GOAL: Agree to the Phase to Ground Clearance Values for 1.5 kV through 230kV
The WG and Survey results agreed to use the values contained in NEMA TR1-1980.
The NEMA TR1-1980 lists a single value for each voltage.
C57.12.00-2012, Table 4 lists multiple BILs for each voltage.
This proposed table attempts to merge the NEMA TR1-1980 values with the voltage and BIL.
NOTE: Clearance Values for 345kV and up are based on SIL and will be discussed AFTER we finalize the values for 1.5kV through 230kV.
Changes:
Expanded each voltage for BILs contained in C57.12.00, Table 4
Added Col 3 - 8
Provided clearances for Power Transformers for 1.5kV, 30 kV BIL
Provided clearances for Power Transformers for 121kV and 145kV, 450 kV BIL
Provided clearances for Power Transformers for 169kV and 242kV, 825 kV BIL
"Matched" Distribution Transformer 95, 110, 125 and 150 kV BIL with NEMA TR1-1980 values.
Graphs show proposed clearances, test gap spacing (50% flashover clearance) and 110% test gap spacing for reference.
Power Transformer clearances are shown on two graphs to clearly show the comparison of the values.
PROPOSED C57.12.00 TABLE 11
Maximum
System
Voltage
(kV rms)
Col 1
1.5
1.5
3.5
3.5
6.9
6.9
11.0
11.0
17.0
17.0
26.0
26.0
36.0
36.0
36.0
48.0
48.0
72.5
72.5
121
121
121
145
145
145
169
169
169
169
242
242
242
242
Nominal System
Voltage
(kV rms)
Col 2
1.2
1.2
2.5
2.5
5.0
5.0
8.7
8.7
15.0
15.0
25.0
25.0
34.5
34.5
34.5
46.0
46.0
69.0
69.0
115.0
115.0
115.0
138.0
138.0
138.0
161.0
161.0
161.0
161.0
230.0
230.0
230.0
230.0
345
500
765
1000
362.0
550.0
800.0
1200.0
Winding line-end BIL
(kV Minimum Clearance between live parts Minimum Clearance between live parts of
different phases
Crest) (from Table 4)
of one phase and ground
Miminum clearance between top shed of
insulator of bushings of different phases
Distribution
Power
Transformers Transformers
(kV Crest)
(kV Crest)
Col 3
Col 4
30
30
--45
45
45
--60
60
60
--75
75
75
--95
95
95
110
110
125
--150
150
125
--150
--200
200
200
200
250
250
250
250
350
350
--350
--450
--550
--450
--550
--650
--550
--650
--750
--825
--650
--750
--825
--900
Distribution
Transformers
mm
(in)
Col 13
Col 14
25
1
----25
1
----38
1.5
----51
2
----64
2.5
76
3
114
4.5
152
6
114
4.5
152
6
203
8
203
8
305
12
305
12
483
19
---------------------------------------------------------
1050
1550
1925
Distribution
Transformers
mm
in
Col 5
Col 6
25
1
----51
2
----64
2.5
----89
3.5
----114
4.5
127
5
146
5.75
203
8.0
146
5.75
203
8.0
305
12
305
12
381
15
381
15
584
23
---------------------------------------------------------
Power
Transformers
mm
in
Col 7
Col 8
51
2
51
2
51
2
76
3
76
3
89
3.5
89
3.5
114
4.5
114
4.5
152
6
----203
8
--------305
12
305
12
381
15
381
15
584
23
584
23
762
30
940
37
762
30
940
37
1118
44
940
37
1118
44
1321
52
1448
57
1118
44
1321
52
1448
57
1600
63
Distribution
Transformers
mm
(in)
Col 9
Col 10
25
1
----51
2
----64
2.5
----102
4
----127
5
140
5.5
178
7
228
9
178
7
229
9
330a
13
330a
13
432
17
432
17
635
25
---------------------------------------------------------
Power Transformers
mm
(in)
Col 11
Col 12
51
2
51
2
51
2
76
3
76
3
102
4
102
4
127
5
127
5
165
6.5
----229
9
--------330
13
330
13
432
17
432
17
635
25
635
25
838
33
1041
41
838
33
1041
41
1245
49
1041
41
1245
49
1448
57
1600
63
1245
49
1448
57
1600
63
1778
70
2286b
4064b
c
c
(90)
(160)
Power Transformers
mm
(in)
Col 15
Col 16
25
1
25
1
25
1
38
1.5
38
1.5
51
2
51
2
64
2.5
64
2.5
89
3.5
----152
6
--------203
8
203
8
305
12
305
12
483
19
483
19
686
27
914
36
686
27
914
36
1118
44
914
36
1118
44
1321
52
1118
1321
44
52
1651
65
2159
3937
c
c
(85)
(155)
a It should be noted that ANSI C57.12.22-1989 [B5] specifies a phase-to-phase clearance of 165 mm (6.25 in) for 25 kV and 229 mm (9 in) for 34.5 kV nominal system voltage. The smaller
clearances are acceptable since the bushings are always located within a metal enclosure and are not subject to the same conditions that occur with bushings exposed to the elements.
