On unreliability of exponential load models

Abstract

Abstract This paper addresses the issue of power system load modelling. In power system and voltage stability studies, only aggregate loads at high voltage buses are needed. Due to difficulties in determining appropriate load models at high voltage buses, the classical exponential static load model is still often used. This paper shows that under certain circumstances, e.g. presence of power factor correcting the condensators, the standard approach of modelling real and reactive power as exponentially dependent on voltage may lead to unrealistic values of reactive power voltage exponents. The development of load models where real and apparent power are exponentially dependent on voltage is proposed to avoid unreliability of the reactive power voltage exponent. The constant power factor relationship between real and reactive power is also discussed. The error that could be made by assuming constant power factor of the load during voltage variation is estimated.