Measurements and correction of no-load losses of power transformers

This paper investigates the practice of correcting the results of no-load loss measurements of power transformers for the effect of distorted supply voltage waveform. A three-phase 700-MVA power transformer is tested twice: first with its low-voltage windings connected line-to-neutral, with nearly sinusoidal test voltage conditions, and then for the second test with its windings connected line-to-line with more distorted voltage waveforms. The test data obtained during the measurement was reproduced at the National Research Council (NRC) Laboratory to demonstrate the limits of the application of the loss correction formula currently used.