b For phase-to-phase switching impulse voltages other than 3.8 per unit, the following formula may be used to establish the minimum external clearance for peak switching impulsevoltages
between 1000 kV and 1800 kV only:
X = .121(Y) - 45
where
X is the minimum clearance between live parts of different phases (in)
Y is the switching impulse voltage from phase to phase (peak kV) (applicable only from 1000 kV and 1800 kV)
c Power transformers, at nominal system voltages of 765 kV and 1100 kV, are usually single phase so that clearances between live parts of different phases is not an issue.
C57.12.00-2010 Table 11
Nominal
Maximum
system system voltage,
voltage, rms (from ANSI
rms
C84.1)
(Kv)
(kV rms)
1.2
--2.5
--5.0
--8.7
--15
--25
--34.5
--46
48.3
69
72.5
115
121.0
138
145.0
161
169.0
230
242.0
345
500
765
1000
362.0
550.0
800.0
1200.0
Minimum Clearance between live
parts of different phases
Distribution
Transformers
mm
(in)
25.4
(1)
50.8
(2)
63.5
(2.5)
102
(4)
140
(5.5)
178a
(7)
a
330
(13)
432
(17)
635
(25)
Power
Transformers
mm
(in)
50.8
(2)
76.2
(3)
102
(4)
127
(5)
165
(6.5)
229
(9)
330
(13)
432
(17)
635
(25)
1041
(41)
1245
(49)
1448
(57)
1778
(70)
2286b
4064b
c
c
(90)
(160)
Miminum clearance between top
shed of insulator of bushings of
different phases
Distribution
Transformers
mm
(in)
25.4
(1)
25.4
(1)
38.1
(1.5)
50.8
(2)
76.2
(3)
114
(4.5)
203
(8)
305
(12)
483
(19)
Power
Transformers
mm
(in)
25.4
(1)
38.1
(1.5)
50.8
(2)
63.5
(2.5)
88.9
(3.5)
152
(6)
203
(8)
305
(12)
483
(19)
914
(36)
1118
(44)
1321
(52)
1651
(65)
2159
3937
c
c
(85)
(155)
a It should be noted that ANSI C57.12.22-1989 [B5] specifies a phase-to-phase clearance of 165
mm (6.25 in) for 25 kV and 229 mm (9 in) for 34.5 kV nominal system voltage. The smaller
clearances are acceptable since the bushings are always located within a metal enclosure and are
not subject to the same conditions that occur with bushings exposed to the elements.
b For phase-to-phase switching impulse voltages other than 3.8 per unit, the following formula may
be used to establish the minimum external clearance for peak switching impulsevoltages between
1000 kV and 1800 kV only:
X = .121(Y) - 45
where
X is the minimum clearance between live parts of different phases (in)
Y is the switching impulse voltage from phase to phase (peak kV) (applicable only from
1000 kV and 1800 kV)
c Power transformers, at nominal system voltages of 765 kV and 1100 kV, are usually single
phase so that clearances between live parts of different phases is not an issue.
