Improved Detection of Power Transformer Winding Movement by Extending the FRA High Frequency Range

FRA tests in the frequency range up to 10 MHz were investigated using simulations and measurements. It was found that the FRA test was more sensitive to changes in the transformer at frequencies above 1 to 3 MHz than at lower frequencies. However, the effects of the conventional test circuits mask the changes at the higher frequencies. A new test method is proposed that is effective up to at least 10 MHz.