PERFORMANCE EVALUATION OF STATIC VAR COMPENSATED SYSTEM WITH AUXILIARY CONTROLS

Static VAR system is a new kind of reactive power and voltage control equipment. It can be used not only to improve dynamic and transient stability of power system, but is especially suitable for voltage control of long distance bulk power transmission lines.To improve power system dynamic and transient stability, in addition to voltage feed-back, rotor speed of synchronous machines, bus frequency deviation, and derivative of bus voltage can be used as auxiliary control signals for SVS. The measurement of generator bus frequency deviations and transmission of rotor speed of generators are difficult in single/multi-machine power systems particularly when the SVS is located at the mid point on transmission line.But, power flow over transmission lines can be conveniently and locally measured. In this paper, an attempt is made to use power flow over lines (derivative of active power/reactive power) as auxiliary control signal for SVS. The auxiliary controller parameters are obtained using eigen-value analysis and by employing two criteria namely, (a) Damping factor of two sensitive eigen values is made nearly equal and (b)Synchronising torque is made constant;while improving the damping factor. The power system performance with SVS (with and without auxiliary controls) and with fixed susceptance is studied in detail using digital simulation under fault conditions.