JP2011130591A - Digital protection relay - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital protection relay for performing a protection operation without being affected by a direction of current flowing to a main circuit. <P>SOLUTION: The digital protection relay is equipped with: a current detecting circuit 1 measuring the current of the main circuit; a central processing unit 3 computing data output from the current detecting circuit 1; storage devices 4a and 4b recording; storing and calling data with the central processing unit 3; and a trip output contact 8 performing the protection operation by output from the central processing unit 3. Protection characteristic data in the direction of the forward and reverse currents of the main circuit, are stored in the storage device 4b. Protection characteristic data in either direction is called by a signal determined by a current direction detecting means in the central processing unit 3 so as to operate the trip output contact. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a digital protection relay that performs a protection operation by detecting an overcurrent of a main circuit.

  2. Description of the Related Art Conventionally, a power distribution control device uses a digital protection relay that performs a protection operation that detects when an overcurrent flows in a main circuit and opens a circuit breaker or the like (see, for example, Patent Document 1). .)

  Here, the direction of the current that the digital protection relay performs the protection operation is with respect to the direction that flows from the power source side of an electric power company or the like. However, recently, NAS batteries and the like that are charged with nighttime power and discharged in the daytime when demand is high have become widespread, and when power is supplied from the NAS battery, the current is reversed. That is, a bidirectional current flows through the main circuit.

JP 2003-79045 A (second page, FIG. 1)

  In the above-described conventional digital protection relay, the direction of the current flowing through the main circuit corresponds to one direction, and it is difficult to cope with the reverse direction. For this reason, there has been a demand for a digital protection relay capable of performing overcurrent protection with respect to the direction of current from the power source side such as a power company and from the NAS battery side.

  The present invention has been made to solve the above problem, and an object of the present invention is to provide a digital protection relay capable of performing a protection operation without being affected by the direction of a current flowing through a main circuit.

  In order to achieve the above object, a digital protection relay of the present invention includes a current detection circuit that measures a current of a main circuit, a central processing unit that performs arithmetic processing on data output from the current detection circuit, and the central processing unit In a digital protection relay comprising a storage device for recording, storing and recalling data between and a trip output contact for performing a protection operation with an output from the central processing unit, the storage device includes the main circuit The protection characteristic data of the forward direction and the reverse direction of the current is stored, and the central processing unit calls the protection characteristic data in any one direction according to the signal determined by the current direction detection means, and outputs the trip output The contact is operated.

  According to the present invention, an overcurrent protection operation can be performed without being affected by the direction of the current flowing through the main circuit.

The figure which shows the structure of the digital protection relay which concerns on Example 1 of this invention. The figure which shows the structure of the digital protection relay which concerns on Example 2 of this invention. The figure which shows the structure of the digital protection relay which concerns on Example 3 of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  First, a digital protection relay according to a first embodiment of the present invention will be described with reference to FIG. 1 is a diagram illustrating a configuration of a digital protection relay according to a first embodiment of the present invention.

  As shown in FIG. 1, the three-phase main circuit current is extracted by the current detection circuit 1, converted from an analog value to a digital value by the A / D conversion circuit 2, and the data is input to the central processing unit 3. The central processing unit 3 is connected to a first storage device 4a and a second storage device 4b. Further, a switch circuit 5 for setting and changing the protection characteristics from the outside and a display circuit 6 for displaying a current value and the like are connected. A trip output contact 8 for operating a circuit breaker connected to the main circuit is connected to the output side of the central processing unit 3 via a relay drive circuit 7 that performs a protection operation.

  Here, the first storage device 4a records, saves, and calls the measured current value, and the second storage device 4b stores the protection characteristic data of the main circuit. The protection characteristic data includes a current-time characteristic supplied from a large-capacity power supply such as an electric power company and a current-time characteristic supplied from a small-capacity power supply such as a NAS battery. The former is forward protection characteristic data, and the latter is reverse protection characteristic data. The directions of the currents of the large-capacity power supply and the small-capacity power supply are opposite to each other, and the large-capacity power supply has a smaller system resistance and a larger current change rate of overcurrent. Also, the noise superimposed on the commercial frequency is large.

