U n i v e r s i t y of Missouri " E l e c t r i c
F i e l d Strength a t Ground h e t o High Voltage Overhead Transmission
Lines. Its Cause and E f f e c t s ; Methods of Reduction" by J. C. P r o c a r i o
and S. A. Sebo, October 21-22, 1974.
7.
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IEEE Midwest Power Symposium, U n i v e r s i t y of C i n c i n n a t i , " I n v e s t i g a t i o n
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\
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Power System F a u l t s by P h a s e Impedance M a t r i x Method I1 U n b a l a n c e s and T r a n s i e n t A n a l y s i s " , by P. K . Dash,
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Number 37, "Computation of Zero-Sequence Impedances o f Power L i n e s and
Cablest', J u l y 1936.
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US. UMANMEIIT PRlNllffi OFFICE 1976- 6 2 1 - 8 9 1 / b y 1 2
"
EXHIBIT
Paper No. 90-3509
A N ASAE MEETING
PRESENTATION
COMPLEX ELECTRICAL IMPEDANCE OF COWS:
MEASUREMENT AND SIGNIFICANCE
D.J. Aneshansley, Member
Associate Professor
C.S. Czarniecki
Research Equip. Tech.
Department of Agricultural and Biological Engineering
Cornell University
Ithaca, NY 14853
Written for presentation at the
1990 International Winter Meeting
sponsored by
THE AMERICAN SOCIETY OF AGRICULTURAL ENGINEERS
Hyatt Regency
Chicago, Illinois
Dec. 18-21, 1990
SUMMARY:
Complex impedances were measured in Holstein
cows (1st through 4th lactation) between 10
and 100,000 Hz. A circuit model developed
for humans appears to be appropriate for
cows. Currents delivered at frequencies q
about 1000 Hz were well above perception @
levels at 60 Hz but caused no behavioral*
response.
,-
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.
American
Society
of Agricultural
Engineers
1
KEYWORDS:
.
,
..
Stray Voltage, Dairy Cattle
This is an or~ginalpresentation
contents.
of lhe authoqs) who alone are responsible for ~ t s
The Society 1s not responsrble lor statements or o p ~ n ~ o nadvanced
s
In reports or
expressw at its meetings. Repons are not sublect to the formal pesr revlow oroCess
by ASAE edllorlal committees; theretore. are not to be represented as referee0
publicatlQns.
at ASAE meetings am considered to be the OrOQertY
of pe
,na
tn
,ts
the3oclety. Quotat~onfrom tnts work snould stale that 11 I S from a Presenralion
mad.
autmrs, at 1, ,,st,,,
ASAE meeting.
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St. Joseph, MI 49085-9659 USA
Acknowledgements:
T h i s p r o j e c t has received f i n a n c i a l support
from t h e Empire S t a t e E l e c t r i c Energy R e s e a r c h C o r p o r a t i o n ,
Wisconsin E l e c t r i c a l Research U t i l i t y F o u n d a t i o n and t h e C o r n e l l
U n i v e r s i t y A g r i c u l t u r a l Experiment S t a t i o n .
The a u t h o r s a r e
happy t o acknowledge and e x p r e s s a p p r e c i a t i o n f o r t h e e x c e l l e n t
t e c h n i c a l a s s i s t a n c e provided t o o u r r e s e a r c h by Linda P r i c e a n d
t h e a d v i c e of P r o f . R . C . Gorewit.
CORNELL UNIVERSITY I S AN EQUAL OPPORTUNITY, AFFIRMATIVE ACTION
EDUCATOR/EMPMYER.
INTRODUCTION
The e l e c t r i c a l impedance of d a i r y cows i s i m p o r t a n t i n t h e
s t u d y of s t r a y v o l t a g e . Cow a r e s e n s i t i v e t o c u r r e n t b u t
g e n e r a l l y exposed t o v o l t a g e . A l l v o l t a g e s o u r c e s have a s o u r c e
impedance o r a n impedance i n series w i t h v o l t a g e p o t e n t i a l .
T h e r e f o r e , knowledge of t h e v o l t a g e s o u r c e ( v o l t a g e and s o u r c e
impedance) and t h e c o w ' s impedance a r e n e c e s s a r y i f t h e c u r r e n t s
d e l i v e r e d t o t h e cow a r e t o b e determined.
R e s i s t a n c e v e r s u s Impedance
The e l e c t r i c a l r e s i s t a n c e o f cows a t 50 o r 60 Hz h a s been
measured f o r many pathways ( T a b l e 1) and by many r e s e a r c h e r s (18).
An a v e r a g e v a l u e o r range of v a l u e s o f r e s i s t a n c e s can b e
s p e c i f i e d f o r t h e r e s i s t a n c e of most pathways.
Although, t h e s e
a r e s t a t e d a s r e s i s t a n c e s t h e y a r e a c t u a l l y t h e r e s u l t of t h e
measurement of t h e magnitude of t h e complex impedance o f t h e
a n i m a l a t 50 o r 6 0 Hz.
There a r e three p a s s i v e e l e c t r i c a l elements; r e s i s t o r s ,
c a p a c i t o r s , and i n d u c t o r s . R e s i s t o r s a r e f r e q u e n c y i n s e n s i t i v e ,
t h e i r v a l u e s d o n o t change a s frequency changes. C a p a c i t o r s and
i n d u c t o r s a r e f r e q u e n c y s e n s i t i v e ; t h e i r v a l u e s i n c r e a s e and
decrease with frequency, respectively.
I f w e l i m i t our
d i s c u s s i o n t o s i n u s o i d a l waveforms f o r c u r r e n t and v o l t a g e , it is
p o s s i b l e t o d e v e l o p a s e t of r e l a t i o n s h i p s between v o l t a g e ,
c u r r e n t and impedance t h a t t a k e s i n t o a c c o u n t t h e f r e q u e n c y
s e n s i t i v i t y of t h e s e components. T h e f o l l o w i n g e q u a t i o n s h o l d
t r u e f o r r e s i s t o r s , c a p a c i t o r s and i n d u c t o r s :
where R i s r e s i s t a n c e i n ohms, C i s c a p a c i t a n c e i n f a r a d s , L i s
i n d u c t a n c e i n h e n r i e s , and w i s f r e q u e n c y i n r a d i a n s / s e c o n d .
The
r e l a t i o n s h i p between s i n u s o i d a l v o l t a g e s and c u r r e n t s c a n change
i n two ways. T h e a m p l i t u d e s c a n v a r y and t h e t i m e a t which t h e y
c r o s s z e r o c a n b e d i f f e r e n t . Impedance i n d i c a t e s t h e magnitude
of t h e r a t i o of t h e a m p l i t u d e s of v o l t a g e and c u r r e n t and t h e
synchrony of t h e two waveforms ( i n p h a s e o r o u t of phase and by
how much). Complex impedances have r e a l and imaginary p a r t s .
The s q u a r e r o o t o f t h e sum of t h e s q u a r e s of r e a l and i m a g i n a r y
p a r t s p r o v i d e s magnitude i n f o r m a t i o n . The a r c t a n g e n t of t h e
r a t i o of t h e i m a g i n a r y p a r t t o t h e r e a l p a r t p r o v i d e s p h a s e
i n f o r m a t i o n . For t h e r e s i s t o r , t h e magnitude i s R a n d , a s t h e r e
i s no i m a g i n a r y p a r t t o t h e impedance (no i w t e r m ) , t h e a r c
t a n g e n t of 0 , i s 0 d e g r e e s . For t h e c a p a c i t o r , t h e magnitude i s
l / w C and t h e p h a s e a n g l e is -90 d e g r e e s ( - a r c t a n g e n t of wC/O,
b e c a u s e wc is i n t h e denominator)
For t h e i n d u c t o r , t h e
magnitude i s wheel and t h e phase a n g l e is t 9 0 d e g r e e s ( a r c
F i g u r e 1 d e m o n s t r a t e s t h e magnitude and p h a s e
t a n g e n t of wL/O).
a n g l e s of a r e s i s t o r , c a p a c i t o r and an i n d u c t o r i n a l o g - l o g p l o t
of t h e h p e a a n c e v e r s u s frequency.
.
-
Electrical Model of Body Impedance
The human body has been represented by a combination of
passive components shown in Figure 2, where the parallel
resistors-capacitor combinations (Rcl-Ccl and Rc2-Cc2) represent
the skin interfaces with electrodes and Rb represents the
internal body resistance (9). A general analysis of this
circuit for magnitude of the impedances is shown in Figure 3, in
which it is assumed that Rcl=Rc2 and Ccl-Cc2. The magnitude of
the impedance is equal to the sum of the three resistors (Rcl +
~b + Rc2) at low frequencies, when the capacitors act like open
circuits. At high frequencies, when the capacitors act like
short circuits, the magnitude of the impedance is equal to Rb.
The actual solution for the network is:
V(iw)/I(iw)
= Rb (iw
+ w2) / (iw + wl)
where wl = l/(RC) and w2 = (1+2R/Rb)wl, assuming that Rcl=Rcl=R
and Ccl=Cc2=C.
OBJECTIVE
The objective of this experiment was to examine the
impedance of the cow between the muzzle and rear hooves as a
function of frequency.
MATERIAL AND METHODS
Animals
Four first parity and 4 multiparous (2nd to 4th lactation)
Holstein cows were used, hereafter referred to as heifers and
cows, respectively. Animals were selected from Cornell
University's dairy herd. Cattle were placed in tie-stalls in an
environmentally controlled monitor room that held 4 animals.
Measurement technique
The impedance of the cow was measured between the muzzle and
the rear hooves. The cow was restrained and a stainless steel
paddle (ca. 10 cm x 10 cm) was held tightly against the muzzle of
the cow. When restrained, the cows rear hooves stood on a
stainless steel grid. These two areas provided the electrical
contacts to the cow. A function generator (Hewlett Packard,
Rockville, MD 30850, Model HP3312A) with a frequency range of .O1
Hz to 10 MHz and a 11 V r m s output provided the source of voltage.
Between the function generator and the cow was an ammeter
(Keithley Instruments Inc., Cleveland, OH 44139, Model 177
Digital Multimeter) and a voltmeter (Keithley Instruments Inc.,
Cleveland, OH 44139, Model 177 Digital Multimeter) as shown in
Figure 4. Furthermore, an oscilloscope (Phillips Test and
Measurement Dept. Inc., Woburn, MA 01801, Model 3055) monitored
the voltage across the ammeter (an indication of current) and the
voltaggacfoss the -cow. The magnitude of the impedance could be
calculated from the rms values of voltage and current indicated
by t h e multimeters.
The o s c i l l o s c o p e p r o v i d e d peak v a l u e s of
v o l t a g e and c u r r e n t and t h e t e m p o r a l r e l a t i o n s h i p between
waveforms e i t h e r i n t i m e t r a c e s o r L i s s a j o u s f i g u r e s . Thus,
m a g n i t u d e and p h a s e a n g l e o f t h e cow's impedance c o u l d b e
d e t e r m i n e d from t h e s e measurements. O s c i l l o s c o p e measurements
w e r e u s e d t o d e t e r m i n e impedance w h i l e m u l t i m e t e r r e a d i n g s o f
c u r r e n t and v o l t a g e w e r e u s e d a s a check o f t h e m a g n i t u d e o f t h e
impedance.
The f r e q u e n c y o f t h e v o l t a g e s o u r c e was changed from 10 t o
1 0 0 , 0 0 0 Hz a t f i x e d p o i n t s ( l o , 60, 100, 600, 1000, 6000, 10000,
60000, a n d 100000 H z ) w i t h a m p l i t u d e of t h e v o l t a g e a t a b o u t 1 . 0
Vrms
.
RESULTS
The measurements o f v o l t a g e and c u r r e n t w i t h t h e m u l t i m e t e r s
a n d t h e o s c i l l o s c o p e p r o v i d e d d a t a from which t o c a l c u l a t e t h e
m a g n i t u d e and p h a s e o f t h e cow a t e a c h o f t h e f r e q u e n c i e s t e s t e d .
F i g u r e 5 shows t h e c a l c u l a t e d magnitude a n d phase a n g l e f o r t h e
cow a t e a c h o f t h e f r e q u e n c i e s t e s t e d . P l o t s f o r a l l 8 cows were
s i m i l a r i n form b u t w i t h a b s o l u t e v a l u e s changing s u b s t a n t i a l l y .
Although s e n s i t i v i t y of t h e animal a s a f u n c t i o n o f
f r e q u e n c y was n o t an o b j e c t i v e o f t h i s s t u d y , t h e r e a r e some
i n t e r e s t i n g o b s e r v a t i o n t h a t c a n be made i n t h i s r e s p e c t ,
V o l t a g e l e v e l s used i n t h e s e t e s t s were below b e h a v i o r a l
s e n s i t i v i t y a t 60 Hz. ( . 2 - . S V rms), however t h e v o l t a g e was
i n c r e a s e d a t h i q h e r f r e q u e n c i e s ( . 5 -1.0 V rms). A t 60 H z . ,
-
behavior of t h e animals.
DISCUSSION
The form o f t h e magnitude and p h a s e a n g l e ( F i g u r e 5 ) f o r t h e
cows a s a f u n c t i o n o f f r e q u e n c y w a s q u i t e s i m i l a r t o t h a t
e x p e c t e d from t h e human e q u i v a l e n t c i r c u i t . T h i s e q u i v a l e n t
c i r c u i t w a s used t o p r e d i c t t h e magnitude and p h a s e a n g l e o f t h e
cows impedance, w i t h t h e a s s u m p t i o n t h a t t h e c o n t a c t r e s i s t a n c e s
( R c l and R c 2 ) and c a p a c i t o r s ( C c l and C c 2 ) were b o t h e q u a l .
V a l u e s f o r R c and Rb are p r e d i c t e d from t h e low and h i g h
f r e q u e n c y r e s p o n s e s . A v a l u e o f C c i s p r e d i c t e d by e s t i m a t i n g
t h e f r e q u e n c y a t which t h e magnitude o f t h e impedance c h a n g e s t o
.707 o f t h e low f r e q u e n c y impedance- F i g u r e 6a shows t h e a c t u a l
m a g n i t u d e o f t h e cowls impedance and t h a t p r e d i c t e d by t h e model.
F i g u r e 6b shows t h e a c t u a l p h a s e a n g l e of t h e cow's impedance and
t h a t p r e d i c t e d by t h e model. F o r b o t h t h e magnitude and p h a s e
a n g l e , t h e r e a r e some d i s c r e p a n c i e s .
I n r e a l i t y , t h e c o n t a c t r e s i s t a n c e and c a p a c i t a n c e a r e n o t
t h e s a a e . - I f t h i s - i s t h e case, t h e n t h e model impedance becomes
a more complex f u n c t i o n s , a c t u a l l y t h e r a t i o of two s e c o n d o r d e r
functions.
Two overdamped second o r d e r f u n c t i o n s c o u l d provide a model t h a t
more t r u l y r e p r e s e n t s t h e c h a r a c t e r i s t i c s of t h e measured
impedance of t h e cow.
The d e c r e a s e d s e n s i t i v i t y t o c u r r e n t s a t h i g h e r f r e q u e n c i e s
h a s been d e m o n s t r a t e d i n d i r e c t l y i n o t h e r r e s e a r c h ( 1 0 , l l ) . I n
t h e s e s t u d i e s , cows have r e q u i r e d l a r g e r c u r r e n t s t o e x h i b i t t h e
b e h a v i o r s a t what would be c o n s i d e r e d waveforms w i t h frequency
c o n t e n t h i g h e r t h a n 60 Hz. Of i n t e r e s t h e r e , is t h a t v o l t a g e may
n o t have t o i n c r e a s e t o produce t h e s e c u r r e n t s because of t h e
d e c r e a s e d magnitude of t h e c o w ' s impedance. The impedance
c h a r a c t e r i s t i c of t h e cow w i l l a l s o b e i m p o r t a n t i n d e t e r m i n i n g
t h e c u r r e n t d e l i v e r e d by v o l t a g e t r a n s i e n t s . S e n s i t i v i t y t o
h i g h e r f r e q u e n c i e s w i l l a l s o be important i n t h e s e c a s e s a l s o .
The o t h e r p o i n t o f i n t e r e s t i s t h a t c o n t a c t impedances a r e
v e r y i m p o r t a n t i n d e t e r m i n i n g t h e t o t a l impedance of t h e animal
a t 50/60 Hz. A s s e e n i n t h e above a n a l y s i s , t h e c o n t a c t
r e s i s t a n c e s c a n p r o v i d e up t o 2/3 of t h e t o t a l r e s i s t a n c e a t
50/60 Hz.
I t i s t h e r e f o r e v e r y i m p o r t a n t t o d e f i n e t h e way i n
which e l e c t r i c a l c o n t a c t is made t o t h e animal. I t a l s o means
t h e e n v i r o n m e n t a l f a c t o r s may p l a y a s i g n i f i c a n t r o l e i n
d e t e r m i n i n g t h e c u r r e n t d e l i v e r e d t o an animal.
REFERENCES :
1. Appleman, R.D. a n d R . J . G u s t a f s o n . 1985. S o u r c e o f S t r a y
v o l t a g e a n d E f f e c t o f C o w H e a l t h and P e r f o r m a n c e . J . D a i r y S c i .
68: 1554-1567.
2 . C r a n e , L.B., M.H. E h l e r s a n d D.K. Nelson.
p o t e n t i a l s and d o m e s t i c water s u p p l i e s . Agr.
1970. E l e c t r i c a l
Engr. 5 1 ( 7 ) : 4 1 5 .
3 . D r e n k a r d , D.V. Henke, R.C. G o r e w i t , N.R. S c o t t , a n d R. S a g i .
1 9 8 5 . M i l k p r o d u c t i o n , h e a l t h , and e n d o c r i n e r e s p o n s e s of cows
exposed t o e l e c t r i c a l c u r r e n t s d u r i n g milking.
J. Dairy S c i .
68:2694.
4 . L e f c o u r t , A.M.
1982. B e h a v i o r a l R e s p o n s e s o f d a i r y cows
s u b j e c t e d t o c o n t r o l l e d v o l t a g e s . J. Dairy S c i . 65:672.
5. N o r e l l , R . J . ,
G u s t a f s o n , R . J . and R.D. Appleman. 1983.
B e h a v i o r a l S t u d i e s o f D a i r y Cow S e n s i t i v i t y t o Electrical
C u r r e n t s . T r a n s . ASAE 2 6 ( 5 ) : 1 5 0 6 .
6.
P h i l l i p s , D.S.M.
and R.D.J.
Parkinson.
1963. The E f f e c t s of
s m a l l v o l t a g e s on m i l k i n g p l a n t s ; t h e i r d e t e c t i o n and
e l i m i n a t i o n . Dairy F a n n i n g Annual ( N e w Zea1an.d) 79-90.
7 . W h i t t l e s t o n e , W.G.,
M.M. M u l l o r d , R. K i l g o u r and L.R. Cate.
1 9 7 5 . E l e c t r i c s h o c k s d u r i n g machine m i l k i n g . N . Z . V e t . J o u r .
23 :105-108.
8 . Woolford, M.W. 1972. Small v o l t a g e i n m i l k i n g p l a n t s . P r o c .
2nd Seminar on f a r m Machinery and Equipment. P u b l i c a t i o n 645, N e w
Z e a l a n d Dept. o f A g r i c u l t u r e , H a m i l t o n , N>A. pp. 41-47.
9 . Smoot, A.W. a n d N . Mogan. 1983. Methods o f c a l c u l a t i n g
e l e c t r i c a l body impedance and equipment f o r measuring l e a k a g e
c u r r e n t s . I n N E l e c t r i c a l Shock S a f e t y C r i t e r i a n , J . E . B r i d g e s ,
G . L . F o r d , I . A . Sherman, M. V a i n b e r g , Eds.
Pergamon P r e s s , N e w
York, NY.
10. Currence, H . D . ,
B.J. S t e e v e n s , D.F. W i n t e r s , W.K. Dick and
G.F. Kause. 1987. D a i r y cow a n d human s e n s i t i v i t y t o 60 H z
c u r r e n t s . ASAE P a p e r No. 87-3036, ASAE, S t . J o s e p h , M I .
11. G u s t a f s o n , R . J . , 2. Sun a n d T.D. Brennan. 1988. Dairy cow
s e n s i t i v i t y t o s h o r t d u r a t i o n e l e c t r i c a l c u r r e n t s . ASAE P a p e r No.
88-3522, ASAE, S t . J o s e p h , M I .
FIGURE LEGENDS
Figure 1: Plots of the logarithm of the magnitude of the
impedance of passive electrical components (resistor,
capacitor and inductor) versus the logarithm of
frequency. Plots of the phase angle of impedance of
passive electrical components versus the logarithm of
frequency. Such plots are called Bode Plots.
Figure 2: Theoretical equivalent circuit that models a human
body, according to Smoot et al. (9).
Figure 3: Plot of the logarithm of the magnitude of the impedance
of human body model (Figure 2) versus frequency.
Figure 4: Circuit diagram indicating the instruments used to
measure the cow's impedance and their interconnections.
Figure 5: Bode Plot of the cow's impedance (magnitude and phase
angle) based upon the measurements of the cow 3813.
Figure 6: Comparison of the theoretical model to the actual
measurements for A) magnitude of the cow's impedance
and B) phase angle of the cow's impedance. (See text
for details of estimation of model parameters.)
TABLE
Table 1:
Resistance of Various Electrical Pathways Through the
cow*
b
BODE PLOTS (LOG (Z)VERSUS LOG (F or w )
LLI
A
.-.-----+90 c
z5
n
n
.-3
<
V
N
0
w
(3
LU
cn
4
I
0
0,
J
-90
LOG (f or w)
FIGURE 1
;
J
IMPEDANCE MODEL FOR HUMANS
Rc I
Rb
Rc2
Cc 1
Cc2
R c I& R c 2 c o n t a c t resistances.
Cc 1 & C c 2 contact capacitance
~b - body resistance
FIGURE 2
v
b
BODE PLOTS (LOG (Z) VERSUS LOG (F or w )
(MAGNITUDE ONLY)
n
n
.-3
2Rc + Rb
N
(cap. open)
w
v
Rb
CJ
0
A
I
I
I
t
I
Wo
Kwo
LOG (f or w)
(cap. short)
FIGURE 3
L
FIGURE 4
OSClLLOSCOPE
CHA
COM
CH B
FUNCTION
GENERATOR
h
P
MAGN. AND PHASE OF COWS IMPEDANCE
1000
-45
h
magnitude
-
n
3813
+ phase angle
4
I:
0
w
w
-
n
-
0
Z
4
Lrl
4-
w
-
-
w
a
a
W
CI
u
W
#
/
-
#
*
0
+-
4'
--
-3
-
a
z
a
-
w
62
a
I
0.
\
0
b
.
/
#
'
100
V1
- - Y
I
10
I
1000
I
I
I
0
100,000
FREQUENCY (HERTZ)
FIGURE 5
*
k
-
A
L
MAGNITUDE OF COW'S IMPEDANCE
1000
n
Rc=170ohms
R b = 1 7 5 ohms
a
Z
-
0
-
V)
I
0
V
w
z
a
a
W
-
Cc=lufd
3805
-
a
e
Z
-
-.
100
8
I
S
10
1000
FIGURE 6 A
FREQUENCY
i
8
I
100,000
(HERTZ)
I)
*
PHASE ANGLE OF C O W ' S IMPEDANCE
h
tn
w
45
W
a
36
w
-a
27
a
18
w
9
W
1
z
a
tn
-
Rc= 1 7 0 ohms
R b = 175ohms
Cc = 1 ufd
38 13
-
a
x
a
0
i
10
FLGURE 6B
1000
log freq(hertz)
100,000
Table 1: Resistance of Various Electrical Pathways Through the cow(1)
Pathway
n
Resistance
Mean
Range
(ohms) (ohms)
Mouth-all hooves
70
28
350
361
324-393
244-525'
60
60
2
5
Mouth-rear hooves
28
475
345-776"
60
5
Mouth-front hooves
28
624
420-851
60
5
Front leg-rear leg
5
13
300
362
250-405
302-412
60
60
4
4
Front to rear hooves
28
734
496-1152'
60
5
Rump-all hooves
7
680
420-1220
50
7
Chest-all hooves
5
?
980
1000
700-1230
50
50
7
8
Teat-all hooves
28
4
594
880
402-953
640-1150
60
50
5
7
Teat-rear hooves
28
594
402-953"
60
5
Teat-front hooves
28
874
593-1508
60
5
1320
1000
860-1960
50
50
7
?
12
1700
650-3000
60
3
All teats-all hoovesb
Udder-all hooves
6
?
?
Current
Frequency
(Hz)
Ref.
6
" Ranges given are for 10-90% percentile, or percent of cows with
measured resistance below the reported limit.
Exhiblt R--(DJA-2)
W~tnessDanicl J A11es:ianslt
Dntc
Februan, 21) 2001
Pzp:
192of312
9 5 3 621
Paper No.
An ASAE M e e t i n g P r e s e n t a t i o n
HOLSTEIN COW IMPEDANCE
FROM MUZZLE TO FRONT, REAR AND ALL HOOVES
[-]
2!Zak&t
,Daniel J, Aneshansley,
Roger A. Pellerin, James A. Throop and David C. Ludington
Cornell University
Department of Agricultural and ~iologicalEngineering
Ithaca, NY 14853
Written for presentation at the
1995 Annual International Meeting
ASAE
-- The
sponsored by
society for engineering in agriculture, food,
and biological systems
Hyatt Regency
Chicago, Illinois
June, 18-23., 1995
Summary:
Electrical impedance of Holstein cows decreases with
frequency and can be modelled with a resistivecapacitive network similar t o models proposed for
humans, Impedance does not change with current levels
that are above or below perception. Different contact
surfaces cause low frequency difference in impedance
but little change in high frequency impedance. Measured
responses for cows (voltage and currents with respect
to time) to steady state voltages and simulated
transients are similar to those predicted and measured
from the electrical model of the cow.
