To discriminate between faults near the end of the protected transmission line and at the beginning of the next line, a time delay is used to coordinate tripping of impedance relays when the fault occurs in a zone spanning approximately 20 percent line length near the end of the protected line. It would be advantageous if the distance protection could be made to operate without the time delay, when the fault occurs at any point on the protected line. Although the basic characteristics of the impedance relays are such that they do not meet this requirement, they can be modified to accomplish fast full-line tripping under certain conditions. A tripping scheme which gives fast full-line tripping for distance protection is described in this paper. In this scheme the principle of operation, called " succession", is to accelerate the second zone time delay of the distance protection when the zero sequence current changes twice. The second change occurs when the circuit breaker at the opposite end of the faulted line trips. To describe the basic principle of full-line trip immediately in succession, consider a typical transmission line with distance protection and circuit breakers at each end of the line as shown in Fig. 1. For a fault at point P in the second zone, the distance protection at line end L normally trips circuit breaker CL with time delay t2l. At the time the fault appears at P, the current through CL and the voltage at busbar L change suddenly.