Abstract: This paper takes an abnormal event of capacitance and dielectric loss data in a routine experiment of an on-site transformer as an example. It used the test principle and the structural design of the transformer to build an equivalent RC circuit model to simulate and analyze the instance. It studied the pattern which the influence of the grounding high-resistance transformer core on transformer windings capacity and dielectric loss measurement. It also explained the abnormal that the capacitance and dielectric loss data. Results showed that the measured capacitance and dielectric loss data became abnormal when the high-resistance iron core was in grounding mode. The capacitance value decreases slightly when the grounding resistance value increases. In this situation, the dielectric loss data rises sharply. The impact of the high-resistance grounding of the core on the measured capacitance and dielectric loss data of each winding is related to the capacitance of the tested winding itself. The influence of the grounding iron core on the measured capacitance and dielectric loss data determined by the capacitance of the tested winding.

    Key words: transformer; capacitance; dielectric loss; RC equivalent model; high-resistance grounding