Coordinated AVQC operations of EHV transformer´s tap changer by fuzzy expert control system

In this paper, we first outline the original fuzzy expert AVQC (automatic voltage and reactive control) method that has been in use at Tohoku Electric Power Company. We then investigate the mechanism of the inadequate motion of a transformer´s tap changer. We propose an improved fuzzy expert control method to prevent unnecessary tap changer action. In order to validate the improved method, simulations of tap changer behavior under various operating conditions are conducted. The results of the simulations and analyses are also presented. In the last section, we briefly recommend utilizing on-load tap changers under critical operating conditions in terms of transient stability of a power system.