Download Table 2

Table 1 (All Classes in 1 Table)
This revision combines the Delta and the Wye-Connected Tables from Revision 8 into the new Revision 9
Applied Test
From C57.12.00
Table 7 in kV
Max
Nominal
System
System
Voltage in Voltage
kV
(V, in kV) Delta Gr Y
Induced Test, in kV
Dist. &
Class I
Class 2, >72.5 kV
2V
Imp Y
3
One Enhanced
Hour
7200 cy
Basic Insulation Level, in kV
Min.
Alternates
Neutral BIL, in kV
GrY
Impedance
Distribution and Class I Power Transformers, ≤69 kV Nominal System Voltage
1.5
1.2
10
10
10
1.4
30
45
30
30
3.5
2.5
15
15
15
2.9
45
60
45
45
6.9
5
19
19
19
5.8
60
75
60
60
8.7
75
75
75
75
11
26
26
26
10
75
95
15
34
26
26
17.3
95
110
26
25
50
26
34
28.9
125
150
75
95
38
34.5
70
26
50
39.8
150
200
75
125
48.3
46
95
34
70
53.1
200
250
95
150
72.5
69
140
34
95
79.7
250
350
95
200
120
115
173
34*
95*
N/A
105
120
350
450
550
110
250
145
138
207
34*
95*
N/A
125
145
450
550
650
166
161
242
34*
95*
N/A
145
170
550
650
750
244
230
345
34*
95*
N/A
210
240
750
825
900
362
345
518
34*
95*
N/A
315
360
1050
1175
550
500
N/A
34*
95*
N/A
475
550
1425
1550
765
735
N/A
34*
95*
N/A
750
850
1950
2050
800
765
N/A
34*
95*
N/A
795
885
1950
2050
17.2
125
400
Class II Power Transformers, > 72.5 kV Nominal System Voltage
Notes:
1.*
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
1675
850
110
250
110
350*
110
350*
110*
350*
110*
350*
110*
350*
110*
350*
Insulation level to conform with service requirements but never less than the level shown.
The BIL serves both as a test level for the full wave lightning impulse tests and as the primary identity of a set of
coordinated insulation levels.
Front-of-wave Impulse levels must be specified prior to design of the transformer.
Front-of-wave tests are not recommended on low voltage or tertiary windings that are not exposed to lightning.
The Insulation levels for Distribution, Class 1 and Class 2 transformers shall be selected from this table for both the highvoltage and low-voltage windings.
All test levels are line to ground.
The applied test levels are not applicable to wye-connected windings unless they have been specified to be suitable for
application on ungrounded systems.
Minimum Phase-to-Phase Induced test levels for 3 phase Distribution Transformers shall be not less than 2.0 times nominal
system voltage, and never less than the applied test level from line to ground.
Minimum Phase-to-Phase Induced test levels for 3 phase Class I Power Transformers shall be not less than 1.65 times
nominal system voltage, and never less than the applied test level from line to ground.
When specified, Y-Y connected transformers using a common solidly grounded neutral may use a neutral bushing sellected
in accordance with the requirements of the low voltage winding.
Voltages greater than Maximum System Voltage shall use the next higher voltage class test levels.
Neutral BIL shall be a minimum of 2.5 times neutral applied potential test level.
Single phase distribution and power transformers and regulating transformers for voltage ratings between terminals of 8.7
kV and below are designed for both Y and Delta connection so that a single line of transformers serves for the higher than
needed for their voltage rating.
For Series windings in transformers, such as regulating transformers, the test values to ground shall be determined by the
BIL of the series windings rather than the rated voltage between terminals.
This example shows Table 1 split into two tables by transformer class:
Table 1a (Distribution and Class 1)
This revision combines the Delta and the Wye-Connected Tables from Revision 8 into the new Revision 9
Max
System
Voltage
(kV)
Nominal
System
Voltage
(kV)
Applied Test
From C57.12.00
Table 7 (kV)
Delta
Gr Y
Induced Test in kV
2V
Imp Y
3
Basic Insulation Level
(kV)
Min.
