CCVT impact on the TD21 function security

The use of high-speed protection relays allows an increasing of the power transmitted in transmission lines that are already in operation. The function analyzed in this paper uses instantaneous values of the incremental voltages and currents for the calculation of the fault position in relation to a protected zone, presenting average operation times smaller than those obtained through traditional phasor-based functions. In this way, the impact of the coupling capacitive voltage transformers (CCVT) on the security of the time-domain distance protection function TD21 is analyzed, comparing its performance when primary and secondary voltages signals are taken into account.