How to avoid the impact of TCSC on protection schemes

Because of its undoubted advantages, the Thyristor Controlled Series Capacitor (TCSC) is one of the most widely used power-electronic controllers in power systems. However, the TCSC has also been a cause of concern in protective relaying because of its impact on the impedance seen by conventional distance relays, which may lead to an incorrect assessment of fault distance and, consequently, an erroneous relay tripping. To overcome these difficulties, this paper proposes using schemes based on traveling waves for protecting TCSC series compensated transmission lines. Since the method avoids using impedance-based techniques, it is not prone to under-reach or over-reach problems, among others. The approach is based on traveling wave analysis using the discrete wavelet transform. The different case studies show the effectiveness and accuracy of the proposed algorithm in a TCSC environment.