Application of Pseudo-Random Impulse Perturbation for Characterizing Capacitor Voltage Transformer Frequency Responses

Capacitor voltage transformers are widely used as voltage transducers for metering and protection applications in high voltage transmission networks. The frequency response of the voltage transformation ratio of a capacitive voltage transformer, however, exhibits resonant characteristics, which limits the usefulness of these transducers for wideband application such as the measurement of harmonic voltage components. The measurement errors induced by this non-ideal frequency response can, in principle, be corrected using the measured or estimated transformation ratio frequency response of the transformer. This paper explores the use of a pseudorandom impulse sequence perturbation signal to measure the frequency responses of a capacitive voltage transformer and determine the associated equivalent circuit parameters. In the proposed test topology, the perturbation signal is applied to the secondary terminals of the test device, and the model parameters are estimated from the frequency response of the secondary input impedance. Estimated parameter values, and measured and simulated frequency responses, are presented for the secondary input impedance, secondary to primary transformation ratio, and transconductance ratio of a 400 kV/110 V capacitive voltage transformer. It is shown that frequency responses simulated with the estimated parameters correlate closely with the measured responses.