Investigation into local dynamic indicators of power system voltage stability

The long terra dynamic behaviour of a power system following a significant disturbance is a complex phenomena involving thè response of many voltage controllers including automatic voltage regulation of generators (AVR), automatìc voltage contrai of transformer on-load tap-changers (OLTC), Static Var Compensatore and Mechanically Switched Capacitors (MSC). The bang-bang contro! of MSC devices, for instance, is usually performed using a target voltage signal and a fixed deadband. Due to thè change in System impedance following disturbances such as thè tripping of a criticai line, thè sensitivity of voltage to reactive power injection can increase significantly presenting difficulties in setting a suitable deaband. In this paper we present an investigation into thè use of locally derived indicators which could enhance thè control system of automatic voltage regulators by dynamically adapting thè deadband according to system conditìons, and which may give an indication of thè proximity of thè system to voltage instability.