Measurement of short circuit load losses in large three phase power transformers using an alternating current comparator bridge

The application of a high-voltage alternating-current-comparator capacitance bridge to the measurement of the short circuit load losses of large three phase power transformers at rated current is described. Input of the transformer current to the bridge is provided through a 1000/1 ratio two-stage current transformer with a single turn primary winding Insulated for 50 kilovolts. Voltage input is provided through a loss-free gas dielectric capacitor which serves as the reference. Measurements on typical transformers ranging in size from 450 MVA to 750 MVA; with currents from 600 to 2100 amperes and short-clrcuit power factors from one percent to four percent, are discussed. Comparisons to appropriately corrected wattmeter measurements (aided by low-loss capacitors connected in parallel with the transformer) indicate an overall agreement of better than one percent.