Hiroto Nakagawa

Improvement of power system stability by high-speed power control of adjustable speed machines

Large-capacity adjustable speed machines (ASMs) at pumped storage power stations have been put into full operation and their operating characteristics have been highly evaluated from the viewpoint of power system operation. The output power (input power) of ASMs can be controlled very quickly by applying a vector control scheme to the excitation control. This quick responsive feature of ASMs can make it possible to improve the stability of the neighbor subpower system. For improvement of transient stability, the output power of ASMs is reduced very quickly in order to control the acceleration of neighbor generators during and after transmission line faults. For improvement of dynamic stability, the output power of ASMs is modulated in accordance with the stabilizing signals detected from the swing of generator rotor or the power flow fluctuation on the transmission line. This paper describes the design concepts and method of control system for improving the transient and dynamic stability and proposes a power system stabilizing control system. The effects of the proposed stabilizing control system have been verified by a power system simulator.

Improvements of transient performance of pump turbine upon load rejection

Transient performance of the pump turbine having so-called S-characteristics upon load rejection can be improved drastically without causing transient reverse flow by optimizing control of the governor. Brief description of the improved control as well as some computer simulation studies to demonstrate the new control methods are presented. Possibilities for reduction of the penstock design pressure, minimizing the suction head margin against the water column separation and such construction cost saving effects are also discussed.

Computer Simulations of Dynamic Performance of 400 MW Adjustable Speed Pumped Storage Units

Two units of the world largest 400 MW adjustable speed pumped storage units for Ohkawachi Power Station, The Kansai Electric Power Inc. , Japan were commissioned in December 1993 and June 1995 respectively.