INFLUENCE OF SINGLE-PHASE EXCITATION AND MAGNETIZING REACTANCE ON TRANSFORMER LEAKAGE REACTANCE MEASUREMENT

Low voltage and single-phase excitation are often used to measure leak age reactance or short-circuit impedance of transformers. Winding dist ortion may be detected by comparing field results with factory namepla te values measured at 25-100% of the rated current using three-phase e xcitation. The results of single-and three-phase excitation will not a lways correlate. If the voltage applied in the field is not properly s elected then the data may be influenced by the magnetizing reactance. The resulting difference between the nameplate value and the field dat a might then lead to erroneous analysis of test results and could be i nterpreted as an indication of winding distortion. The intent of this paper is to analyze the physics of the process and gain insight on tes t circuit selection and analysis of the results. Methods for avoiding erroneous test results are suggested.