A Guide to Transformer Ratio Measurements

Transformers are subject to mechanical impact and vibration. Problems or faults occur due to poor design, assembly, handling, poor environments, overloading or poor maintenance. Measuring the polarity and turn ratio of a transformer winding assures that the connections are correct and there are no severe mismatches or opens. Many transformers have taps built into them. These taps allow the ratio to be increased or decreased by fractions of a percent. If any of the ratio changes involve a mechanical movement of a contact from one position to another, these tap changes should also be checked during a ratio test.