Keywords:
Electrical impedance measurement, transfer function
model, frequency, cows, transients
The authoxts) is solely responsible for the content of this tedmical presentatioh The technical p m @ t i o n does not n e c e s s a e
d e c t the offidal position of ASAE, and its p r h l h g and distribution does not constitute an endorsemint of views which may be
=P&
T e c a l pn=entatiorts are not subject to the formal p e r review p m e s by ASAE editorial committeg; therefore, they are not to
be presented as refpublications.
Quotation from this work should state that it is from a presentation made by (name of author) at the (listed) ASAE meeting.
EXAMPIX
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For information about sffuring permission to reprint or reproduce a technical presentation please address inquiries to ASAE.
ASAE, 2950 Niles Rd., St. Joseph, M 490859659 USA
Voice: 616.429.0300 FAX: 616.4293852
Case N0.U-I !6R..i
~.. .
Eshibir: R - ( D J A - 2 )
Wirness: Daniel J. A;:csl~:r;slz;
Date:
F e b r u q 20, ,7001
?.?z:: 19;of;l2
Acknowledgements: This project has received f i n a n c i a l support
from t h e Empire .State e l e c t r i c Energy Research Ccrporation
including t h e N e w York S t a t e E l e c t r i c Research and Development
C o r p , t h e Center for Advanced Technology a t Cornell U n i v e r s i t y ,
and t h e Cornell University Agricultural Experiment S t a t i o n . The
authors acknowledge and express appreciation f o r the e x c e l l e n t
technical assistance provide t o o u r research e f f o r t s by P r o f .
R.C. G o f e w i ~ , M r s . Karen R i z z o , M r . George Hoffman and M r .
Richard Krizek.
CORNELL UNIVERSITY I S AN EQUAL OPPORTUNITY, AFFIRMATIVE ACTION
EDUCATOR/EMPLOYER.
ASAE Paper N o . 9 5 3 6 2 1 , Page 2
G i O C 1hU.U- I 1 O M
Exhibit: R--(D.:A-~)
Witness: Dani-i .I.Arteshs;~clc.!
Date:
Febrt~arj20: 200 j
Gags:
I94oC312
ABSTRACT
E l e c t r i c a l impedance of Holstein cows was measured w i t h
r e s p e c t t o current and frequency. Impedance was measured w i t h 6 0
Hz c u r r e n t s below and above p e r c e p t i b l e l e v e l s , from -1 t o 8 ma.
No s i g n i f i c a n t difference i n impedance was observed. Impedance
were a l s o measured w i t h i n c r e a s i n g c u r r e n t ( .1 t o 8ma) a t 2KHz
and 60KHz but were probably a l l below perception l e v e l s . No
s i g n i f i c a n t d i f f e r e n c e i n impedance was observed i n t h e s e c a s e s
Impedance was measured between nose/muzzle and f r o n t ,
either.
r e a r and a l l hooves with r e s p e c t t o frequency (10Hz t o 100KHz) .
Impedance a t
Impedance was r e s i s t i v e a t low and high frequency.
low frequency was highest between nose/muzzle and f r o n t hooves
and lowest between nose/muzzle and a l l hooves. A t high
frequencies t h e impedance d i f f e r e n c e between pathways decreased.
D i f f e r e n t types of connections t o t h e nose/muzzle
demonstrated t h a t t h e d i f f e r e n c e s i n c o n t a c t impedance g e n e r a l l y
disappeared a t high frequency .
T r a n s i e n t wavef o m s (exponentially decaying s i n u s o i d t o a
constant amplitude sinusoid) were a p p l i e d t o t h e cow and the
temporal response recorded. These responses were c o n s i s t e n t w i t h
a n a l y s i s and measurements of a simple e l e c t r i c a l model u s e d f o r
humans b u t w i t h component values based on t h e impedance a s a
function of frequency .
INTRODUCTION
The e f f e c t s of steady s t a t e voltage and c u r r e n t on l i v e s t o c k
has been widely studied and the r e s i s t a n c e of various animal
pathways reported (Appleman and Gustaf son, 1985; Lef court e t a 1 .
1 9 9 1 ) . For d a i r y cows, t h e r e s i s t a n c e of a t y p i c a l cow i s given
as approximately 500 ohms a t 60 Hz although values from l e s s t h a n
300 t o over 1 0 0 0 ohms depending on cow and pathway have been
reported. The impedance of the animal i s important as animal
s e n s i t i v i t y i s generally expressed i n terms of c u r r e n t d e l i v e r e d
t o the animal. Animal exposure i s measured a s v o l t a g e between
two p o i n t s t h e animal can contact. To convert these v o l t a g e i n t o
current d e l i v e r e d t o the animal, two impedances need t o be known.
The s e r i e s impedance associated with the source of v o l t a g e and
animal's impedance a s both of t h e s e impedances l i m i t the c u r r e n t
d e l i v e r e d t o t h e animal.
The p o s s i b l e e f f e c t s of short duration e l e c t r i c a l e v e n t s on
l i v e s t o c k has only r e c e n t l y been s t u d i e d (Brennan and Gust a f son,
1 9 8 6 ; Currence e t a l . 1 9 9 0 ; Gustafson e t a l . 1 9 8 8 ; Reinemann e t
al. 1994a,b) . Because s h o r t duration e l e c t r i c a l events can
c o n s i s t of frequencies much higher than 60 Hz, i t i s important t o
know what t h e impedance of the animal i s a t these f r e q u e n c i e s .
I t i s a l s o important t o know how the impedance of t h e animal
changes with, frequency. Previous s t u d i e s (Aneshansley, 19 90) )
have shown t h e impedance of Holstein cows from the muzzle t o r e a r
hooves i s n o t purely r e s i s t i v e b u t has some capacitance
a s s o c i a t e d w i t h them.
ASAE Paper No. 953621, Page 3
--
Lase M.U-11684
Exhibit: R - ( D J A - 2 )
Witness: Dwiel J. Anes!lan;ley
Dzte: Fehruar). 20. :001
P;I:::
195of312
A simplified electrical equivalent circuit (Figure 1) for
the human body (Smoot and Mogan, 1983) . The parallel capacitors
and resistors (R,//C, and R2//C2) represent contact impedance with
the points at which voltage is present. The single resistor (R,)
represents body resistance. A simplified analysis of this
circuit at low frequency (w [radians/sec]=2*pi*frequency[HzI ) ,
where the capacitors are "open circuitsn (l/wC, >> R, and l/wC2 s s
R,) , shows the low frequency impedance to be resistive and sum of
the three resistors. An analysis at high frequency, where the
capacitors are I1shortcircuitsn (l/<
<< R, and l/wc2 tc R,),
shows the high frequency impedance also to be resistive and close
to R,. The actual solution for the impedance is:
Z(iw)
=
V(iw) =R, (iw + w,)
I (iw)
(iw + w,)
where wl = 1/RC and w, = (1+2R/R,,)and w,, assumizlg that R,=K=R
and C,=C,=C.
In general, the two contact points have different electrical
characteristics (resistance and capacitance) which leads to a
more complicated form for the impdance.
where
wo
=
(Rl+R2+Rb)
/ (ClC2RlR$j,)
Again analysis of low and high frequesries gives resistive
impedances at low frequency equal to zfe sum of the three
resistors and resistive impedance at 3igh frequencies equal to
R,.
All other measures include both iIl~utcapacitances as well
as input resistances, making it impossible to separate the
contact impedance components.
The objective of this study was to investigate electrical
impedance of cows. Specifically, our objectives were to measure
the electrical impedance of dairy cows at current levels below
and above levels of perceptions, from muzzle/nose to all hooves;
t o measure electrical impedance over frequencies from 10 Hz to
60KhZ; to investigate different types of contact surfaces; to
test transients events on the cow and compare an electrical model
of the cow to the cow.
ASAE Paper No. 953621, Page 4
.-
MATERIAL AND METaODS
A stall in the experimental parlor at Animal Science's
Teaching and Research Center at Hartford, NY was modified to
allow the impedance of cows from muzzle/nose to front, rear or
all hooves to be measured. Two metal grids were mounted on cow
mats and placed on the floor of the stall such that the animals
front hooves were on one grid and the rear hooves on the other
grid. A wire was connected to each grid. all other parts of the
stall that the cow could contact were isolated with multiple
wraps of 5 mil mylar from the vertical pipes that were set in the
concrete floor. Other connections were isolated with plastic
connections. for those stall components that could not be
isolated, the cow was isolated from the component with a rubber
liner. A nose clip (four variations) was connected to nostrils
of the cow or placed against her muzzle- Therefore, electrical
connection could be made between the nose/mzzle and the front,
rear or all hooves (by connecting the wires from each grid
together) .
Preliminary test have been done on four cows and complete
measurements have been completed on 2 cows. All cows were in
their third or more lactation. For these tests, no other
criteria were used to select cowsAll isolated parts of the stall were tested at frequencies
between 10 Hz and loOKHz or more. The output voltage of a
functibn generator (Phillips PMS13L?, Fluke Corp . Everett Wa
98206-9090) was connected to a 510 o h resistor and the metal
grids for the hooves. The function senerator voltage and voltage
between the isolated stall compon=r and metal grid are monitored
with a two channel oscilloscope (EfE'54600A,Hewlett Packard Co . ,
Test & Measurement, Santa Clara, Ca- 55052 . Each grid is tested
alone with respect to each isolata stall component and then the
grids are connected together a d izected again. Isolation is
typically over 100Kohms at lKHz a d =re than 7Kohms at 100KHz.
The isolation of each grid with ressect to ground of the
oscilloscope and function generators a d the grids from each
other are also tested in a similar manner.
To measure the cows' impedance, the output voltage of the
function generator was connected to a 510 ohm resistor which was
connected in series to the muzzle/nose connector. The ground of
the function generator was connected to the ground of the
oscilloscope and to the front-hoove grid, the rear-hoove grid or
the parallel connection of the front and rear-hoove grids
depending upon which impedance was to measured(Figure 2) . The
oscilloscope monitored the function generator's output voltage
(V,-Channel 1) and cow's voltage (V,-Channel 2) . The difference
between these two voltages is the voltage across the resistor znd
i s directly proportional to the current delivered to the cow.
The diffgre~cein phase angle (a) between these two voltages also
provides information about the impedance of the animal. Measures
of voltages and phase differences V , V, and a) were made at
multiple frequencies. Measurements of impedance were also made
ASAE Paper No. 953621, Page 5
L,;ISt:
iY0.U-1 I O W
Ex!iibit: R - ( D J A - I )
Witness: Daniel J. Ancshhnslr'y
Datc:
Februap 21). 2GO I
Past: 1973f312
at fixed frequencies (60 Hz, 2KHz and 60KHz) and multiple current
levels.
The complex impedance of the cow is given by the following
expression for magnitude I Z : and phase angle (b) of the
impedance:
lZl
=
(
510 * V2
[v,-v2cos(a)I '+ [V2sin(a)I 2
0.5
b = a + tan-1 [V2sin(a)/ (V,-V,cos (a)) 1
(Eq. 4)
Transient waveforms.(exponentially decaying sinusoLda1
voltages at various frequencies) were programmed for a computer
controlled function generator (CompuGen 840A Waveform Generator
card for IBM PC, Gage Applied Sciences Inc., Montreal Quebec,
Canada H4S 1S1) . The output 05 this function generator was then
used in place of the Philllips Function Generator to provide
transient voltage inputs to a 510 ohm resistor in series with the
cows or an electrical model of a cow . The function generator
board was inserted into a personal computer(286S~/25,Gateway
2000, N. Sioux City, SD 57049). The output voltage of the
function generator and the voltage across the cow.were monitored
on the oscilloscope as before., The data collected by the
oscilloscope was transferred as an ASCII file to a second
personal computer making use of measurement and storage module
(HP54568A, Hewlett Packard Co., Test & Measurement, Santa Clara,
CA 95052) and software for transferring the data ( Scopelnk,
Hewlett Packard Co., Test & Measurement, Santa Clara, CA 95052).
These data were then manipulated in a spreadsheet to obtain the
instanteous voltage and current (difference in two measured
voltages divided by the 510 ohm resistance) of the cow.
'
RESULTS AND DISCUSSION
Impedance as function of current at 60Hz, 2K, and 60KHz is
shown in figures 3a and b. At 60Hz, current was increased from
below levels of perception (c1 ma rms) to well above levels of
perception (8 ma rms). At 2KHz, currents approach perception at
8 ma for a small percentage of cows but are below the mean
perception level of 12-15 ma and, at 60KHz, currents are all
below perception levels (Reinemann et all 1994). Linear
regression analysis of the impedance on 60 Hz current show some
decrease in resistance (-7.3 and -1.1 ohms/ma for cow 4423 and
5384 respective) but with poor correlation coefficients (R2= -74
and -31 respectively). Linear regression analysis at the other
frequencies showed less slope (-2.23 to -.I9 ohms/ma) and even
poorer correlation (R2 = .43 to -006).
~mp~dan'ce
as a function of frequency for nose/muzzle to
front, rear and all hooves are shown in figures 4a and b. The
plots show impedance decreases with frequency for all pathways
and with a similar pattern. Impedances from nose/muzzle ro front
hooves is highest and impedance from nose/muzzle to all hooves
ASAE Paper No. 953621, Page 6
Cnw No.U-11534
i f s ! ~ i h i ~K---(DJA-2)
:
\Yi~nrbs:Daniel J . ~\neshanjley
Dutc:
Februan. 20.20Q;
' a :
198 of312
i s lowest. This i s i n agreement with previous measurements a t 60
Hz. (Norell e t a l l 1 9 8 3 ) where t h e mean value of r e s i s t a n c e s w a s
624, 475, and 350 f o r t h e mouth t o f r o n t , rear and a l l hooves,
r e s p e c t i v e l y . The p l o t s a l l have the form p r e d i c t e d by E q . 1,
r e s i s t i v e a t low and high frequency with a l a r g e r value a t low
frequency than high.
Four d i f f e r e n t nose/muzzle connections were t e s t e d . A b r a s s
s p r i n g loaded c l i p with p l a t e s were used i n a l l the previous
experiments. Three other devices were t e s t e d . A chrome s p r i n g
loaded c l i p , a nose " t w i s t e r w and a s t a i n l e s s steel paddle from a
water bowl. The spring loaded c l i p s a p p l i e d a reasonably
r e p e a t a b l e f o r c e when attached. The nose " t w i s t e r u and t h e
paddle could not be applied i n a c o n s i s t e n t manner, p a r t i c u l a r l y
t h e paddle. The p l o t s , Figure 5A and B, show v a r i a t i o n a t t h e
low frequency were t h e contact impedance p l a y s t h e . g r e a t e s t role
i n the animal impedance. I t would be expected t h a t a t h i g h
frequency, most of t h e contact impedance would be n e g l i g i b l e and
t h i s appears t o be the case f o r the most p a r t although t h e r e i s
some v a r i a t i o n a t high frequency.
An e l e c t r i c a l model of cow ( F i g u r e 6) g i v e s an impedance
p l o t t h a t i s f l a t t e r a t high and l o w frequency and with a s t e e p e r
slope i n t h e mid-frequency range. T h e e l e c t r i c a l model shown
here was used t o examine t r a n s i e n t waveforms.
Exponentials decaying sinusoicial t o a f i x e d l e v e l s i n u s o i d a l
were applied t o cows and the e l e c t r i c a l model. The iQli,-1e_s- . a .hp
of th&>-si.ne wave was J--or,90
degrees and t h e s i n e wave &as
produce$ a ~ v g e t ~ ~ f x e g u . e (nt hcr e~e =
of ~ which a r e shown,
6Oi H
~ Hz and
O 100KHz) . The c z n v o l t a g e and c u r r e n t a r e
For a 60 Hz 5ecaying s i n e wave w i t h no
shown (Figure 7 A - F ) .
~ a t cow v o l t a g e and c u r r e n t
phase o f f s e t (Figure 7A), i t i s S E t h
a r e p r a c t i c a l l y i n phase and therf is no apparent transient a t
,
,
-*- C"4.-s
.
-ir;--
The animal r e s i s t a n c e i s approximz~ely200 ohms ( h i g h frequency
impedance a t t h i s i n s t a n c e ) . This is expected from the model.
The input c a p a c i t o r s a r e short cirzllLts t o t h i s r a p i d change a d
t h e r e f o r e t h e i n i t i a l current is azrermined by t h e body
impedance. The capacitors quickly charge and t h e impedance drops
as can be seen by t h e decrease i n current a s t h e v o l t a g e
increases.
I n t h e mid frequency r a g e (2000 Hz) and w i t h no phase
o f f s e t , t h e phase difference between cow v o l t a g e and c u r r e n t i s
apparent (Figure 7 C ). The same frequency, b u t w i t h a 90 d e g r e e
phase o f f s e t (Figure 7 D ) , shows a current t r a n s i e n t similar t o
t h e 60 Hz waveform with 9 0 degrees phase o f f s e t . F i n a l l y , a
lOOKHz waveform with 90 degrees phase o f f s e t (Figure 7 E ) , shows
s i m i l a r &ran-sients i n i t i a l l y and has t h e cow c u r r e n t and cow
voltage back i n phase a s would be expected from t h e model.
S i m i l a r t r a n s i e n t s were applied t o the e l e c t r i c a l e q u i v a l e n t
c i r c u i t . Figures 8 A and 8B, show waveforms f o r 6 0 Hz t h a t match
ASAE Paper N o .
953621, Page 7
--
LLUC
I.".V-I
.
,s
I
Exhibit: R - ( D J A - 2 )
Witncss: Daniel J. Ancshansley
Date: February 20.2001
Paz;:
199 of 3 12
those of the cow. This was true for transients at other
frequencies also.
PRELIMINARY CONCLUSIONS
Based upon the limited data collected at this point, the
following preliminary conclusions are made:
1. The impedance of the cow does not change significantly as
current increases above perception levels. (Changes at 60 Hz in
the two cows were -1.8%/ma and -0.4%/ma)
2 . Complex impedance can be modeled with an electrical circuit
similar to the simple model used for humans but with different
values for the components of the circuit.
3. The model predicts response of the cow to transients voltage
wavefo m s .
4. Cow impedance between 60 and 6OKhz decreases by a factor of 2
to 3.
5. Based on the reported decrease in sensitivity to current from
60 Hz to 50 KHz of 180 on average, there should be a decrease in
voltage sensitivity of factor of 60 to-90on average.
ASAE Paper No. 953621, Page 8
-
tul)ibit: R - ( D J , \ - 2 )
Witncss: Daniel J. Aneshansley
Dale:
Fcbiuay 20,2001
Page: 200 of; 1 2
REFERENCES
Appleman, R.D. and R.J. Gustafson. 1985. Source of Stray voltage
and effect on cow health and performance. J. Dairy Sci. 68:15541567.
Aneshansley, D.J. and C.S. Czarniecki. 1990. Complex electrical
impedance of cows: Measurement and significance. ASAE Paper No.
90-3509. St. Joseph, MI.
Brennan, T.V. and R.J. Gustafson. 1986. Behavioral study of dairy
cow sensitivity to short AC currents. ASAE Technical Paper No.
NCR-86-202. ASAE, St. Joseph, MI.
Currence, H . D . , B . J . Stevens, D.F. Winter, W.K. Dick and G.F.
Krause. 1990. Dairy cow and human sensitivity to short duration
60 Hz currents. App. eng. in Agriculture, 6(3):349-353.
Gustafson, R.J., Z. Sur, and T.V. Brennan. 1988. Dairy cow
sensitivity to short duration electrical currents. ASAE Paper No.
88-3522. ASAE, St. Joseph, MI.
Lefcourt, A.M., ed. 1991. Effects of electrical voltage/current
on farm animals: How to detect and remedy problems. U.S.
Department of Agriculture, Agriculture Handbook No. 696, 142pp
Norell, R .J. , R.J. Gustafson, and R. D . >~>pleman.1983 . Behavioral
studies of dairy cow sensitivity to electrical currents. Trans.
ASAE 26 (5):1506.
Reinemann, D.J., L.E. Stetson, N. LaugLin. 1994a. Response of
dairy cattle to transient voltages a d ~zgneticfields. Proc.
LEEE, Rural Electric Power Conf. April 1 9 9 4 , Colorado Springs,
CO .
Reinemann, D.J., L.E. Stetson and N. L ~ ~ a h l i n1994b.
.
Effects of
frequency and duration on the sensitivity of dairy cows to
transient voltages. AS- Paper No 9 4 - 3 5 9 7 . St. Joseph, MI.
Smoot, A.W. and N. Mogan. 1983. Methods of calculating
electrical body impedance and equipment for measuring leakage
currents. In "Electrical shock safety criteriau, J.E. Bridges,
G.L. Ford, I .A. Sherman, M. Vainberg, EDs. Pergamon Press, New
York, NY.
ASAE Paper No. 953621, Page 9
.-
Exhibit: R - ( D J i Z - 2 )
Witness: Daniel 1. Ancshansley
Date:
February 20.2001
Pagc: 101of3l.l
FIGURES
.
Figure 1: Simplified electrical circuit of human impedance.
Figure 2 : Circuit used for the measurement of cow impedance.
Figure 3: Impedance as a function of increasing current at three
frequencies (60Hz, 2KBz and 60KHz). A is cow 4 4 2 3 and B
is cow 5 3 8 4 .
Figure 4 : Impedance as a function of frequency. A is cow
and B is cow 5 3 8 4 .
4423
Figure 5 : Impedance as a function of frequency and muzzle/nose
connections. A is cov 4423 and B is cow 5 3 8 4 .
Figure 6: Electrical model of cow,
Figure 7: Transient response of cow 4 4 2 3 to exponentially
decaying sinusoid. Cow current, voltage and input
voltage is shown in a c h plot. A. 60 Hz with 0 phase
angle offset. B: 60 9z vith 90 degree phase angle
offset. C. 2000 Hz with 0 Lcgree phase angle offset.
D. 2000 Hz with 90 degree cbiise angle offset.
Figure 8: Transient response of el~crricalcircuit simulation
cow. A. 60 Hz with G c i q e e r ~ h a s eangle offset and 33.
60 Hz with 90 degree p k s e a b l e offset.
ASAE Paper No. 953621, Page 10
LSt. N0.U-I 1684
Exhibit: R - ( D J A - 2 )
Vii:n:ss: Daniel J. Anrshallsle)
Dn:e:
February 20.20Ol
P q c : 202 01'312
I
IMPEDANCE MODEL FOR HUMANS
Rc 1 & Rc2 contact resistances.
Cc 1 & Cc2 contact capacitance
Rb body resistance
-
FIGURE 1
I
y-, , , - ,
j
.:.--..
r
(ah3
:::-:.:?.+r
.-. .- ..:m:
.----
fl;:
-
51 02
w
,
FIGURE 2
.
,
IL
J
"
*I
COW
i
li
F
-
IMPEDANCE MEASUREMENT CIRCUIT
Case N0.U-11684
Exhibit: R--(GJ,\-2)
Witness: Dank! J. Antshansley
Date: Fehruac 2 0 . ~ 0 0 1
Page: 203 cf 3 12
Cow Impedance (Muzzle all Hooves)
Cow Current - ma
-
0
2
-
-
Cow 4423
1
-
4
6
Cow Current - ma
ASAE Paper No. 953621, Page
Cow 5384
1
F I G U R E 3A
8
FIGURE 3B
--.-. . - . -
Eshi bit: R - ( D J A - 2 )
Witness: Daniel J. Aneshansley
Datc: February 20,200)
Page: 201 of 3 12
Cow 4423
1E2
FIGURE
1E3
1E4
Frequency - Hz
Cow 5384
C
A
Frequency - Hz
-
Front Hooves
FIGURE 4B
A
Rear Hooves
All Hooves
Exhibit: R - ( D J , ~ - 2 )
ivitness: Daniel J. A n e ~ h a r , ~ l ~ ~
Dxe:
February 20, ~ 0 0 1
P q e : 205 of 312
Cow 4423 - Vario-us Muzzle Attachments
Frequency -
Hz
FIGURE 5A
Cow 5384 - Various Muzzle Attachments.
Frequency - Hz
-I+
FIGURE 5B
* Nose Lead
Brass Clip
Chrome Clip
Water Paddle
+
Case N0.U-11681
Eshibit: R - ( C J A - 2 )
Witness: Daniel .I.
Aneshansle)
Date: February 20,2001
Page: 206 of 3 12
- . . ....
.,
COW EQUIVALENT CIRCUIT
FIGURE 6
TRANSIENT RESPONSE OF-COW (4423)
TO EXPONENTIALLY DECAYING SINUSOIDAL
TIME (milliseconds)
FIGURE 7 A
Li-C
1YO.U-1 lob+
Eshihit: R - ( D J A - 2 )
\vitness: Daniel J. Aneshansley
Datc: February 20,2001
TRANSIENT RESPONSE OF COW (4423) page:
TO EXPONENTIALLY DECAYING SINUS0IDA.L
h
w
B
z
2d
5
U
2070f312
14
12
10
8
6
TIME (milliseconds)
FIGURE 7B
TRANSIENT RESPONSE OF COW (4423)
TO EXPONENTIALLY DECAYING SINUSOIDAL
TIME (milliseconds)
FIGURE
Case N0.U-11684
Exhibit: R - ( D J A - 2 )
Witness: Daniel J. Aneshansley
Date: Februay 20,2001
Page: 208 of 312
TRANSIENT RESPONSE OF COW (4423)
TO EXPONENTIALLY DECAYING SINUSOIDAL
n
3
22
Y
20
-E
W
?5
p:
p:
--
u
?O
D
*a
1L
z:
8
h
2
" = o
I3
d
-2
0
-4
w
-6
3
W
a
2
g
-8
-:O
-12
-0.2
S
5'-L
- --=
r.
