Voltage Issue Alleviation in Low Voltage System with High PV and EV Penetration using Distribution Transformer with On-Load Tap Changer (OLTC)

Abstract

As the use of solar photovoltaic (PV) systems and electric vehicles (EVs) becomes more prevalent, maintaining stable voltage levels in distribution systems has become a challenge. In urban areas, green housing estates equipped with large amounts of rooftop solar panels can create daytime voltage spikes due to reverse power flow, while EV charging behavior in the evenings can result in significant load and voltage drops. These fluctuations can push voltage beyond acceptable service levels. To address this challenge, the Metropolitan Electricity Authority (MEA) in Thailand is exploring solutions and has discovered that a distribution transformer with on-load tap changer (OLTC) can alleviate the voltage issue. The OLTC can dynamically adjust the transformer's ratio to maintain voltage stability at the secondary side. This paper analyzes two OLTC operation modes: constant secondary voltage and active power-dependent voltage adjustment. The study compares these modes with a non-OLTC transformer through simulations, and the results indicate that the OLTC, particularly when operated in active power-dependent mode with optimized settings, can effectively maintain voltage levels within the service boundaries.