On-Load Tap Changer (OLTC) Selection and Optimization in Large Power Transformers

Large power transformers are critical components of the electrical distribution network in complex energy projects, facilitating the seamless transmission of power across multiple voltage levels. The On-Load Tap Changer (OLTC) is an essential component within these transformers, responsible for regulating the voltage ratios and adapting to variations in load and supply conditions. Three-winding transformers with two secondary windings require regulation taking into consideration the loading on both windings which may be different. Other important parameters that users must consider include selection of impedance to achieve desired short circuit levels downstream, large motor starting, location of tap changer that may impact the size and arrangement of the transformer. This technical paper provides an in-depth review of the function and application of OLTCs, implementation on high voltage (HV) versus low voltage (LV) winding(s), space considerations and optimization strategies for large power transformers. Proper specification and application of the OLTC by users in large power transformers is key to reduce cost, minimize complexity of the design, and bring the best value for the project.