Investigation Of CVT Transient And Its Influence On Distance Relays Applied To Series Compensated Line Protection

With the development of technology on high voltage instrument transformers, the Capacitive Voltage Transformer(CVT) has been used in High Voltage and Extra High Voltage systems widely. However, they create certain problems for distance relays. During line faults, when the primary voltage collapses and the energy stored in the stack capacitors and the tuning reactor of a CVT needs to be dissipated, the CVT generates severe transients that affect the performance of protective relays and cause the transient overreach of distance relays. The transients overreaching is influenced by the parameters of the CVT itself, the load and the inception voltage angle when a fault occurs. This transient error is increased significantly when applies to the protection of series compensated line.This thesis proposes a new algorithm aiming to improve the transient performance of distance relays. The thesis analyses of the equivalent circuit of a CVT, examines the contributing factors of CVT transients, and performs transient simulation study on the influence of CVT transients on the performance of digital distance relays when applied to series compensated lines. The proposed approach takes an approach combining the outputs from a full-cycle and a half-cycle Fourier transformation to overcome the transient overreach.Expensive RTDS (Real Time Digital Simulator) simulation tests indicated that the proposed method is feasible and reliable, and the distance algorithm utilizing the proposed method is able to stay stable when a fault causing severe CVT transient. The new algorithm also ensures distance relays applied for series compensated line protection operate correctly during faults condition with severe CVT transient.