a transformer fault analyzer provides on site fault analysis of electrical distribution transformers , relying on patterns of parameter variation in transformer winding ratios , winding resistance and magnetizing impedance , and comparison of these parameters to predetermined values . in a preferred embodiment the analysis considers transformer ratio balance and magnetizing impedance balance . the transformer analyzer may be used with the transformer under load or no load conditions , and thus can be used to test transformers in the field as well as surplus or refurbished transformers .