I
*
2
1.6
TIME (milliseconds)
2
24
FIGURE 7.D
Case h'0.U-11684
Exhibit: R - ( D J A - 2 )
Witness: Daniel J. Aneshansley
Date:
February 20, 2001
Page: 209 o f 3 12
TRANSIENTS ON ELECTRICAL EQUIVALENT OF COW
60Hz WITH O0 PHASE OFFSET
:
Icow
:
FIGURE 8A
6OHz WITH 90° PHASE OFFSET
3;
*----------.---,-------------------------------------.-----.----
..
Time - seconds
FIGURE
Paper No. 993152
An ASAE Meeting Presentation
SENSITIVITY OF HOLSTEINS TO 60 HZ AND OTHER
WAVEFORMS PRESENT ON DAIRY FARMS
BY
D.J. Aneshansley, Associate Professor
Department of Agricultural and Biological Engineering
RC. Gorewit, Professor
Department of Animal Science
Cornell University
Ithaca, New York 14853
Written for Presentation at the
1999 ASAEICSAE-SCGR Annual International Meeting
Sponsored by ASAE
Toronto, Ontario Canada
July 18-21,1999
Summary:
The current sensitivity (ma-rms, ma-AC rms, ma-peak) of 16 lactating
Holstein cows was determined for transient, momentary, steady state and
combined voltages (AC with DC bias and 60 and 180 Hz voltages). The
results for steady state, transient and momentary wavefonns are in
agreement with previous results. The combined voltages indicate that
aresensitive to eak-to;pez$c
currents rather than rms<or
-.._Holstein c - 0 3-&J...L."---.. .. geakvalues.
---4-
Keywords:
z
.
<--
%.-
. ' - B ,
&-,.a-
stray voltage, animal sensitivity, transients, momentaries, steady state;
harmonics, current, voltage, water bowl
The author(s) is solcly responsible for the content of thi technical pramlation The technical prcscntation d w not necessarily reflect
the olficial position ofASAE, and itt printing and dimbution d w not constitute an endoncment of v i m which may be aprcsscd.
Technical prescntations are not subject to the f o d peer m i e w process by ASAE editorial comminta;
prcscntcd as nfaeed publications.
Quotation from this work shwId st*
therefore. they arc not to be
that it is from a presentation madc by (name of author) af thc (listed) ASAE meeting
-
EXAMPLE From Author's Last Namc, Initials. Titlc of Presentation" Prcscnud at thc Datc and nUc of meeting, Paper No X
ASAE* 2950 Nila Road.
St. Joseph. MI 49085-9659USA For information about securing permission to reprint or reproduce a
uchn~calpra;ntation, please address inquiries to ASAE.
ASAE. 2950 Nila Rd.. St Joseph. MI 49085-9659USA
Voicr 616.429.0300 FAX: 616.4293852 E-Mail:<hq@asae.org>
INTRODUCTION:
Management of animal agricultural facilities is a complicated process that
involves mechanical, electrical and biological systems. A problem in any of these areas
as well as others can cause difficulties in the operation of the facility. Animal contact
voltages, sometimes referred to as stray voltage or other terms, if large enough can cause
undesirable effects.
A comprehensive review of stray voltage research is available (Lefcourt 1991) as
is a more recent surnmary(Fick and Surbrook 1996). The research described in these
reports addresses mainly steady state 60150 Hz voltage/current levels with some minor
exceptions. Other temporal forms of voltage and current were identified as possible
research areas (Lefcourt 199 1). In particular, events with frequencies higher than 60 Hz
and short duration 60 Hz events associated with motor starts.
Working definitions have been suggested for non-steady state events and
appropriate measurement techniques described (Stringfellow et al, 1996). There are three
temporal definitions that are used in this paper. Transients are events that are less than
1/60 of second (less than one cycle of 60 Hz). This is a slight variation on other
definitions of transients (Hendrickson and P.otoch, 1998) which specify transients as
"non-repetitive" voltage and current of short duration, less than one-half cycle, and
possibly of larger amplitude than that of the normal steady state supply. Momentaries
are events that are from 1160 of second to one second in duration (M.F.
Stringfellow
personal communication). Steady state events are event which constant for more than
one second. These definitions allow the classification of most events that occur in
agricultural facilities. There have been reports of transient currentslvoltage on dairy farms
(Dashio et al., 1994; Aneshansley et al., 1997; Hendrickson and Patoch, 1998).
Sources of the short duration events on dairy on farms can be characterized
according to the duration of the event. Transient e v e n (less than L/6Q_of a second) are
due to electric fence and cow- trainer
---- conGoll&s,
-.
c~&tor &d s~&h qlo.~s~s, and DC
'power supplies Garticularry tho& used with vhable speed drives). -Mog-eutary events .
arc typically due to lam-e
tumed.on.and.off. Steady&te events are due to
~ ~ that run for perio* of more
- . than
. a second at constant load
240 VAC and 1 2 3 . v loads
or current.
*
l
*
.
.
'.Wt
.,r--
There ~ ~ e t y & w & ~ ~ ~ $ a ~ ~ c _ o .expected
~ d . . in
b te h e s -. d
. .
of agricultural animals to every
such
--.--. t h a ~ $ i ~ ~ i g p ~ s sto,.exarnine
i b l.e- -~. ,. . . the
. . sensitivity
possibility. It is possible to break most signals that occur in the real world into set of
~ e ~ c y ~ ~ _ ~ . z ! ~ ~ ~ 8 ~If ~th&!~.al-s.ensiti~
& ~ ~ g ~ ~ ~to ethese
~ ~ ~ s . i s .
_
the.
_
seps.i~ivity
_
i ~ ~ r a y i t r n a i,..b .l ~ r p r e d i ~ to. . any
iiiiing'ttie~sensitiv~ty
of animals to different fiequenciesJt&
n e c m tqtest combined-als
to determine if there is an additive, synerglst~cor no
.w-'
effect of h a v i,*z w ~ n e signals.
d ~.,
,.~~
.
. ,
..
.
--e-..
,
''
-
Lr.=.P
~ ~ , u ; v ~ $ . .:*
,~
,r<
~-~
. -*.7:::~:L .
'2r.ee-.-&
-&d:&z&..::.y
ASAE Paper NO. 993152
:~&<.,:$
_
A
- '
,
.-+-.Li_
i -
g
Experimental Design:
Holstein dairy cow's sensitivity to current was determined increasing eIectrical
stimuli in the form of a voltage between water bowls, from which cow drank, and a metal
grid, on which their rear hooves stood. Voltage and current to the cow were monitored.
As'the voltage increased, the cow eventually quit drinking the electricd circuit became
open and the current dropped to zero. The current just before the cow quit drinking was
used as her sensitivity to that particular waveform.
To insure that the cows would drink repetitively, the water was turned off by use
of an electronic valve controlled by timers. The water supply was turned off 4 hours
before milking and the experimental treatments were applied after milking.
After milking, the cows were given four treatments. Treatments for the,four cows
in the test facility were setup as a 4 x 4 Latin square design (Table 1). Each treatment
was an electrical voltage (with measured current) that was' increased until the cows
TREATMENT
4
3
2
1
2
3
4
1
removed their muzzles froin the water (broke the eleciricai contactj. The current
delivered at the time they removed their muzzle was recorded as the level to cause the
aversion response.
Five sets of experimental treatments were tested on 4 groups of 4 cows.
Sensitivity to steady state 60 Hz was included in each set of treatments. The treatment
sets were the following (not including the 60 Hz steady state voltage tested in each set of
treatments):
1. Steady state voltages at 600,6000 and 30,000 hertz.
2. Mono-polar voltage pulses at durations of 100,200 and 400 microseconds
of 60 Hz voltage once a second with durations of 6, 15 and 30 cycles
,. 3. Pulses(0.1,
0:25,0. .5 second) combined with a continuous level of 60 Hz.
4. Steady state voltage at 60 Hz with DC bias voltages of 0.5, 1.0 and 2.0 volts.
5. Steady state voltage at 180 Hz and combinations of 60 and 180 Hz with
0-degree phase shift and 180 degree phase shift.
ASAE Paper NO.
993152
5 of 1 3
Results
1. Transient Events
Sensitivity to steady state voltages at frequencies from 60 to 30.000 Hz: The
average current (rms-ma) to get the cow to quit drinking as a b c t i o n of frequency is
given in Table 2. The value for each animal is the average of four tests. Table 2 also
provides the average current for the 16 cows at each fiequency. There is himy
signJfic-gt-diffkr,e~ensiti~vitybe-tteeg
,main
e&e_qpency
bged.upon pair t-test.
5ensitivit-y
. *.--I
.-..
decrease?
.. wihjncre-g
frequency that is similar to the results ob&ed in
previous studies (heshansley and Czarniecki 1990, Reinemann et al 1996).
8
Sensitivity to mono-polar short duration ( 100,200,400 microsecond)
pulses: The average current ( m a - p e a k G t h e cow to quit drinking as a b c t i o n of
short duration uni-polar pulses is given in Table 3. The value for each animal is the
average of four tests. J'&&J also provides the average current for the 16 cows at each
c a -n .t in sensitivity between each frequency
treatment. T h e ~ e , , k @ ~ y ~ ~---.. @Cdifference
E
with
~ s h o i i e X i t i o n which is s&~& to the
basesupnpair
..--...,
t-test.
*Iresults obtained in pre?ious studies (Gustafson et dm,Reinemann et al 1996).
.
-.,-YV_13
ASAE Paper NO. 993152
2. Momentaries
Sensitivity to current from voltage pulses of 60 Hz with durations of 0.1 to 0.5 s:
The average current (ma-rms) to get the cow
_ to %it.-..-----drinking-asa funcfion of short
duration
---....- pulses of 60
F -~q,ii.gi~e~~
.~.
The value for each animal is the average of
four tests. T a k 4 also provides the average current for the 16 cows at each treatment.
There is h-~~c~t~djIffere,9.ce&,semiti~ity~ee~een.the 0.1 s treatment and the 60
Hz steady .~t.attetrea,tn,egi
...
..-.
..,
( n o 6 ~ u l s e s and
) between the 0.25 Hz treatment and the
6 6 Hz steady state treatment b&ed upon paired t-test. Sensitivity decreases with shorter
durationwhich is similar to the results obtained in previous studies (Currence et al.
1987).
A A
+
.
,
,
.
.
.
*a-
-
.. .
~' .
3. Combined Electrical Stimuli
Sensitivity to current from steady state 60 Hz voltape with DC bias: The average
current (ma-AC ims) to et the cow to qu&drinking as a function of short
--duration pulses
of 60 Hz is given in Table The value for each animal is the average of four tests.
Table 5 also provides the average current for the 16 cows at each treatment. m
o
significant difference in s e e v i t y between the 60 Hz steady state voltage with no DC
bias &id
of the 60 Hz steady state voltages with DC bias. This indicates that there is
no effect due to DC bias voltage which is identical to previous results (Aneshansley et al.
1996).
/
ei-
ASAE Paper NO. 993152
"
ASAE Paper NO. 993152
Fick, R.J. and Truman C. Surbrook. 1996. "A Review of Stray Voltage Research: Effects
on Livestock." Extension Bulletin E-2606 of Michigan State University 6:96-2MKMF, File 18.34(Electrical Wiring)
Gorewit, KC.,D.J. Aneshansley, D.C. Ludington, R.A. PeIlerin and X.2hao. 1989. AC
Voltages on water bowls: Effects on lactating cows. J. of Dairy Science
72(8):2 184-2 192.
Gustafson, R.J., 2. Sun, and T.D. Breman. 1988. "Dairy Cow Sensitivity to Short
Duration Electrical Currents". Presented at the 1988 International Meeting, Paper
No. 883522, ASAE, 2950 Niles Rd., St. Joseph, MI 49085-9659, USA.
Hendrickson, R.C. and J.W: Patoch. "Electrical Environment on 17 Dairy Farms."
Presented at the 1998 International Meeting, Psper No. 983001, ASAE, 2950
Niles Rd., St. Joseph, MI 49085-9659, USA.
.r~-
Lefcourt, A.M., ED. 1991. Effects of electrical Voltage/Current on Farm Animals. How
To detect and Remedy Problems. U.S. Dept. of AgricuIture Handbook No. 696,
Washington, D.C..
Reinemann, D.J.,+L.Stetson,N. Laughlin. "Effects of frequency and duration on the
sensitivity of dairy cows to transient voltages." Presented at the 1998 International
Meeting, Paper No. 94-3597, ASAE, 2950 Niles Rd., St. Joseph, MI 49085-9659,
USA.
Reinemann, D.J., L.E. Stetson, N.K. Laughlin. "Response of Dairy Cattle to Transient
Voltages and Magnetic Fields. 1994b. IEEE Paper 94-C5, Rural Power
Committee LAS.
Stringfellow, M.F., D.J. Aneshansley and T.C. Surbrook. "Measuring Short-Duration
Animal Contact Voltages and Currents". Presented at the 1996 International
Meeting, Paper No. 963085, ASAE, 2950 Niles Rd., St. Joseph, MI 49085-9659,
USA.
ASAE Paper NO. 993152
I
PAPER N0.87- lo-::?
TRANSMISSION OF NEUTRAL/EARTH CURRENT I N DAIRY BARNS
D . C . Ludington, P r o f e s s o r
R.A. P e l l e r i n , R e s e a r c h A s s o c i a t e
D . J . Aneshansley, A s s o c i a t e P r o f e s s o r
Department of A g r i c u l t u r a l E n g i n e e r i n g
Gorewit, A s s o c i a t e P r o f e s s o r
Department of Animal S c i e n c e
R.C.
Cornell University
I t h a c a , NY 14853
For p r e s e n t a t i o n a t t h e 1987 Summer Meeting
AMERICAN SOCIETY OF AGRICULTURAL ENGINEERS
Baltimore Convention C e n t e r
B a l t i m o r e , MD
J u n e 28 - J u l y 1, 1987
SUMMARY:
A farm s t u d y was c o n d u c t e d t o i n v e s t i g a t e c u r r e n c flow
i n a d a i r y b a r n . C u r r e n t f l o w i n g t o e a r c h chrough
equipment grounds i s a p r o d u c e r o f s c r a y v o l t a g e .
N e u t r a l / i s o l a t e d ground v o l t a g e , which i s t h e d r i v i n g
f o r c e f o r t h i s c u r r e n t , i s n o t a good measure of s t r a y
v o l t a g e . S t r a y v o l t a g e i s measured b e ~ w e e nanimal
c o n t a c t p o i n t s w i t h a p p r o p r i a t e equipment.
KEYWORDS :
S t r a y v o l t a g e , Dairy Housing, E l e c t r i c Wiring
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Transmission o f Neutral/Earth
D.C.
Ludington,
R.A.
Pellerin, D.J.
Current i n Dairy Barns
hne'shansely and R.C.
Gorewit
I n t r o d u c t i o n and Background
An a n i m a l m u s t come i n c o n t a c t w i t h t w o p o i n t s t h a t a r e a t
clifrerent voltage l e v e l s i n order t o receive a shock.
The
v o l t a g e b e t w e e n t h e s e two p o i n t s i s cermed s t r n y v o l t n g c ? .
r11 n
b a r n , t h e o n l y way a n A C s t r a y v o l t a g e c a n b e p ' r o d u c e t l is c o h ; i - r r .
AC c u r r e n t flowing chrough a r e s i s t a n c e .
I f s t r a y T~ol:nge ~:.:iscs
i n t h e s t a n c h i o n s o r t h e m i l k i n g p a r l o r , t h e r e must be c ~ ~ r r e n c
f l o w i n g through t h e s e a r e a s and t h e r e must be e l e c t r i c a l impedances t o t h i s current flow.
The magnitude of t h e s t r a y v o l t a s e
w i l l be a f u n c t i o n o f t h e c u r r e n t flow and t h e l o c a l impedance.
Impedance is t h e r e s u l t a n t o f r e s i s t i v e , c a p a c i t i v e and i n d u c t i v e
loads.
E l e c t r i c a l r e s i s t a n c e s d o e x i s t i n many p l a c e s i n a b a r n .
Examples a r e : c o r r o d e d o r l o o s e p i p e clamps i n t h e s t a n c h i o n s .
j o i n t s between p i p e s and c o n c r e t e , t h e c o n c r e t e i t s e l f , s u r f a c e
c o n t a c t s between o b j e c t s , s u c h a s t h e l e g s o f milk t a n k , and
c o n c r e t e f l o o r , and s o i l .
Reducing these r e s i s t a n c e s and chus
che s t r a y voltage is t h e purpose of e s t a b l i s h i n g an " e q u i potential plane".
E l e c t r i c a l c u r r e n t w i l l s t i l l f l o w t h ~ - . - o l . ~ g thh e
"equipotential plane".
Because t h e r e s i s c i n c e has been reduced,
t h e c u r r e n t f l o w may e v e n i n c r e a s e .
I f t h e e l e c t r i c a l s y s t e m i n a b u i l d i n g i s s o u n d , i e n o ~ n u l r sc n d
meets Code, t h e o n l y s o u r c e o f AC c u r r e n c f o r producing s t r a y
v o l t n g e i s izhe n e u t r a l ( g r o u n d e d ) c o n d u c t o r v i a t h e b o n d i n s ?..~ir.h
the grounds.
T h i s b o n d i n g may t a k e p l a c e a t ? h e b a r n s e r v i c e
entrance panel o r a t the supply end of a four wire s i n s l e - p h a s e
f e e d e r . (Surbrook and Reese, 1984)
B o n d i n g a l l o w s c u r r e n c izo
flow t o metal wacer p i p e s , l i g h t n i n g p r o t e c t i o n and b r a n c h
c i r c u i t equipmznt ground w i r e s .
C u r r e n t w i l l flow i n t h e s e c o n d a r y n e u t r a l wire due t o unbalanced
120 V loads i n the barn and t h e e l e v a t e d v o l t a g e a t t h e j u n c t i o n
of t h e primary and secondary n e u t r a l .
Current flowing i n the
n e u t r a l m u s t r e t u r n t o ' t h e p o w e r s o u r c e : t h e t r a n s f o r m e r f o r izhe
d e l t a d i s t r i b u t i o n s y s t e m a n d t h e s u b s t a t i o n f o r a wye system.
The a u t h o r s a r e : P r o f e s s o r , R e s e a r c h A s s o c i a r e a n d A s s o c i a ~ e
P r o f e s s o r , A g r i c u l t u r a l E n g i n e e r i n g , a n d ~ s s o c i n t eP r o f c ! s s o r .
Ani-tnnL S c i e n c e , C o r n e l L U n i v e r s i t y , 1 t h a c a , N Y 1 4 8 5 7
A c k q o w l c d g e m e n t : - T h i s p r o j e c t was f u n d e d by Empire S t a z e l l e c : - L c a l Energy Research C o r p o r a t i o n and t h e Wisconsin E l e c cric.11
Research U t i l i t y Foundation.
For e i t h e r case the current will flow through two major p n t t t ~ ;
(1) the s e c o n d a r y and primary neutral wires and (2) all t h e
grounds a t the b a r n and through the earth to the ground rods a t
the t r a n s f o r m e r , a t the primary neutral grounds or at the
substation. T h e amount of current f l o w i n g i n each path will
depend o n the impedance o f the path.
Equipment g r o u n d wires are required to p r e v e n t or reduce s h o c k i n
case of a n electrical fault. T h e u s u a l c o n c e p t is that ground
wires b o n d equipment to the ground via the n e u t r a l - g r o u n d b a r a n d
d r i v e n g r o u n d r o d s . H o w e v e r , this same w i r e forms a path from
the n e u t r a l - g r o u n d bar to the equipment and to the earth i f there
is a path. P a r t o f this path may b e a p o o r conductor like c o n crete. T h u s the grounded milk tank (grounded via the equipment
ground) b e c o m e s part of the current path from the n e u t r a l - g r o u n d
bar b a c k to the power source.
~ l l
the e q u i p m e n t ground wires vhich h a v e a path to earth are in
parallel w i t h the service entrance ground a n d the secondary
neutral.
T h e n e u t r a l - g r o u n d bar functions a s a current divider.
The c u r r e n t f l o w i n a particular equipment ground wire will
depend o n its impedance to the power s o u r c e and the voltage
between the n e u t r a l - g r o u n d bar and l o w s i d e of the power s o u r c e .
Measuring S t r a y Voltage
Stray v o l t a g e h a s been linked to w h a t is commonly called n e u t r a l t o - e a r t h v o l t a g e . N e u t r a l - t o - e a r t h v o l t a g e #ill be referred to
as NIGV ( n e u t r a l - t o - i s o l a t e d ground voltage) in this paper. N I G V
is a large part o f the driving forces f o r stray voltage b u t is
n o t , in i t s e l f , stray voltage. NIGV is the voltage measured
between the n e u t r a l - g r o u n d bar and a n isolated ground rod. T h i s
rod s h o u l d b e isolated from other g r o u n d s . H o w e v e r , there are n o
firm g u i d e l i n e s o r standards to f o l l o w f o r locating where this
rod s h o u l d be driven. Unfortunately the magnitude of the NIGV
will be influenced by the location and q u a l i t y o f the isolated
ground particularly when a resistor is u s e d i n parallel with the
voltmeter.
Stray v o l t a g e o n - t h e - o t h e r - h a n d is the v o l t a g e between two p o i n t s
which a n animal may contact a t the same time. This is the
voltage w h i c h w i l l produce a shock (current flow). To measure
stray v o l t a g e , the measurements must b e made between these
contact p o i n t s . Accurate measurements o f stray voltage is v e r y
difficult i f n o t impossible. The m a i n problem is =he c o n t a c t
resistances. Gustafson (1984) s t a t e s , " I f p o i n t - t o - p o i n t
measurements i n the animal area are being m a d e , the contact
resistances o f the measurement circuit w i l l likely be very
different from those of an animal."
e.
.-
-
-
This p r o b l e m w i l l be most severe w h e n one o f the contact points
is n o n - m e t a l l i c , high resistance material such as concrete.
Unfortunately concrete is o f ~ e none o f the contacr points. h
second c o m p l i c a t i n g factor is chat the m o s t common approach to
measuring s t r a y v o l t a g e is t o u s e a v o l t m e t e r wich t h e poiltred
probes provided with the meter.
P o i n t e d p r o b e s on a c o n c r e t e
s u r f a c e w i l l have h i g h c o n t a c t r e s i s t a n c e a n d p r e v e n t good
measurements even w i t h a high i n p u t impedance v o l t m e t e r .
To
c o m p o u n d t h e p r o b l e m f u r t h e r , t h e r e c o m m e n d a t i o n i s made t o p l ~ c e
a r e s i s t o r o f a b o u t 400 R ( v a l u e s e l e c t e d from d a t a p r e s e n t e d by
A p p l e m a n , l 9 8 4 a n d C l o u d , 1 9 8 7 ) i n p a r a l l e l w i t h t h e m e t e r when
measuring s t r a y voltage.
The p u r p o s e o f t h e r e s i s t o r i s t o
The r a s i s c o r
s i m u l a t e a cow b e t w e e n t h e two c o n t a c t p o i n t s .
c a u s e s a much l a r g e r c u r r e n t f l o w c h r o u g h t h e c o n t a c t p o i n t s
producing a g r e a t e r voltage drop, p a r t i c u l a r l y across the contzcc
point with a high resistance material.
To q u a n t i f y t h e p r o b l e m o f c o n t a c t r e s i s t a n c e s , a s e r i e s o f t e s t s
were conducted i n t h e C o r n e l l Teaching Barn.
Table 1 presents
information concerning this barn.
A v o l t a g e was a p p l i e d b e t w e e n
v a r i o u s components o f t h e stanchions and a n i s o l a t e d ground r o d .
The c i r c u i t d i a g r a m f o r t h e equipment u s e d t o a p p l y t h i s v o l t a g e
i s shown i n F i g u r e 1.
A schematic showing t h e system and the
measuring p o i n t s i s given i n Figure 2.
T h e DMMs ( d i g i t a l
m u l t i m e t e r ) u s e d h a d a n i n p u t impedance o f 10 XR.
Two v o l t s r m s A C w a s a p p l i e d b e t w e e n
Stray voltages
i s o l a t e d ground "Z".
t h e c o n c r e t e s t a l l f l o o r and t h e s t a
rnents w e r e made u n d e r f o u r d i f f e r e n t
s t a l l d i v i d e r 9RD and
were t h e n measured between
ll divider.
Thsse rneasureconditions.
1.
A
2.
i n . square copper p l a t e with four l a y e r s of
paper cowel soaked with 3 p e r c e n t s a l t s o l u t i o n wich
p r e s s u r e a p p l i e d by o n e ' s f o o t ( t h e c o n c r e t e w a s d r y
b e E o r e t h e t e s t s were made)
a . no r e s i s t o r
b. with resistor
p o i n t e d m e t e r p r o b e i n d ~ i r e c tc o n t a c t w i t h
concrete
a.
no r e s i s t o r i n p a r a l l e l w i t h m e t e r
b.
w i t h 400 Q r e s i s t o r
A 4
T h e d a t a p r e s e n t e d i n T a b l e 2A s h o w s t h e c o n t r a s t b e t w e e n t h e
v o l t a g e s measured i n t h e s e f o u r ways.
