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Tech: Why need to do inductance withstand voltage test?2021-01-03

Why need to do inductance withstand voltage test? 

In the power system, the induction withstand voltage is an important functional test to assess the insulation strength of electrical equipment such as transformers, reactors and voltage transformers. 

In DL/T474.4-2006 "Guidelines for the Implementation of Field Insulation Tests", it is clearly specified that beside the main insulation test of  mutual inductor and transformers, the insulation performance test of the longitudinal insulation of mutual inductors and transformers between turns, layers, and breaks should also be maded to effectively check the integrity of the winding coils!

Induction withstand voltage test method

Power frequency withstand voltage is to apply a power frequency high voltage on the primary side. 

Inductive withstand voltage is to apply a frequency multiplier voltage that is of certain multiple of rated voltage on the low voltage side of mutual inductor or transformer. 

The electromagnetic induction of its own obtains the required test voltage on the high-voltage winding to test the longitudinal insulation performance of the transformer.  especially the transformer with neutral point graded insulation, because the external high voltage cannot be used for the power frequency AC withstand voltage test, then inductive withstand voltage test is used for evaluation of both main insulation and longitudinal insulation.

Triple frequency power generator or multi-frequency generator is usually used to do inductive withstand volage test.

Difference between inductive withstand voltage and power frequency withstand voltage

The power frequency withstand voltage test measures the withstand voltage of the main insulation, such as insulation between live part and ground part, insulation between HV coil and LV MV coil, coil and the iron core post and yoke.

The induction withstand voltage test measures vertical insulation withstand voltage. When power transformer coil is subjected to various overvoltage impacts, especially under effect of lightning overvoltage, the uneven voltage distribution along coil sometimes even causes oscillation process, so it is necessary to measure the vertical insulation of transformer and voltage transformer--between turns, layers ,sections and phases.

They complement each other but cannot replace each other.

Inductive withstand voltage has the following functions

(1) Assess the longitudinal insulation of fully insulated transformers, semi-insulated transformers, and fully insulated transformers;

(2) Assess part of the main insulation and longitudinal insulation of the graded insulation transformer.