Transformers for phase angle regulation considering the selection of on-load tap-changers

The growth of electric power consumption combined with environmental pressures causing delays and cancellations of new transmission lines is forcing the Electric Utility Co. to use the existing networks with high efficiency and high reliability. Legal regulations may increase these demands even further. The use of phase shifting transformers (PST) can help to control the real power flow in transmission lines and system interties. To realize a variable phase angle shift, OLTCs are used in PSTs. During the planning stage of such transformers the appropriate selection of OLTCs is of great importance for the optimal design of a PST. This paper describes the different principles of phase angle regulation and gives some guidelines for the selection of OLTCs.