Additional daca, plotted
i n Figure 3 , i l l u s t r a t e s the impact o f t h e c o n t a c t r e s i s c a n c e on
T h e m o s t common
t h e v o l t a g e m e a s u r e d , e v e n w i t h a 1 0 Mn DXX.
method o f m e a s u r i n g s t r a y v o l t a g e ( v o l t m e t e r wich r e s i s t o r and
poinced p r o b e ) gave v a l u e s t h a t were n e a r o r a t z e r o w h i l e
v o l t a g e s m e a s u r e d w i t h t h e same v o l t m e t e r a n d p r o b e b u t u s i n g a
m e t a l p l a c e a n d wee t o w e l s were a b o u t 0 . 3 V .
This difference nay
n o t s e e m l i k e m u c h b u t when d e a l i n g w i t h v o l t a g e c h r e s h o l d s t h a t
rnzy Ibe r n t h e t e - n c h s o f v o l t s , 0 . 3 i s s i g n i f i c a n t .
The p l a t e ;
:owel s y s t e m a l s o r e d u c e s t h e v a r i a b i l i t y i n r e a d i n g s a s c o m p z r e d
t o the p o i n t e d probe d i r e c t l y on the c o n c r e t e .
The c a n t a c t
r e s i s t a n c e d e p e n d s o n slhecher t h e p r o b e i s on a scone o r c r l ~ ~ t . : l t .
s c h e m a t i c d i a g r a m o f t h e c i r c u i t s i n s t a l l n o . 8 i s shown i n
Figure 4.
R e p r e s e n t a t i v e v o l t a g e s t a k e n f r o m T a b l e 2A a r e u s e d .
The v o l t a g e between t h e s t a l l d i v i d e r and t h e c o n c r e t e f l o o r i s
assumed t o be 0.42 V because t h e volEage drop a c r o s s t h e p l a t e
a n d w e t t o w e l w a s v e r y s m a l l when a 1 0 M Q m e t e r w a s u s e d .
The
p l a t e and towel were measured t o have a r e s i s t a n c e o f a b o u t 10 Q .
The v o l t a g e d r o p a c r o s s t h e c o n c r e t e - p r o b e c o n t a c t p o i n t was 0 . 0 8
V ( 0 . 4 2 - 0 . 3 4 ) when m e a s u r e d w i t h o u t a r e s i s t o r a n d a d r o p o f 0 . 4 2
V (0.42-0.003) with a r e s i s t o r .
A
The f o l l o w i n g r e c o m m e n d a t i o n i s made: w h e n e v e r a n o n - m e t a l l i c
'material, high resistance material is involved i n a contact
v o l t a g e m e a s u r e m e n t , a p l a t e be u s e d e v e n i f t h e m a t e r i a l i s
covered w i t h wet manure.
Should the surface be dry o r rough,
some t y p e o f t h i n p a d s o a k e d i n a s a l t s o l u t i o n m u s t b e u s e d
between t h e p l a t e and concrete.
Neutral-to-Isolated
Ground V o l t a g e and S t r a y V o l t a g e
s t a t e d e a r l i e r , NIGV has been linked with s t r a y v o l t a g e .
In
t h e mind o f some, t h e m a g n i t u d e o f NIGV i s e q u a l i n m a g n i t u d e t o
stray voltage.
This c o u l d be t h e case only i n r a r e c o n d i t i o n s ,
when o n e a n i m a l c o n t a c t p o i n t i s a t i h e same p o t e n t i a l a s t h e
neutral-ground bar and another point a t the p o t e n t i a l of e a r t h .
T h i s would be r a r e .
S u r b r o o k (1984) s t a r e s , "The r e s i s t a n c e o f
t h e animal i t s e l f , however, is only part of the t o t a l c i r c u i t
resistance".
C r a i n e ( 1 9 6 9 ) w r i t e s , "The c o n t a c t r e s i s t a n c e o f
mouth t o m e t a l , t h e i n t e r n a l r e s i s t a n c e o f t h e a n i m a l , t h e
grounding r e s i s t a n c e , and t h e v o l t a g e s o u r c e impedance determine
t h e c u r r e n t t h a t w i l l f l o w f o r g i v e n w a t e r s y s t e m v o l t a g e 1 ' . The
a n i m a l w o u l d , a l m o s t a l w a y s , be a c u r r e n t p a t h i n s e r i e s w i t h and
i n parallel to other resistances.
AS
R e s i s t a n c e s were measured between d i f f e r e n t p o i n t s w i t h i n t h e
t e a c h i n g b a r n and r e f e r e n c e ground t o e x p l o r e t h e magnitude of
t h e s e p a r a l l e l and s e r i e s r e s i s t a n c e s .
These measurements were
made w i t h a n A E X C G r o u n d T e s t e r w h i c h u s e s t h e F a l l o f P o t e n t i a l
p r i n c i p l e of a l t e r n a t i n g c u r r e n t c i r c u l a t i n g between a n a u x i l i a r y
e l e c t r o d e and the "ground" under t e s t .
T h r e e r o d s w i t h 62
p e r c e n t s p a c i n g were employed.
T h i s u n i t u s e s a 225 Hz s q u a r e
wave A C v o l t a g e s o t h a t t h e r e a d i n g s a r e n o t i n f l u e n c e d b y t h e
p r e s e n c e o f s i n e w a v e AC, o r DC v o l t a g e s .
F i g u r e 5 shows a
schematic diagram o f t h e arrangement of ground rods and t h e
measured p o i n t .
Table 1 l i s t s t h e v a l u e s o f t h e measured r e s i s t a n c e s .
These
r e s i s t a n c e s a r e b e t v e e n a known p o i n r w i t h i n t h e b a r n a n d
r e f e r e n c e g r o u n d . T h i s i s n o t t h e r e s i s t a n c e b e t w e e n two s p e c i f i c
p o i n t s b u t a p o i n t and t h e surrounding e a r t h .
The p a t h w a y i s n o t
j u s t s o i r but w i l l inclkde metal, concrete and s o i l .
The m a g n i t u d e o f t h e r e s i s t a n c e s t o s u r r o u n d i n g g r o u n d v a r i e d f r o m 1 .2 R
( f r o m t h e s t a n c h i o n s , i n t a c t w i t h a l l v a t e r a n d vacuum p i p e s ) t o
5 0 0 0 CI ( f o r t h e p a t h f r o m a d r y m e t a l p l a t e o n a d r y cow m a t ) .
When :he w a t e r a n d -.racuum p i p e s w e r e d i s c o n n e c r e d f r o i n t h e
s t a n c h i o n s . t h e r e s i s t a n c e o f t h e s r a n c h i o n s i n c r e a s e d t o 11 fl.
The i m p a c t o f t h e s e r e s i s t a n c e s o n s t r a y v o l t a g e , a s rrie;ls~~r~.tl
wit!^ a r e s i s ~ n r , i s s h o w n i n T a b l e s 2 B . C a n d D .
I f the assu~lpt i o n i s made t h a t t h e s t a n c h i o n s o r p a r t o f t h e s t a n c h i o n s w e r e
to a c h i e v e t h e s a m e p o t e n t i a l a s t h e n e u t r a l - g r o u n d b a r , t h e n t h e
a p p l i e d v o l t a g e s shown i n T a b l e s 2B, C a n d D c a n b e t h o u g h t o f a s
NZGV.
The s t r a y v o l t a g e s , a s m e a s u r e d w i t h a r e s i s t o r , a r ?
f r a c t i o n s of the applied voltage.
The NIGV had t o h e incr(-ased
t o 1 8 V AC rms i n o r d e r t o r a i s e t h e s t r a y v o l t a g e t o a b o u t 0 . 1 V
when m e a s u r e d w i t h a r e s i s t o r .
E q u i v a l e n t c i r c u i t diagrams showing r e s i s t o r s and v o l t a g e s f o r
s t a l l d i v i d e r ( 9 R D ) a r e p r e s e n t e d i n F i g u r e s 6A a n d B .
Values
f o r s t r a y v o l t a g e a r e g i v e n f o r two c o n d i t i o n s , w i t h o u t a n d w i r h
a 410 0 r e s i s t o r i n p a r a l l e l w i t h t h e DMM.
This represents a
v e r y s i m p l e s i t u a t i o n where t h e s t a l l d i v i d e r has a n e u t r a l / e a r t h
v o l t a g e o f 2 . 0 V w i t h o u t r e s i s t o r a n d a cow i s s t a n d i n g i n t h e
s t a l l and touching the s t a l l d i v i d e r .
Depending on t h e c o n t a c c
r e s i s t a n c e s w i t h t h e c o n c r e t e , t h e cow w o u l d b e s u b j e c t e d t o a
v o l t a g e from 0 . 0 0 t o 1.20 V .
The b e s t e s t i m a t e would b e t h e
v o l t a g e measured with t h e p l a t e and r e s i s t o r , 0.32 V .
T h e cow i s
i n s e r i e s w i t h a 900 0 r e s i s t a n c e and i n p a r a l l e l w i t h a 170 R
resistance.
C u r r e n t Flow
AC c u r r e n t does f l o w through a l l t h e ground pachs. The g r o ~ ~ n d
p a t h s c o u l d be t h e ground r o d s a t t h e m e t e r o r s e r v i c e e n t r a n c e ,
t h e b o n d i n g t o a w a t e r p i p e a n d may b e t h e l i g h t n i n g p r o t e c t i o n
system which i s i n t e r c o n n e c t e d t o t h e s t a n c h i o n s , m e t a l r o o f and
w a l l s and o t h e r metal o b j e c t s along with its ground rods and a l l
t h e e l e c t r i c a l equipment grounds which have p a t h s t o ground.
The
c o m p l e x i t y o f t h i s s y s t e m o f " g r o u n d s " b e c o m e s o v e r w h e l m i n g ye:
t h i s i s a system and there is c u r r e n t flowing through a l l of i t
i f t h e r e is a path t o ground.
As stated earlier, the neutralground b a r serves a s a c u r r e n t d i v i d e r , the c u r r e n t flow being
d e t e r m i n e d by t h e NIGV and t h e r e s i s t a n c e of each p a t h .
To g a i n a n u n d e r s t a n d i n g o f t h i s s y s t e m a n d t h e c u r r e n t f l o w s , ii
s t u d y was c o n d u c t e d i n a h e i f e r b a r n a t t h e Space Farm n e a r
Ithaca.
T h i s b a r n had a 120/240 V t h r e e w i r e s e r v i c e e n t r a n c e
s e r v e d d i r e c t l y From t h e m e t e r p o l e .
The p r i m a r y d i s t r i 1 , t t r i o n
was a d e l t a s y s t e m .
T h e r e w e r e f o u r 1 2 0 V b r a n c h c i r c u i ~ si n t h r
barn.
Figure 7 is a schematic diagram of the e l e c t r i c a l scrvici.
entrance f o r the h e i f e r barn.
The l i g h t n i n g p r o t e c t i o n s;~scen!
was a t t a c h e d t o t h e n e u t r a l w i r e a t t h e d r i p l o o p a n d t o t h e
entrance ground wire before the ground rods.
There a r e four
d r i v e n grounds f o r the l i g h t n i n g p r o t e c t i o n .
Table 3 presents
d a t a concerning ihe loads served by the four breakers ( f i v e
c i r c u i t s ) , t h e r e s i s r a n c e s o f varLous grounds and t h e r e s i s t a ? . c e s
of iAe E i v e equipmen: g r o u n d s .
The r e s i s t a n c e o f e a c h e q u i p m e n t
~ r o u n dw i r e t o r e f e r e n c e g r o u n d w a s m e a s u r e d u s i n g t h e A E X C
Ground T e s t e r by r e m o v i n g t h e w i r e f r o m t h e n e u t r a l - g r o u n d b a r
T h e s e r v i c e e n t r a n c e g r o u n d h a d t w o r o d s a s s u m e d t o b e e i g h t feat
l o n g abou: two f e e t a p a r t .
T h e i r c o m b i n e d r e s l s t z n c e rGas 2 1 E .
C i r c u i : n o . 2 a s e r v e d f o u r i n t e r i o r m e r c u r y v a p o r L a m p s zol.:n:~-d
on t h e p o l e s i n t h e barn.
T h e r e was n o m e a s u r a b l e r e s i s t a n c e f o r
t h e equipment ground t o reference ground.
C i r c u i t n o . 4 was f o r
c o n v e n i e n c e o u t l e t s o n l y a n d a g a i n t h e r e w a s no m e a s u r a b l e
r e s i s t a n c e f o r t h e equipment ground.
C i r c u i t n o . 2b s e r v e d a n
o u t s i d e lamp ( m e r c u r y v a p o r ) .
Apparently t h e equipment ground
was s e c u r e d t o t h e l a m p w h i c h w a s m o u n t e d o n t h e e x t e r i o r s h e e t
metal wall of t h e barn.
T h i s m e t a l w a l l was g r o u n d e d v i a t h e
l i g h t n i n g p r o t e c t i o n system.
Thus t h e r e s i s t a n c e f o r t h i s
e q u i p m e n t g r o u n d w i r e was l o w , o n l y 3 . 2 Q .
Circuit no. 3 served three heated stock waterers.
The r e s i s t a n c e
o f t h e e q u i p m e n t g r o u n d t o r e f e r e n c e g r o u n d was 9 . 7 f 2 .
The
r e s i s t a n c e o f i n d i v i d u a l w a t z r e r s r a n g e d f r o m 2 3 t o 38 Q .
The
r e s i s t a n c e o f e a c h o f t h e t h r e e w a t e r e r s was i n p a r a l l e l b e t w e e n
t h e equipment ground and r e f e r e n c e ground.
NIGV i s a d r i v i n g f o r c e f o r s t r a y v o l t a g e . T h e NIGV i s a f u n c t i o n
of the c u r r e n t flow i n the n e u t r a l (grounded) conductor.
The
r e l a t i o n s h i p b e t w e e n NIGV a n d n e u t r a l c u r r e n t f o r t h e h e i f e r b a r n
s t u d i e d i s shown i n F i g u r e 8 .
D a t a f o r t h i s g r a p h was t a k e n o n
five d i f f e r e n t days.
The u n b a l a n c e d l o a d , i n t h e f o r m o f a n
e l e c t r i c h e a t e r w i t h a n a u t o t r a n s f o r m e r , was p l u g g e d i n t o c i r c u i t
no. 4 .
NIGV w a s m e a s u r e d w i t h a DMM.
The e q u a t i o n o f t h e l i n e a r
regression line i s
V
=
0.0136
+
0.0514A
w i t h a n ~ ~ 2 v a l u e of 0 . 9 8 .
The s l o p e o f t h e r e g r e s s i o n l i n e ( 0 . 0 5 1 ) w o u l d b e t h e a c c u m u l a t i v e impedance of t h e n e u t r a l c i r c u i t .
T h i s r e s i s t a n c e i s low
b u t t h i s should be expected because t h e secondary s e r v i c e
e n t r a n c e n e u t r a l w i r e was t h e m a i n d e t e r m i n e r o f t h i s r e s i s t a n c e .
The s t a t e m e n t w a s made e a r l i e r t h a t t h e n e u t r a l - g r o u n d b a r s e r v e s
as a current divider.
The c u r r e n t f l o w i n two g r o u n d s ( s e r v i c e
e n t r a n c e g r o u n d and n o . 3 c i r c u i t e q u i p m e n t g r o u n d ) i s shown i n
F i g u r e 9 a s a f u n c t i o n o f NIGV. The n o . 3 e q u i p m e n t g r o u n d
c a r r i e s more c u r r e n t ehan t h e e n t r a n c e g r o u n d b e c a u s e o f a l o w e r
The
r e s i s t a n c e , 9 . 7 v s 2 1 Q a s measured w i t h t h e ground t e s t e r .
s l o p e o f t h e two r e g r e s s i o n l i n e s i n F i g u r e 9 a r e 0 . 1 2 7 a n d 0 . 0 6 9
eopc T L €A$.
which r e l a t e s t o a r e s i s t a n c e of 7 . 8 and 1 6 . 4 Q,
T h e s e r e s i s t a n c e s a r e n o t e q u a l t o t h o s e m e a s u r e d by t h e g r o u n d
t e s t e r b e c a u s e t h e p a t h and t h u s t h e r e s i s t a n c e f o r t h e c u r r e n t
f l o w f r o m t h e n e u t r a l - g r o u n d b a r :o t h e t r a n s f o r m e r v i a a n
e q u i p m e n t g r o u n d i s n o t t h e same a s t o t h e r e f e r e n c e g r o u n d .
T h e r e i s a l s o t h e p o s s i b i l i t y t h a t some c a p a c i t i v e l o a d e x i s t s
w h i c h w o u l d n o t b e m e a s u r e d by t h e g r o u n d t e s t e r .
The c u r r e n t f l o w i n g t h r o u g h t h e e q u i p m e n t g r o u n d w i r e p a s s e s
There a r e
t h r o u g h :,he w a t e r e r o n i t s way t o t h e t r a n s f o r m e r .
r e s i s t a n c e s t o t h i s c u r - r e n t f l o w becween t h e w a t e r e r and t h e
c o n c r e t e p l a t f o r m on which t h e animal s t a n d s .
This combination
of c u r r e n t and r e s i s t a n c e c a u s e s s c r a y v o l t a g e t o occur between
t h e w a t e r e r and c o n c r e t e .
F i g u r e 10 shows t h e r e l a t i o n s h i p
b e t w e e n t h e c u r r e n t f l o w a n d s t r a y v o i t a g e a s m e a s u r e d v i t h a h10
-
r e s i s t o r b e t w e e n t h e m e t a l h o u s i n g o f t h e w a t e r e r a n d ;I p l ; i t c
on t h e c o n c r e t e f l o o r n e a r t h e w a t e r e r .
The c o n c r e t e was w e l l
c o v e r e d w i t h w e t m a n u r e s o no t o w e l was u s e d .
A current of only
0 . 0 2 8 A i n t h e equipment ground t o v a t e r e r no.1 produced a s t r a y
v o l t a g e of 0 . 2 6 v o l t s .
When t h e e q u i p m e n t g r o u n d w a s d i s c o n n e c t e d from t h e n e u t r a l - g r o u n d b a r t h e s t r a y v o l t a g e a t t h e
waterers decreased t o near zero.
Q
With t h e r e l a t i o n s h i p between N I G V and c u r r e n t f l o w , and c u r r e n t
f l o w a n d s t r a y v o l t a g e e s t a b l i s h e d , F i g u r e 11 c o m b i n e s t h e s e t w o
t o i l l u s t r a t e t h e r e l a t i o n between NIGV and s t r a y v o l t a g e .
For
w a t e r e r n o . 1 s t r a y v o l t a g e i s a b o u t 65 p e r c e n t o f N I G V a n d f o r
n o . 4 w a t e r e r , a b o u t 25 p e r c e n t .
This d a t a i l l u s t r a t e s again the
problem o f p r e d i c t i n g s t r a y v o l t a g e by m e a s u r i n g N I G V .
Had N I G 7 1
been measured with a r e s i s t o r i n p a r a l l e l with the voltmeter,
t h e s e p e r c e n t a g e s would have been h i g h e r .
Conclusions
1. S t r a y v o l t a g e s i s produced by c u r r e n t flowing through
r e s i s t a n c e s i n t h e v a r i o u s g r o u n d p a c h s i n t h e d a i r y b a r n . The
v o l t a g e w i l l v a r y d e p e n d i n g on t h e r e s i s t a n c e s a l o n g t h e s e p a t h s
a n d t h e NIGV. T h e n e u t r a l - g r o u n d b a r f u n c t i o n s a s a c u r r e n t
divider.
2.
S t r a y v o l t a g e must be measured between p o s s i b l e animal
c o n t a c t p o i n t s w i t h a p p r o p r i a t e equipment t o minimize the concacz
point resistance.
Where a p o o r c o n d u c t o r s u c h a s d r y c o n c r e t e i s
i n v o l v e d , a m e t a l p l a t e and a pad s o a k e d w i t h a s a l t s o l u ~ i o n .i f
needed, must be u s e d .
3.
N e u t r a l - t o - i s o l a t e d ground v o l t a g e i s n o t a good i n d i c a t i o n
of s t r a y voltage. S t r a y voltage i s , almost always, a f r a c t i o n of
t h e NIGV.
D a t a f r o m t h i s s t u d y showed s t r a y v o l t a g e t o he 25 t o
4 5 p e r c e n t o f NIGV.
3.
N e u t r a l - t o - i s o l a t e d ground v o l t a g e i s s e e n a s t h e major
producer of s t r a y v o l t a g e i n a d a i r y barn by causing currelit t o
flow i n the a l l the paths to ground.
Faulrs can produce s t r a y
v o l t a g e d i r e c t l y o r by r a i s i n g t h e qIGV.
Recommendations
f o r Reducing S t r a y Voltage
1.
I n s u r e t h a t t h e n e u t r a l w i r e i s p r o p e r l y s i z e d , minimum
number o f s p l i c e s a r e u s e d , and t h e z o n n e c t i o n s a n d s p l i c e s a r e
i n good c o n d i t i o n .
:4-inimize t h e - u n b a l a n c e d 120 V l o a d s
2.
primary n e u t r a l conductor voltage.
3.
Reduce
the
resistance
of
the
i n t h e b a r n a n d :he
ser--.ice e n t r a n c e
ground.
4. R e t u r n to using metal pipe between the well and the b a r n or
include a n appropriately sized ground wire attached to the well
c a s i n g and buried next to plastic pipe.
5 . Increase the resistance to earth o f the electrical paths
f o r m e d b y the equipment grounds.
6 . C o n s i d e r separating the equipment ground and the n e u t r a l
wires. T h e NIGV a t the d a i r y barn would n o t influence s t r a y
voltage.
The current f l o w i n the equipment grounds would be
c o n t r o l l e d by the voltage at the transformer neutral.
References
A p p l e m a n , R.D. and R.J. Gustafson. 1984. Behavioral experiments
q u a n t i f y i n g animal sensitivity to AC and DC currents. Proceeding
f o the National Stray Voltage Symposium. A S A E , S t J o s e p h , MI.
C l o u d , H . A . , R . D . Appleman a n d R . J . Gustafson. 1987. S t r a y
v o l t a g e problems with dairy c o w s . Department o f Agricultural
E n g i n e e r i n g , University o f M i n n e s o t a , St P a u l , M N .
C r a i n e , L . B . , M.H. Ehlers and D . K . Nelson. 1969. Effects o f
d i s t r i b u t i o n system ground voltages appearing o n domestic water
s y s t e m s . Paper No. 6 9 - 8 1 4 , A S A E , St. J o s e p h , MI.
G u s t a f s o n , R.J. 1 9 8 4 . Instrumentation for stray v o l t a g e . P r o c e e d ings o f the National Stray Voltage Symposium. A S A E , S t J o s e p h ,
MI.
S u r b r o o k , T. and N . R e e s e . 1984. Importance o f source elimination
and adherence to the National Electrical Code. P r o c e e d i n g s o f
the National Stray Voltage Symposium. A S A E , St J o s e p h , MI.
S u r b r o o k , T . , N . Reese and A . Kehrle. 1984. Stray v o l t a g e :
sources and solutions. Conference paper n o . 8 4 C H 1 9 6 9 - 5 . I E E E ,
345 E 4 7 t h S t . , New Y o r k , N Y 10017.
.-.
Q
Table 1
D e s c r i p t i o n o f C o r n e l l T e a c h i n g Barn
Stanchions
remodeled about 10 y e a r s ago
1 2 s t a n c h i o n s , 4 0 " b e t w e e n s t a l l d i v i d e r s , a s s e m b l e d wiri-,
b o l t clamps
26 s t e e l pipes i n concrete
m e t a l p i p e vacuum l i n e
no m i l k p i p e l i n e
m e t a l water bowls and w a t e r supply pipe
n e u t r a l w i r e bonded t o w a t e r s u p p l y p i p e a t s e r v i c e enczance
Numbering of
s t a l l s and d i v i d e r s involved with s t u d y
S t a l l No.
11
10
---- ------ ------
D i v i d e r No.
11RD*
8
9
7
6
------ ------ ------ ------
lORD
9RD
8RD
- - - hRD
7RD
R e s i s t a n c e s o f v a r i o u s c o m p o n e n t s o f t h e b a r n co a r e f e r 2 n c e
g r o u n d ( m e a s u r e d w i t h a n AEMC Ground T e s c e r )
COMPONENT
Stanchion system
( i n t a c t w i t h w a t e r a n d vacuum l i n e s )
Stanchion system
( i s o l a t e d from w a t e r a n d vacuum l i n e s )
Single steel pipe
(8RD)
(9RD)
(10RD)
Concrete surface
i n middle of
160
150
210
s t a l l no.8
dry p l a t e on d r y c o n c r e t e (150 l b s )
lead s h i e l d and l a g screw
d r y p l a t e o n d r y cow m a t
one plate** w i t h w e t t e d c o n c r e t e and
f o u r l a y e r s of paper cowel+
two p l a t e s v i t h w e t t e d c o n c r e c e a n d
four layers of paper towel
*
R e f e r s t o t h s r i g h t h a n d d i v i d e r Ln s t s l l n o . l l
4 inch square copper p l a t e
+ saturated w i t h 9 p s r c e n t s a l : s o l u t i o n
*yk
-
180
LOO
220
Table 2
A.
Voltages measuredA i n the t e a c h i n g barn under v a r i o u s
conditions.
See Figure 2 f o r a d e s c r i p t i o n of t h e
system and l o c a t i o n of t h e v a r i o u s p o i n t s
monitored.
~ p p l i e dv o l t a g e :
2 . 0 V AC b e t w e e n " 2 " a n d s t a l l d i v i d e r ( 9 R D )
which had been i s o l a t e d from t h e s t a n c h i o n s
Location
Voltage
d i r e c t probe
NR*
WR*
B. Applied voltage:
c o ~ p e r late
VK
NR
2 . 0 V AC b e t w e e n " 2 " a n d s t a n c h i o n s w i t h
w a t e r and vacuum p i p e s i n t a c t
Voltaee
NR
Location
Voltage applied:
(V AC)
2 . 0 V AC between " Z "
Distance+ from 9RD
inches
Voltave:
NR
(V AC)
WR
and s t a l l d i v i d e r 9RD
9RD t o concrete
WR
Table 2 con't
C.
