Influence of a TCSC in the behaviour of a transformer differential protection

In the last years, a large number of studies have been made on Flexible AC Transmission Systems (FACTS) with the purpose of facilitating their incorporation into the power system. Because of the many advantages of these devices, resulting from their quick and continuous regulation, there is a trend to increase their use in the future. Logically, before they are incorporated into the power system, it will be necessary to study their effect on other elements located in the electrical network such as, for instance, protection devices. The influence of a Thyristor Controlled Series Capacitor (TCSC) in the behaviour of a transformer differential protection is discussed in this paper. Specifically, the case of a differential protection device with discrimination based on the 2nd and 5th harmonics is analysed. As a general conclusion, the TCSC can be said to influence the performance of transformer differential protection. The most significant feature is that it modifies the safety margin for the operation of protection relay. (C) 2004 Elsevier B.V. All rights reserved.