Generator Circuit Breaker Issues in Pumped Storage Station

摘要

The generator motors of subject project are supplied with an 18 kV generator circuit breaker (GCB) of the gas insulated (SF6) type. Because of the pumped storage operation, the units pump at night, and generate during the day at operating periods selected by the system dispatcher. The normal means of connecting and disconnecting a unit to the power system is via the GCB, and all operations are automatic. All switching operations occur at near zero unit load except for pump tripping and emergency tripping. Although it is possible to trip the GCB at zero load for pump shutdown, this was deemed not advisable by the turbine manufacturer because of the extreme loading of the wicket gate components during this condition, no matter the short duration. This magnitude of forces would cause unplanned wear in turbine parts, leading to shorter life. Switching imposes three forms of wear on the GCB: mechanical, electrical and age. As a consequence, the GCB already requires rebuilding on a regular basis. Tripping the pump at a non-zero load will increase amount of electrical wear, and thus require more frequent rebuilding of the GCB. This paper discusses why it was deemed better to rebuild the GCB than the alternative of rebuilding turbine components.