Applied voltage:
Location
Y to
Y to
Y to
Y to
Y to
Y to
Y to
Y to
A
*
and the stanchions
V o l t a e e WR
(V A C )
W a t e r a n d Vacuum
Stanchions Isolated
Pioes Intact
0.085
0.060
0. 108
0.111
0.110
0.025
A one 4
i n c h s q u a r e c o p p e r p l a t e was u s e f o r m e a s u r i n g v o l c a g e s
a t the concrete surface.
NR means n o
410
-t
6RD
7RD
8RD
9RD
lORD
llRD
w a t e r bowl
C
1 8 V AC b e t w e e n " Z "
r e s i s t o r i n p a r a l l e l w i t h v o l t m e t e r a n d !JR
resistor in parallel.
D i s t a n c e s m e a s u r e d p a r a l l e l t o t h e g u t t e r ant1 i n l i n e
s t a l l divider pipes enter the concrete.
metins
wliel-c!
n
L!I~!
Table 3
Data concerning the h e i f e r barn a t
t h e S p a c e Farm
Loads on branch c i r c u i t s and r e s i s t a n c e s of equipment
grounds.
Branch
circuit
120 V
Loads
Resistance of equipment
grounds t o reference ground
Average
Range
1
Waterer no. 4
Receptacles
33-39 0
2a
Four i n t e r i o r
Lights
2b
One e x t e r i o r
3
Waterers no.
2 and 3
4
Receptacles
2.7-4.2
1,
9.0-19
Resistance of grounds
Grounds
Service entrance
Stock waterer
no.1
no. 2
no. 3
no.4
T o t a l g r o u n d sysrern
I s o l a t e d ground
R e s i s t a n c e t o r e f e r e n c e ground
Range
Average
18-26
21 n
STEP-DOWN
TRANSFORMER
0-20 Vac
ROOS USED FOR GFOUNDS
CIRCUIT USED TO APPLY VOLTAGE
TO PARTS OF STANCHIONS
Figure
i
C i r c u i t Used
Stanchions
t o Apply Voltage
t o V a r i o u s C o m p o n e n ~ scf
TALL DIVIDER
=:
=
+I
130 FT
90 FT-
1''
"2"
-
-
.
;.c;cn:i
011
of
!:round
Rods
a n d Tes:
% i r ~ t s i n
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I
o
0
z
i
-
0.90
0.80
0
L)
~ f l
0
0.70
a
0.60
0.50
>
.a
0.40
0.30
&
0.20
4
I
.u-
0,
0
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0
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-
1 .oo 1.20
1.10
0.10
0.00
-0.1 0
Plate and towel
Without resistor
I
i
-
I
-
&thPd~t~resistor
I
-
-
I
A
I
i
Plate and towel
With resistor
-
No plate with resistor
-
I
I
I
I
0
I
I
I
20
10
1
I
I
30
I
40
D i s t a n c e f r o m 9RP (inches)
Figure 3
Variation in Voltage Between Stall Divider and Stall
Floor with Four Measuring Techniques
STALL DIVIDER
APER TOWEL
ISOtATED GROUND
"2"
rC
Z
Figure 4
I
m
-
410 OHM RESISTOR
-.
-
Schematic o f Stall with Values of Applied and Measured
AC Voltage
yi0;1
NUU BALANCE GROUND TESTER
?FU L[Lly,/
p~
AUXILIARY
CURRENT
ELEc-fmx 7
I
AUXILIARY POTENTIAL
m
r
igure
S c h e m a t i c Diagram o f AEMC Ground T e s t e r ,
f o r E l e c t r o d e s and Neasurement P o i n t
a n d Lo c a c i o n
I
CONTACT POINT (stall dividers)
I
RETE SURFACE
ISOLATED
REFERENCEGROUND
Figure 6A
Measurement o f Stray Voltage Without a Resistor
CONTACT POINT (stall dividers)
RETE SURFACE
REFERENCE GROUND
I
-
41 0 OHM RESISTANCE
r l- g u r e 6 B
7-
Yeasur~rnent o f Stray Voltage With a R e s i s ~ o r
HEIFER BARN ELECTRICAL SERVICE ENTRANCE
240 Volts
I
I
Neutral
v
I
I
I
I
I
L
L1 Red
I
FGEFmcEGR3CIND
L2 BI
I
II
1
I
-----
#1 EQT GRD
#2 a EQTGRO
#3 EQT GRD
#4 EQT GRD
BRANCH CIRCUIT
NEUTRALS
~
Figure
7
C GROUND/
E
LIGHTNING PROTECTION
,
Schematic o f E l e c t r i c a l Ser-rice Entrance a t t h e Space
Farm H e i f e r B a r n
Unbalanced Ampere Load (A)
Figure 8
-x
V
3
0
u
C
w
L
L
3
U
0.13
0.12
0.11
0.10
0.09
0.08
0.07
0.06
0.05
Relationship Between Unbalanced Electrical Load and
Neutral\Isolated Ground Voltage
-
Equipment Ground No. 3
A = 0.0208
R ~ =0.999
+
0.1273V
-
-
Service Entrance Ground
A = 0.0040
R'= 0.998
0
-
-
0.2
-
0.4
+
0.6
Voltage, Neutral/lsolated Ground
Figure 9
0.06098V
0.8
I
1
[V)
Curren: F l o w i n Equipment G r o u n d s P r o d u c e d by Neutral',,
Isolatsd Ground Voltage
-
4.
-I
i
4
Waterer No. 4
= -0.063
= 0.984
%
+
17.80A
-1
!
+
I)
Waterer No. 1
SV = -0.0225
+
p= 0.995
I
1
10.59A
i
I
I
I
I
+
0.00
i
I
1
I
I
I
0.004
I
1
I
1
0.01 2
0.008
0.01 6
I
I
I
0.02
I
0.024
-1
Current in Equipment Ground (A)
Figure
0.06
10
0.05
S t r a y V o l t a g e at W a t e r e r P r o d u c e d by C u r r e n t F l o w i n
Equipmerlt G r o u n d W i r e
I
-
I
0.1 5
I
I
0.25
I
I
0.35
I
I
I
0.45
I
0.55
Voltage, Neutral/lsolated Ground (V)
F t g u r e II
Relationship Between Stray Voltage ac Waterer
Neutral\Isolated Ground Voltage
and
1
Lloyd B. Craine
Melvin H. Ehlers
D. K. Nelson
Electrical Engineering
Animal Sciences
Animal Sciences
Washington State University
Pullman, Wash.
E Zectric PotentiuZ~
Domestic W ~ t e rSwlie~
Do cattle detect electric potentials on domestic water systems? Does it affect their water consumption?
How does this affect productivity?
- ,
w
HY was milk production poor in this Washington
herd? Fresh Jerseys .brought onto the farm
dropped substantially in milk production within
a few weeks and didn't regain past performance. The dairyman, a competent university graduate, noted that he once
received an annoying shock while milking and also felt
tingles while hosing down the milking barn.
The pr~marysupplying the farm was the usual singlephase two-wire system with multiple grounded neutral. T h e
farm secondary was single-phase three-wire, with the neutral solidly connected to the primary neutral and to the farm
water system. T h e power utility checked lines for open
grounds and found none. The voltage between the water
system and a separate ground electrode was measured,
varied with the daily load, and reached a maximum of 7 v.
While this wasn't considered hazardous, the utility did
place more ground rods because Individual rods had over
23 ohms resistance. A11 farm ground rods and the well casing were interconnected with uninsulated copper cable.This
reduced the grounding resistance of this interconnected
ground system to about 5 ohms but didn't affect the water
system voltage to a measurement ground electrode. Milk
production still was not good.
An analysis of the equivalent electric circuit and the
experience of another utility in a human shower annoyance
problem showed that more ground rods at the farm would
not decrease the voltage. T h e engineers suggested that the
grounded neutrals of the primary distribution be separated
from the farm secondary system. When this was done,
secondary neutral voltages were reduced to 1 to 2 v. Dairy
production soon became normal! The cows recovered their
gloss; feeding and drinking habits seemed normal; the
problem apparently was solved.
This experience raised several questions. How widespread is the problem? How well recognized is it as a possible production problem? What voltage levels are
.~cceptable?How can water supply to earth ground voltages
be reduced to appropriate levels?
The problem of annoying voltage on a grounded conductor has been observed before and isolated "fixes" made.
T h e single-phase two-wire multiple-grounded system with
primar). distribution and secondary utilization neutrals
solidly bonded together is a standard, simple technique
used by many utilities for outlying loads. Unfortunately a
neutral-to-ground voltage of some magnitude can appear.
As loads are increased and distribution lines extended to
remote regions onder soil conditions that give high grounding resistance, an annoying voltage level may occur.
The Voltage Source
-
The potential between a grounded metalIic conductor
rind a separate ground electrode arises from either a fault
Electrical engineers at the Washington State University
College of Engineering then were consulted. A quick trial
with one Jersey cow showed that voltages of a level considered satisfactory by the utility gave a noticeable effect on
This i s a condensation. For a copy of the complete report request Paper No. J-814 from ASAE, St. Joseph, Mich. 49085. Price
's $1.00 per copy
or your ASAE Member Order Form.
-
the cow. The current passing through this cow was in the
high "let go" region for humans.
1970
JUlY
-
AGRICULTURAL ENGINEERJNG
current from defective equipment or is a natural consequence of the single-phase return current flow through the
neutral conductor. The relative impedance between the
neutral conductor and the grounding resistance at any point
causes some current to flow through the grounding resistance; thus a voltage drop to e x t h is present. This voltage
will vary with lond and the rel.~tiveimpedances. A substation with a good grounding system also can have a neutral
conductor voltage to earth. While the highest neutral to
earth voltage may appear anyn-here along the line, the far
end usually has the highest voltage. The return current path
415
. . .Electric Potentials in Water Systems
may receive small shocks. A thirsty animal that is wellgrounded in mud has a total resistance of a few hundred
ohms. A t 5 to 10 v, currents between 10 and 20 ma can
flow through the animal. The contact resistance of mouth
to metal, the resistance of the animal, the grounding resistance, and the voltage source impedance determine the current flowing for given water system voltages. The degree
of annoyance depends on the current level and the animal's
sensitivity.
An Experimental System
Daily water consumption as a percentage of the confrol
Fig. 2 Amount in gallons per drink a t specifed voltages
for Holstein heifers
Fig. 1
group
I
Gallons Per Dri*-L'eeklg
Averages A C
Speclfled Voltages
may follow a con~pleximpedance matrix. Decreasing the
grounding resistance at one point may only increase the
current going to ground at that point and change the direction of current flow in a portion of the primary neutral.
Additional grounds will not remove the potential entirely.
Typical primary neutral impedance may be in the 1 to
j ohms per mile range, but the grounding resistance of individual ground rods may range from several hundred ohms
to perhaps 10 ohms, depending on soils and moisture conditions. The metallic water system is normally connected to
the secondary neutral which connects to the primary neutral.
Depending on its extent, depth of burial, condition of
joints, and soil conditions it may have a grounding resistance of 5 ohms or more. Neutral voltages to earth during
normal, unfaulted operation have been measured from 0.1
v to 40 v. From j to 10 r often occurs and doesn't concern
most utjlities. ,
Resistance of Mammals
T h e low potential on a water system causes a current to
pass through a grounded mammal touching the system.
Humans, with insulating skin and foot coverings, have a
resistance to ground of 10,000 to 100,000 ohms. Thus the
current is in microamperes and below the perception level.
A wet human with 1500 ohms resistance in bath or shower
dl4
An electrified fountain system was built to test effects of
controlled water system voltages on animal water consumption. Voltages are referenced to earth by a high-resistance
voltmeter and separate grounding electrode. T h e current
drawn by the animal was measured by a strip chart recording milliameter. A total resistance representing animal resistance plus its grounding resistance could be calculated. A
constant voltage transformer maintained the set voltage
during tests. Water fountains were carefully insulated so
there were no alternate paths for current flow.
A 70 head herd of mixed Guernsey, Jersey and Holstein
heifers 12 to 24 months old were confined in a feedlot and
pasture at the WSU Dairy. Three electrified watering fountains were available for free choice. The 60 cycle sine wave
voltages were set at 0, 3 and 6 rms v to earth. Graphs recorded the current drawn at each contact with the fountain.
The 0 v fountain had sufficient galvanic current that (with
amplification) records could be made of animal contacting
characteristics. The voltages on the fountains were randomly
exchanged to eliminate any learning pattern. A student
observed the drinking procedure 8 hr a day; water consumption from each fountain was recorded daily.
Some heifers would taste from an electrified fountain,
leave, perhaps feed, return to a fountain, taste, and if it
chanced to be the 0 v fountain, drink. Others would drink
from an electrified fountain until voltage reached 4 v;
larger heifers were more tolerant. Fountain 1 with the
highest over-all usage was nenrest the gateway from the
feedlot to the pasture.
This data (Table I) shows that water consumption,
number of tastes and number of drinks were lowest for the
fountain with the highest voltage and that heifers can detect and preferably won't drink from an electrified system.
Then 30 Holstein heifers of uniform size and weight
were separated into two groups of 15, placed in similar
adjacent pens in the feedlot, and fed the same alfalfa silage
ration. T h e control group had access to a single fountain
set at 0 v; the test group had one electrified fountain. Tests
were in July and August, with high daytime temperatures
and low humidity. N o rain fell. Animal water intake was
only from the food or from the fountain.
For six days no voltage was used on either fountain.
The voltage level was then set on the test fountain for five
days, reduced to 0 over the weekend, then set at the next
higher voltage level. This sequence continued until at 8 v
the test group refused to drink for 8 hr in the heat of the
day. They drank sparingly in the next 1 6 hr.
Fig. 1 gives water consumption of the test group as a
percentage of the control group's consumption. Although
consumption was erratic, the test group consumed lesb waAGRICULTURAL ENGINEERING
.
JULY
' 1970
ter as the voltage increased. After the test herd refused to
drink for 8 hr (Sept. 1, 1969) the test group's consumption
returned to near the controI group level when the voItage
was reduced to 0 v.
Fig. 2 shows the average gallons per drink for the test
and control groups and the relationship of the voItage level.
At the lower voltages the test herd averaged fewer galIons
per drink. At the disturbing 8 v level (causing an average
current flow of 19 ma) the test group took more water per
drink.
TABLE I. WSU KNOTT DAIRY CENTER
Voltage on Water Line Test - 70 Cattle Mixed Breed Herd
1Vater Cossumption in Gallo7rs
-
Voltage
Level
(Each Value for 1 Day
Period)
Drinking Fountain
1
2
3
Averages
0
49 1
298
238
342
3
6
302
258
350
120
26
148
11 1
177
109
Averages
44
T h e equivalent total resistance of the mouth contact,
the animal and its grounding resistance were calculated
from the measured voltage to earth and the current. T h e
resistance appeared to increase slightly during the test.
Total resistance of 1000 Ib heifers under these conditions
of wet footing ranges from 324 to 393 ohms. A useful resistance for approximate current calculations where the
neutral voltage is known would be 350 ohms.
131
Number of Drijrks
(8 h r Obsenation Period per d a y )
Drinking Fountain
2
1
Voltage
Level
3
Averages
87
31
98
57
12
7
26
53
41
o
126
3
77
83
65
6
57
86
Averages
Nu7~berof Tastes
(8 hr Observation Period per
dal-)
Drinking Fountain
1
2
Voltage
Level
3
114
96
98
102
3
6
84
62
86
77
41
71
27
28
51
62
43
Averages
...Animal Waste Management
in an antiseptic atmospl~ere.There might
not even be space for the domestic animal
as such -nor can the world now afford
the inefficiencies of reprocessing feed
through animals. The geneticist nfill devel0p a cereal grain containing all nutrients and vitamins necessary for human
life, including protein in digestible form.
But the livestock industry and the public cannot wait for that distant future!
The immediate future begins now. The
the
engineer is
problem with
lo Start to work On
today's technology.
/Conti~l~red
from psge 4 1 4 )
tank to become a digester. The developof cheap fuels
and
manures to be dehydrated
allow
and incinerated without air pollution and
with minimum ash.
~~~~i~~ such advances in meat, egg
milk production, society
support
which seeks
for these
livestock products. Soybean meal and
other protein sources will compete with
that thick tender steak.
merit
The Distant Future
Imagine an animal eating a ration that
eliminates body odors and repelIs insects.
That part of the ration passed as escrement (assuming there is still some) has
no objectionable odor. The animal is
trained to deposit all waste in a hydraulic
conveying system. At a processing center
a centrifuge separates liquids from solids.
The solids are sterilized and shipped to
grain producers to lbe ~ l a ? e d in fields
(urban lawns ill be carpeted). Liquids
will be processed into medicines, fertilizers, insecticides and perfumes.
Or imagine ham and steak cells dividing and redividing as they feed in solution
1970
Averages
o
.
JULY
AGRICULTURAL ENGINEERING
Measured Current Levels
T h e current magnitude and path through the body determine the effect of electricity on mammals. T h e voltage
level is not the primary criteria, as different voltages may
cause the same current to flow depending on the animal
resistance to earth and the source impedance. At 20 ma,
within the upper limits of human "let go" currentj, Holstein heifers also have reached the limit of their tolerance.
Conditions which cause current flow at this level must be
corrected.
Use the Product Directory
in your
agricultural
engineers
YEARBOOK
All ASAE members receive AEY.
-
Non-members may purchase it.
Price - $10.00. Extra copies for
members - $4.00
American Society of
Agricultural Engineers
2950 Niles Rd., St. Joseph,
Michigan 49085
ASAE proudly announces
microfiche editions
of a l l papers presented
a t ;ts two yearly
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..
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about 4 0 0 papers in all. Or, for
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Meeting or Winter Meeting papers; $100 for both.
-
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477
V
NATIONWIDE OCCURRANCES
OF
ELECTRICAL NEUTKAL-TO-EARTII VOLTACE
ON
DAIRY FARMS
Lloyd B. C r a i n e
Professor , E l e c t r i c a l Engineering
Washington S t a t e U n i v e r s i t y
Pullrnan, WA 99164
I
I
F o r p r e s e n t a t i o n a t t h e 1980 ' d i n t e r Meeting
AMERICAN SOCIETY OF AGRICULTURAL ENGINEERS
t'dlmer House H o t e l
Chicago, I l l i n o i s
December 2 - 5 , 1 9 8 0
Tile n e u ~ r a l - t o - e a r f l ~
v o l t a g e p r o b l e m 9n d a i r y f a r m s
i s shown t o b e w i d e s p r e a d t h x ~ o u g ~ j o it ~l t~ ec o u n t r y
a l t h o u g h it h a s p r e v i o u s l y b e e n c o n s i d e r e d t o be ,1
s i n g u l a r and l o c a l i z e d problem p e c u l i a r t o a f a r m ,
t y p e o f power d i s t r i b u t i o n s y s t e m , o r u n i q u e a r e a .
Papers presented before ASAE meetings are considered to be the property of the Society.
In general, the Society reserves the right of first publ~cationof such papers, in complete
form. However, it has no objection to publication. in condensed form, with credit to the
Society and the author. Permission to publish a paper in full may be requested from ASAE.
P.O. Box410, St. Joseph, Michigan49085
The Society is not responsible for statements or opinions advanced In papers or discussions
at its meetings. Papers have not been subjected to the review process by ASAE editorial
committees; therefore, are not to be considered as refereed.
NATIONWIDE OCCURRENCES OF ELECTRICAL
1/
NEUTRAL-TO-EARTH VOLTAGES ON D A I R Y FARMS-2/
Lloyd B. CraineABSTRACT
Most p e r s o n s c o n f r o n t e d w i t h a low v o l t a g e c o n d i t i o n between " e l e c t r i c a l l y
grounded" m e t a l l i c f a r m s t r u c t u r e s and t h e e a r t h i n a d a i r y have assumed t h a t
t h e problem i s u n i q u e t o t h e farm. A r e v i e w o f t h e l i t e r a t u r e , c o r r e s p o n d e n c e
and d i s c u s s i o n s w i t h numerous p e r s o n s have shown t h a t a l o w v o l t a g e problem
w i t h s i m i l a r c h a r a c t e r i s t i c s c a u s i n g stress i n a n i m a l s h a s o c c u r r e d i n numerous
areas i n t h e United S t a t e s a n d i n f o r e i g n c o u n t r i e s . T h i s v o l t a g e i s l e s s t h a n
t h e " s a f e t y " v o l t a g e o f t e n c o n s i d e r e d r e a s o n a b l e f o r human e x p o s u r e . Two c o n d i t i o n s
are r e c o g n i z e d . One i s where t h e n e u t r a l v o l t a g e s o u r c e i s on t h e farm, and w i t h
d i l i g e n c e c a n be f o u n d a n d c o r r e c t e d . The o t h e r is o f f t h e f a r m a n d a p p e a r s on
t h e common power d i s t r i b u t i o n a n d l o c a l s e r v i c e n e u t r a l . The problem i s demons t r a t e d t o b e w i d e s p r e a d a n d may have a n effect on d a i r y p r o d u c t i v i t y . C h a r a c t e r i s t i c s o f t h e "FYoblem" are d i s c u s s e d , c o n c l u s i o n s r e a c h e d o n t h e e x t e n t o f t h e
problem, and recommendations f o r t h r e s h o l d v o l t a g e l e v e l s a r e made, a b o u t which
a c t i o n should be t a k e n . A r e a s n e e d i n g r e s e a r c h t o a s s i s t i n p r o v i d i n g economical
s o l u t i o n s are o u t l i n e d .
INTRODUCTION
A c o n c e r n f o r t h e p o s s i b l e e f f e c t s o f v o l t a g e s a p p e a r i n g o n m e t a l l i c cond u c t i n g m a t e r i a l s a c c e s s i b l e t o humans and a n i m a l s h a s been e x p r e s s e d f o r t h e
p a s t s e v e r a l d e c a d e s . The c o n c e r n p r i m a r i l y h a s been t o r e d u c e e l e c t r o c u t i o n
h a z a r d s from e l e c t r i c a l f a u l t s . E l e c t r i c a l c o d e s r e q u i r e t h a t m e t a l l i c s t r u c t u r e s
i n c o n t a c t w i t h e l e c t r i c a l equipment and t h e e l e c t r i c a l n e u t r a l b e c o n n e c t e d
t o g e t h e r and be grounded f o r s a f e t y on a c o n s u m e r ' s p r e m i s e s .
Power companies
have been moving toward a d i s t r i b u t i o n system where t h e h i g h v o l t a g e system
n e u t r a l i s m u l t i p l e grounded a l o n g t h e l i n e , and c o n n e c t e d t o t h e s e c o n d a r y low
v o l t a g e n e u t r a l a n d i t s ground system a t t h e d i s t r i b u t i o n t r a n s f o r m e r . Some
p r o p o r t i o n o f t h e r e t u r n l o a d c u r r e n t f l o w s t h r o u g h t h e n e u t r a l impedance and
t o ground t h r o u g h t h e p u n d i n g r e s i s t a n c e s . A v o l t a g e c a n b e d e v e l o p e d between
t h e n e u t r a l and e a r t h on e i t h e r o r both n e u t r a l s y s t e m s . Although t h e n e u t r a l
is "grounded", it may n o t b e a t e a r t h p o t e n t i a l f o r p e r s o n s o r a n i m a l s i n c o n t a c t
w i t h t h e e a r t h and t o u c h i n g m e t a l connected t o t h e n e u t r a l . These low v o l t a g e s
may c a u s e a stress problem w i t h a n i m a l s i n a wet d a i r y e n v i r o n m e n t .
INTERNATIONAL OCCURENCES
E a r l y i n d i c a t i o n s o f power l i n e n e u t r a l v o l t a g e problems i n r u r a l a r e a s were
r e p o r t e d i n Canada i n t h e 1 9 4 0 ' s by Waghorne C251 and Buchanan C31. These r e p o r t s
were prim&-ily'concerned- w i t h n e u t r a l v o l t a g e s p o s s i b l y p r o v i d i n g a h a z a r d t o
humans, o r b e i n g i n v o l v e d i n t h e e l e c t r o c u t i o n o f a n i m a l s . I n t h e 1 9 5 0 - 6 0 1 s ,
Paper p r e p a r e d f o r p r e s e n t a t i o n a t t h e Annual Meeting o f the American S o c i e t y
o f A g r i c u l t u r a l E n g i n e e r s a t Chicago, I l l i n o i s , December 2-5, 1980.
h o f e s s o r o f E l e c t r i c a l engineer in^, Washington S t a t e U n i v e r s i t y , Pullman,
Washington 99164
P h i l l i p s , S a l i s b u r y , C u r r y , e t a l , [16,17,18,19,8] r e p o r t e d on t h e i r e x p e r i e n c e s
i n New Zealand on t h e effects of low n e u t r a l - t o - e a r t h v o l t a g e s a f f e c t i n g m i l k
p r o d u c t i o n and s u g g e s t e d r e m e d i e s .
I n Europe i n t h e 1 9 7 0 ' s t h e problem h a s been
f u l l y d i s c u s s e d f o r Sweden by S b r l i n C223 and i n a l e t t e r t o t h i s a u t h o r h e h a s
i n d i c a t e d t h a t West and E a s t Germany and A u s t r i a have r e c o g n i z e d t h e problem and
p r o v i d e d m i t i g a t i n g p r o c e d u r e s . What was known i n o t h e r c o u n t r i e s g e n e r a l l y h a s
n o t been a p p a r e n t t o U.S. dairymen o r t o t h e u t i l i t y s e r v i n g them.
