Abstract: In a three terminal power line current differential protection system, all three phase current values (IA, IB and IC) are obtained from all three terminals. The current values for each phase are processed in three successive processing operations, using in turn the current values from each terminal as local current values and the combination of the other two terminal current values in each case as the remote current values. The resulting local and remote current values are then processed against preselected values which establish a restrain region in the current ratio (alpha) plane. Current values for each set of local and combined remote currents which result in the ratio being within the restrain region result in a blocking signal while current values which result in a ratio outside of the region result in a tripping signal. If the outputs of the three processing operations agree, then that signal is the system output.

Abstract: A delta filter for use in a protective relay which includes an input circuit for receiving phasor signals representative of electrical signal quantities on the power line. A difference value, if any, is determined between the phasor signals at a present time and the phasor signals at a past point in time (delayed), the delay typically being one cycle. A first incremental output value is produced if there is a difference. When a power line disturbance is first noted by the recognition of a first incremental output value, the phasor signal value at the beginning of the disturbance is stored and then used as a reference value for comparison with subsequent present time phasor signals to determine continuing change in power system condition.

Abstract: In a fault location system, selected information concerning the power signal is obtained at each terminal location on a multi-ended power line. Typically, protective relays are positioned at the terminal locations. The selected information includes the magnitude value of the negative sequence current and the magnitude and angle of the negative sequence impedance of the power signal, at approximately mid-fault in time. An automatic calculation circuit is provided for calculating from the negative sequence values a fractional value m of the total line length representing the point on the line where the fault has occurred, and a system for calculating the distance to the fault from the fault location calculation terminal using the value m and the total distance between the two terminals.

Abstract: The system first identifies the existence of a fault involving ground using the phase angle difference between negative sequence and zero sequence current on the power line. Phase angle differences within three specific ranges provide an indication of the presence of particular faults. Once a particular fault has been identified, such as a BC-to-ground fault, the fault condition is monitored to determine if the fault evolves, such as to a C-to-ground fault from the BC-to-ground fault. If an evolution is recognized, the protective relay is reset so as to coordinate its operation with downstream protective elements for the evolved fault.

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 system impedance ratio (SIR) is determined for the original zone 1 distance element reach of a protective relay. The reduction in the original zone 1 reach is then determined, using the SIR value and a known table of reduced values. When a fault is recognized the minimum reach to just detect the fault is determined. A trip signal is provided without any delay if the minimum reach is less than or equal to the reduced reach. The trip is delayed for a selected time if the minimum reach is greater than the reduced reach but not greater than the original reach.

Abstract: The system for determining protection quality of a protective relay and related functions of the protection system include obtaining information concerning the output status of the various protective elements in the relay. The status of various operations in the protective element are also evaluated against specific standards. The operation of supervisory and control elements affecting the action protective elements are also evaluated. Other aspects of the relay, including the availability of the relay and the operation of the voltage and current transformers are also evaluated. In addition, associated aspects such as the status of the communication channels, the station voltage availability and the condition of the trip and close circuits are monitored. All of the above is analyzed in a summary report to provide an indication of protection quality for the relay and associated protection system functions.

Abstract: The positive sequence voltage on the power line is measured at a given time, i.e. the present time, and also for one cycle earlier, and the ratio thereof is then compared against a threshold value of 0.9. There are four other supervisory tests which also must be true for a loss of potential condition to be indicated. These include determination of change in positive sequence current and angle and zero sequence current and angle. If the change in those values is smaller than selected thresholds, then a loss of potential condition is indicated.

Abstract: Negative sequence, positive sequence and zero sequence quantities are determined from voltage and current values for a power signal on a radial distribution feeder line. Negative sequence quantities are evaluated against selected threshold standards; the negative sequence impedance is also determined, which is then evaluated to determine fault direction (if a fault is indicated). If a reverse fault is declared, the trip output of overcurrent elements in the protective relay for the feeder is blocked for a selected period of time. The same evaluation process is carried out for zero sequence quantities. A selection process determines whether the negative sequence or the zero sequence element is to be enabled. Further, voltages and currents of all three phases of the power signal are evaluated to determine relative change over a period of one cycle. If within the one cycle there is a decrease of both voltage and current in all three phases of approximately 10%, the overcurrent elements are also blocked.

Abstract: At least two different time constants are used to produce the polarizing memory reference voltage which in turn is used in a protective relay for power transmission lines. For most conditions, a relative short time constant of 1.75 cycles is used, while under other specific conditions, determined automatically, a longer time constant of 15.75 cycles is used.

