Study of the abnormal phenomena of capacitor voltage transformer (CVT) at Taiwan Power Company

In a power system capacitor voltage transformer (CVT) is usually used to provide the low voltage replica of the high line voltage both in magnitude and phase for protective relays or meters. A large number of CVTs are installed in many substations in Taiwan Power Company (TPC) and have experienced abnormal phenomena while in operation. The problems of the CVTs involve the frequent firing or failure of the gas discharging tube in the CVT installed both in 345 KV and 161 KV systems. This dissertation has devoted to investigating the cause of the firing of the CVT's gas discharging tube.; Two possible causes to the problems are suspected. The first one is the ferroresonance. Ferroresonance, known as the result of the interaction between capacitor and saturable inductor, is able to produce sustained over-voltage and damage the devices. In this dissertation Electro-Magnetic Transient Program (EMTP) is used to study the mathematical model of the CVT provided by the manufacturer. The ferroresonance phenomena of CVT are observed by EMTP simulation, which shows that ferroresonance should not be the cause of the whole problems.; The second possible cause is the induced voltage. Any disturbance, for example switching operation or lightning, in a substation may result in strong induced voltage on the low voltage circuit. In this dissertation, the mathematical model of the induced voltage and program are developed and confirmed by the field tests of TPC. The program is proved to be a good tool for the simulation of the induced voltage. The simulations show that the induced voltage can be the cause of the tube's firing and recommendations are given to solve the problem.