UNITED STATES - EXAMPLE CASE
One o f t h e e a r l y U.S. o c c u r r e n c e s of c o n t i n u a l low l e v e l annoyance v o l t a g e s
a f f e c t i n g m i l k p r o d u c t i o n w a s a c o m p l a i n t by a C l a r k County, Washington, dairyman
t o t h e E l e c t r i c a l E n g i n e e r i n g Department a t Washington S t a t e U n i v e r s i t y i n 1968.
T h i s i n v e s t i g a t i o n w i l l be d e s c r i b e d i n d e t a i l , a s it i l l u s t r a t e s t h e f e a t u r e s
o f many s u c h c o m p l a i n t s h e a r d s i n c e t h e n from o t h e r p a r t s o f t h e c o u n t r y .
The dairyman had l o w e r p r o d u c t i o n t h a n h e e x p e c t e d , and when new p r o d u c i n g
a n i m a l s were added t o t h e h e r d , t h e i r p r o d u c t i o n d r o p p e d . The a n i m a l s were
n e r v o u s and tended t o k i c k and d i d n ' t l i k e t o e n t e r t h e m i l k i n g p a r l o r and s t a l l s .
T h e r e was some m a s t i t i s problem. The e f f e c t s seemed t o come and go. S e v e r a l y e a r s
work w i t h m i l k i n g machine r e p r e s e n t a t i v e s , n u t r i t i o n i s t s and V e t e r i n a r i a n s d i d n o t
d i s c o v e r a r e a s o n f o r t h e p o o r p r o d u c t i o n o r e x p l a i n t h e a n i m a l s b e h a v i o r . On
s e v e r a l o c c a s i o n s t h e dairyman n o t e d "Tingles" when c u t s i n h i s s k i n came i n c o n t a c t
w i t h t h e m i l k i n g p a r l o r m e t a l l i c s t r u c t u r e s . These s t r u c t u r e s were bonded t o
t h e farm e l e c t r i c a l g r o u n d i n g c o n d u c t o r which was c o n n e c t e d t o t h e n e u t r a l a t
t h e b u i l d i n g s e r v i c e e n t r a n c e a n d b o t h were grounded i n a c c o r d a n c e w i t h t h e s t a t e
e l e c t r i c a l code. The farm w a s s e r v e d by a two c o n d u c t o r s i n ~ l ep h a s e d i s t r i b u t i o n
line.
The dairyman c a l l e d i n l o c a l e l e c t r i c i a n s who c o u l d f i n d no e l e c t r i c a l e q u i p ment f a u l t o r l e a k a g e problem, b u t d i d measure a v o l t a g e hetweer: t h e "grounded"
m i l k i n g p a r l o r s t a l l s and t h e c o n c r e t e f l o o r , and d r a i n g r a t e s . T h i s v o l t a g e
v a r i e d , b u t p e r s i s t e d even when t h e f a r m power was d i s c o n n e c t e d a t t h e farm s e r v i c e
e n t r a n c e . The l o c a l p u b l i c u t i l i t y s t a f f was a s k e d t o i n v e s t i g a t e .
The u t i l i t y s t a f f c o n f i r m e d t h e e x i s t a n c e o f t h e n e u f r a l t o e a r t h v o l t a g e and
s u g g e s t e d improving t h e bonding and grounding system a t t h e f a r m a f t e r v e r i f y i n g
t h a t t h e r e was no a p p a r e n t f a u l t o r l e a k a g e from t h e farm e l e c t r i c a l equipment.
A d d i t i o n a l bonds between m e t a l l i c s t r u c t u r e s i n t h e d a i r y were made, and a d d i t i o n a l
p u n d r o d s were d r i v e n . When t h i s d i d n o t a f f e c t t h e v o l t a g e , a d d i t i o n a l c o n d u c t o r s
were l a i d on t h e ground t o p a r a l l e l t h e e x i s t i n g l o c a l s e r v i c e n e u t r a l and i n t e r c o n n e c t a l l p o u n d i n g p o i n t s . A c o n d u c t o r w a s l a i d t o a d i s t a n t d e e p w e l l and
connected t o t h e metal c a s i n g . These e f f o r t s d i d n o t appreciably a f f e c t t h e
n e u t r a l - t o - e a r t h v o l t a g e i n t h e d i a r y p a r l o r . T h i s posed a p e r p l e x i n g problem,
not i n t h e i r experience.
The dairyman a s k e d WSU-EE R e s e a r c h t o h e l p i n t h i s problem, and a n on-farm
i n v e s t i g a t i o n w a s made [ 4 ] .
D i f f e r e n t v o l t a g e s v a r y i n g from 0 . 5 t o 7 v o l t s were
measured a t v a r i o u s t i m e s a n d i n v a r i o u s p l a c e s from metal s t r u c t u r e s grounded t o
t h e n e u t r x l arid a r e a s i n - c o n t a c t w i t h t h e e a r t h . These e a r t h c o n t a c t s i n c l u d e d
c o n c r e t e f l o o r s , m e t a l d r a i n g r a t e s , w a t e r and w a s t e d r a i n p i p e s ( m e t a l ) and t h e
e a r t h i t s e l f . Using a l o a d r e s i s t o r , it was shown t h a t t h e v o l t a g e s o u r c e would
f u r n i s h c u r r e n t i n t h e m i l l i a m p e r e r a n r e between t h e "grounded" n e u t r a l and t h e s e
e a r t h e d a r e a s . The v o l t a g e f l u c t u a t e d c o n s t a n t l y and u s u a l l y r e a c h e d a maximum
d u r i n g heavy l o a d t i m e s o n t h e d i s t r i b u t i o n l i n e .
Opening f u s e s and c i r c u i t b r e a k e r s t o c u t o f f s e p a r a t e l o a d s o r t h e e n t i r e
f a r m l o a d d i d not a p p r e c i a b l y a f f e c t t h e n e u t r a l - t o - e a r t h v o l t a g e . T h i s i n d i c a t e d
t h a t t h e measured v o l t a g e s were n o t d u e t o equipment o r w i r i n g i n s u l a t i o n problems
on t h e farm, and checks o f t h e n e u t r a l secondary v o l t a g e between grounding p o i n t s
when c a r r y i n g normal c u r r e n t s d i d n o t show b r e a k s o r h i g h r e s i s t a n c e s . The s i n g l e
phase l i n e served a l l t h e farms a l o n g t h e c o u n t y r o a d , however t h i s was t h e o n l y
dairy.
Common p r a c t i c e w i t h t h i s and many o t h e r power u t i l i t i e s was f o r t h e h i g h
v o l t a g e primary d i s t r i b u t i o n l i n e n e u t r a l and t h e low v o l t a g e s e c o n d a r y l o c a l
s e r v i c e n e u t r a l t o he s o l i d l y connected t o g e t h e r a t t h e distribution t r a n s f o r m e r .
The d i s t r i b u t i o n l i n e was c o n s t r u c t e d i n normal p r a c t i c e , havinp ground r o d s a t
i n t e r v a l s along t h e l i n e and a t each t r a n s f o r m e r . T h i s m u l t i p l e grounding proc e d u r e l e d t o a common b e l i e f t h a t t h e n e u t r a l and m e t a l l i c s t r u c t u r e s bonded
t o t h e n e u t r a l were a t ground ( e a r t h ) p o t e n t i a i . Measurements showed t h e a r e a
had r e l a t i v e l y high s o i l r e s i s t i v i t y , t h u s making it d i f f i c u l t t o o b t a i n a low
grounding r e s i s t a n c e w i t h t h e u s u a l ground r o d . A s i s u s u a l p r a c t i c e , t h e ground
r o d s were p u t i n p l a c e b u t t h e r e s i s t a n c e was n o t measured. It was presumed t h e y
would be adequate. The h i g h s o i l r e s i s t i v i t y was b e l i e v e d due t o t h e s o i l m a t e r i a l
and t h e l e a c h i n g a c t i o n o f t h e h i g h r a i n f a l l i n t h e a r e a .
The u t i l i t y b e l i e v e d grounding w a s t h e o n l y problem and had a t t e m p t e d t o
r e d u c e t h e m e u t r a l - t o - e a r t h v o l t a g e by a d d i n g more grounds.
T h i s was n o t s u c c e s s f u l . It appeared t h a t a s t h e t o t a l grounding r e s i s t a n c e a t t h e farm was r e d u c e d ,
more c u r r e n t went t o e a r t h t h e r e , and t h e n e u t r a l - t o - e a r t h v o l t a g e remained much
t h e same.
The q u e s t i o n o f why d i f f e r e n t v o l t a g e s were measured from t h e "grounded" m e t a l
s t r u c t u r e s t o t h e f l o o r s , g r a t e s o r d r a i n s i n v a r i o u s p l a c e s was r e s o l v e d . Measurements were made of t h e v o l t a g e between a ground rod and e a r t h p o i n t s a t v a r i o u s
d i s t a n c e s from t h e r o d . Each p o u n d r o d s e t up a v o l t a g e d i s t r i b u t i o n g r a d i e n t
a b o u t i t s e l f . I t was l i k e a p o t e n t i a l h i l l t h a t f e l l away n o n - l i n e a r l y w i t h
d i s t a n c e and d i r e c t i o n . Depending where t h e f l o o r , g r a t i n g o r d r a i n w a s on t h e
p o t e n t i a l g r a d i e n t c u r v e , any v o l t a g e between a minimum r e p r e s e n t i n g c l o s e t o a
p o u n d r o d , and a h i g h v o l t a g e r e p r e s e n t i n g f a r e a r t h c o u l d be o b t a i n e d .
A s e a r c h of t h e U.S. l i t e r a t u r e showed t h a t n o t much had been p u b l i s h e d on
t h i s problem. D i s c u s s i o n s w i t h o t h e r u t i l i t y p e r s o n n e l i n d i c a t e d t h e y c o n s i d e r e d
t h i s problem a n i s o l a t e d case and w e r e s u r p r i s e d a d d i t i o n a l grounding had n o t cured
t h e problem. They were aware of t h e t i m e s f a u l t y e l e c t r i c a l equipment o r a broken
o r high r e s i s t a n c e n e u t r a l had l e d t o h i g h v o l t a g e n e u t r a l - t o - e a r t h problems.
G e n e r a l l y t h e s e were d i s c o v e r e d by a n i m a l s b e i n g knocked down o r e l e c t r o c u t e d , o r
t h e farmer being shocked. These could be f i x e d by l o c a t i n g t h e f a u l t y equipment.
Lower v o l t a g e ( l e s s t h a n 1 0 t o 1 5 v o l t s ) on t h e n e u t r a l was c o n s i d e r e d below t h e
" s a f e t y " t o humans v o l t a g e , and t h u s w i t h i n a n a c c e p t a b l e o p e r a t i n g r a n g e .
The recommended s o l u t i o n a t t h i s farm w a s t o i n s t a l l an i s o l a t i o n t r a n s f o r m e r
t o a l l o w t h e primary and secondary n e u t r a l s t o be s e p a r a t e d w i t h r e a s o n a b l e e l e c t r i c a l s a f e t y . The n e u t r a l t o e a r t h v o l t a g e was reduced t o a low l e v e l c o n s i s t i n g
of t h e u q b a l a ~ c ecurrent-. f l o w i n g i n t h e low r e s i s t a n c e o f t h e s e c o n d a r y n e u t r a l Herd p r o d u c t i v i t y slowly i n c r e a s e d i n t h e weeks f o l l o w i n g t h e i s o l a t i o n o f t h e
primary and secondary n e u t r a l s .
One o f t h e c r i t i c a l q u e s t i o n s r a i s e d by t h i s i n v e s t i g a t i o n w a s t h e v o l t a g e
l e v e l t h a t a c t u a l l y produced a measurable e f f e c t on a d a i r y a n i m a l . WSU r e s e a r c h
i n 1969 w i t h t e s t and c o n t r o l h e r d s o f 1 5 h e i f e r s each e s t a b l i s h e d t h a t 8 v o l t s
a p p l i e d between a d r i n k i n g f o u n t a i n and e a r t h would completely s t o p t h e t e s t
a n i m a l s from d r i n k i n g f o r e i g h t h o u r s on a h o t August day.
The e f f e c t o f s u c h
v o l t a g e l e v e l s on d a i r y p r o d u c t i v i t y is a p p a r e n t .
Lower v o l t a g e s produced n o t i c e a b l e b u t l e s s d r a s t i c e f f e c t s . The c u r r e n t a t 8 v o l t s was about 1 9 m i l l i a m p e r e s
The t e s t s i n d i c a t e d a n a v e r a g e a n i m a l t o t a l
depending o n t h e a n i m a l and i t s c o n t a c t s .
r e s i s t a n c e o f a b o u t 350 ohms between t h e tongue/mouth and hooves c o n t a c t s . L 5 1
This r e s e a r c h p u t an upper l i m i t on v o l t a g e / c u r r e n t l e v e l s t h a t would p u t
u n a c c e p t a b l e l e v e l s o f stress on d a i r y a n i m a l s .
UNITED STATES - CONTINENTAL EXPERIENCE
S i n c e t h e e a r l y 7 0 ' s , a d d i t i o n a l l o w v o l t a g e d a i r y problems have s u r f a c e d
i n a number o f a r e a s .
I n t h e e a r l y p a r t of t h e d e c a d e , a dairyman o r h i s c o n s u l t a n t s sometimes would d i s c o v e r a d a i r y v o l t a g e problem. D e f e c t i v e equipment o r
i n s u l a t i o n , unbalanced n e u t r a l c u r r e n t s o r h i g h r e s i s t a n c e n e u t r a l s c o u l d he found
and c o r r e c t e d w i t h s u f f i c i e n t knowledge. When t h e r e was no a p p a r e n t d e f e c t i v e equipment, t h e primary/secondary n e u t r a l v o l t a g e problem began t o he s u s p e c t e d . Attempts
t o s a t i s f a c t o r i l y s o l v e t h i s problem were more d i f f i c u l t
Neither t h e d a i r y i n d u s t r y
o r t h e power u t i l i t i e s were much aware o f t h i s low v o l t a g e animal s t r e s s problem, o r
t h a t s e v e r a l a r e a s were e x p e r i e n c i n g similar e f f e c t s
.
.
I n t h e mid-70's
i n B r i t i s h Columbia, t h e R.C.
Department o f P u b l i c Works had
a number o f dairymen w i t h c o m p l a i n t s o f " t r a n s i e n t " v o l t a g e s .
Wed Feistmann o f
t h e B.C. Dept. o f A g r i c u l t u r e and Robert White o f DeLavel, I,td., d e v i s e d a s u c c e s s -
f u l r e t r o f i t e q u i p o t e n t i a l p l a n e t o r e d u c e t h e v o l t a g e i n m i l k i n g p a r l o r s and
dairymen i n s t a l l e d a number o f them [ll].
About t h e same t i m e i n Whatcom County, Washington, dairymen heard mention o f
d a i r y p a r l o r v o l t a g e s a s a p o s s i b l e p r o d u c t i v i t y i n f l u e n c e . They measured v a r i o u s
l e v e l s o f v o l t a g e and wanted t h i s v o l t a g e r e d u c e d . Finding and r e p a i r i n g d e f e c t i v e
equipment d i d n o t always e l i m i n a t e t h e problem, and a s a low c o s t s o l u t i o n , t h e
"disconnect", ( s e v e r i n g t h e connection between t h e primary and secondarv n e u t r a l s
a t t h e d i s t r i b u t i o n t r a n s f o r m e r ) was done a t a number of farms. There are p o s s i b l e
s a f e t y h a z a r d s w i t h t h e "disconnect" a l t h o u g h t h e r e a r e d i f f e r e n c e s o f o p i n i o n
about t h e r i s k . There was i n t e r e s t i n v e r i f y i n g t h e e q u i p o t e n t i a l p l a n e a s t h e
s o l u t i o n t o t h e problem. A consorturn o f a p r i v a t e u t i l i t y , two d a i r y m e n ' s
o r g a n i z a t i . o n s , and t h e S t a t e Dairy P r o d u c t s Commission funded a r e s e a r c h program.
wSU conducted t h e r e s e a r c h , d e s i g n i n g a n e q u i p o t e n t i a l p l a n e f o r r e t r o f i t .
I t should be noted t h a t as word o f d a i r y v o l t a g e a s a p o s s i b l e p r o d u c t i o n
I n Whatcom County,
problem g o t a r o u n d , more dairymen began t o have " t h e problem".
measurements i n some p a r l o r s gave v o l t a g e s between 0.5 t o 1 v o l t and i n some,
somewhat h i g h e r . Near t h e end o f t h e r e s e a r c h p e r i o d , one farm was measured t h a t
had 1 2 t o 1 4 v o l t s d u r i n g t h e h e a v i e s t l i n e l o a d p e r i o d u n t i l he was p l a c e d on
a n o t h e r d i s t r i b u t i o n l i n e and n e u t r a l . A " s e n s i t i v i t y " was developed.
I
-
The e q u i p o t e n t i a l p l a n e was i n s t a l l e d i n a c o o p e r a t i n g d a i r y m a n ' s p a r l o r
Measureand it r e d u c e d t h e p a r l o r v o l t a g e s t o t h e t e n s of m i l l i v o l t l e v e l s [ 6 ] .
ments i n o t h e r a r e a s of t h e farm i n d i c a t e d t h a t p o t e n t i a l g r a d i e n t s e x i s t e d
away fiom ground r o d s and t h a t t h e r e was a s u r f a c e g r a d i e n t i n a l o a f i n n a r e a .
The s u r f a c e p o t e n t i a l g r a d i e n t w a s s u f f i c i e n t t o p a s s a c u r r e n t o f a h o u t 1 m i l l i ampere t h r o u g h a r e s i s t a n c e e q u i v a l e n t t o t h a t of a n a n i m a l when t h e e a r t h c o n t a c t s
w e r e p l a c e d a d i s t a n c e a p a r t c o r r e s p o n d i n g t o f r o n t t o r e a r hooves on a f u l l s i z e d
cow. Thus t h e e q u i p o t e n t i a l p l a n e , w h i l e e f f e c t i v e i n e l i m i n a t i n g n e u t r a l - t o - e a r t h
v o l t a g e s i n t h e p a r l o r a n d p r o t e c t i n g t h e a n i m a l s from f a u l t c u r r e n t s d i d n o t s o l v e
t h e v o l t a g e problem f o r t h e e n t i r e farm. T h i s a u t h o r f e l t t h a t an i s o l a t i o n t r a n s f o r m e r whose i n s t a l l a t i o n c o s t might be a b o u t a s much a s a r e t r o f i t e q u i p o t e n t i a l
p l a n e , would be a more c o m p l e t e s o l u t i o n C71.
L a t e r i n t h e 7 0 1 s , d a i r y v o l t a g e problems w e r e r e p o r t e d t o l o c a l e x t e n s i o n
a g e n t s , m i l k i n g machine m a n u f a c t u r e r s , USDA r e p r e s e n t a t i v e s , power u t i l i t : e s ,
p u b l i c u t i l i t y commissions, and u n i v e r s i t y r e s e a r c h p e r s o n n e l i n v a r i o u s p a r t s o f
t h e c o u n t r y . A s a r e s u l t more i n f o r m a t i o n became a v a i l a b l e . W i l l i a m s C263 i n
washington p r e p a r e d s e v e r a l a r t i c l e s on h i s e x p e r i e n c e and made recommendations.
H e r e c e n t l y s u g g e s t e d upward o f two hundred f a r m s i n h i s a r e a may have a v o l t a g e
problem. T h e i r e x p e r i e n c e s i n C a l i f o r n i a and Washington l e a d F a i r b a n k and C r a i n e
t o r e a l i z e t h e problem m i g h t be more widespread t h a n t h e i r i n d i v i d u a l e x p e r i e n c e s
i n d i c a t e d , and two
t o inform t h e p u b l i c w e r e p r e p a r e d ~ 9 , 1 0 1 .
I n Minnesota, Appleman a n d Cloud [ l l , S e e l i n g C201 and G u s t a f s o n El21 have
produced p a p e r s on s t r a y . v o l t a g e problems i n d a i r i e s .
So f a r t h e y have e x p e r i e n c e s w i t h o v e r 1 0 0 d a i r i e s . I n Iowa, Soderholm [21] r e v i e w e d h i s work and
s u g g e s t e d measurement t e c h n i q u e s and c o r r e c t i v e m e a s u r e s .
I n Wl' s c o n s i n , Ra smussen
h a s t o l d o f t h e P u b l i c U t i l i t y Commission's c o n c e r n o v e r t h e problem. I n Nebraska,
S t e t s o n , e t . a l . [ 2 3 , 2 4 3 have worked on t h e cow problem and r e p o r t e d a c a s e s t u d y
o f n e u t r a l - t o - e a r t h v o l t a g e e f f e c t s i n a swine f a r r o w i n g u n T t . I n Michipan,
L i l l m a r s and Surbrook [13] have r e p o r t e d t h e i r s t r a y v o l t a g e e x p e r i e n c e . TVA
c o v e r s Tennessee. m a i o r arts o f Kentuckv. and n o r t h e r n a r e a s o f G e o ,r ~ i -a . Alabama.
and M i s s i s s i p p i . ' ~ a i d o x ' a n d ~ z e l ~ h a i n
v d iec a t e d n r o b l e m s ~ v ~ e e n
r e p o r t e d i n e a c h o f t h e s e areas. Raird [ 2 ] h a s r e p o r t e d a n a s s o c i a t i o n between
mastitis and low v o l t a g e s o n d a i r y f a r m s i n Nova S c o t i a and New Firunswick.
Much o f t h e i n f o r m a t i o n on p a r t i c u l a r e x p e r i e n c e s is n o t p u h l i s h e d .
Individu a l s h a n d l e t h e c o m p l a i n t s and t r y t o r e d u c e t h e problem by some means when it is
r e c o g n i z e d . From p e r s o n a l d i s c u s s i o n ( i n c l u d i n g h e a r s a y ) t h e d a i r y v o l t a g e problem
h a s been r e c o g n i z e d i n P e n n s y l v a n i a , New York, North C a r o l i n a , South C a r o l i n a ,
IYissouri, Oregon, a n d I d a h o .
UNITED STATES - ASSOCIATED PROBLEMS
The n e u t r a l - t o - e a r t h v o l t a g e c a n a f f e c t more t h a n d a i r i e s . O t h e r a n i m a l
o p e r a t i o n s a l s o may b e a f f e c t e d . A s d i s t r i b u t i o n l i n e n e u t r a l c u r r e n t s and l i n e
l e n g t h s i n c r e a s e t h e v o l t a g e may i n c r e a s e .
I n d i c a t i o n s o f human d i f f i c u l t y w i t h
n e u t r a l - t o - e a r t h v o l t a g e s have been heard from owners o f m o b i l e homes, swimming
p o o l s , showers, o u t s i d e f a u c e t s , and o t h e r p l a c e s where p e o p l e a r e i n b a r e s k i n
e l e c t r i c a l c o n t a c t w i t h t h e e a r t h and a l s o t o u c h a m e t a l l i c o b j e c t "grounded" to
t h e neutral.
IAWSUITS
6
-. . . .
The s e r i o u s n e s s o f t h e s i t u a t i o n i s emphasized hy i n c r e a s i n g l i t i g a t i o n .
I a w s u i t s i n s e v e r a l s t a t e s have been f i l e d , a r e p e n d i n g , have been s e t t l e d b e f o r e
g o i n g t o t r i a l , o r h a v e n o t been p u r s u e d . Lower p r o d u c t t o n t h a n e x p e c t e d o r p r e v i o u s l y e x p e r i e n c e d i s a s e r i o u s economic problem f o r t h e d a i r y f a r m e r . Because
of t h e many f a c t o r s a f f e c t i n g p r o d u c t i o n t h a t c o n s t a n t l y change on t h e f a r m , t h e
p r e s e n c e o f v o l t a g e c a p a b l e of p r o v i d i n g s i g n i f i c a n t c u r r e n t c a n be c o n s i d e r e d o n l y
o n e of t h e p o s s i b l e factors. I n c r e a s e d d i s t r i b u t i o n l i n e l o a d s may i n c r e a s e
t h e s e problems i n t h e f u t u r e . U n l e s s t h e problem is r e c o g n i z e d e a r l y and cooperat i v e l y r e s o l v e d by t h e r e a l p a r t i e s c o n c e r n e d , l a w s u i t s may i n c r e a s e and g i v e
d i f f i c u l t p r e c e d e n t s w i t h which t o workUNITED STATES - SOURCES OF NEUTRAL-TO-EARTH VOLTAGES
Normal l o a d c u r r e n t f l o w i n g i n e i t h e r t h e p r i m a r y o r s e c o n d a r y n e u t r a l l i n e
impedance w i l l c a u s e a v o l t a g e d r o p a l o n g t h e c o n d u c t o r . I n normal p r a c t i c e b o t h
n e u t r a l s w i l l be m u l t i p l e g r o u n d e d . The g r o u n d i n g system w i l l have a r e s i s t a n c e
t o e a r t h . P a r t o f t h e n e u t r a l c u r r e n t w i l l f l o w t o t h e e a r t h and r e t u r n t o t h e
n e u t r a l a t a n o t h e r p o i n t d e p e n d i n g on v o l t a g e and phase c o n d i t i o n s a l o n g t h e
n e u t r a l . Large n e u t r a l c u r r e n t s , h i g h n e u t r a l impedances and h i g h g r o u n d i n g r e s i s t a n c e s make for h i g h e r v o l t a g e s on e i t h e r p r i m a r y o r s e c o n d a r y n e u t r a l s . Unbalanced
n e u t r a l c u r r e n t s , equipment o r c o n d u c t o r m i s c o n n e c t i o n s o r i n s u l a t i o n f a i l u r e s c a n
l e a d t o o f f s e t v o l t a g e s on n e u t r a l s . The f a i l u r e may n o t l e a d t o c u r r e n t s s u f f i c i e n t
t o o p e r a t e standard f u s e s o r c i r c u i t breakers.
