DAVID J. KVALTINE, PE
GAINESVILLE REGIONAL UTILITIES
Gainesville, Florida
LIGHTNING PROTECTION - A STROKE OF LUCK,
THEORY AND APPLICATION
2005 APPA ENGINEERING AND TECHNICAL CONFERENCE
APRIL 18, 2005
Memphis, Tennessee
GRU Service Territory
Number of Electric Customers
Service Area
Transmission
Underground Distribution
Overhead Distribution
Distribution Substations
86,000
127 square miles
597 circuit miles
1340 circuit miles (55%)
743 circuit miles (45%)
9 (138 kV/12.47 kV)
LIGHTNING PERFORMANCE OF DISTRIBUTION LINES
‰ The Utility must determine the level of performance they would like to achieve
‰ Overhead line performance is dependent on the following
• Line insulation flashover due to indirect strikes
• Line insulation flashovers due to direct strikes
• Line insulation flashovers due to equipment failures
FLASHOVERS DUE TO INDIRECT STRIKES
‰ Generally designing a structure with a minimum BIL of 300 kV will
minimize line flashovers due to nearby lightning strikes.
FLASHOVERS DUE TO INDIRECT STRIKES
BIL Calculations for Wood Poles:
BIL = CFO(0.9)
Insulator BIL= 155(.9) = 139.5 kV
Total Insulator BIL = 2 x (139.5) = 279 kV
Wood does add some additional insulating
value depending on the length of the wood.
100 kV/foot
90 kV/foot
75 kV/foot
10-30 kV/foot
10"
20"
10"
20"
10"
CFOair 200 kV/foot
CFOair = 200 kV x 2.5 feet = 500 kV
66" TYP.
96" M AX.
FLASHOVERS DUE TO INDIRECT STRIKES
BIL Calculations for Concrete Poles:
10"
BIL = CFO(0.9)
20"
Insulator BIL = 203(.9) = 183 kV
Total Insulator BIL = (183) kV
10"
Concrete does not add any additional
insulating value. The insulators provide all
the insulation
20"
CFOair 200 kV/foot
10"
CFOair = 200 kV x 2.5 feet = 500 kV
66" TYP.
96" MAX.
FLASHOVERS DUE TO DIRECT STRIKES
• Determine flashovers per mile of line in open country
• Estimate shielding of line from other structures and trees
• Calculate the number of flashovers per mile of line due to
direct strikes
FLASHOVERS DUE TO DIRECT STRIKES
LIGHTNING STRIKES TO AN OVERHEAD LINE IN OPEN COUNTRY
Noc = GFD x 0.0085 x H 0.6 x L
Noc - Number of strikes to a line without any shielding
GFD - Ground Flash Density - strikes/sq. mile/year
H - Height above ground in feet
L - Length of the distribution line in miles
Ground Flash Density (GFD) Contour Map for Florida
Gainesville
Ground Flash Density (GFD) in the area shown
ranges from 26 -36 strikes/sq. mile/year with an
average of 31 strikes/sq mile/year
LIGHTNING STRIKES TO OVERHEAD LINE IN OPEN COUNTRY
Calculation:
GFD = 36 strikes/sq mile/year
L = 1 mile
H - top phase above ground = 47 feet
Noc = 36 x 0.0085 x (47) 0.6 x 1
Noc = 3 strikes/mile/year
Typical Shielding Factors
Sf -Shielding factor, the number of lightning strikes that are intercepted by other
objects other than the distribution line.
Nsh - Number of strikes to the shielded line
Nsh = Noc x (1-Sf)
For shielding factor of:
Sf = 0.7
Nsh = 3 x (1-.0.7)
Nsh = 0.9 or approximately 1 strike/mile of line/year
Sf = 0.4
Nsh = 3 x (1- 0.4)
Nsh = 1.8 or approximately 2 strikes/mile of line/year
MUST CONSIDER SHIELDING ON BOTH SIDES OF THE LINE
EVEN TREES, 1/2 THE HEIGHT OF THE LINE WILL PROVIDE SOME SHIELDING
Shielding by trees
Sf = 1.0
Shielding by trees
Sf = 0.7
Shielding by trees
Sf = 0.4
METHODS OF LIGHTNING PROTECTION
SHIELDING
The process where a lightning flash terminates on an overhead wire
above the phase conductors and the lightning current is channeled to
ground through a ground wire. The lightning current does not flow
through the phase conductors.
