MODELING AND SIMULATION OF AUTOMATIC VOLTAGE CONTROL RELAY

Abstract

Today voltage control is necessary for electrical power system for both at distribution and transmission levels.
Present voltage control in distribution networks is primarily carried out by On Load Tap Changing (OLTC) transformers and
Automatic Voltage Control (AVC) relays, which is mostly used in 11kV network. The AVC relay, acting on the secondary
control of the OLTC transformer, is designed for passive distribution networks with unidirectional power flows. The increasing
connection of distributed generation in a distribution network may lead to unacceptable voltage rise. Hence the capacity of
distributed generation that may be connected to a distribution networks is limited by the operation of the AVC relay. By
measuring critical voltage points along a distribution feeder, an automatic voltage reference setting device is applied to the
AVC relay voltage reference setting. The AVC relay and the OLTC transformer are then used to control voltage rise in
distribution networks with distributed generation. A number of factors that can influence the optimum tap position are primary
voltage level, load level, power factor, distributed generation and circulating current. This thesis presents, firstly, an overview
of automatic voltage control methods for transformers and also presents an attempt to design an AVC relay based on Fuzzy
Logic. It has been observed that fuzzy logic based control has simple and fast controlling, simplify design complexity and
reduce the hardware costs etc. The structure of the proposed Fuzzy Logic based-AVC relay is presented and the results that
show its performance into distribution network are also presented and discussed.