What is the basis for selecting the test voltage for an AC Hipot test?
Test voltage is determined by the equipment's rated insulation level (Um, BIL) and the applicable product standard - there is no single universal voltage.
Voltage selection by equipment type:
|
Equipment |
Standard |
Test Voltage |
Duration |
|
Power Transformer (Um ≤ 72.5 kV) |
IEC 60076-3 |
1.7 × Um / √3 (induced) + PD |
30 s at test + 5 min at Um/√3 |
|
Power Transformer (Um > 72.5 kV) |
IEC 60076-3 |
1.7 × Um / √3 (short-duration induced) |
60 s |
|
Distribution Transformer |
IEC 60076-11 |
2.0 × rated voltage |
60 s |
|
Power Cable (MV) |
IEC 60502-2 |
2.5 × U₀ |
30 min (accept) / 60 min (maint) |
|
Power Cable (HV) |
IEC 60840 |
2.0 × U₀ |
60 min |
|
GIS / Switchgear |
IEC 62271-1 |
1.2 × Um |
60 s |
|
Bushing |
IEC 60137 |
1.2 × Um (PF test) |
60 s |
|
CT / VT |
IEC 61869-1 |
1.3–1.5 × Um/√3 (induced) |
60 s |
Practical field guide:
• Always consult the nameplate (lists Um, BIL).
• Reduce voltage by 80% for field testing of aged equipment (IEEE 400.2 for cables).
• Never exceed nameplate BIL.
• Verify the product standard before selecting voltage - transformer vs. cable voltage differs for the same class.