The Influence of Limiters UEL and OEL (The power angle, stator's current and excitation current) ot the possibility of voltage collapse development

Voltage stability has been a major concern for power system utilities because of event of voltage collapses in the recent past. Sometimes, power system events have shown the need for generators to operate in the overexcited and underexcited region to support stable operation. Modern excitation systems include devices for controlling or limiting machine terminal voltage (overvoltage limiters), volts per hertz ratio (V/Hz limiters), maximum machine field current (overexcitation limiters), and the reactive load absorbed by the machine (underexcitation limiters). This paper analyzes the effects of acting limiters caused by low voltage in power system. It is shown that the stability region is enlarged by properly working limiters.