System islanding considerations for improving power system restoration at Manitoba Hydro

System islanding and load shedding concepts have been discussed throughout the industry and considered for years at Manitoba Hydro. The aim is to preserve stable areas of load and generation to aid in system restoration following a major outage. If the islanding scheme operates correctly system restoration may be less complex and overall restoration time reduced by one hour or more. This paper documents studies pertaining to the islanding scheme currently in service. Following a total loss of Manitoba Hydro HVDC, considered to be one of the more significant outages that can be experienced on the power system, the system naturally forms an island due to existing relays. Due to severe undervoltages, the island may disintegrate almost Immediately after its formation. Results show that if high speed under-frequency relays are installed at the natural islanding locations, forcing the island to form at a predetermined system frequency of 59.0 Hz, and prior to its natural formation, a relatively stable northern island can be formed and preserved. The integrity of this island is sensitive to the chosen islanding frequency and speed at which separation can occur in forming the island, TRVs across associated circuit breakers must be considered.