Two Methods of Shielding include:
•Overhead static
•Overhead neutral
METHODS OF LIGHTNING PROTECTION
SHIELDING - OVERHEAD STATIC
•30 degree shielding angle above phase
conductors
•BACKFLASH V = Ri + Ldi/dt
•Typical L value is 0.4 uH/foot
•Rise times can be 1-10 usec.
•Maximum recommended ground resistance
is 10 ohms
•Recommended structure BIL 500-600 kV
•Overhead shields can reduce flashovers from
induced voltages
SHEILDING - OVERHEAD STATIC
METHODS OF LIGHTNING PROTECTION
SHIELDING - OVERHEAD NEUTRAL
•Same basic issues as OH static
•Does not provide any additional
reduction from nearby strikes
•Shorter poles may be able to be used
SHIELDING--OVERHEAD NEUTRAL
SHIELDING WILL WORK ON DISTRIBUTION LINES IF PROPERLY DESIGNED
METHODS OF LIGHTNING PROTECTION
SHUNTING
The process where a lightning flash is allowed to terminate on a
phase conductor and the surge current is shunted to ground by
either an insulation flashover or through a lightning arrester.
Would prefer to shunt the lightning current through an arrester.
GRU ARRESTER APPLICATION GUIDELINES
Placement of Arresters for Overhead Line Protection
Framing Configuration
Approximate
Distance
From
Deadend
Min Max
Maximum
Number
Of
Spans
Approximate
Distance
Between
Arresters
Min
Max
Maximum
Number
Of
Spans
Wood Poles
Triangular and vertical without static
200'
300'
1
1150' 1350'
6
Concrete Poles
Horizontal, triangular and vertical without static
200'
300'
1
400'
3
All Equipment
All Switches
All Deadends
600'
GRU ARRESTER APPLICATION GUIDELINES
Transformer Lead Lengths
Try to keep lead lengths
3 feet or less
GRU ARRESTER APPLICATION GUIDELINES
Placement of Arresters for UG Line Protection
• Open Loops
• Radial Cable Terminations
• Terminal Poles
GRU ARRESTER APPLICATION GUIDELINES
Single Phase
Open Loop Transformer
Three Phase
Open Loop Transformer
GRU ARRESTER APPLICATION GUIDELINES
Single Phase Radial Transformer
Radial Configuration
Radial Type Three Phase Transformer
Radial Configuration
Loop Type Three Phase Transformer
GRU ARRESTER APPLICATION GUIDELINES
Termination Pole Lead Lengths
• Typical designs use 1.6 kV per foot but can be as high as 6-10 kV/ft
• Try to keep lead lengths 3 feet or less
Incorrect
Correct
IEEE UG APPLICATION GUIDELINES
• Use termination, open point and mid point arresters (mid point should not
be closer than 150 - 350 feet)
• Should consider using rise times of 1 - 2 usec or 3 - 8 kV/ft
• Minimize arrester lead lengths at terminal poles
SUMMARY
‰ Determine Level of Protection
‰ Keeping Structure BIL at 300 kV will protect lines from Indirect Strikes
‰ Two Methods of Protection from Direct Strikes
• Shielding
• Shunting
‰ Typically distribution lines use lightning arrester for protection
GRU ARRESTER APPLICATION GUIDELINES
Introduction
The protection of distribution circuits from lightning induced
interruptions is dependent on a number of factors which must be considered in
the design and construction of any overhead line. An overhead line should have
due consideration for basic insulation levels, line configuration, ground
resistance and arrester application. In this guideline an attempt has been made
to outline a consistent set of rules for the application of arresters on the
distribution system. These rules are primarily applicable to overhead
distribution lines, but certain special consideration has been given to arrester
protection of cable and equipment on underground systems.
