Abstract:Critical Clearing Time (CCT) is the largest possible time for which a power system is allowed to remain in fault condition without losing stability. Appropriate CCTs settings of protective equipments on power system greatly determine the reliability of power supply. This paper determines the CCTs for all the transmission lines in the Nigerian 24-bus, 39-lines 330kV transmission system. The Transient Stability Analysis (TSA) program adopted used the method of partitioned approach with explicit integration method. The result of TSA was considered satisfactory since about 87% of the values obtained fall within acceptable international range. It was concluded that the determination of appropriate CCTs for the Nigerian power system will enhance the operation of the power system by limiting effects of faults on the power system.

In t his paper, a model f or U nified P ower F low Controller ( UPFC) i s su ggested w ith Ne wton-Raphson po wer flow program included. The main control of UPFC series element is r ealized a s a combination o f t he f our control f unctions. T he supplementary c ontrol o f U PFC i s a dded f or damping p ower oscillation. The integrated UPFC model is then incorporated into the conventional t ransient a nd s mall s ignal s tability p rogramswith the Nigeria 330kV network. The tests on the interconnected power system show that the suggested UPFC model method work effectively. T he r esults a lso show t hat t he suggested U PFC control s trategy ca n re alize power f low co ntrol f airly well a nd improve system dynamic performance significantly.

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