(Ground f a u l t d e t e c t o r t y p e
c i r c u i t breakers can respond t o t h i s c o n d i t i o n . )
On t h e consumer's p r e m i s e s by t h e n a t i o n a l e l e c t r i c a l c o d e ( g e n e r a l l y a d o p t e d
by a l l s t a t e s ) e l e c t r i c a l equipment and t h o s e c o n d u c t i n g s t r u c t u r e s t o which t h e v
a r e a t t a c h e d must h e grounded t o t h e e l e c t r i c a l n e u t r a l and t o a ground p o i n t . T h i s
grounding may n o t l e a d t o a l l s t r u c t u r e s on t h e s e c o n d a r y b e i n g e f f e c t i v e l y a t
e a r t h potential in a l l cases o r a t a l l times.
The d i s t r i b u t i o n p r i m a r y n e u t r a l a l s o may have a p o t e n t i a l t o e a r t h . I n many
systems t h e primary and s e c o n d a r y n e u t r a l s a r e c o n n e c t e d t o g e t h e r a t t h e d i s t r i b u t i o n
t r a n s f o r m e r forming a common n e u t r a l s y s t e m . Common n e u t r a l s y s t e m s may t r a n s f e r
secondary n e u t r a l v o l t a g e problems t o a n o t h e r s e c o n d a r y n e u t r a l . D i s t r i b u t i o n
s y s t e m s a r e handled by a d i f f e r e n t c o d e , t h u s t h e r e a r e d i f f e r e n c e s o f o p i n i o n
r e g a r d i n g a n y r e q u i r e m e n t t o i n t e r c o n n e c t p r i m a r y and s e c o n d a r y n e u t r a l s . Local
d e c i s i o n s a s t o s t a t e o r l o c a l r e g u l a t i o n s , d e s i r e a b l e system o p e r a t i n g c o n d i t i o n s ,
i n t e r p r e t a t i o n s o f s a f e t y c o n s i d e r a t i o n s , and r i s k f a c t o r s from p o s s i b l e l i g h t n i n g ,
l i n e c r o s s e s o r f a l l downs o r o t h e r f a c t o r s may i n f l u e n c e t h e i n t e r c o n n e c t i o n o f
n e u t r a l s t o meet b r o a d e r needs o f a l l power consumers and s u p p l i e r s .
UNITED STATES - CONCLUSIONS
From t h i s i n f o r m a t i o n , i t i s a p p a r e n t t h a t n e u t r a l - t o - e a r t h v o l t a g e s a r e
e x p e r i e n c e d a t v a r i o u s l e v e l s t h r o u g h o u t t h e c o u n t r y . C o n s i d e r i n g t h e number o f
o c c u r r e n c e s , t h e problem c a n n o l o n g e r be c o n s i d e r e d a s i n g u l a r and u n i m p o r t a n t
e v e n t . I t h a s been shown t h a t it is n o t p e c u l i a r t o a p a r t i c u l a r farm t y p e , a
s p e c i f i c kind of d i s t r i b u t i o n l i n e , a c e r t a i n u t i l i t y , a l o c a l i z e d a r e a , o r r e s u l t
from i n d i v i d u a l e l e c t r i c a l c o d e s . The prohlem c a n h e e x p e c t e d t o o c c u r i f c e r t a i n
c o n d i t i o n s a r e met. The s o u r c e o f t h e v o l t a g e c a n b e d e t e r m i n e d i f s u f f i c i e n t
i n g e n u i t y and t i m e a r e s p e n t . Though t h e problem is complex, e l e c t r i c a l l a w s s t i l l
S y s t e m a t i c and l o c i c a l p r o c e d u r e s can be u s e d .
o p e r a t e , t h e r e is nothinp, "magic".
The i n c r e a s i n g exchange o f i n f o r m a t i o n between g r o u p s c o n c e r n e d w i t h t h e
complex aEpect> o f t h e p5oblem h a s s e n s i t i z e d a number o f g r o u p s t o t h e b e n e f i t o f
a l l . E f f o r t s t o u n d e r s t a n d t h e f u l l d i m e n s i o n s of t h e problem a s it a p p l i e s t o
animal h e a l t h and p r o d u c t i v i t y a r e i n c r e a s i n g . D i s c u s s i o n s w i t h many i n v o l v e d
p e r s o n s shows t h a t competent h e l p , knowledgeable and e x p e r i e n c e d i n t h i s problem
a r e a s h o u l d be c o n s u l t e d . The problem c a n he i n t r i c a t e and may be i n t e r m i t t a n t .
RECOMMENDATIONS
I t is now b e l i e v e d t o be u s e f u l t o minimize t h e d i r e c t c o n t a c t v o l t a ~ e(and
c u r r e n t ) t o which animals a r e exposed. There i s no r e s e a r c h a s y e t t h a t d e f i n e s a
t h r e s h o l d l e v e l f o r known r e s p o n s e s .
It is i m p r a c t i c a l t o have a z e r o v o l t a g e
environment.
I n t h e absence o f r e s e a r c h , it i s b e l i e v e d t h a t v o l t a g e s t h a t a n i m a l s
can c o n t a c t g r e a t e r than a b o u t 0 . 5 v o l t s A . C . should be i n v e s t i g a t e d and t h e s o u r c e
found. C u r r e n t flow should be measured, and judgement used a s t o t h e p o s s i b l e
p a t h t h e c u r r e n t might t a k e through t h e a n i m a l and i t s p o s s i h l e e f f e c t s . L i t t l e
is known a b o u t D.C. v o l t a g e s / c u r r e n t s o r t r a n s i e n t s (momentarv h i g h e r v o l t a g e
"kicks").
The f i r s t p r i o r i t y should be t o make s u r e t h e s o u r c e is not i n t h e farm second a r y l o c a l s e r v i c e system. When it is known t h e farm is meeting modern e l e c t r i c a l
s t a n d a r d s , t h e e f f o r t s t o i d e n t i f y o f f - f a r m s o u r c e s should be made. The l o c a l
u t i l i t y may p r o v i d e h e l p . A r t i c l e s on p r o c e d u r e s t o t r o u b l e - s h o o t and recommended
ways t o r e d u c e v o l t a g e problems a r e i n c l u d e d i n a Bibliography on t h e d a i r y v o l t a g e
problem by Gustafson and C r a i n e (12).
U n i v e r s i t y p e r s o n n e l i n Cooperative E x t e n s i o n , Animal ScLences, and E l e c t r i c a l
Engineering, USDA p e r s o n n e l , power u t i l i t i e s , m i l k i n g machine and o t h e r e l e c t r i c a l
s u p p l i e r s , and some p r i v a t e c o n s u l t a n t s c a n p r o v i d e a s s i s t a n c e . S t a t e d a i r y commiss i o n s o r u t i l i t y commissions may p r o v i d e i n f o r m a t i o n .
S t a t e and n a t i o n a l groups
involved i n p r e p a r i n g and e n f o r c i n g e l e c t r i c a l c o d e s may need t o c o n s i d e r t h e
g e n e r a l problem o f t h e common o r i s o l a t e d n e u t r a l between d i s t r i b u t i o n l i n e and
consumer. I t i s g e n e r a l l y recognized t h a t a d d i t i o n a l d e f i n i t i v e knowledge is needed
through r e s e a r c h .
NEEDED RESEARCH
There i s need f o r r e s e a r c h t o u n d e r s t a n d t h e e f f e c t s o f c u r r e n t f l o w through
t h e a n i m a l v i a s e v e r a l o f t h e common e n t r y p a t h s (mouth, udder, hooves) a s r e l a t e d
t o s t r e s s o r d i s e a s e . Acceptable t h r e s h o l d l e v e l s f o r animals when eat in^, d r i n k i n g ,
being milked, o r l o a f i n g is needed s o economic s o l u t i o n s can be found. Procedures
f o r e a s i l y i d e n t i f y i n g and c o r r e c t i n g v o l t a g e s o u r c e s on t h e farm a r e needed.
Research is needed on economical and s a f e methods o f r e d u c i n g n e u t r a l - t o - e a r t h
v o l t a g e s where needed. The r e l a t i v e r i s k s o f t h e s e methods need a s s e s s m e n t .
L e ~ a land r e g u l a t o r y c o n s i d e r a t i o n s need t o be e v a l u a t e d and t h e consequences o f
changes c o n s i d e r e d . F i n a l l y , comprehensive p u b l i c a t i o n s on v a r i o u s a s p e c t s of
t h e problem a r e needed t o be widely d i s s e m i n a t e d t o a l e r t farmers and u t i l i t i e s t o
t h e problem and what c a n be done. Some r e s e a r c h i n t h e s e a r e a s i s a l r e a d y s t a r t e d ,
but i s n o t completed a t t h i s t i m e .
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D. a n d H . A . Cloud ( 1 9 8 0 ) . S t r a y v o l t a g e p r o b l e m s w i t h
d a i r y cows.
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[2]
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L-
r
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e l e c t r i c a l hazards i n livestock buildings) Jordbrukstekniska i n s t i t u t e t
( S w e d i s h I n s t i t u t e o f A g r i c u l t u r a l E n g i n e e r i n g ) B u l l e t i n No. 3 4 1 ; 3 8 p .
C233
S t e t s o n , L. E . a n d A . D . B e c c a r d , J . A . DeShazer ( 1 9 7 9 ) .
s w i n e f a r r o w i n g u n i t - a c a s e s t u d y . ASAE 79-3502.
[24]
S t e t s o n , L. E. a n d L. H .
v o l t a g e s . ASAE 80-3505.
Soderholm H . S h u l l ( 1 9 8 0 ) .
[25]
Waghorne, J . H .
69:660-663.
Rural n e u t r a l p o t e n t i a l s .
C261
W i l l i a m s , Grady F. ( 1 9 7 5 ) . V o l t a g e l e a k s a n d t h e i r e f f e c t s o n D a i r y c a t t l e .
E x t e n s i o n Keport Washington S t a t e U n i v e r s i t y Research and E x t e n s i o n C e n t e r ,
P u y a l l u p , WA .
(1979).
(1950).
RURAL ELECTRIC
S t r a y - v o l t a g e problems i n d a i r y m i l k i n g p a r l o r s .
Stray voltages i n a
I n v e s t i g a t i o n s of s t r a y
AIEE TRANSACTIONS
I
'
L I A Z I L I T Y FOR NEUTRAL-TO-EARTH VOLTAGE ON FARI.IS~/
L l o y d E. C r a i n e -2/
ABSTRACT
V o l t a g e s - t o - e a r t h a r i s e f r o m c u r r e n t f l o w t h r o u g h v a r i o u s impedances i n
a c c o r d a n c e w i t h e l e c t r i c a l c i r c u i t p r i n c i p l e s . The magnitudes o f t h e s e c u r r e n t s
and t h e impedances can be c o n t r o l l e d b y t h e group d e s i g n i n g , s e l e c t i n g
m a t e r i a l s, i n s t a l 1 i n g , o p e r a t i n g , m o d i f y i n g and r e p a i r i n g t h e e l e c t r i c a l system.
T h e r e i s i r ~ c r e a s e dc o s t a s s o c i a t e d w i t h a we1 1- d e s i g n e d and m a i n t a i n e d s y s t e ~ .
Some o f t h e groups i n v o l v e d i n b u i l d i n g c o n s t r u c t i o n , p r i m a r y power d i s t r i b u t i o n
o r secondary c i r c u i t u t i 1 iz a t i on shoul d be more know1 edgeabl e a b o u t t h e p r o p e r
a p p l i c a t i o n o f e l e c t r i c a l p r i n c i p l e s t o reduce v o l t a g e - t o - e a r t h problems t h a n
I t i s t h e r e s p o n s i b i l i t y o f each ~f t h e s e knowledgeable groups as
others.
d e s c r i b e d i n t h i s paper t o p r o p e r l y p e r f o r m t h e i r p a r t i n t h e d e s i o n ,
i n s t a l 1a t i o n and o p e r a t i o n , and .in t h e t r o u b l e s h o c t i n g s h o u l d p r o b l e m o c c u r .
Some o f t h e s e groups do n o t have t h i s knowledge and must r e l y on t h ~ s ew i t h
expertise f o r solutions.
Power d e l i v e r y a ~ duse r e q u i r e s some v o l t a g e s t o
e x i s t . The 1 i r n i t s o f t h e v o l t a g e s - t o - e a r t h and t h e r e s u l t i n g c u r r e n t s t h r o u g h
a n i m l s and humans t h a t cause s t r e s s have n o t been d e f i f i e d a l t h o u g h some l i m i t s
i n p a r t i c u l a r cases a r e a c c e p t e d .
It i s the r e s p o n s i b i l i t y o f the e l e c t r i c a l l y
knowledgeable groups t o use p e r m i t t e d v a r i a t i o n s i n e l e c t r i c a l codes t o meet t h e
needs f o r l o w v o l t a g e s - t o - e a r t h i n c e r t a i n s i t u a t i c n s where a n i m a l s o r hurnacs
a r e expcsed t o e l e c t r i c a l s t r e s s .
From t h i s r e s p o n s i b i l i t y f o r p r o p e r
performance i s d e r i v e d t h e 1i a b i l i t y .
E l e c t r i c a l problems i n d a i r i e s and o t h e r animal h o u s i n g f a c i l i t i e s , o f t e n
c a l l e d stray, t i n g l e o r neutral-to-earth
v o l t a g e s have r e c e i v e d i n c r e a s 3 d
a t t e n t i o n f o r t h e i r p o s s i b l e e f f e c t s on f a r m p r o d u c t i o r ~ [I].The problem has
been f o u n d t o be w i d e s p r e a d i n t h e U n i t e d S t a t e s and Cariada [ 2 ] b u t n o t as
p r e v a l e n t i n Europe [3].
The p r o b l e m i s t h a t v o l t a g e s e x i s t between metal
s t r u c t u r e s t h a t t h e a n i m a l s t o u c h and t h e c o n c r e t e / e a r t h t h e y s t a n d o r l i e on
and s t r e s s t h e a n i m a l s .
They may a l s o be a f f e c t e d by a p o t e n t i a l g r a d i e n t
a c r o s s t h e s u r f a c e t h a t p r o d u c e s a c u r r e n t t h r o u g h t h e a n i m a l f r o m h o o f t c hoof.
I n some o f t h e s e cases, l a w s u i t s have ensued.
The l i t i g a t i o n has been
p r i m a r i l y between i n d i v i d u a l f a r m o p e r a t o r s and an e l e c t r i c a l u t i l i t y o r a n
equipment. m a n u f a c t u r e r .
I n g e n e r a l , t h e problem has been s e t t l e d o u t c o u r t .
The s e r i o u s n e s s o f t h e v o l t a g e p r o b l e m i s a p p a r e n t as t h e s e t t l e m e n t s have
r a n g e d f r o m t e n s and hundreds o f thousands of d o l l a r s t o t h e m i l l i o n s .
L/
2/
-
Paper p r e p a r e d f o r p r e s e n t a t i o n a t t h e Annual b i e e t i n g o f t h e American
S o c i e t y o f A g r i c u l t u r a l E n g i n e e r s a t Chicago, I l l i n o i s , December 14-17,
1982.
Prwfessor o f E l e c t r i c a l E n g i n e e r i n g , Washington S t a t e U n i v e r s i t y , Pullman,
Washington 99164-2210
p o i n t s , b u t none of t h e s e may be a t e a r t h p o t e n t i a l . Thus a v o l t a g e - t o - e a r t h
f r o m t h e n e u t r a l can e x i s t .
F i g u r e 1 shows t h e v a r i o u s impedances i n t h e secondary complex n e t w o r k
i n c l uding Z
n e u t r a l c ~ n d u c t o r impedance;
g r o u n d i n g r e s i s t a n c e ; Re, e a r t h
resistance;
, g r o u n d i n g r e s i s t d n c e a t R ? y he t r a n s f o r m e r ; and t h e c u r r e n t
f l o w i n g i n the%e impedances.
f r o m o p e r a t i n g equipment
The l o a d c u r r e n t IL
passes t h r o u g h t h e n e u t r a l impedance, w i t h some p r o p o r t i o n T g g o i n g t o e a r t h
t h r c u g h each g r o u n d i n g r e s i s t a n c e .
The e a r t h c u r r e n t I, r e t u r n s t h r o u g h t h e
transformer
grounding r e s i s t a n c e t o
the d i s t r i b u t i c n transformer.
The
n e u t r a l - t o - e a r t h v o l t a g e . VNE r e s u l t s from t h e c u r r e n t f l o w t h r c u g h t h e v a r i o u s
impedance.
D i f f e r e n t v o l t a g e t o e a r t h w i l l o c c u r a t d i f f e r e n t p1ccr.s on t h e
farm.
The power l i n e t o t h e farm d i s t r i b u t i o n t r a n s f o r m e r p r i m a r y w i n d i n s a l s o
has a n e u t r a l c o n d u c t o r .
On s i n g l e phase arid some t h r e e phase l i n e s , t h i s
neutral c a r r i e s primary load current.
Tht? f l o w t h r o u g h t h e n e u t r a l impedance
a l s o s e t s up a v o l t a g e and a l t h o u g h t h e d i s t r i b u t i o n n e u t r a l i s grourided a t each
d i s t . r i b u t i o n t r a n s f o r m e r and a t i r i t e r v a l s a l o n g t h e l i n e , t h e g r o u n d i n g
r e s i s t a n c e ruay be h i g h enough t h a t s u b s t a n t i a l n e u t r d l - t o - e a r t h ( i i - E )
v o l t a g e s can develop i n t h e same wzy as shown i r ; F i g u r e I. biost u t i l i t i e s
r e q u i r e t h a t t h e p r i m a r y and secondary n e u t r a l s be bonded t o g e t h e r a t t h e
d i s t r i b u t i o n transformer.
T h i s i n t e r c o n n e c t i o n i s p e r m i t t e d b y s e c t i o n 97B2 b u t
i s n o t r e q u i r e d b y s e c t i o n 97D o f t h e N a t i o n a l . E l e c t r i c a l S a f e t y Code ( 5 ) .
T~IJS
a v o l t a g e t o e a r t h on a s e c o n d a r y o r p r i n l a r y n e u t r a l i s t r a n s f e r r e d t o t h e c t h e r
n e u t r a l by t h e i n t e r c o n n e c t i o n p r a c t i c e . The v o l t a g e t o e a r t h p r o b l e m o c c u r s
aue t o h i g h n e u t r a l currenEs, and t h e n e u t r a l arid g r o u n d i n g impedances.
A second s c u r c e f o r t h e v o l t a g e s t o e a r t h i s l e a k a g e c u r r e n t f r o m t h e
e n e r g i z e d coriductor t o t h e equipment g r o u n d i n g conductot. o r t o t h e n e u t r a i .
T h i s can i n c r e a s e t h e c u r r e n t t h r o u g h t h e s e impedances, o i t e r i w i t h o u t t r i p p i n g
the overcurrent protective devices.
F i g u r e 2 shows t h e r e 1 a t i onsh ip between a
l e a k a g e c u r r e n t I t o an equipment ground c o n d u c t o r and n e u t r a l . T h i s c u r r e n t
adds t o t h e n e u t r a'lK
c u r r e n t , and depending on t h e r e l a t i v e c u r r e n t and i n p e d a ~ c e
values, increases the voltage t o earth.
A t h i r d source i s l e a k a g e c u r r e n t f r o m t h e e n e r g i z e d c o n d u c t o r o r d e v i c e t o
earth.
T h i s can o c c u r where c o n d u c t o r i n s u l a t i o n i s damaged e x p o s i n g t h e
c o n d u c t o r o r where a c o n d u c t i v e l e a k a g e p a t h o c c u r s a c r o s s t h e s u r f a c e s a s shown
i n F i g u r e 2. The l e a k a g e c u r r e n t ( I LK) goes t o e a r t h and t r a v e l s back o v e r
s e v e r a l p a t h s t o t h e s o u r c e t r a n s f u r m e r . The p r o p o r t i o n of c u r r e n t i n each p a t h
Depending on t h e c u r r e n t
depends on t h e r e l z t i v e impedance o f t h e paths.
c a r r y i n g r a t i n g of t h e c i r c u i t p r o t e c t i v e d e v i c e and t h e o t h e r l o a d c u r r e n t s
t h r o u g h i t , heavy u n n o t i c e d c u r r e n t s c o u l d f l o w t o e a r t h and cause n e u t r a l t o
e a r t h v o l t a g e s . One example i s a power c o n d u c t o r l o c a t e d n e a r o r u n d e r ground
w i t h damaged i n s u l a t i o n . A number o f l e a k a g e paths, each o f r e l a t i v e l y s m a l l
c u r r e n t c o u l d c o n t r i b u t e t o c o n s i d e r a b l e leakage c u r r e n t o v e r a p o o r l y
m a i n t a i n e d system.
Where c u r r e n t e n t e r s t h e ground, a v o l t a g e t o e a r t h i s s e t up due t o t h e
f i n i t e earth con'ductivity.
F i g u r e 3 shows t h e v o l t a g e d e v e l o p e d t o d i s t a n t
e a r t h f o r two d i f f e r e n t e a r t h c o n d i t i o n s .
The p o t e n t i a l d e c r e a s e s i n an
e x p o n e n t i a l form, t h e change b e i n g g r e a t e s t n e a r t h e p o i n t o f c o n t a c t . Animals,
o r humans w i t h h o o f s o r f e e t s p a n n i n g a d i s t a n c e h a v i n g a v o l t a g e d i f f e r e n c e a r e
s u b j e c t t o a " s t e p - p o t e n t i a l " t h c t can cause c u r r e n t t o f l o w t h r o u g h them. The
l e a k a g e - c u r w n t i n c r e a s e s t h e n e u t r a l - t o - e a r t h v o l t a g e as i t r e t u r n s t o t h e
s o u r c e t r a n s f o r m e r t h r o u g h one o r more impedance p a t h s . A n i m a l s w i t h h o o f s t h a t
a r e a g r e a t e r d i s t a n c e a p a r t t h e r ~ humans and n o t i n s u l a t e d w i t h f o o t w e i i r a r e
s e n s i t i v e t o c u r r e n t s i n t h e l o w m i l l iampere range.
'kT
'
U n d e r s t a n d i n g t h e ways t h e n e u t r a l - t o - e a r t h v o l t a g e s a r e d e v e l o p e d , t h e
r e s p o n s i b i l i t y of each g r o u p p a r t i c i p a t i n g i n t h e d e s i g n ,
installation
o p e r a t i o n , m o d i f i c a t i o n and m a i n t e n a n c e o f t h e farm system cat) be assessed.
These r e s p o n s i b i 1 it i e s o f t e n o v e r 1 ap.
BUILDING DESIGNERS/CONTRACTORS
The d e s i g n e r o f t h e fcrm b u i l d i n y ( s ) has a r e s p o n s i b i l i t y f o r p r o p e r d e s i g n
t o modern b u i l d i n g codes w h e t h e r t h e b u i l d i n g i s new, u n d e r g o i n g m a j o r
m o d i f i c a t i o n , o r j u s t r e v i s i o n t o e l i m i n a t e problems.
F o r animal housing
s t r u c t u r e s , t h e b u i l d i n g s h o u l d have a c o n c r e t e f l o o r w i t h embedded s t e e l
reinforcing.
The r e i n f o r c i n g r o d s o r s c r e e n s h o u l d be bcnded t o g e t h e r t o f o r m
an e q u i p o t e n t i a l p l a n e f o r t h e a n i m a l s t o s t a n d / l i e cjn. The r e i n f u r c e m e n t must
be p r o p e r l y connected t o t h e e l e c t r i c a l c e u t r a l / g r o u n d syster;~. K h e r e a n i m a l s
e n t e r o r l e a v e t h e s t r u c t u r e , a p o t e n t i a l g r a d i n g system s h o u l d be i c s t a l l e d
c o n s i s t i n g o f r e i n f o r c i n g r o d s encased i n c o n c r e t e and bonded t o t h e s l a b r o d s .
These encased r o d s s h o u l d fan o u t and yo d e e p e r away f r o m t h e e n t r a n c e t o f o r m a
c o n t r o l l e d v c l t a g e g r a d i e n t s l o p e t o a l l o w t h e a n i m a l s t o g e t on t h e
e q u i p o t e n t i a l p l a n e s u r f a c e w i t h o u t s t r e s s . S i m i l a r g r a d i n g may need t o be done
a t human e n t r a n c e s , a l t h o u g h t h e b o o t s u s u a l l y worn i n t h i s e n v i r o n m e n t p r o v i d e
some i n s u l a t i o n .
A l l n e t a l s t r u c t u r e s w i t h i n t h e b u i l d i n g s h o u l d be bcnded t o each o t h e r , t o
t h e n e u t r a l , and t o t h e r e i n f o r c i n g r o d . The e l e c t r i c a l system s h o u l d meet t h e
e l e c t r i c a l code, i n p a r t i c u l a r A r t i c l e 547 f o r A g r i c u l t u r a l b u i l d i n g s [43.
Cue
c o n c e r n s h o u l d be t a k e r t h a t if any p a r t may g e t wet f o r any r e a s o n i n c l u d i n g
o c c a s i o n a l wash-down, a w a t e r p r o o f e l e c t r i c a l .system s h o u l d be i n s t c l 1 ed.
