Abstract: The insulation degradation of the secondary terminal board of a capacitive voltage transformer can lead to large errors in the dielectric loss test data of the capacitive voltage divider, and can also cause the insulation resistance test of the intermediate transformer to fail. To address this issue, the basic principles of dielectric loss and the measurement principles of digital automatic dielectric loss meters are analyzed, an equivalent analysis circuit model for dielectric loss measurement are constructed, and the error data of dielectric loss tests for three types of capacitive voltage transformers(positive connection method, reverse connection method, and self-excited method)are calculated. The conclusion is that the positive connection method and self-excited method have larger errors, while the reverse connection method has smaller errors. Based on this, the optimal method can be guided for on-site use. The insulation structure characteristics of the intermediate transformer in capacitive voltage transformers is analyzed, and shielding method is used to measure the insulation resistance or dielectric loss of the secondary terminal board to determine the insulation condition of the secondary terminal board. Then, by measuring the dielectric loss of the primary winding of the intermediate transformer to the secondary winding, and combining the capacitance and dielectric loss data of the secondary terminal board, the dielectric loss value of the intermediate transformer winding can be calculated to accurately determine whether the insulation of the intermediate transformer is good.

Key words: secondary terminal panel, deteriorate, insulation resistance, dielectric loss, intermediate transformer, equivalent analysis circuit