Abstract: A fault protection system is configured to detect a fault in an electric power system. The fault protection system obtains a differential measurement signal. The differential measurement signal may, for example, indicate, as a function of time, the difference between currents or voltages measured at two or more terminals or boundaries of a fault protection zone of the electric power system. Regardless, the fault protection system generates a fault detection signal by cross-correlating the differential measurement signal with a reference signal. The reference signal may for instance be the differential measurement signal that is expected upon occurrence of a fault. The fault protection system performs fault detection, for detecting a fault internal to the fault protection zone, as a function of the fault detection signal.

Abstract: Methods and systems for detecting a falling power line in a power transmission or distribution system are described. Electrical measurements at various points in the power distribution system are used to detect changes in a power line indicating that the conductor has broken or become disconnected. Upon detection, control mechanisms are used to deenergize the conductor while the conductor is falling and/or before it contacts the ground.

Abstract: Methods and systems for detecting a falling power line in a power transmission or distribution system are described. Electrical measurements at various points in the power distribution system are used to detect changes in a power line indicating that the conductor has broken or become disconnected. Upon detection, control mechanisms are used to deenergize the conductor while the conductor is falling and/or before it contacts the ground.

Abstract: Methods and systems for detecting a falling power line in a power transmission or distribution system are described. Electrical measurements at various points in the power distribution system are used to detect changes in a power line indicating that the conductor has broken or become disconnected. Upon detection, control mechanisms are used to deenergize the conductor while the conductor is falling and/or before it contacts the ground.

Abstract: Methods and systems for detecting a falling power line in a power transmission or distribution system are described. Electrical measurements at various points in the power distribution system are used to detect changes in a power line indicating that the conductor has broken or become disconnected. Upon detection, control mechanisms are used to deenergize the conductor while the conductor is falling and/or before it contacts the ground.

Abstract: A distributed bus differential relay system has a separate differential relay element at each feeder location to trip the associated circuit breaker in response to a fault in the protected bus. The only conductors between feeders form a set of leads connecting current transformers in each of the feeders in parallel. Preferably, the current transformer in each feeder also serves as the current transformer for the associated circuit breaker and the differential relay element is incorporated into the overcurrent relay or trip unit of the circuit breaker which is implemented by a microprocessor. Compliance voltage across the cts is limited by a varistor or saturating reactor which is protected from overheating by a time delayed shorting device.

Abstract: A protective relaying system includes a local protective relay operatively coupled to a protected line segment at a first location, and a remote protective relay operatively coupled to the protected line segment at a second location. The remote protective relay generates a signal (PILOT RECEIVE) to indicate the detection of a fault. This signal is communicated to the local protective relay and employed therein to supervise single-pole trip operations.

Abstract: Disclosed is a protective relaying system that trips a local circuit breaker (BL) connected to a transmission line by providing a trip signal ("TRIP.sub.-- BL") to the circuit breaker. The system comprises a local filter operatively coupled to the transmission line, and a local relay operatively coupled to the filter. The local filter receives inputs indicative of phase currents on the transmission line and provides an output ("VFL.sub.k ") derived from the inputs. The local relay (1) receives the output (VFL.sub.k) of the local filter, (2) receives an output ("VFR1.sub.k ", "VFR2.sub.k ") of at least one remote filter, and (3) generates the trip signal. The local filter and relay preferably employ substantially all digital electronic circuitry to generate the trip signal.

Abstract: A power bus fault detector for detecting faults in a predefined portion of an electrical power bus having at least one phase. Power feed lines are coupled to the predefined portion of the power bus by circuit breakers. Current transformers are used to detect the current flowing through each phase of each power feed line which is coupled to the predefined portion of the power bus. A summer generates a current differential signal for each phase that is equal to the sum of the currents detected by the current transformers. A fault detector generates a trip signal which causes the feed line circuit breakers to disconnect the feed lines from the power bus when a fault is detected in the predefined portion of the power bus. The fault detector includes a detector which detects when the current differential signal in any of the power bus's phases is substantially nonsinusoidal in shape.

Abstract: Protective relay apparatus for providing a compensated fault impedance measurement for the determination of a better estimate of fault location along a transmission line is disclosed. In a power system network including local and remote generating sources disposed at respective ends of a transmission line segment of the transmission line, the protective relay apparatus is disposed at the local end of the line segment to measure the fault impedance for use in determining fault location. However, load flow conditions rendered by the generating sources interact with a fault which contributes resistance substantially to the fault impedance of the transmission line to cause an erroneous component in the fault impedance measurement rendering the determination of an erroneous fault location.

Abstract: A nonlinear noise-blanking circuit with memory. An information signal corrupted by a noise signal is input to the nonlinear noise-blanking circuit. The information signal is blanked during noise impulses and an estimate for the blanked information signal is inserted therein. Various embodiments of the invention disclose means for determining an appropriate estimate. For example, the estimate can be a simple positive or negative dc value corresponding to the sign of the information signal prior to noise corruption. Alternatively the first and second derivatives of the information signal prior to noise corruption can be used to generate an expected future trajectory of the information signal, and this value inserted in the information signal during the blanked interval. Also, a sample and hold circuit can be used to "remember" the value of the information signal prior to the inception of a noise impulse. This "remembered" value is then inserted in the information signal during the blanked interval.

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: A regenerator for providing detection, remodulation, and retransmission of a digital data signal propagated in the differential mode over a pair of bundle conductors of a power line. The electric power signal, propagated in the common mode over the same bundle conductors, is conducted through the regenerator and provides a power supply voltage for the regenerator electronics. A series of electrical traps prevent the electric power signal from being conducted into that portion of the regenerator utilized for processing of the data signal. The regenerator also includes bypass switches for by-passing the regenerator electronics when a power supply voltage sufficient to operate the electronics is unavailable.

Abstract: A communication system for transmitting baseband digital signals on an electrical power line. A pulse generator produces digital signals which are limited to a frequency spectrum of 30 kHz to 300 kHz and applied directly, i.e., without modulation, to an electrical power line. At the receiving terminal an amplifier compensates for attenuation characteristics of the electrical power line and the received signal is then sampled to extract the information from it. To avoid interference when both a transmitting and receiving link are located at a substation, the baseband system incorporates a mimic network to mimic the interference signal erroneously picked up by the receiving link from the transmitting link located at the same substation. The mimic signal is then subtracted from the interference signal to neutralize the effect of the latter.

Abstract: Differential protective relay methods and apparatus which include a differential current function supervised by both a harmonic restraint function and a voltage change function. The voltage change function determines whether or not the differential current function requires harmonic restraint supervision, preempting such supervision when it is not required, to enable faster trip decisions to be made by the differential current function.

Abstract: A method of, and apparatus for, detecting shorted turns in an electrical reactor. The impedance of the reactor, and its rate of change, are monitored. A reduction in impedance which exceeds a predetermined rate of change indicates the impedance change is due to shorted turns, and not to some normal cause, such as temperature.

Abstract: A polyphase time overcurrent detector provides a variably delayed control signal wherein the delay is inversely related to both the current magnitude and the number of faulted phases. Current transducers produce input signals representative of the current flowing in each phase of the polyphase system. The input signals are added together to produce a charging signal. If at the end of a predetermined time period the fault has not been cleared, the charging signal will begin to charge a capacitor. If the capacitor charges to a predetermined voltage level within a fixed time period, the control signal is initiated.