Search

Dense smoke from wildfires within a 500-kV line corridor led to several line protection trips over a three-day period. A switchable line-connected reactor, provided to control Ferranti voltages, tripped and locked out twice by its protection shortly after the line was de-energized. Lockout operation prevented quick reactor reinsertion and impeded operational flexibility until visual inspections of the reactor were conducted on both occasions. Forensic investigation of the event concluded that the smoke increased the line capacitances. This created a near 60-Hz zero sequence resonant circuit when the line tripped and became de-energized along with the reactor. The resonant circuit amplified the capacitively coupled zero sequence 60-Hz voltage induced from circuits which run adjacent to the line for a short distance. The voltage amplification drove enough current through the reactor to trip the sensitive ground overcurrent protection. A holistic mitigation is designed to avoid reoccurrence of the incident and improve overall line reliability. The intent of this paper is to share lessons learned from the event investigation with peer utilities because this problem of unexpected operation of line shunt reactor protection has not previously been reported. [ABSTRACT FROM AUTHOR]

Shunt reactors are applied to long extra high-voltage (HV) transmission lines to compensate for their natural capacitance which otherwise could cause overvoltages under light load conditions. However, when the level of compensation approaches around 65% or higher, these reactors themselves can, due to contingency, become the cause of hazardous overvoltages during unbalanced open-phase conditions on the healthy line. This paper reports on an overvoltage incident that occurred on a 500-kV 72% shunt-compensated line in the BC Hydro system. The overvoltage occurred when one of the breaker poles failed to interrupt the current following an inadvertent three-phase trip of the healthy line. The uninterrupted current kept one phase energized for an extended time. Temporary overvoltages during this condition and restrike transients eventually led to surge arrester failures at both terminals. Analysis of voltage and current recordings provided useful insight into the mechanism responsible for the damaging overvoltages as well as the protection and control responses during the disturbance. The intent of this paper is to share the knowledge gained from analyses of the recorded waveforms with other utilities either having or planning for highly compensated lines. [ABSTRACT FROM PUBLISHER]