Max in kv Table 1 (All Classes in 1 Table) From C57.12.00 Table 7 in kv Nominal 2V (V, in kv) Delta Gr Y Imp Y 3 Induced Test, in kv Dist. & Class I Class 2, >72.5 kv Basic Insulation Level, in kv Neutral BIL, in kv One Hour Enhanced 7200 cy Min. Alternates GrY Impedance Distribution and Class I Power Transformers, =69 kv Nominal 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 95 110 125 75 75 26 25 50 26 34 28.9 125 150 75 95 38 34.5 70 26 50 39.8 150 200 75 125 72.5 69 140 34 95 79.7 250 350 400 95 200 Class II Power Transformers, > 72.5 kv Nominal 120 115 173 34* 95* N/A 105 120 350 450 550 110 250 145 138 207 34* 95* N/A 125 145 450 550 650 110 250 166 161 242 34* 95* N/A 145 170 550 650 750 850 110 350* 244 230 345 34* 95* N/A 210 240 750 825 900 110 350* 362 345 518 34* 95* N/A 315 360 1050 1175 110* 350* 550 500 N/A 34* 95* N/A 475 550 1425 1550 1675 110* 350* 765 735 N/A 34* 95* N/A 750 850 1950 2050 110* 350* 800 765 N/A 34* 95* N/A 795 885 1950 2050 110* 350* 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 Distribution, Class 1 and Class 2 transformers shall be selected from this table for both the highvoltage 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 8. Phase-to-Phase Induced test levels for 3 phase Distribution Transformers shall be not less than 2.0 times nominal 9. Phase-to-Phase Induced test levels for 3 phase Class I Power Transformers shall be not less than 1.65 times nominal 10. 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. 11. s greater than Maximum shall use the next higher voltage class test levels. 12. Neutral BIL shall be a minimum of 2.5 times neutral applied potential test level. 13. 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. 14. 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) Max (kv) Nominal From C57.12.00 Table 7 (kv) (kv) Delta Gr Y Imp Y Induced Test in kv 2V Distribution Transformers 3 Basic Insulation Level (kv) Neutral BIL (kv) Min. Alternates GrY Impedance 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 39.8 125 150 200 75 125 Class I Power Transformers, =69 kv Nominal 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 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 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 21. Phase-to-Phase Induced test levels for 3 phase Distribution Transformers shall be not less than 2.0 times nominal 22. Phase-to-Phase Induced test levels for 3 phase Class I Power Transformers shall be not less than 1.65 times nominal 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. s greater than Maximum 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.
Max (kv) Table 1b (Class II Transformers) Induced Test (kv) From C57.12.00 Table 7 (kv) Class 1 Class 2, >72.5 kv Basic Insulation Level (kv) Neutral BIL (kv) Nominal (kv) Delta Gr Y Imp Y =69 kv One Hour Class II Power Transformers, > 72.5 kv Nominal Enhanced 7200 cy. Min Alternates GrY Impedance 120 115 173 34* 95* N/A 105 120 350 450 550 110 250 145 138 207 34* 95* N/A 125 145 450 550 650 110 250 166 161 242 34* 95* N/A 145 170 550 650 750 850 110 350* 244 230 345 34* 95* N/A 210 240 750 825 900 110 350* 362 345 518 34* 95* N/A 315 360 1050 1175 110* 350* 550 500 N/A 34* 95* N/A 475 550 1425 1550 1675 110* 350* 765 735 N/A 34* 95* N/A 750 850 1950 2050 110* 350* 800 765 N/A 34* 95* N/A 795 885 1950 2050 110* 350* 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 8. Phase-to-Phase Induced test levels for 3 phase Class I Power Transformers shall be not less than 1.65 times nominal 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. s greater than Maximum 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 Chopped Wave Front Of Wave Switching Impulse 1.2 X 50 µ-sec 1.1*BIL 30 33 1.0 45 50 1.5 60 66 1.5 75 83 1.5 95 105 1.8 165 0.5 110 120 2.0 195 0.5 125 138 2.3 220 0.5 150 165 3.0 260 0.5 200 220 3.0 345 0.5 250 275 3.0 435 0.5 0.83*BIL 350 385 3.0 580 0.58 280 450 495 3.0 N/A unless specified 375 550 605 3.0 N/A unless specified 460 650 715 3.0 N/A unless specified 540 750 825 3.0 N/A unless specified 620 825 900 3.0 N/A unless specified 685 900 990 3.0 N/A unless specified 745 1050 1155 3.0 N/A unless specified 870 1175 1290 3.0 N/A unless specified 975 1300 1430 3.0 N/A unless specified 1080 1425 1570 3.0 N/A unless specified 1180 1550 1705 3.0 N/A unless specified 1290 1675 1845 3.0 N/A unless specified 1390 1800 1980 3.0 N/A unless specified 1550 1950 2145 3.0 N/A unless specified 1620 2050 2255 3.0 N/A unless specified 1700 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 4. Phase to ground specified Switching impulse levels are not always possible for low voltage windings.
Table 1b Max (V) Nominal From C57.12.00 Induced Test Table 7 2V Basic Insulation Level Neutral BIL (V) Delta Gr Y Imp Y 3 Min. Alternates 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 39.8 125 150 200 75 125 Class I Power Transformers, < or = 69 kv Nominal 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 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 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 19. Phase-to-Phase Induced test levels for 3 phase Distribution Transformers shall be not less than 2.0 times nominal 20. Phase-to-Phase Induced test levels for 3 phase Class I Power Transformers shall be not less than 1.65 times nominal 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. s greater than Maximum 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 Front Of Wave Switching Impulse 1.2 X 50 µ-sec 1.1*BIL 30 33 1.0 45 50 1.5 60 66 1.5 75 83 1.5 95 105 1.8 165 0.5 110 120 2.0 195 0.5 125 138 2.3 220 0.5 150 165 3.0 260 0.5 200 220 3.0 345 0.5 250 275 3.0 435 0.5 0.83*BIL 350 385 3.0 580 0.58 280 450 495 3.0 N/A unless specified 375 550 605 3.0 N/A unless specified 460 650 715 3.0 N/A unless specified 540 750 825 3.0 N/A unless specified 620 825 900 3.0 N/A unless specified 685 900 990 3.0 N/A unless specified 745 1050 1155 3.0 N/A unless specified 870 1175 1290 3.0 N/A unless specified 975 1300 1430 3.0 N/A unless specified 1080 1425 1570 3.0 N/A unless specified 1180 1550 1705 3.0 N/A unless specified 1290 1675 1845 3.0 N/A unless specified 1390 1950 2145 3.0 N/A unless specified 1550 1950 2145 3.0 N/A unless specified 1620 2050 2255 3.0 N/A unless specified 1700 1. Front-of-Wave tests must be specified prior to the design of the transformer. 5. Front-of-wave tests are not recommended on low voltage or tertiary windings that are not exposed to lightning. 6. The Insulation levels for Distribution, Class 1 and Class 2 transformers shall be selected from this table for both the highvoltage 7. Phase to ground specified Switching impulse levels are not always possible for low voltage windings.