Transformer Corona Measurement Using Condenser Bushing Tap and Resonant Measuring Circuits

Analysis of resonant measuring circuits is given for measurement of corona in transformers, using a bushing capacitor tap connection and a narrow frequency band corona meter. The use of the bushing tap connection and an induced test voltage simplify the test setup. They eliminate the need for corona-free high-voltage connections and for the high-voltage coupling capacitor. Furthermore, in most cases it permits corona testing without the facilities of a shielded room. The use of the resonant measuring circuit greatly improves the sensitivity of corona measurement when the bushing tap connection is used. The circuit may be readily calibrated to render the same numerical values of corona microvolts as the standard National Electrical Manufacturing Association test, yet with a greatly simplified test setup.