Optimization of dynamic performance of WAPDA power system using excitation systems

In past, oscillations and seasonal overloading in WAPDA power system network have caused a severe disruption and resulted in widespread blackouts. The main reason of these oscillations has been high power flow on EHV lines, especially on 500 kV transmission line between Guddu and Multan. The interconnection is then tripped off and causes the whole system to collapse, leaving some parts to operate independently. To avoid such situation, an increase in damping of system is desirable. System damping can be enhanced by artificial signals introduced through excitation systems. The desirable excitation system characteristics are a fast response and a high ceiling voltage. Modern quick response exciters, with proper design and compensation, have been found very beneficial to handle such problems. We have compared all such exciter on a 500 kV network to find out the best one for system stability. A complete data base of generators, exciters and governors has been made by collecting data from all generating stations. Simulating the present WAPDA system, we have identified the machines prone to instability. Then we checked the response of other exciters and selected the best one for stability. On the basis of simulation results we have given recommendations to improve the stability of WAPDA system using excitation control.