Tuning CCVT Frequency Response Data for Improvement of Numerical Distance Protection

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Abstract
A new method to numerically estimate the primary voltage waveform of coupling capacitor voltage transformers is presented. The outcome is a simple digital filter suitable for the frequency range from 10 to 60 Hz, enabling to recover the transformer primary voltage waveform from its secondary voltage waveform. Unlike the techniques reported in the literature, the method does not depend directly on the transformer topology nor on the operational characteristics of the protected system, once only the coupling capacitor voltage transformer frequency response is required as input. The evaluation of the technique is performed through digital simulations using transmission line data from the Brazilian National Power System Grid. Frequency and time domain analysis of two coupling capacitor voltage transformers with different topologies and voltage levels are presented. It is shown that the proposed method is effective for the dynamic correction of low frequency disturbances which may improve the speed, reliability and security of the numerical distance relay.

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