TRVs across circuit breakers of series compensated lines: status with present technology and analysis for the Turkish 420 kV grid

The analysis of transient recovery voltages (TRVs) across circuit breakers of EHV lines, compensated with modern series capacitors protected by varistors, is presented. The applicable measures for limiting TRVs with present station equipment technology are updated. A physical explanation of the phenomenon is presented. This is useful for classifying the series compensation transmission schemes on the basis of the TRV magnification they can cause. Series capacitors protected by varistors result in higher TRVs than capacitors protected by spark-gaps, because trapped charge voltage remains on the capacitors following clearing of faults of any type and location. Simplified formulas are provided for a quick approximate estimation of TRVs. Means for limiting TRVs are reviewed. A solution, namely varistors branched across line breaker contacts, is explored. Results are presented of EMTP TRV analysis performed for three groups of series compensated 420 kV lines in Turkey, and measures for limiting TRVs are described. It is shown that line outage contingency cases and line fault clearing by breaker failure protection may cause a magnification of TRVs, to which attention must be paid