The transformer turns ratio test is one of the fundamental routine tests for transformer inspection. This test is used as an indicator of various problems with the transformer windings, such as shorted turns. According to international standards, the pass/fail criterion for turns ratio deviations is ± 0.5 %. This places high demands on the accuracy of the test devices.
The measurement accuracy depends on the test device accuracy and test voltage applied. A higher test voltage applied to the high voltage (HV) transformer side will induce a higher voltage on the low voltage (LV) side, providing a more accurate measurement. Also, higher test voltage will result in higher transformer saturation, leading to more accurate results. The relation between test voltage and accuracy will be elaborated, and the implications for the turns ratio test will be discussed. Case studies that support the importance of using the higher test voltage when the transformer turns ratio test is performed will be presented as well.
July 13, 2021