GRU ARRESTER APPLICATION GUIDELINES cont.
I.
Basic Considerations
A. Standard Arrester Types
The standard arrester for use on this system is the metal oxide varister (MOV) design.
Three types of MOV arresters are available for use in specific applications:
1)
Stock # 58930-6, standard distribution arrester for general overhead line applications.
2)
Stock # 58935-7, riser type arrester for underground terminations from the overhead
system.
3)
Stock # 78266-1, elbow arrester for use in elbow connected pad mounted equipment.
4)
Stock # 62245-1, parking stand arrester.
GRU ARRESTER APPLICATION GUIDELINES cont.
B. Proper Lead Lengths/Placement
1)
Regardless of the type of arrester installed one basic principle should always be
observed in order that the full protective capability of the arrester is utilized. The
arrester line lead and ground lead should be as short as possible. Often this can be
accomplished by carrying the line and ground connections to the arrester terminals
first, and then on to the equipment terminals of the protected equipment.
(See Fig. 1a,b)
2)
Arresters should be positioned such that a blown ground lead isolator will not effect
other energized equipment.
3)
Arresters should be installed on source side of cutouts to avoid possible fuse operation
on current inrush.
Incorrect
Fig. 1a
Correct
Fig. 1b
GRU ARRESTER APPLICATION GUIDELINES cont.
II. Required Applications (using standard distribution arrester)
A.
Overhead Oil-filled Equipment - The following overhead mounted equipment shall have the
standard distribution arrester (stock # 58930-6) applied:
1)
2)
3)
4)
5)
B.
Overhead Switches - The following overhead equipment shall have the standard distribution
arrester (stock # 58930-6) applied on both sides of a switch on the same pole which can be
source fed from both directions:
1)
2)
3)
C.
Transformers.
Reclosers (apply @ both sides).
Sectionalizers (source side only when used at underground termination).
Regulators (apply @ both sides).
Capacitors.
All normally open hook stick operated switches.
All group operated switches.
Normally open in-line switches (may be installed on adjacent poles).
Other Overhead Locations - The following overhead equipment shall have the standard
distribution arrester (stock no. 58930-6) applied:
1)
2)
3)
All deadends (not including double deadends that are jumpered across or corner poles).
Distribution lines built under transmission lines shall have arresters applied in same
manner as any other distribution line.
Arresters shall be applied for line protection in accordance with the following table:
GRU ARRESTER APPLICATION GUIDELINES cont.
Placement of Arresters for Overhead Line Protection
Framing Configuration
Approximate
Distance
From
Deadend
Min Max
Maximum
Number
Of
Spans
Approximate
Distance
Between
Arresters
Min
Max
Maximum
Number
Of
Spans
Wood Poles
Horizontal & vertical with static
Horizontal without static
Triangular and vertical without static
400‘
200'
200'
600'
300'
300'
2
1
1
2400' 2600'
400'
600'
1150' 1350'
12
3
6
Concrete Poles
Horizontal & vertical with static
Horizontal, triangular and vertical without static
200'
200'
300'
300'
1
1
1150' 1350'
400'
600'
6
3
NOTE:
1) Arresters applied on all three phases for equipment protection may also be considered as line protection.
2) Distances for spacing of arresters are approximate, and are intended as a guideline to good practice.
Actual spacing will depend on actual span lengths.
GRU ARRESTER APPLICATION GUIDELINES cont.
III. Required Applications (using riser type arrester)
A.
Overhead to Underground Terminations - The following terminations shall have the riser pole
arrester (stock # 58935-7) applied:
1) All modular type terminations and porcelain terminations with or without disconnect switches.
2) All switchgear.
IV. Required Applications (using elbow type arrester)
A.
Radial and Open Loop Points - The following terminations shall have the elbow type arrester
(stock # 78266-1) applied: (See Fig. 2a, 2b)
1) Single phase pad transformers fed radially.
