Abstract: A starting relay for a power transmission line protection system.Where long line sections have to be protected, confusion can arise between normal heavy loads and distant faults having comparable line impedance. The invention provides a starting relay which limits operation of the normal distance relay to conditions within the starting relay characteristic, this being derived by phase and amplitude monitoring of the load at the relay station. The characteristic accepts heavier line currents at potentially normal phase angles than at abnormal phase angles.Certain unbalanced faults do however exhibit normal phase angles and these are detected by substantial line voltage drops. A described combination of phase, current and voltage detectors thus covers substantially all faults.The starting relay finds particular application in a carrier-blocking fault detection scheme employing duplicates of the basic characteristic.