The d e s i g n e r s h o u l d use l i n e - t o - l i n e c o n n e c t i o n f o r l c e d s i n s t e a d o f l i n e
t o n e u t r a l t o m i n i m i z e n e u t r a l c u r r e n t s , and where such n e u t r z l c u r r e n t !odds
a r e needed, t h e y s h o u l d be b a l a n c e d b o t h i n n e u t r a l impedance and i n t h e t i m e
on. The s e r v i c e e n t r a n c e s h o u l d be l o c a t e d t o m i n i m i z e t h e l e n g t h o f n e u t r a l s
and e q u i p m e n t g r o u n d i l i g c o n d u c t o r s , and t h e y s h o u l d be o f adequate s i z e . The
s p e c i f i c a t i o n s f o r t h e e l e c t r i c a l syst-em s h o u l d i n c l u d e t h e i n s t a l l a t i o n of
ground f a u l t i r i t e r r u p t i o n s (GFI ' s ) on c i r c u i t s where humans o r a n i m a l s may t o u c h
The
p a r t s e n e r g i z e d from l e a k a g e c u r r e n t throucjh m o i s t u r e , d i r t o r damage.
power p a n e l s s h o u l d have more t h a n s u f f i c i e n t c i r c u i t s o f adequate c a p a c i t y and
It i s the
t h e p r o p e r o v e r atid l e a k a g e c u r r e n t p r o t e c t i v e d e v i c e s .
r e s p o n s i b i l i t y o f t h e b u i l d e r s t o make a modern i n s t a l l a t i o n t h a t m i n i m i z e s t h e
voltage t o earth.
When b u i l d i n g s a r e m o d i f i e d , i t i s t h e r e s p o n s i b i l i t y o f t h e r e v i s o r s t o
i n c l u d e e q u i p o t e n t i a l p l a n e s and t o m o d e r n i z e o l d e l e c t r i c a l systems i n
accordance w i t h t h e s e p r i n c i p l e s .
ELECTRICAL COriTRACTOK/ELECTRICIAN
The b u i l d i n g s t r u c t u r e i n v o l v e s t h e e l e c t r i c a l c o n t r a c t o r who m u s t c o n i p l e t e
t h e e l e . c t r i c a 1 system i n accordance w i t h t h e d e s i g n makir,g s u r e t o u s e t h e
a p p l i c a g l e e l e c t r i c a l -'codes.
The t e m p t a t i o n t c use m a t e r i a l s s u i t a b l e f o r a
l e s s e x a c t i n g environmerit b u t n o t s u i t a b l e f o r t h e m o i s t u r e , d i r t : wetfiess of
f a r m b u i l d i n g s must be r e s i s t e d . I t i s f a l s e eccrlomy t o have t o h u n t o u t a c d
r e p a i r / r e p l a c e a system t h a t g i v e s t r o u b l e due t o i m p r o p e r s e l e c t i o n o f
m a t e r i a l s o r i n s t a l l a t i o n . The system must m i n i m i z e t h e v o l t a g e t o e a r t h i n s i d e
e l e c t r i c a l i n s p e c t o r s h o u l d have t h e knowledge t o n;ake s u g g e s t i o n s t h a t o t h e r s
c a n do t o t e s t f o r , d i s c o v e r and f i x t h e problem and t o s u g g e s t a l t e r n a t i v e s .
These c o u l d i n c l u d e changes t o remove o b j e c t i o n a b l e ground c u r r e n t s , o r t o s e t
u p a s e p a r a t e l y d e r i v e d system t h a t meets t h e Code.
Inspectors often are not
accustomed t o u s i n g t h e s e p a r t s of t h e Code.
FARM OPERATOR
The farm o p e r a t o r i s t h e p r i m a r y d e c i s i o n maker on b u i l d i n g o r on
modification,
r e p a i r o r operating
electrical
system new c o n s t r u c t i o n ,
procedures.
he/she u s u a l l y has t h e t - e s p o n s i b i l i t y f o r t h e s e l e c t i o n o f any
c o n t r a c t o r s t o do t h e work and t h e acceptance of t h e completed j o b .
The
competer~cy of v a r i o u s t y p e s o f c o n t r a c t o r s i s d i i f i c u l t t o assess, t h u s once
s e l e c t e d , t h e respor-,sibil i t y t o r p r o p e r performance o f t h e i r t o t a l j o b ,
i n c l u d i n g m i n i n ~ i z a t i o no f v o l t a g e s - t o - e a r t h , s h c u l d be k e p t Gn t h e co1:tractor.
The farm c p e r a t o r becomes r e s p o n s i b l e if he/she r e q u i r e s s u b s t i t u t i o n o f
r , i a t e r i a l s o r t e c h n i q u e s i n o p p o s i t i o n t o t h e c o n t r a c t o r s b e s t judgemer~t. The
farm o p e r a t o r has t o be knowledgeable abc.ut a l a r g e nur:]ber o f v a r i e d and
d i f f i c u l t tasks.
I t i s n o t t c b e expected t h a t e x p e r t i s e i n d e s i g n i n g o u t ,
discovering o r correcting voltages-to-earth i s his/her r e s p o n s i b i l i t y .
This
s h o u l d l i e w i t h t h o s e whose d a i l y e x p e r i e n c e i s i n s o l v i n g e l e c t r i c a l problems.
The farr.3 cqu-ipment must cope w i t h a harsh, d i r t y , wet, c o r r o s i v e , d a c ~ a g i n g
environment.
I t i s t h e r e s p o n s i b i l i t y o f t h e o p e r a t o r t o s e l e c t and i n s t a l l
o n l y t h o s e m a t e r i a l s s u i t a b l e f o r t h i s environment.
When making e x t e n s i o n s o r
r e p a i r s , i t i s t e m p t i n g t o use t h e i n e x p e n s i v e o f f - t h e - s h e l f
items o f t h e
o r d i r i a r y hardware s t o r e , and t o make t h e i n s t a l 1 a t i ~ nu s i n g f a r m personnel
U n l e s s t h e o p e r a t o r i s knowledgeable about t h e many f a c t o r s t h a t can cause t h e
system t o have v o l t a g e problems, i t i s b e t t e r t o have an e l e c t r i c a l c o n t r a c t o r
assume t h e 1 i a b i l ity. Farm o p e r a t o r s fieed t o r e p l a c e a n t i q u a t e d systerns t h a t
a r e o r may cause, problems.
.
COMFENTS ON THE FAR14 SECOllDAFY SYSTEiil
I t i s u s u a l l y p o s s i b l e t o o b t a i n n e u t r a l - t o - e a r t h v o l t a g e s t h a t do n o t
cause t r o u b l e on a farrnstead s i n g l e phase secondary n e u t r a l s y s t e s ~ . I t i s
n e c e s s a r y t o keep t h e n e u t r a l and equipment g r o u n d i c g c o n d u c t o r s r e l a t i v e l y
s h o r t , and i n s t a l l e d a ~ dm a i n t a i n e d t o have l o w impedance. I t i s a l s o necessary
t h a t t h e n e u t r a l and equipment g r o u n d i n g c u r r e n t b e m i n i m i z e d b y h a v i n g most
l o a d s cofinected l i n e t o l i n e i n s t e a d o f l i n e t o n e u t r a l , w i t h 1 i t t l e l e a k a g e
current.
Leakage c u r r e n t t o t h e e a r t h , f r o m damaged underground, o r n e a r ground
c o n d u c t o r s a r e a n o t h e r s o u r c e of secondary problems. These 1eakage c u r r e n t s nay
n o t be e n ~ u g ht o o p e r a t e t h e l i n e o v e r c u r r e n t p r o t e c t i o n d e v i c e s , y e t be enough
t o cause n e u t r a l - t o - e a r t h o r e a r t h v o l t a g e g r a d i e n t problems.
Few f a r r i ~ s have
ground f a u l t d e t e c t o r systems.
T h m i t - i s i m p o r t a q t for knowledgeable people u s i n g t h e c o r r e c t instruments
t o d e t e r m i n e if t h e sciurce(s) o f a v o l t a g e - t o - e a r t h on t h e s e c o n d a r y - p r i m a r y
system i s due t o one o r t h e o t h e r , o r t o b c t h systems.
T h i s may r e q u i r e t h a t
t h e u s u a l c o n n e c t i o n between t h e secondary and p r i m a r y n e u t r a l s be d i s c o n n e c t e d .
T h i s w i l l r e q u i r e t h e c o o p e r a t i o n o f t h e d i s t r i b u t i o n u t i l i t y , and p o s s i b l y t h e
t e l e p h o n e , c a b l e TV, w a t e r o r gas system o p e r a t o r s t o make s u r e t h e secondary i s
A k e y q u e s t i o n has been wllo s h o u l d p r o v i d e t h e i s o l a t i o n where t h e p r o b l e m
source
i s the
primary neutral.
U t i l i t i e s generally
claim that
the
n e u t r a l - t o - e a r t h v o l t a g e i s a n e c e s s a r y accompaniment i n t h e d e l i v e r y o f power
t o t h e consumer. U n r e s o l v e d i s t h e a l l o w a b l e magnitude o f t h e v o l t a g e .
The p r o b l e m a f f e c t s more t h a n j u s t farms.
Steel/aluminurn b o d i e d m o b i l e
hone owners,
swimming p o o l owners,
t h o s e h a v i n g shower s t a l l s or1 t h e
concrete/earth,
and o t h e r s a r e t t a v i n g problenls w i t h v o l t a g e - t o - e a r t h .
The
p r i m a r y d i s t r i b u t . i o n n e u t r a l - t o - e a r t h v o l t a g e l e v e l has n o t been r e g u l a t e d .
COMMENTS ON VOLTA6ES TO EARTH
The c e u t r a l - t o - e a r t h v o l t a y e s due t o normal l o a d c u r r e n t s f l o w i n g i n
n e u t r a l c o n d u c t o r impedances, g r o u n d i n g and e a r t h r e s i s t a n c e s c a n o n l y be
r e d u c e d b y r e d u c i n g t h e magnitude o f each o f t h e components. E a r t h c o l s d u c t i v i t y
i s f i x e d i n an l o c a l i t y , t h e g r o u n d i n g r e s i s t a n c e inay be d i f f i c u l t t o reduce,
and if reduced o n l y czt a p a r t i c u l a r p o i n t may cause a d d i t i o n a l c u r r e n t t o go t o
e a r t h a t t h a t pcrint l e a v i n g t h e n e u t r a l v o l t a g e much t h e same. Reducing n e u t r a l
l o a d c u r r e n t by u s i n g l i n e t o l i n e l o a d s cr: p r i m a r y o r secondary c i r c u i t s ,
e i t h e r s i n g l e phase o r t h r e e phase w i l l r e d u c e t h e n e u t r a l c u r r e n t and t h u s t h e
neutral potential.
There i s 2 c o s t t o do t h i s .
f4any customers a r e r e c e i v i n g
s a t i s f a c t o r y s e r v i c e w i t h e x i s t i n g systems. The r e s p c n s i b i l i t y f o r changes when
v o l t a g e - t o - e a r t h p r o b l e n ~ sa r i s e has n o t been d e t e r m i n e d .
Leakage c u r r e n t s e x i s t o v e r unplanned p a t h s where i n s u l a t i o n has b r a k e n
down, been damaged, o r ihzs been bypassed b y a p a r t i a l c o n d u c t o r . These n a y be
d i f f i c u l t t o d e t e c t and I c c a t e , b u t r e s t o r a t i o n o f t h e i n t e g r i t y o f t h e
i n s u l a t i o n removes t h e l e a k a g e p a t h and c u r r e n t . The r e s p o n s i b i l i t y f o r l e a k a s e
c u r r e n t s r e s t s w i t h t h e owner o f t h e system h a v i n g t h e l e a k a g e .
On new
i n s t a l l a t i c r , ~ , d e f e c t i v e f r o m s t a r t - u p , t h e c o n t r a c t o r s h a u l d be r e s p o v s i b l e .
REGULATORY BODIES
The n a t i o n a l and s t a t e e l e c t r i c a l codes a r e d e r i v e d f r o m l o n g e x p e r i e n c e
and
chan5e
slowly.
U t i l it i e s ,
electrical
contractors/electricians and
i n s p e c t o r s a r e u s u a l l y o p e r a t i n g under s e c t i o n s of a code t h a t work f o r most of
t h e i r a c t i v i t i e s w i t h t h e g e n e r a l pub1 i c .
When t h e v o l t a g e - t o - e a r t h p r o b l e m
e x i s t s on a farm, t h e y may n o t r e c o g n i z e and a p p l y t h e s e c t i o n s t h a t a l l o w
v a r i a t i o r i s f r o m r e g u l a r p r a c t i c e s . S e p a r a t i o n o f p r i m a r y and s e c o n d a r y n e u t r a l s
i s a l l o w e d (NEC-250-26)
by u s i n g s e p a r a t e l y d e r i v e d syster,ls,
and o t h e r
c o n n e c t i o n schemes can be used t o e l i m i n a t e o b j e c t i o n a b l e c u r r e n t (NEC-250-21).
The s e c t i o n on a g r i c u l t u r a l b u i l d i n g s s h o u l d be c o n s u l t e d and a p p i i e d (NEC-547).
A c c e p t a b l e c u r r e n t l e v e l s t h r c u g h a n i m a l s have n o t be s p e c i f i e d a l t h o u g h i t i s
g e n e r a l l y agreed t h a t an ariimal exposed t o more t h a n 0.5 v o l t nay b e s t r e s s e d .
The O c c u p a t i o n a l S a f e t y and H e a l t h A d n l i n i s t r a t i o n has a c c e p t e d an U n d e r w r i t e r s
L a b o r a t o r y recommendation o f 0.5 t o 0.75 m i l l i a m p e r e s f o r humans a s t h e
U t i l i t i e s have used a 5
a l l o w a b l e c u r r e n t between 120 v o l t a p p l i a n c e s .
m i 11 i a n ~ @ r e s ' " l e t - g o " c u r r e n t 2s a r e a s o n a b l e v a l ue. G r o u ~ df a u l t ir ~ t e r r u p t i n g
d e v i c e s a r e u s u a l l y s e t t o t r i p a t a b o u t 5 n l i l l i a m p e r e s . Research has n o t beer.
completed t o e s t a b l i s h b e t t e r i n f o r m a t i o n a t p r e s e n t from w h i c h new l i m i t s c o u l d
be s p e c i f i e d .
Legend f o r F i g u r e s 1, 2, 3.
r4 R -
Y
R
e
-
R
-
Z
-
e rJ!
R~~
-
t i e u t r a l Conductor Impedance
I
Grounding Resistance
I -
Earth Resistance
I
Leakage R e s i s t t n c e
ILK
E q u i p n ~ e ~Grounding
t
Conductor- irnpeaa1;ce
- Transformer
L i n e Load C u r r e n t
N e u t r a l Cur.r-ent
N
Y
'P~E
-
Grounding C u r r e n t
-
Leakage C u r r e n t
-
Neutral-to-cat-th vol tage
Grcundinc,
Resistance
Vol t a g e equal s c u r r e n t tifiles impedance ( phasor mu1t i p l i c a t i o n )
Behavioral Studies of Dairy Cattle
Sensitivity to Electrical Currents
R. J. Norell, R. J. G u s t a f s o n , R. D. A p p l e m a n , J. B. O v e r m i e r
MEMBER
ASAE
ABSTRACT
of mouth-all hooves and front-rear hooves currents. T h e
L~~~~~~~~ resistance data were collected for eight criteria for assessing cow response were behavioral
through dairy cows. significant variation in indices. In one experiment, shocks were a n aversive
resistance was found between pathways through stimulus to a learned food acquiring response. T h e
individual cows and between
~h~ mean path indicator was a partial suppression or slowing down of
resistances ranged from 359 ohms for a mouth-all hooves the learned
pathway t o 738 oh
for a f r -rear hooves pathway.
In a
approach, response
~h~ distri<ution
hooves pathway functions to random front-rear hooves and mouth-all
showed 25% ofthe population below 302 ohms and 75% hooves shocks were determined. The shock were random
below 441 ohms. ~h~~~ experiments assessing animal in that the initiation of the shock was not under the cow's
sensitivity to current based on behavioral indicators were ~ 0 n t r 0 laS in experiment one. T h e response indices were
performed. NO suppression of a learned response to the displaying of a learned escape to a front-hooves shock
obtain food was found up to 6.0 mA front-rear hooves and a shock elicited mouth opening due to a mouth-all
shock. However, muzzle-all hooves shocks as low as 1.0
mA suppressed plate pressing behavior. A specific
REVIEW O F LITERATURE
avoidance response to a mouth-all hooves shock was
exhibited 13.8% of the time at 1.0 mA a n d 92.3% at 4.0
Resistance variability between cows and pathways is
mA, while a learned escape response to a front-rear clearly evident from the available data. Phillips and
hooves shock above a m r m a l activity level occurred Parkinson (1963), Craine et al. (1 970), Woolford ( 1 972),
between 2.0 and 3.0 mA.
Whittlestone et al. (1975) and Lefcourt (1982) reported
average resistances in the range of 250 to 1200 ohms for
INTRODUCTION
various pathways. A combination of differences in
Awareness of the presence of stray voltage in livestock method of measurement, contact resistances, and actual
the five-fold or more
facilities has risen rapidly in the last few years. However, path resistances likely
very limited data are available on the electrical differences in resistances between specific pathways.
Altered animal behavior and milking characteristics,
characteristics and current sensitivity of farm animals.
The first component of this paper reports data collected increased incidence of mastitis, and lowered milk
on the resistance to alternating current (ac, 60 Hz) for production have been reported as a 'Onsequence
likely pathways through dairy cows. ~h~ second electric shocks (Fairbank and Craine, 1978; Cloud et a].,
component reports results of three experiments 1981; Surbrook and Reese, 1981; Williams, 1981). The
measuring sensitivity to electrical currents based on
between
and
intensity are poorly understood and have received limited
behavioral indicators.
~h~ specific objectives of the resistance measurement study. The majority of the existing research involved the
component of this study were to: (a) measure resistance application of shocks during the act of milking. shocks
from the milking machine had a minimal effect on milk
of eight pathways through dairy cows, ( b ) determine
s
correlations bewteen cow attributes (body
wither flow characteristics or milking times ( ~ h i l l i ~and
and
!s9;
a
nd
height, body length and age) and measured pathway
197z). However, in the latter two studies,
resistances, and (c) estimate the contribution of the *$01ford,
cattle were reluctant t o enter the parlor a n d exhibited
hooves to the total path resistance.
signs
of annoyance such as increased hoof movement.
The objective of the current sensitivity component of
that
gradients
this study was t o study cow response t o graduated levels
t h e ' ~ a r l o rfloor o r bzween the parlor plpework and floor
%ay be moke botherso-& t o the cow than shocks from
e milking maxe-Article was submitted for publication in January, 1983; reviewed and Ph
approved for publication by the Electric Power and Processing Div. of
Whittlestone et al. (1975) obtained threshold
ASAE, 1983. Presented as ASAE Paper No. 82-3530.
responses for four animal pathways likely to be exposed
Published as Paper No. 13,214 of the scientific journal series of the
to shocks in the milking parlor. The body pathways
Minnesota Agricultural Experiment Station.
studied were: one teat-all hooves; all teats-all hooves;
The authors are: R d . NORELL, Assistant Professor and Extension
hooves; and chest-a11
The
Dairyman, Animal Science Dept., University of Idaho, Idaho Falls; R.
response was a change in preference of a paddle pressed
1. GUSTAFSON, Associate Professor, Agricultural Engineering Dept.,
and R. D. APPLEMAN, Professor and Extension Dairyman. Animal
for a grain reward. O n e paddle turned the current "on"
Science Dept., 1. B. OVERMIER, Professor, Psychology. University of and the other turned it
A~~~~~~ threshold voltages
Minnesota, St. Paul.
and
currents
were:
teat-all
hooves,
6.2 V/7.1 mA; all
Acknowledgment: The authors wish to acknowledge support
received from the National Rural Electric Cooperative Assn. for stray tests-all hooves, 7.8 V15.6 mA; rump-all hooves, 4.3
voltage research at the University of Minnesota.
V/6.1 mA; and chest-all hooves, 4.0 V/4.0 mA.
Epathways
fMhh-all
.
1506
O
1983 American Society of Agricultural Engineers 0001-2351/83/2605-1506302.00
TRANSACTIONS of the ASAE-1983
VOLTMETER I
STEP DOWN
ISOLATING
TRANSFORMER
TABLE 1. AVERAGE PATHWAY RESISTANCE MEASURED UNDER DRY
AND WET HOOF-GRID CONTACT CONDITIONS. OUTLIER RLWOVED
(n = 10 JERSEYS).
STEP DOWN
AUTO
TRANSFORMER
-
r---1
Condition
FIXED RESISTANCE
R: 79 kn
I
w & :
COW
PATH WAY
VOLTMETER 2
Fig. 1-Electrical
resistance measurement circuit.
Lefcourt (1982) studied cow response to graded shock
increments applied to a front-rear leg pathway.
Electrodes were attached above one front and one rear
hoof. Average currents and voltages corresponding to a
milk and strong response were: milk, 0.8 "12.5 m ~
strong, 1.1 V/3.5 mA.
(1982) studied the response of four cows
Henke et
to udder-hooves shock. An electrode was attached at the
back of the udder beneath the tail while the animal stood
on perforated steel. Behavioral responses occurred at
currents of between 2 ,.,A and 4 m ~ ~.
~
respon;es were poorly correlated with shock intensity.
RESISTANCE MEASUREMENTS
Equipment and Procedure
The
a
tie
was adapted
make separate contacts with front and rear hooves. Two
expanded metal grates (0.8 m x 0.9 m) isolated by a
section of cow mat and rubber matting were placed on
the stall floor. Other contact points were established by
bit in the cow's mouth and (b) an
(a) a
foil-lined teat cup inflation (plus EKG paste) attached to
the left front teat. Eight different circuits or pathways
through the cow were defined using these connections.
Theelectricalcircuitusedforresistancemeasurements
(Fig. 1) was designed to maintain a constant current. A
fixed impedance source as described by Masterton and
Campbe11
was used. With this
variation in cow resistance was expected to produce less
than a 1.5% change in current level.
Digital volumeters were used to measure voltage across
and cow pathway- The current flow
the fixed
through the circuit was adjusted to 0.1 mA. Calculated
cow pathway resistance was recorded as the average of
five determinations. Standard errors of the mean were
small for the five determinations, usually 5-10 ohms.
Results
Experiment IR-Dry and Wet Hooves Conlparisons
The objective of this experiment was to compare the
influence of wet versus dry hooves on pathway resistance.
The hypothesis was that a wet hoof would lower the hoofgrid contact resistance and thereby decrease the overall
pathwaF resishnce. Data we're coIlected in two different
sessions. In one session, the underside of the hoof was
brushed to remove dry manure and bedding. This was
the dry hoof condition. In the other session, the hooves
were carefully washed and the metal dampened before
resistance measurement. The grids and hooves were
sprayed with water between determinations to maintain
the wet hoof conditions.
1983-TRANSACTIONS of the ASAE
x
Wet
--
DN
SD
x
SD
- - - ...- ...-.- . - - - - - . - - o h r n s .
Front-rear hooves
Mouth-front hooves
Mouth-rear hooves
1562
1265
621
(470)
(378)
(191)
1479
1161
647
(275)
(321)
(173)
Mean
dlfferenrr
(bluet)
Standard
emor
- -.-.
-..- -.-.-..- - ...
83
98
-26
101
95
16
The resistance of a front-rear hooves, mouth-front
hooves, and mouth-rear hooves pathway were
determined, under wet and dry hoof conditions, on
eleven Jersey cows. Statistical comparisons were paired
t-tests of pathway resistance measured under wet and d?
hoof conditionsUp0n analyzing different pairs (dry-wet for a n
individual cow), it was found that data for one cow
;accounted for the large inequality in variance between
hoof conditions. The reasons for the greater dry hoof
resistance of this outlier cow are not known. Data from
this cow indicated pathway resistance may be
increased under
Deleting these data from the analyses nearly halved the
pathway
d resistance
~ variance
~ between
~ cows under
i
the dry
~
measurement
Average pathway
resistances and differences between dry and wet
conditions for the reduced data set are in Table 1.
Variances in pathway resistance between measurement
conditions were not significantly different in the reduced
data set. Mean differences between wet and dry hoof
resistances on the expanded metal grids were also not
significant.
~
~
~2 ~ - ~ ~ o f~~ i g~
i h pathways
t~ ~ ~~ , , ~ i ~
The electrical resistance of eight defined cow pathways
,%,ere measured on twenty-eight ~
~ cows. l
~
~~~i~~~~~~
determinations were made under the =a,et
hoof-grid- contact conditions as defined for Experiment
l ~ pathway
.
resistances were
with a
randomized block statistical design. Cows were the
blocks and pathways were the treatments. A log 10
transformation was used to make the pathway resistance
data more normal and to reduce variance inequality.
Mean pathway resistances and their associated
standard deviations are presented in ~
~ 2. ~b
l ~ ~
~
the measured pathways from lowest to highest resistance
yields: (a) mouth-all hooves; (b) mouth-teat; (,-) mouthrear hooves; (d) teat-all hooves; (e) mouth-front hooves:
(0 teat-rear hooves; (g) front-rear hooves; and (h) teatfront hooves.
TABLE 2. MEAN RESISTANCES A N D STANDARD
DEVIATIONS FOR THE EIGHT MEASURED COW PATHWAYS
(n = 2 8 HOLSTEINS).
- - - Log
-
Pathway
X
10 o h m s -
--
SD
Geometric
mean, ohms
Front-rear hooves
Mouth-front hooves
Mouth-rear hooves
,Mouth-all hooves
Mou th-teat
Teat-front hooves
Teat-rear hooves
T e a t - d hooves
1507