2) Single phase pad transformers fed in a loop, applied at the open loop point on both cables.
3) Any other elbow connected equipment with an unused bushing which is fed radially or which
is located at an open loop point.
B.
Radial three phase transformer configurations.
1) Three phase radial type transformers fed radially. (See Fig. 3a)
GRU ARRESTER APPLICATION GUIDELINES cont.
B. Radial three phase transformer configurations.
1) Three phase radial type transformers fed radially.
(See Fig. 3a)
Radial
Fig. 2a
Radial Configuration
Radial Type Transformer
Fig. 3a
Open Loop
GRU ARRESTER APPLICATION GUIDELINES cont.
2) Three phase loop type transformers fed in a loop,
applied
at the open loop point on both cables. (See Fig. 3b)
Line
B
Only
Line
A
Only
Feed
Thru
3) Any other elbow connected equipment with an
unused bushing which is fed radially or which is
located at an open loop point. (See Fig. 3c)
Line
A&B
Radial Configuration
Loop Type Transformer
NOTE:
Three phase loop-configuration
transformers are equipped with a four-way
switch which permits feed-through (with
transformer de-energized), line A only,
line B only and line
A + B operation. Switch is normally in the
line A + B position.
Loop Configuration
Loop Type Transformer
REFERENCES
IEEE Std. C62.11-1999, IEEE Standard for Metal Oxide Surge Arresters for AC Power Circuits >1000 volts
IEEE Std C62.22-1997, IEEE Guide for the Application of Metal Oxide Surge Arresters for Alternating Current Systems
IEEE Std 1299/C62.22.1-1996, IEEE Guide for the Connection of Surge Arresters to Protect Insulated Shielded Electric Power
Cable Systems
IEEE Std 998-1996, IEEE Guide for Direct Lightning Stroke Shielding of Substations
EPRI Report EL-6782 "Characteristics of Lightning Surges on Distribution Line", Project RP2542-1, First Phase, May 1990
EPRI Report TR-100218, "Characteristics of Lightning Surges on Distribution Lines", Project RP2542-1, Final Report,
December 1991.
"Lightning Protection Manual for Rural Electric Systems" Rural Electric Research Project 92-12, National Rural Electric
Cooperative Association, 1993
"Electrical Distribution-System Protection", Cooper Power Systems, Third Edition
"Insulation Coordination for Power Systems", Andrew R. Hileman, Marcel-Dekker Inc. 1999
Parrish, D.E.; "Lightning-Caused Distribution Circuit Breaker Operations"; Power Delivery, IEEE Transactions on, Vol 6,
Issue 4, October 1991, Pages 1395-1401
Parrish, D.E.; "Lightning-Caused Distribution Transformer Outages on a Florida Distribution System", Power Delivery,
IEEE Transactions on, Vol 6, Issue 2, April 1991, Pages 880-887
Parrish, D.E.; Kvaltine, D.J.; "Lightning Faults on Distribution Lines", Power Delivery, IEEE Transactions on, Vol 4, Issue 4,
October 1989, Pages 2179-2186
REFERENCES cont.
Barker, P.P; Mancao, R.T.; Parrish, D.E.; Kvaltine, D.J.; "Characteristics of Lightning Surges Measured at Metal Oxide
Distribution Arresters" Power Delivery, IEEE Transactions on, Vol 8, Issue 1, January 1993, Pages 301-310
Jacob, P.B.; Grzybowski, S.; Ross, E.R.; "An Estimation of Lightning Insulation Level of Overhead Distribution Lines"; Power
Delivery, IEEE Transactions on, Vol 6, Issue 1, January 1991, Pages 384-390
Ross, E.R.; Grzybowski, S.; "Application of the Extended CFO Added Method to Overhead Distribution Configurations";
Delivery, IEEE Transactions on, Vol 6, Issue 4, October 1991, Pages 1573-1578
"Working Group Report: Calculating the Lightning Performance of Distribution Lines", Power Delivery, IEEE Transactions on,
Volume 5, Issue 3, July 1990, Pages 1408-1417