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In this paper, a new protection scheme for transmission lines is presented. The method has some advantages in comparison with conventional line protection schemes. Faster fault detection and instantaneous coverage of almost 100% of the line are the main advantages of the new method. A full-cycle averaging window is used for fault detection. While the power system is in normal operation conditions, this average is approximately equal to zero. As soon as the faulty signals enter the window, the average is changed to a nonzero value. It is shown that the product of this average value for voltage and current of the faulty phase, in a specific time interval after fault inception, is negative for the forward faults and positive for the reverse faults. The fault is detected by communication between the local and the remote relays. Simulation and experimental results show the efficiency of the proposed method in fast detection of line faults in less than a half cycle.