Equal transfer processes-based distance protection of EHV transmission lines

•Coupling capacitor voltage transformers can cause the distance relay overreach.•We make the voltages and currents to have the same transfer links.•We re-structure the voltage at the fault point.•The virtual digital transfer method is used.•The measuring error is within 5% at 15ms after fault occurrence. The overreach of the distance protection caused by CCVT is still a serious problem for high-speed line protections. Based on the theory of Equal Transfer Process of Transmission Lines (ETPTLs), a new high-speed distance relay scheme is proposed in order to overcome above problem. The solution is to make the three-phase voltages and currents at the relay location and the voltage at the fault point have the same transfer links by virtue of a new design. Three major steps of the new method are demonstrated: re-structuring of the voltage at the fault point, the virtual digital transfer method and solving the R–L differential equation. A variety of ATP simulation tests show that the new method effectively reduces the transient error caused by CCVT and improves the operating speed by a series of technical countermeasures including three major steps, iterative calculations of the fault distance and an inverse time delay setting criterion. The distance measuring error is within 5% at approximately 15ms after fault occurrence, which is superior to various adaptive protection algorithms based on CCVT transient error estimation or source impedance ratio (SIR).