  Next, the operation will be described. When an overcurrent equal to or greater than a set value flows in the main circuit, the central processing unit 3 determines an abnormality and calculates, for example, a current change rate to determine a current direction. For example, when the current change rate is equal to or greater than a predetermined value and the current is from the large-capacity power supply side, forward protection characteristic data is called from the second storage device 4b, and when the set value is exceeded, the relay drive circuit 7 The protection operation for operating the trip output contact 8 is performed via the. If the current is from the small-capacity power supply side, the protection characteristic data in the reverse direction is called and the protection operation is executed.

  Here, the determination of the direction of the current in the main circuit based on the current change rate or the like is defined as a current direction detecting means.

  In the protective operation, an operation such as instantaneous overcurrent protection is performed. However, if the current is in the forward direction and the power receiving side is determined to be an accident, the load side instantaneous overcurrent protection is locked. I have to. As a result, an unnecessary protection operation that protects the load side in the event of an accident on the power receiving side can be prevented.

  According to the digital protection relay of the first embodiment, since the protection characteristic is selected according to the direction of the current flowing through the main circuit and the trip output contact 8 is operated, it is influenced by the direction of the current flowing through the main circuit. Therefore, a protection operation against overcurrent can be performed.

  Next, a digital protection relay according to a second embodiment of the present invention will be described with reference to FIG. FIG. 2 is a diagram illustrating the configuration of the digital protection relay according to the second embodiment of the present invention. The second embodiment is different from the first embodiment in that current direction information is taken in. In FIG. 2, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 2, an input detection circuit 9 is provided so that a signal indicating the direction of the current flowing through the main circuit is taken into the central processing unit 3. For example, a current transformer serving as a current direction detecting means is connected to the main circuit.

  According to the digital protection relay of the second embodiment, since the direction of the current flowing through the main circuit can be reliably detected by the current transformer, the protection operation against the overcurrent can be performed without being influenced by the direction of the current. it can.

  Next, a digital protection relay according to a third embodiment of the present invention will be described with reference to FIG. FIG. 3 is a diagram illustrating the configuration of the digital protection relay according to the third embodiment of the present invention. The third embodiment is different from the first embodiment in that a voltage element is introduced. In FIG. 3, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 3, a transformer is connected to the main circuit, and a voltage detection circuit 10 for detecting a voltage is provided. The output of the voltage detection circuit 10 is input to the A / D conversion circuit 2, and power is calculated by the central processing unit 3.

  Since the sign of the calculated electric power changes depending on the direction of the current, for example, if it is positive, it is a forward current supplied from the large-capacity power supply side, and if negative, it is the reverse direction supplied from the small-capacity power supply side. Current. Then, the protection characteristic data of the determined direction is called from the second storage device 4b, and the protection operation is executed.

  Here, calculating a current element composed of the current detection circuit 1 and a voltage element composed of the voltage detection circuit 10 to obtain a positive or negative power signal is defined as current direction detection means.

  According to the digital protection relay of the third embodiment, since the direction of the current flowing in the main circuit is detected from the positive and negative power signals, the protection operation against the overcurrent can be performed without being influenced by the direction of the current.

DESCRIPTION OF SYMBOLS 1 Current detection circuit 2 A / D conversion circuit 3 Central processing unit 4a, 4b Memory | storage device 5 Switch circuit 6 Display circuit 7 Relay drive circuit 8 Trip output contact 9 Input detection circuit 10 Voltage detection circuit

Claims (3)

A current detection circuit for measuring the current of the main circuit;
A central processing unit that performs arithmetic processing on the data output from the current detection circuit;
A storage device for recording, storing, and recalling data with the central processing unit;
In a digital protection relay provided with a trip output contact that performs a protection operation with an output from the central processing unit,
The storage device stores protection characteristic data in which the current direction of the main circuit is forward and reverse,
A digital protection relay characterized in that the central processing unit calls up the protection characteristic data in one of the directions according to the signal determined by the current direction detecting means and operates the trip output contact.   The digital protection relay according to claim 1, wherein the current direction detection unit obtains a signal from a current transformer connected to the main circuit.   The digital protection relay according to claim 1, wherein the current direction detection unit calculates a current element and a voltage element to obtain a positive and negative power signal.

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