NEMA TR-1 1980
Pub. No, TR 1
Part 0 Page 6
MANUFACTURING
TR
1-O.O? EXTERNAL CLEARANCES BETWEEN LIVE PARTS
Winciing
Imui.ation
Ciass,
Kv
2.5
Minimum Clearance Between lvtinimum Clearance Between b{inimum Clearance Be*reen
Live Parts of Different Phases Top SheC of Porcelain of
Li*-e* Parts of
Bruhings of Different Phases'
or Live Parts of Different
One Phase and Ground,
Inches
l^/indinss,
Inches
lnches
Power
Dstribudon
Power
burion
Di.stf
Power
Disrrihurioa
Transformers
Tramicrmers Trareforu:ers TransforrnerS Traixformers
1
2
I
2
I
t
2
e
2
o(
J
I
1.5
4
1.5
2
3.5
3.5
4.5
4
1q
o
c
b.i
18
b. ,o
25
I
8
\L
!2
46
15
69
23
ot
115
5.0
d. t)o
u.5
138
2
2.5
6.5
o
3.5
I
I
D
o
13
13
IA
77
17
l4
oa
25
25
i.9
-tY
30
30
33
33
27
21
37
or
4L
41
36
&a
4a
44
M
44
;;
AE
234
t
"
E
98
d
L2
4
,a
o'!
5?
2E?. 5
Transformen
,o
?0
65
65
to
81
108
84
108
'19
o9
103
?9
103
ThLs does nclr necessarily apply rc the buehln[s themselveso the str:.king Cisrances of which are determ.ined by
the busiiing characteristics given
ia
Table 9 of USAS
C57.12.0ffi
iq"?3
NO?E-T.'ire extemal clearaace-s gi'ren in theabove t.ible aie for transforinersinteuded fol oreration at altitudes
of 3300 feet (1000 meteri) or 1ess. For operalicn at airirudes in exce+s of 33t10 feet {1000 rretetsi, the external
clearancet shail be incr*aseC ro comperisaie fol rhe. clecrease in sparitover vokaee at the rate of one percent
(0.C.1) per330fee: (tr0i)msie$) i1creaseiaaltjilCeicexcesscf
?R
33i10
leer (1000mete$).
1.0"C8 VACUUM F'ILLTNG
When tr:nsforme$ are
lo
L'e dexigned
for vacuum
filling ir: the iieli, tire iank siiaii be d'-signed for
ard tested at approximatell' 1*o inches of mercuy,
aixolure pressure, because of. Ig:itations in ccm:rercial pumpine ecuipmen:. ii is :o be understood
that thepr:rpose of iacuuut filiingi: srmpl;rtoquickly
.eurove entiapped air wf:iclr rri3hi h;lvc a temporary
a.dverse effect ort tie dielecidc sitengrh.
Au thorizerj Engir:eeriirg lofolnatirrt 5 - 1 I - I 93 9.
External Clearances for Distribution Transformers 30 - 350 kV BIL (PhGnd)
25
E
x
t 20
e
r
n
a
l
15
C
l
e
a
r 10
a
n
c
e
Test Gap Spacing
Proposed
Spacing +10%
(
5
)
i
n
0
0
50
100
150
200
BIL (kV)
250
300
350
400
External Clearances for Power Transformers: 30 - 250 kV BIL (Ph-Gnd)
16
14
E
x
t
e 12
r
n
a
10
l
C
l
e
a
r
a
n
c
e
Test Gap Spacing
8
Proposed
Spacing +10%
6
4
(
)
i
n
2
0
0
50
100
150
BIL (kV)
200
250
300
External Clearances for Power Transformers: 250 - 1050 kV BIL (Ph-Gnd)
90
80
E
x
t 70
e
r
n
60
a
l
50
C
l
e
a 40
r
a
n 30
c
e
Test Gap Spacing
Proposed
Spacing +10%
(
20
)
i
n
10
0
0
200
400
600
BIL (kV)
800
1000
1200