Sequential tripping refers to a special fault clearing status that occurs when the distance relays located at each end of a line trip in different times. To be precise, one of the relays may trip after only the circuit breaker located at the other end of the line has opened. This paper conducts an investigation into this phenomenon by using the symmetrical components theory. It will be demonstrated how source impedance, fault resistance and power angle affect the impedance location in RX plane with respect to protective zones and cause sequential tripping. Using MATLAB<sup>®</sup>, we will simulate different fault and system conditions resulting in sequential tripping. The simulation results can be used to provide the idea when this phenomenon can occur.
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