High Voltage Testing - ac（高压测试ac）.pdf

9 High Voltage Testing 9.0 High Voltage Testing Procedure Electrical equipment must be capable of withstanding overvoltages during operation. Thus by suitable testing procedure we must ensure that this is done. High voltage testing can be broadly classified into testing of insulating materials (samples of dielectrics) and tests on completed equipment. The tests carried out on samples of dielectric consist generally of the measurement of permittivity, dielectric loss per unit volume, and the dielectric strength of the material. The first two can be measured using the High Voltage Schering Bridge. The tests carried out on completed equipment are the measurement of capacitance, the power factor or the total dielectric loss, the ultimate breakdown voltage and the flash-over voltage. The breakdown voltage tests on completed equipment is only done on a few samples since it permanently damages and destroys the equipment from further use. However since all equipment have to stand up to a certain voltage without damage under operating conditions, all equipment are subjected to withstand tests on which the voltage applied is about twice the normal voltage, but which is less than the breakdown voltage. 9.1 General tests carried out on High voltage equipment 9.1.1 Sustained low-frequency tests Sustained low frequency tests are done at power frequency (50 Hz), and are the commonest of all tests. These tests are made upon specimens of insulation materials for the determination of dielectric strength and dielectric loss, for routine testing of supply mains, and for work tests on high voltage transformers, porcelain insulators and other apparatus. Since the dielectric loss is s