A Novel Line Stability Index (NLSI) for Voltage Stability Assessment of Power Systems

The management of power systems has become more difficult than earlier because power systems are operated closer to security limits, environmental constraints restrict the expansion of transmission network, the need for long distance power transfer has increased and fewer operators are engaged in the supervision and operation of power systems. Voltage stability has become a major concern in many power systems and many blackouts have been reported, where the reason has been voltage instability. This paper presents a novel line stability index (NLSI) referred to a line initiated from the voltage quadratic equation at the sending and resaving end of a representation of a 2-bus system. The line index in the interconnected system in which the value that is closed to one indicates that the line has reached its instability limit which could cause sudden voltage drop to the corresponding bus caused by the active and reactive load variation. The proposed index consider both active and reactive power to investigate the voltage stability because this index provides more precise results than those which consider only reactive power. To indicate the ability of proposed index, NEW ENGLAND 30 bus is utilized and simulation results show good conformity with the other stability index that proposed in literature. Key-Words: Voltage stability index, Maximum permissible load, NLSI factor.