Abstract: New logic circuitry for a directional comparison blocking protective relay scheme. A forward-reaching and a reverse-reaching protective relay located at the local and remote terminals of a protected line segment determine whether a fault is internal or external to the protected line segment. To carry out this function, the protective relays produce signals representative of fault location and communicate with each other via a communications channel. A fault detector and logic circuitry is provided at each terminal for processing the produced signals to determine the fault location and avoid tripping when the fault character changes. By using fault detectors to determine the existence of a fault, the logic at each terminal for combining the signals is simplified and security against false tripping is improved.

Abstract: An apparatus for predicting the remaining useful life of a motor uses the temperature and past history of the motor to determine the amount of insulation degradation for its prediction. The remaining useful life projection is provided at a display and may be used to trip the circuit breakers supplying power to the motor when projected life is shorter than the expected life or may be used to issue a warning that the rate of motor degradation exceeds the rate necessary to achieve the expected life for the motor.Motor protection is provided by tripping the circuit breakers supplying power to the motor before the actual temperature of the motor windings exceeds the temperature at which catastrophic and irreversible insulation failure would occur while not tripping the breakers for momentary transients.