JP2658110B2 - Digital protection relay - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital protection relay, and more particularly to a method of calculating a direction element.

B. Summary of the Invention The present invention provides an action function that is obtained by using a directional element from the amount of polarity to determine the direction of a fault point of a power system to be protected (hereinafter referred to as a protection system) and that functions in the event of a near-end accident. In a digital protection relay device that maintains the operation of a directional element, a directional element operation output is obtained by a combination of an impedance element and a directional element, so that reliable operation output can be obtained while ensuring and coordinating protection. It is like that.

C. Prior Art Digital protection relays convert analog amounts of voltage and current of a protection system into digital amounts by sampling to perform protection operations for various relay functions. Among the relay functions, the distance relay or the like uses the amount of polarity, which becomes the phase of the system voltage and current, in the protection calculation in order to perform protection in which the fault direction of the protection system is also determined. In a protective relay having a directional element based on this polarity amount, in the case of a near-end accident, the polarity amount becomes close to zero due to the disappearance of the system voltage, making it impossible to determine the direction.

Therefore, some digital protection relay devices have a memory action function in which when the polarity amount becomes close to zero, the memory value of the polarity amount immediately before the accident is used to determine the polarity amount after the occurrence of the accident. In this memory action function, for example, as shown in FIG. 4, the voltage and current sample values are stored and updated in the memory, and when the voltage input disappears when an accident occurs (time t ₁ ), the memory is indicated by a broken line. The stored value is read out, and assuming that the polarity amount immediately before the accident continues even after the occurrence of the accident, the calculation and output of the direction element are obtained from the phase comparison with the current sample value.

D. Problems to be Solved by the Invention In the conventional operation method of the direction element by the memory action function, the polarity amount stored in the memory is limited to several cycles. For this reason, the operation output of the directional element can be obtained only for a few cycle periods from its detection due to the occurrence of an accident, and there is a problem as described below.

(1) For time coordination on the system, a timer is added when the protection section overlaps the next protection section even at the minimum set value of the distance relay, and the trip is delayed until after the trip time of the next protection section. Such time coordination time (10
0ms to 10 seconds), the trip output is delayed.
If the timer action is longer than the short operation duration (several tens of milliseconds) of the memory action, trip output cannot be obtained.

(2) When the local backup function is added as a measure against circuit breaker non-operation, the timer delay of the local backup becomes impossible to output as in the case of the timer period described above, and the backup becomes impossible.

In order to solve the above-mentioned problem due to the restriction on the operation duration of the memory action function, there is a method of temporarily retaining the operation output signal itself for a predetermined time in the operation output of the direction element. This method has the following problems.

(3) A cumbersome time setting is required to hold the operation output of the direction element in accordance with the time cooperation on the system.

(4) If the system fault is temporary, the output continues even when the fault condition is cleared, and the reliability of the backup relay when the circuit breaker does not respond is reduced.

(5) A malfunction may occur when a failure occurs after returning from the memory action.

E. Means and Action for Solving the Problems The present invention has been made in view of the above problems, and determines the direction of the fault point of the power system to be protected from the polarity amount that becomes the phase of the voltage and current of the system. A digital protection relay device having a directional element and having a memory action function of obtaining an operation output to the directional element using a stored value of the polarity amount immediately before the accident at the time of a near-end accident of the system, An impedance element for detecting a decrease in the impedance of the protection system;
A storage element that is set when the operation output of the directional element and the operation output of the impedance element are simultaneously established and that is reset when the output of both elements disappears, and a directional element operation in which the operation output of the directional element or the storage element is set An OR element for obtaining an output, detecting the state by the impedance element before the operation output of the direction element disappears, storing the state in the storage element and holding the operation output of the direction element, and the operation output of the direction element and the impedance element When both disappear, the storage element is reset to reset the operation output of the direction element.

F. Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention. The direction element 1 detects an accident in the protection direction by digital operation in the same manner as in a conventional digital protection relay. The impedance element 2 obtains an operation output when the impedance becomes equal to or less than the set value from the voltage and current change of the protection system.
The AND element 3 detects both the detection state of the direction element 1 and the impedance element 2, and the AND element 4 detects the non-detection state of both the direction element 1 and the impedance element 2. The storage element 5 is set when the AND element 3 is detected, and is reset when the AND element 4 is detected. The OR element 6 obtains a direction element operation output in the detection state of the direction element 1 or the set state of the storage element 5.

In such a configuration, when an accident occurs in the protection system, the directional element 1 overlaps the operation output according to the operation characteristics shown in FIG. Next, when the occurrence of an accident is at the very near end and the system voltage is extinguished, the output of the direction element 1 is maintained for several cycle times by the memory action function. During this period, the impedance element 2 obtains an operation output from the characteristics shown in FIG. 3, and causes the storage element 5 to be set by the output of the AND element 3 to obtain the directional element operation output from the OR element 6. When the operation outputs of the impedance element 2 and the directional element 1 disappear due to separation of the protection section or the like, the storage element 5 is reset and the directional element operation output is reset.

Therefore, the directional element operation output is obtained as an output stored in the storage element 5 by a logical product of the directional element 1 and the impedance element 2 that does not use the amount of polarity even though the output of the directional element 1 disappears. Then, when the operation outputs of the impedance element 2 and the direction element 1 disappear, the direction element operation output is reset. Thus, the inconvenience of time coordination and local backup by the conventional timer, the inconvenience of setting the time of the timer, and the like are eliminated.

Note that the impedance element 2 can be easily obtained by coefficient multiplication or the like using the operation result of the direction element 1, and does not increase the load of the operation processing.

G. Effects of the Invention As described below, according to the present invention, the operation output holding of the directional element is performed by a set of storage elements in combination with the impedance element, and the operation output reset is performed by the output disappearance of both elements. The retention of the directional element operation output due to the disappearance of the polarity amount is suitable for protection coordination of the system, and has the effect of ensuring coordination with the local backup of circuit breaker unresponsiveness.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is an operation characteristic diagram of a direction element, FIG. 3 is an operation characteristic diagram of a direction element and an impedance element, and FIG. FIG. 1 ... directional element, 2 ... impedance element, 3,4 ...
AND element, 5... Storage element, 6... OR element.

Claims (1)

(57) [Claims] The present invention has a directional element for judging the direction of a fault point of a power system to be protected from a polarity amount which becomes a phase of a voltage and a current of the system. In a digital protection relay device having a memory action function of obtaining an operation output to the directional element using a stored value of an amount, an impedance element for detecting a decrease in impedance of a power system to be protected, an operation output of the directional element, A storage element that is set when the operation outputs of the impedance element are simultaneously established and reset when the output of both elements disappears, and a logical sum element that obtains the operation output of the direction element or the direction element operation output in the set state of the storage element. A digital protection relay device comprising: