Two-Part Synthetic Test Procedures for the Testing of Medium-Voltage Load Break Switches

Though synthetic test methods are widely used for testing high-power circuit breakers (CBs), synthetic testing has not been reported in the literature as being extended to the testing of medium-voltage (MV) load break switches (LBS). This paper investigates the possibility of type testing of MV LBS using synthetic test procedures. The transient recovery voltage (TRV) required is calculated from both IEC and IEEE standards and it is shown that the IEC TRV specification results in a more severe TRV. It is found that testing with a basic Weil circuit requires two-part testing. In one test, a low-amplitude TRV with a fast rate of rise stresses the early region associated with thermal failure. In the other test, a higher-amplitude slowly rising TRV stresses the later dielectric region. However, the two-part test using the unmodified Weil circuit is shown to cause significant TRV overstressing. Insertion of a precharged capacitor and additional damping resistors into the Weil circuit at critical times using triggered spark gaps are found to be effective to reduce overstressing. Simulation results show that it is possible to use a modified synthetic test circuit to test LBS with voltage ratings of up to 38 kV and load currents of 800 A.