Master-follower method for controlling paralell transformers implemented in a numerical protection system

Along last decades, the power system protection relay has experienced many important changes, from purely electromechanical type to fully numerical relays based on microprocessors. In the transformer protection area, similar changes can be seen. The numerical protection systems have control functions such as on load tap changer control function in combination with protection system so that a protection and control system can be formed within one hardware and software system. This kind of device can be also called as a multifunction protection system (MPS). This paper describes the main features of the master-follower control method and its functionality integrated in a MPS. The paper also present a study case which relieves the way in which the voltage of a bus can be controlled using the master follower method of control.