Alternates
Neutral BIL (kV)
GrY
Impedance
Distribution Transformers
1.5
1.2
10
10
10
1.4
30
30
30
3.5
2.5
15
15
15
2.9
45
45
45
6.9
5
19
19
19
5.8
60
60
60
11
8.7
26
26
26
10
75
75
75
17.2
15
34
26
26
17.3
95
75
75
26
25
50
26
34
28.9
125
150
75
95
38
34.5
70
26
50
39.8
125
150
75
125
48.3
46
95
34
70
53.1
200
250
200
95
150
72.5
69
140
34
95
79.7
250
350
95
200
Class I Power Transformers, ≤69 kV Nominal System Voltage
1.5
1.2
10
10
10
1.4
30
45
30
30
3.5
2.5
15
15
15
2.9
45
60
45
45
6.9
5
19
19
19
5.8
60
75
60
60
11
8.7
26
26
26
10
75
95
75
75
17.2
15
34
26
26
17.3
95
110
75
75
26
25
50
26
34
28.9
150
75
95
38
34.5
70
26
50
39.8
200
75
125
48.3
46
95
34
70
53.1
200
250
95
150
72.5
69
140
34
95
79.7
250
350
95
200
Notes:
1.* Insulation level to conform with service requirements but never less than the level shown.
15. The BIL serves both as a test level for the full wave lightning impulse tests and as the primary identity of a set of coordinated
insulation levels.
16. Front-of-wave Impulse levels must be specified prior to design of the transformer.
17. Front-of-wave tests are not recommended on low voltage or tertiary windings that are not exposed to lightning.
18. The Insulation levels for Distribution, Class 1 and Class 2 transformers shall be selected from this table for both the highvoltage and low-voltage windings.
19. All test levels are line to ground.
20. The applied test levels are not applicable to wye-connected windings unless they have been specified to be suitable for
application on ungrounded systems.
21. Minimum Phase-to-Phase Induced test levels for 3 phase Distribution Transformers shall be not less than 2.0 times nominal
system voltage, and never less than the applied test level from line to ground.
22. Minimum Phase-to-Phase Induced test levels for 3 phase Class I Power Transformers shall be not less than 1.65 times nominal
system voltage, and never less than the applied test level from line to ground.
23. When specified, Y-Y connected transformers using a common solidly grounded neutral may use a neutral bushing sellected in
accordance with the requirements of the low voltage winding.
24. Voltages greater than Maximum System Voltage shall use the next higher voltage class test levels.
25. Neutral BIL shall be a minimum of 2.5 times neutral applied potential test level.
26. Single phase distribution and power transformers and regulating transformers for voltage ratings between terminals of 8.7 kV
and below are designed for both Y and Delta connection so that a single line of transformers serves for the higher than needed
for their voltage rating.
27. For Series windings in transformers, such as regulating transformers, the test values to ground shall be determined by the BIL
of the series windings rather than the rated voltage between terminals.
Table 1b (Class II Transformers)
This revision combines the Delta and the Wye-Connected Tables from Revision 8 into the new Revision 9
Applied Test
From C57.12.00
Table 7 (kV)
Max Nominal
System System
Voltage Voltage
(kV)
(kV)
Delta Gr Y
Imp Y
Induced Test (kV)
Class 1
≤69 kV
Class 2, >72.5 kV
Enhanced
One Hour
7200 cy.
Basic Insulation Level (kV)
Min
Alternates
Neutral BIL (kV)
GrY
Impedance
110
250
110
110
250
350*
Class II Power Transformers, > 72.5 kV Nominal System Voltage
120
115
173
34*
95*
N/A
105
120
350
450
550
145
166
138
161
207
242
34*
34*
95*
95*
N/A
N/A
125
145
145
170
450
550
550
650
650
750
244
362
230
345
345
518
34*
34*
95*
95*
N/A
N/A
210
315
240
360
750
1050
825
1175
900
110
110*
350*
350*
550
765
500
735
N/A
N/A
34*
34*
95*
95*
N/A
N/A
475
750
550
850
1425
1950
1550 1675
2050
110*
110*
350*
350*
800
765
N/A
34*
95*
N/A
795
885
1950
2050
110*
350*
850
Notes:
1.* Insulation level to conform with service requirements but never less than the level shown.
