Simulation Research on Combined Voltage Test Techniques for UHV Switchgear

In the dielectric tests of UHV switchgear, the combined voltage test is used to verify the performance of the longitudinal insulation of the switchgear. Different duty of the combined voltage test may cause different problem correspondingly. For power frequency and power frequency combined voltage test, the reason of phase difference is not exactly 180° between the two voltage sources in out-of-phase conditions is analyzed and the value of this phase difference is calculated. By compensating voltage at one power frequency voltage side, the sum of test voltage applied on the longitudinal insulation can meet the specification of standard and the performance can be verified strictly. For impulse and power frequency combined voltage test, the voltage drop on the power frequency wave will occur at the instant of the peak value of the impulse voltage. With the increasing of impulse voltage, the power frequency voltage drop will enhance. In this paper, the method of using a capacitor connected in parallel to the terminal of the power frequency side is presented and can reduce greatly the voltage drop. At the same time, the performance of longitudinal insulation can be verified by compensating voltage at power frequency side.