Operation of load-ratio control transformers connected in parallel and in networks

SUBSTATIONS equipped with automatic load-ratio control equipment are frequently operated with their secondaries in parallel. The units may be physically together, the secondary tie being a bus; or they may be some distance apart connected together by a tie line or group of tie lines as in a primary network. At the present time large numbers of factory-built distribution substations are being sold, and well over half of them are equipped for some form of network operation. As with most voltage regulators, automatic load-ratio control equipment is usually controlled by means of a line-drop compensator and a contact-making voltmeter.^∗ This automatic control equipment has two principal functions: 1. It serves to maintain some specified voltage regulation at some point on the distribution system. 2. It serves to maintain regulator stability and to keep circulating currents at a minimum.