Capacitor voltage transformer induced ferroresonance—causes, effects and design considerations

Abstract

The combination of the equivalent coupling capacitance and the nonlinear magnetizing inductance of the isolating transformer of a capacitor voltage transformer (CVT) can cause a variety of nonlinear oscillations. In such networks, odd-order subharmonics can appear as stable oscillations, whereas subharmonics of any order can appear as transient oscillations. Such oscillations are known to interfere with the operation of high speed relays. This paper discusses the different types of oscillations that are possible in ferroresonant circuits, the conditions under which they appear, their effect on high speed relays, and the methods for minimizing their influence. It is shown that for a CVT the fundamental frequency voltage signal retains the discriminative features of protection, even in the presence of subharmonic resonance.