Advanced autonomous transformer´s tap changer control system for coordinated secondary voltage control in EHV power systems

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