Effect of UPFC on protection of transmission lines with infeed current

The increasing penetration of flexible AC transmission system devices and renewable generation resources within existing conventional power system networks has necessitated the relook into protective relaying schemes for ensuring grid security and integrity. This paper investigates the impact of a unified power flow controller (UPFC) on Zones 1 and 2 (with infeed current) of the conventional distance relay and pilot protection schemes. Using both analytical and detailed simulation techniques, these schemes have been very thoroughly assessed. The protection impacts for four functions of UPFC are compared with each other comprehensively. The infeed current effect for existing distance relay, as represented by standard MHO characteristics, has been adapted to factor the effect of source and line impedances. In addition, a proposed modification procedure highlights the main reasons for the impedance trajectory changes during faults at Zones 1 and 2 resulting due to the presence of the UPFC. A detailed model of UPFC and six measuring units of distance protection have been developed in the MATLAB/Simulink environment. The accuracy of compensated network and impedance measuring units are verified using Opal-RT's RT-LAB real-time engineering emulator. Copyright (c) 2016 John Wiley & Sons, Ltd.