Equivalent circuit modelling of a capacitive voltage transformer for power system harmonic frequencies

This paper presents a lumped parameter equivalent circuit for a practical capacitive voltage transformer (CVT) for the frequency band associated with power system harmonics. Measured parameter values are presented for a commercial 400 kV unit. Measured and simulated frequency responses are given for a practical CVT and the observed resonant modes are interpreted with reference to the equivalent circuit parameters. It is shown that the frequency response of a practical CVT exhibits marked bandpass and bandstop characteristics due to resonances associated with the capacitive divider, the intermediate voltage inductor and stray capacitive elements, particularly the winding capacitances of the intermediate voltage inductor and the intermediate voltage transformer. The role of the transient damping arrangement and the secondary burden is discussed with reference to the Q-factors of the observed resonance peaks in the overall frequency response