Maximum Power Transfer Limited by Votage Stability in Series and Siunt Compensated Schemes for a.c Transmission Systems

The planning, operation and control of a power system are to a significant extent governed by stability considerations. Transient or steady-state stability of a power system is its capability to operate stably without loss of synchronism after a large or a small disturbance respectively. Voltage stability, on the other hand, is the ability of the system to provide adequate reactive power support under all operating conditions so as to maintain stable load voltage magnitudes within specified operating limits in the steady-state. Since long distance transmission systems for the transport of bulk power, in addition to the use of series capacitors, require shunt reactors to control power frequency voltage, it is necessary to determine the maximum power transfer PRcrit Of such compensated systems when they are operating on the verge of voltage stability. The determination of such limits is the objective of the present paper. Five different schemes. using series and shunt compensation have been considered. These schemes are the same as those discussed by lliceto and Cinieri [1] from the angular steady-state point of view. In the present paper, an expression for the critical clearing angle bcrit, when the system is operating on the verge of voltage stability, is derived in terms of the load power factor angle, and the generalized circuit constants of the line. Next, assuming the sending-end voltage to be fixed, the critical voltage, VRcrit, when the system is on the verge of voltage stability, is determined in terms of ??crit and the line constants.