IMPROVEMENT IN THE PERFORMANCE OF SERIES CONNECTED ON LOAD TAP CHANGER TRANSFORMERS USING LOCAL MEASUREMENTS TO DETERMINE UPSTREAM TAP CHANGER CONTROL ACTIONS

摘要

Transmission and distribution systems operate at multiple voltage levels, with the transformers connecting these levels often requiring on-load tap changers to regulate the voltage and maintain it within statutory limits. When transformers are operating in series conventional time grading is used between each respective tap changer control relay. This ensures that upstream tap changer controllers respond to voltage excursions faster than downstream controllers and hence prevents hunting. A new scheme is presented in this paper which monitors both the transformer secondary voltage and current to estimate the upstream voltage. Using this estimation the tap changer controller is able to adapt to the upstream voltage conditions and minimise its time grading therefore improving the quality of supply by reducing the voltage disturbance time. Communications are not required between different voltage levels and therefore there is no reduction in security and extendibility of the system. Simulation studies are presented to demonstrate the performance of this scheme and compare it with conventional time grading schemes and communication assisted schemes.