2. The BIL serves both as a test level for the full wave lightning impulse tests and as the primary identity of a set of coordinated
insulation levels.
3. Front-of-wave Impulse levels must be specified prior to design of the transformer.
4. Front-of-wave tests are not recommended on low voltage or tertiary windings that are not exposed to lightning.
5. The Insulation levels for Class 1 and Class 2 transformers shall be selected from this table for both the high-voltage and lowvoltage windings.
6. All test levels are line to ground.
7. The applied test levels are not applicable to wye-connected windings unless they have been specified to be suitable for
application on ungrounded systems.
8. Minimum Phase-to-Phase Induced test levels for 3 phase Class I Power Transformers shall be not less than 1.65 times nominal
system voltage, and never less than the applied test level from line to ground.
9. When specified, Y-Y connected transformers using a common solidly grounded neutral may use a neutral bushing sellected in
accordance with the requirements of the low voltage winding.
10. Voltages greater than Maximum System Voltage shall use the next higher voltage class test levels.
11. Neutral BIL shall be a minimum of 2.5 times neutral applied potential test level.
12. For Series windings in transformers, such as regulating transformers, the test values to ground shall be determined by the BIL
of the series windings rather than the rated voltage between terminals.
Table 2
High Frequency Test Tables
BIL
kV Crest
1.2 X 50
μ-sec
Chopped Wave
kV Crest
1.1*BIL
Minimum
Time to
Flashover, μ-sec
Front Of Wave
kV Crest
Minimum
Time to
Flashover, μ-sec
Switching Impulse
kV Crest
0.83*BIL
30
33
1.0
45
60
50
66
1.5
1.5
75
95
83
105
1.5
1.8
165
0.5
110
125
120
138
2.0
2.3
195
220
0.5
0.5
150
200
165
220
3.0
3.0
260
345
0.5
0.5
250
275
3.0
435
0.5
350
450
385
495
3.0
3.0
580
0.58
N/A unless specified
550
650
605
715
3.0
3.0
N/A unless specified
N/A unless specified
460
540
750
825
825
900
3.0
3.0
N/A unless specified
N/A unless specified
620
685
900
1050
990
1155
3.0
3.0
N/A unless specified
N/A unless specified
745
870
1175
1290
3.0
N/A unless specified
975
1300
1430
3.0
N/A unless specified
1080
1425
1550
1570
1705
3.0
3.0
N/A unless specified
N/A unless specified
1180
1290
1675
1800
1845
1980
3.0
3.0
N/A unless specified
N/A unless specified
1390
1550
1950
2145
3.0
N/A unless specified
1620
2050
2255
3.0
N/A unless specified
1700
280
375
Notes:
1. Front-of-Wave tests must be specified prior to the design of the transformer.
2. Front-of-wave tests are not recommended on low voltage or tertiary windings that are not exposed to lightning.
3. The Insulation levels for Distribution, Class 1 and Class 2 transformers shall be selected from this table for both the highvoltage and low-voltage windings.
4. Phase to ground specified Switching impulse levels are not always possible for low voltage windings.
Table 1b
This revision combines the Delta and the Wye-Connected Tables from Revision 8 into the new Revision 9
Max
System
Voltage (V)
Nominal
System
Voltage (V)
Applied Test
From C57.12.00
Table 7
Delta
Gr Y
Induced Test
2V
Imp Y
3
Basic Insulation Level
Min.
Alternates
Neutral BIL
GrY
Impedance
Distribution Transformers
1.5
1.2
10
10
10
1.4
30
30
30
3.5
2.5
15
15
15
2.9
45
45
45
6.9
5
19
19
19
5.8
60
60
60
11
8.7
26
26
26
10
75
75
75
17.2
15
34
26
26
17.3
95
75
75
26
25
50
26
34
28.9
125
150
75
95
38
34.5
70
26
50
39.8
125
150
75
125
48.3
46
95
34
70
53.1
200
250
200
95
150
72.5
69
140
34
95
79.7
250
350
95
200
Class I Power Transformers, < or = 69 kV Nominal System Voltage
1.5
1.2
10
10
10
1.4
30
45
30
30
3.5
2.5
15
15
15
2.9
45
60
45
45
6.9
5
19
19
19
5.8
60
75
60
60
11
8.7
26
26
26
10
75
95
75
75
17.2
15
34
26
26
17.3
95
110
75
75
26
25
50
26
34
28.9
150
75
95
38
34.5
70
26
50
39.8
200
75
125
48.3
46
95
34
70
53.1
200
250
95
150
72.5
69
140
34
95
79.7
250
350
95
200
Notes:
1.
