Impedance surfing method for CVT transient mitigation

The main source of voltage signals used for distance relays are capacitive voltage transformers (CVTs). During line faults CVTs generate transients that influence voltage signals. During the transient period it is difficult to distinguish if the fault occurred within the operating zone or outside the protected line, which might lead to a maloperation and in the worst case, a system blackout. In this paper a new method is proposed for CVT transient mitigation. The method is based on the use of several digital filters that simultaneously calculate the fault impedance. The algorithm “is surfing” on the calculated impedances choosing only those which decrease the likelihood of relay maloperations during the CVT transient period. The speed and security of the proposed method is assessed via 2000 fault simulations where different line loads, SIR's and fault inception angles are considered.