Fuzzy Logic Controller to Improve the Coordination of Cascaded Tap Changers

The transformers which connect the different voltage levels in transmission and distribution systems are supplied with on-load tap changing mechanism. The on-load tap changer maintains the voltage amplitude within the predefined limits at the so called regulation bus. In a radial feeder, the on-load tap changers are cascaded. Poor coordination between cascaded tap changers causes improper voltage profile and unnecessary operations of tap changers. A fuzzy logic controller is presented in this paper which improves the operation of cascaded tap changers as well as parallel ones. The proposed controller monitors both primary and secondary voltages of the transformer and orders an upward or downward tap changing operation. Because of locally measurement, the communication is not required between two substations which are apart. The controller is also able to set the time delay of tap changing operations based on the measured voltages, which improves the performance of controller and provides a chance to reduce the unwanted changes of taps and also an opportunity to correct the voltage in a reasonable time.