Controlling of Power Transformer Tap Positions (OLTC) Using Facts Devices

Abstract

Frequent monitoring of the power transformer is necessary for modern power systems. In previous years, mechanical types of on-load transformers were used. The mechanical transformer tap changes involve issues such as the need for manpower, arcing, frequent maintenance, and service costs. Power electronics and solid-state tap changers were developed to address this challenge. It concerns power semiconductor devices such as IGBT (Insulated Gate Bipolar Transistor) and TRIAC, which enable the development of quick operating on-load tap positions. This power semiconductor aids in addressing flicker and sags. FACTS devices control the voltage by adjusting the tap positions. The control devices, along with power electronic devices, are connected to an AVR (Automatic Voltage Regulator). The tap positions of the FACTS-based power transformer are controlled by injecting voltage from the receiving side of the transformer. This injecting voltage is compared to a predefined voltage in the ALTC device. FACTS devices are deployed in AC transmission grids to enhance voltage regulation, grid stability, and control of transformer tap positions via series and/or shunt compensation with capacitor banks. The connection of these capacitor banks to the transmission system is made via breakers. Automatic load tap changing for power transformers primarily aims to maintain the voltage on the lower-voltage side within a predetermined deadband.