Abstract: The current differential relay operates without adjustable settings, and includes a phase current differential element with a predetermined threshold, responsive to local phase current values and remote phase current values, to detect three-phase faults and producing a first output signal if the threshold value is exceeded. Either a negative sequence current differential element or two phase current differential elements, also having predetermined threshold values and responsive to the local and remote phase currents, detect phase-to-phase faults and phase-to-phase-to-ground faults and produces a second output signal if the predetermined threshold is exceeded. A negative sequence or zero sequence current differential current element, with a predetermined threshold value is responsive to the local and remote phase currents to detect phase-to-ground faults and to produce a third output signal if the threshold is exceeded.

Abstract: The system includes a unipolar A/D converter, which samples analog signal inputs thereto, the A/D converter being used in a protective relay for electric power systems. The unipolar A/D converter is responsive to input voltage values and current values from the power line to produce corresponding digital signals. The A/D converter has a ground pin voltage reference at least as negative as the most negative point of the input signal to be processed.

Abstract: The arc suppression system for electrical contacts includes a transistor, such as an IGBT, which is connected across the contacts. A control circuit controls the operation of the transistor such that the turning on of the transistor results in a current path around the contacts, thereby tending to prevent arcing across the contacts. A current sensor, such as a flyback transformer, is positioned in series with the contacts, wherein when the contacts open, current is interrupted through the contacts and the transformer, a secondary voltage results which is applied to the transistor, which tends to maintain the transistor on for a time which is sufficient to allow the contacts to either open or close without an arc.

Abstract: An electronic device will include physical access protection over which a user has control, such as by a key, and password protection which may have been forgotten or otherwise is not in the immediate possession of the user. The apparatus is configured so that removal of power to the apparatus followed by reapplication of power, such as by a switch or a fuse, is recognized by the apparatus, which is configured to permit the user a predetermined period of time to gain access to the apparatus. After access is gained, the user then has an unlimited time to change the password to an alternate password recognizable by the apparatus or to determine the original password or eliminate the password protection. The user then has the ability to alter the functional configuration of the apparatus, such as through changing user-defined settings, providing upgraded firmware for the apparatus or other functions.

Abstract: The system includes a unipolar A/D converter, which samples analog signal inputs thereto, the A/D converter being used in a protective relay for electric power systems. The unipolar A/D converter is responsive to input voltage values and current values from the power line to produce corresponding digital signals. The A/D converter has a ground pin voltage reference at least as negative as the most negative point of the input signal to be processed.

Abstract: The system provides communication of information between at least two protective relays serving a power system line. The communication comprises a series of successive data messages of four characters, each of which includes eight data bits, on eight data channels. The data bits include output function status bits from the transmitting relay on user selected channels, serialized analog data bits on other user selected channels, and virtual terminal data bits on still other user selected channels. A synchronization channel produces information to synchronize the transmission/receiving of the analog data and the virtual terminal data, on the basis of frames of data, each frame containing 18 messages.

Abstract: The communication system includes two communication channels for communication of protection and control information between two protective relays on a power line portion of an electric power system. A switch provided at the receiving relay connects one communication channel and provides a connecting link between the communication channel and the receiving relay. The transmitted data is applied on both communication channels and processed substantially identically. When the one communication channel is indicated to be faulty, the switch in the receiving relay is operated to connect the second communication channel, thereby substantially preventing delay in the receipt of the data from the transmitting relay.

Abstract: Local source data is first sampled at an original sampling rate and then resampled at a first resampling rate which is equal to the framing rate for transmitting said data to the remote source. The resampled local source data is then delayed by the transmission time between the local and remote data sources. The data from the remote relay which is resampled at the remote source at the first resampling rate and the delayed resampled data at the local source are both then resampled at a second resampling rate, at an original sampling rate, to produce aligned data at the local source.

Abstract: A DC monitoring system is provided in each protective relay in an electric power substation to detect DC grounds on the DC supply system. The DC monitoring system includes a first portion which indicates the presence of a DC ground. In a second portion of the system, the voltages at the contact inputs of the relay are recognized and compared against a standard voltage value range. An indication is provided when the recognized voltage is within said range. The combination of the indications from the first and second portions is useful in determining the location of DC grounds in the substation DC supply system.

Abstract: The arc suppression circuit includes an insulated gate bipolar junction transistor (IGBT) connected across the electrical switch contacts to be protected. When the contacts open, the combination of added Miller capacitance and the gate-to-emitter capacitance of the IGBT results in the IGBT turning on. The IGBT is quickly turned off thereafter by a second transistor, which turns on as the voltage across the suppression circuit rises following turn-on of the IGBT. The turning on of the second transistor results in the first power transistor quickly and abruptly turning off so that relatively little of the load energy is dissipated in the power transistor.

Abstract: An IGBT semiconductor device is connected across switching contacts which are to be protected from arcing. When the contacts are in a normally open configuration, the gate portion of the IGBT is connected to the emitter portion through the contacts, while when the contacts are in a closed configuration, the collector portion of the IGBT is connected to the emitter portion through the contacts. A capacitor is connected in parallel with the gate-collector junction. The combination of the stray collector gate capacitance and the additional capacitor is sufficient to maintain the IGBT device in conduction as the contacts are moving from their closed configuration to their open configuration, thereby preventing arcing across the contacts.