Insulation level to conform with service requirements but never less than the level shown.
13. The BIL serves both as a test level for the full wave lightning impulse tests and as the primary identity of a set of coordinated
insulation levels.
14. Front-of-wave Impulse levels must be specified prior to design of the transformer.
15. Front-of-wave tests are not recommended on low voltage or tertiary windings that are not exposed to lightning.
16. The Insulation levels for Distribution, Class 1 and Class 2 transformers shall be selected from this table for both the highvoltage and low-voltage windings.
17. All test levels are line to ground.
18. The applied test levels are not applicable to wye-connected windings unless they have been specified to be suitable for
application on ungrounded systems.
19. Minimum Phase-to-Phase Induced test levels for 3 phase Distribution Transformers shall be not less than 2.0 times nominal
system voltage, and never less than the applied test level from line to ground.
20. Minimum Phase-to-Phase Induced test levels for 3 phase Class I Power Transformers shall be not less than 1.65 times nominal
system voltage, and never less than the applied test level from line to ground.
21. When specified, Y-Y connected transformers using a common solidly grounded neutral may use a neutral bushing sellected in
accordance with the requirements of the low voltage winding.
22. Voltages greater than Maximum System Voltage shall use the next higher voltage class test levels.
23. Neutral BIL shall be a minimum of 2.5 times neutral applied potential test level.
24. Single phase distribution and power transformers and regulating transformers for voltage ratings between terminals of 8.7 kV
and below are designed for both Y and Delta connection so that a single line of transformers serves for the higher than needed
for their voltage rating.
25. For Series windings in transformers, such as regulating transformers, the test values to ground shall be determined by the BIL
of the series windings rather than the rated voltage between terminals.
Table 2
High Frequency Test Tables
BIL
Chopped Wave
kV Crest
1.2 X 50
μ-sec
Minimum
Time to
Flashover, μ-sec
kV Crest
Minimum
Time to
Flashover, μ-sec
Switching Impulse
kV Crest
0.83*BIL
30
45
33
50
1.0
1.5
60
75
66
83
1.5
1.5
95
110
105
120
1.8
2.0
165
195
0.5
0.5
125
150
138
165
2.3
3.0
220
260
0.5
0.5
200
220
3.0
345
0.5
250
275
3.0
435
0.5
350
385
3.0
580
0.58
450
550
495
605
3.0
3.0
N/A unless specified
N/A unless specified
375
460
650
750
715
825
3.0
3.0
N/A unless specified
N/A unless specified
540
620
825
900
900
990
3.0
3.0
N/A unless specified
N/A unless specified
685
745
1050
1175
1155
1290
3.0
3.0
N/A unless specified
N/A unless specified
870
975
1300
1425
1430
1570
3.0
3.0
N/A unless specified
N/A unless specified
1080
1180
1550
1675
1705
1845
3.0
3.0
N/A unless specified
N/A unless specified
1290
1390
1950
1950
2145
2145
3.0
3.0
N/A unless specified
N/A unless specified
1550
1620
2050
2255
3.0
N/A unless specified
1700
Notes:
1.
5.
6.
7.
kV Crest
1.1*BIL
Front Of Wave
280
Front-of-Wave tests must be specified prior to the design of the transformer.
Front-of-wave tests are not recommended on low voltage or tertiary windings that are not exposed to lightning.
The Insulation levels for Distribution, Class 1 and Class 2 transformers shall be selected from this table for both the highvoltage and low-voltage windings.
Phase to ground specified Switching impulse levels are not always possible for low voltage windings.