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Study of Transient Behaviour of the Capacitor Voltage Transformer

Amit Kumar, Dr. A. G. Thosar, Vivek Moroney

Capacitive Voltage Transformers (CVTs) are widely used as source of voltage signals for monitoring, protection relays and control application at transmission and sub transmission voltage level. The main component of the CVT are the capacitive voltage divider, a tuning reactor, a step down voltage transformer, a Ferro-resonance suppression circuit and the burden made by the relay. CVT are used for protection of high voltage lines, substations and transmission of high frequency signals. These applications required low voltage signal, which is given by output of CVT. The CVT applications require fast and secure protection. The energy storage elements like inductors & capacitors cause CVTs to exhibit transient behaviour. Further the performance of protection devices is also affected by the transient of CVTs. In steady state, the secondary voltage of a capacitor voltage transformer mirrors the primary voltage. Because of the energy-storage elements used, the transient output, caused by sudden change in primary voltage, is no longer a replica of the primary. Transient over voltages, which exceed insulation ratings can stress electrical insulation, leading to abrupt failure or gradual breakdown of the dielectric of electrical component. This paper attempts to study the effects of changes in capacitor values on the transient response of the CVT. Furthermore, the various method which affects the transient response are discussed by simulating the mathematical model using MATLAB