Abstract: An out-of-step blocking circuit is established with two additional zones in the impedance plane, with the circuit determining the time that the positive sequence impedance takes to move between the two zones. The distance elements for selected zones of protection for the relay are blocked if the impedance moves between the two zones at a rate less than a first threshold. However, a trip signal results if the rate of change is greater than the first threshold but less than a second threshold, indicating an unstable swing. Further, an inner blinder zone is established in the impedance plane within the additional two zones of protection. If the positive sequence impedance entering that zone does not move from that zone within a certain time during an otherwise out-of-step condition, the blocking signals are terminated.

Abstract: The voltage and current conditions on a power transmission line are monitored to determine the coincidence of a low voltage condition and a lack of a high current condition. The coincidence of those two conditions is indicative of a CCVT transient, and the tripping action from zone 1 distance elements is delayed for a period of 1.375 cycles. The tripping delay is supervised by a fault impedance determination, which, if a threshold is exceeded, the remaining portion of the time delay is eliminated, so that a trip is allowed if the time delay period has not expired.

Abstract: The directional element produces a quantity related to the zero sequence source impedance of the power system relative to the location of the directional element, from values of zero sequence current and an adjusted value of zero sequence voltage. The impedance quantity is then compared against first and second threshold quantities to identify the direction of a fault. Further, the zero sequence voltage-polarized directional element can be combined with other individual directional elements, including a zero sequence current-polarized directional element and a negative sequence voltage-polarized directional element to form a universal directional element for unbalanced faults, in which the individual directional elements operate in a particular sequence, with the other directional elements being blocked from operating if a prior directional element in the sequence provides a direction indication.

Abstract: Voltage comparisons are made for each of the phase-phase voltages on a low side of a distribution transformer in a power system against a threshold, approximately 0.7 nominal secondary voltage, which is less than the value of at least one phase-phase voltage when only one high side fuse has operated. High outputs result when the phase-phase voltages exceed the threshold. At the same time voltage comparisons are made of each of the phase-phase low side voltages and a second threshold, approximately 0.2 nominal secondary voltage, which is substantially less than the first threshold. High outputs result when the voltages are below the threshold. A circuit output is provided which can be used to trip a low side circuit breaker when at least one output of the first comparisons is high and at least one output of the second comparisons is high.

Abstract: The angle between the negative sequence and zero sequence currents for a power signal on a transmission line is measured and compared against a plurality of successive angle ranges from 0.degree. to 360.degree.. If the angle is 0.degree..+-.30.degree., an AG fault is indicated and a first section output is produced blocking ground elements BG and CG and phase-to-phase elements AB and CA. An angle of 120.degree..+-.30.degree. indicates a BG fault, resulting in a second output blocking ground elements AG and CG and phase-to-phase elements AB and BC, while a phase angle of 240.degree..+-.30.degree. indicates a CG fault, resulting in a third output blocking ground elements AG and BG and phase-to-phase elements BC and CA.

Abstract: A directional element measures the negative sequence voltage and the negative sequence current and from those quantities produces a scalar quantity related to the negative sequence impedance of a power transmission line relative to the location of the directional element. The magnitude of the negative sequence impedance is calculated from the magnitude of the negative sequence voltage and magnitude of the negative sequence current. The scalar quantity is then compared against two threshold quantity settings, one to determine a forward fault and the other to determine a reverse fault. The threshold quantity settings include, respectively, a selected fraction of preselected basic threshold values and a selected fraction of the magnitude of the negative sequence impedance. The scalar quantity must be less than the forward threshold quantity for a forward fault and greater than the reverse threshold quantity for a reverse fault.

Abstract: A directional element measures the negative sequence voltage and the negative sequence current and from those quantities produces a scalar quantity related to the negative sequence impedance of a power transmission line relative to the location of the directional element. The scalar quantity is then compared against two threshold quantity settings, one to determine a forward fault, the other to determine a reverse fault. The scalar quantity must be less than the forward threshold quantity for a forward fault and greater than the reverse threshold quantity for a reverse fault.

Abstract: The polarizing potential transfer switch system takes advantage of an existing loss-of-potential (LOP) circuit (32) in a power transmission line protective system to differentiate between a trip signal produced by the distance elements in a protective relay (22) due to the operation of the transfer switch and a true fault condition. This is accomplished by a logic circuit (40) which includes a first timer (58) which permits the operator of the transfer switch (10) five seconds to complete the potential transfer operation between two buses (14 and 16) and a second timer (68) which gives the LOP circuit (32) a selected number of cycles in which to block a trip signal produced by the distance elements in the relay (22).