Enhancing power system dynamic and steady-state performance with past-switched shunt compensation to postpone major bulk transmission capital investments

Electric power delivery system capability is constrained by several engineering considerations: thermal ratings of equipment; voltage control capability; and dynamic stability. Dynamic stability and voltage control-related restrictions frequently impose transmission system utilization limits significantly lower than those arising from thermal considerations. Management and control of reactive power supply to satisfy increasing use of the bulk power transmission system has become of increased concern for electric utilities. This is because reactive power control determines the power system voltage profile. Relaxing nonthermal transmission limitations often can be achieved by providing adequate amounts of fast-acting reactive power supply capability. Experience at Northern States Power Company (NSP) has shown that high-speed mechanically switched shunt capacitors often are an economical alternative to static VAr compensators. Such capacitors, equipped with properly designed control systems utilizing modem devices, can in certain applications provide the enhanced reactive power control capability required to improve power system performance to levels which permit increased loadability. Postponement of major capital investment in increased transmission capacity is sometimes achievable by such power capacitor installations. Designing a bulk transmission system which is independent of generation supply (and the associated reactive power output) location is important because of the dynamic energy sourcing market expected in the near future.