Application, Selection And Design Of Three-Winding Transformers In LNG And Petrochemical Facilities

Transformers are used in Power systems to transform (step-down) voltages while maintaining the same frequency. Electrical Engineers designing power systems for Liquefied Natural Gas (LNG) or Petrochemical facilities typically use two-winding transformers to feed multiple process units in redundant distribution schemes throughout the facility. This method is repeated further to derive different voltage levels to feed process loads. As the industry moves towards larger production facilities which increase the power demand, multiple large two-winding transformers are utilized. This approach leads to increase in substation footprints, switchgear equipment, power feeders, site works, etc. This paper focuses on an alternative design using three-winding transformers for LNG or Petrochemical facilities. The input and output of a three-winding transformer generally consists of one primary (H) input, and two outputs defined as secondary (X) and tertiary (Y). Three-winding transformers are connected in a redundant configuration to feed multiple process units. In this paper, different types of three winding configurations and construction (radial or axial) methods are reviewed. In addition, this paper addresses the application of tap changers, overall system performance, defining impedance parameters, installation method, applications and specification requirements.