Temperature Co-Efficient of Primary Capacitors Used in Capacitive Voltage Dividers-Case Studies

Coupling capacitors are part of the voltage dividers used in Capacitors Voltage transformer (CVTs). CVTs are generally used for high voltage measurements in EHV & UHV systems. Capacitive divider is critical component of the CVT. Coupling capacitors are a composite di-electric with Oil, polypropylene and paper being the key dielectric material. Divider ratio as established based on the stability of the capacitance values of the coupling capacitor. As most of the CVTs are installed in outdoor air insulated switchyard (AIS) they are exposed to wide temperatures changes throughout the year. The stability of the temperature co-efficient of capacitances over these wide temperature ranges are crucial in establishing the accuracy of voltage measurement as further this also influences power/energy measurements. Hence temperature co-efficient of these coupling capacitors are to be characterized. Studies were undertaken to characterize the temperature co-efficient of two model units of coupling capacitors of different makes and the results are analysed and discussed in this paper.