JP2011130536A - Three-phase overcurrent protective relay - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a low-cost three-phase overcurrent protective relay having a superior noise resistance by measuring a current in two auxiliary CT systems. <P>SOLUTION: The three-phase overcurrent protective relay includes auxiliary CTs 2a, 2b for measuring current of a main circuit, a detection circuit 4 where an output of the auxiliary CTs 2a, 2b is input and a current value of the main circuit is detected, and a CPU 7 where an output of the detection circuit 4 is input via an A/D converter 5 and a multiplexer 6 and a protection operation is executed. The auxiliary CTs 2a, 2b are for two phases, and for the remaining phase, the outputs of the respective auxiliary CTs 2a, 2b are branched and input into an addition circuit 10 composed of hardware to generate signals. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a three-phase overcurrent protection relay in a power distribution system.

  Conventionally, in a three-phase overcurrent protection relay of a power distribution control device such as a switchgear, the three-phase main circuit current is used with three auxiliary CTs, and the ammeter side of each phase is used for overcurrent protection. It was done. In addition, there is one that uses two auxiliary CTs and calculates the ammeter side of the phase not to be measured by software (for example, see Patent Document 1).

  A three-phase overcurrent protection relay of this type is shown in FIG. 3, and the first main circuit CT1a and the second main circuit CT1b are connected to the R phase and the T phase in the three-phase main circuit. The output of the first main circuit CT1a is input to the first auxiliary CT2a that is on the R-phase ammeter side, and the output of the second main circuit CT1b is input to the second auxiliary CT2b that is on the T-phase ammeter side. Has been. The output obtained by adding the first and second main circuits CT1a and 1b is input to the third auxiliary CT2c on the S-phase ammeter side. The outputs of the first to third auxiliary CTs 2a to 2c are noise-cut by the first to third filter circuits 3a to 3c, respectively, and input to the detection circuit 4 that detects the current value. The output of the detection circuit 4 is converted into a digital signal by the A / D converter 5, and the current value is measured and calculated by the CPU 7 via the multiplexer 6. If the current value exceeds a predetermined value as a result of the calculation, the protection operation is executed.

JP 2000-354324 A (FIG. 1)

  In the conventional three-phase overcurrent protection relay described above, the auxiliary CTs 2a, 2b, and 2c are necessary for the three phases, and there is a limit to cost reduction. In addition, in the case of using two auxiliary CTs 2a and 2b and calculating with software, more severe noise countermeasures are required in the calculation circuit. For this reason, there has been a demand for a three-phase overcurrent protection relay that uses two auxiliary CTs 2a and 2b on the ammeter side and calculates the current of a phase not to be measured with hardware that is resistant to noise.

  The present invention has been made to solve the above problem, and an object of the present invention is to provide a three-phase overcurrent protection relay that calculates a phase current that is not measured by hardware, and that is low in cost and excellent in noise resistance. .

  In order to achieve the above object, a three-phase overcurrent protection relay according to the present invention receives an auxiliary CT for measuring a current of a main circuit and an output of the auxiliary CT and detects a current value of the main circuit. A three-phase overcurrent protection relay comprising a detection circuit, and a CPU for performing a protection operation, with the output of the detection circuit being input via an A / D converter and a multiplexer, Two phases are used, and the remaining phases branch the outputs of the auxiliary CTs, and input to an adder circuit configured by hardware to generate a signal.

  According to the present invention, the auxiliary CT is divided into two phases, and the signals of the remaining phases are generated by the hardware addition circuit, so that the reliability of the protection operation can be maintained and the cost can be reduced.

The block diagram of the three-phase overcurrent protection relay which concerns on Example 1 of this invention. The block diagram of the three-phase overcurrent protection relay which concerns on Example 2 of this invention. The block diagram of the conventional three-phase overcurrent protection relay.

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

  First, a three-phase overcurrent protection relay according to Embodiment 1 of the present invention will be described with reference to FIG. 1 is a configuration diagram of a three-phase overcurrent protection relay according to a first embodiment of the present invention. In FIG. 1, the same components as those in the prior art are denoted by the same reference numerals.

  As shown in FIG. 1, the first main circuit CT1a and the second main circuit CT1b are connected to the R phase and the T phase in the three-phase main circuit. The output of the first main circuit CT1a is input to the first auxiliary CT2a that is on the R-phase ammeter side, and the output of the second main circuit CT1b is input to the second auxiliary CT2b that is on the T-phase ammeter side. Has been. The outputs of the first auxiliary CT 2a and the second auxiliary CT 2b are noise-cut by the first and second filter circuits 3a and 3b, respectively, and input to the detection circuit 4 as R-phase and T-phase current values.

  The outputs of the first and second auxiliary CTs 2a and 2b are branched in both phases and input to the adder circuit 10 for adding the signals, and the output is noise-cut by the third filter circuit 3c, and the S-phase is output. The current value is input to the detection circuit 4. The adder circuit 10 is configured by hardware in which electronic components such as resistors and capacitors are combined. The output of the detection circuit 4 is converted into a digital signal by the A / D converter 5, and the current value is measured and calculated by the CPU 7 via the multiplexer 6. If the current value exceeds a predetermined value as a result of the calculation, the protection operation is executed.

  As a result, the number of auxiliary CTs 2a and 2b, which are expensive and important parts, can be reduced (reduction of the conventional third auxiliary CT 2c), and a signal is generated by the adder circuit 10 to execute a protection operation. Costs can be reduced while maintaining the reliability of the protection operation. Since the adder circuit 10 generates a signal corresponding to the S phase by hardware, noise resistance is improved compared to that generated by software. Software may cause software abnormalities such as temporary bit corruption due to disturbance.

  Note that the CPU 7 adds a function of performing a 2 out of 3 operation to execute a protection operation when two phases of the current values in the three phases exceed a set value, thereby causing a failure of electronic components for one phase. Unnecessary operation can be prevented. Further, even in an overcurrent protection relay configured with an analog circuit that does not use the A / D converter 5, the auxiliary CT can be a 2CT system, and a function of 2 out of 3 operation can be added.

  If the main circuit has little noise and the first and second auxiliary CTs 2a and 2b can reduce the noise, the first to third filter circuits 3a to 3c can be omitted.

  According to the three-phase overcurrent protection relay of the first embodiment, the first and second auxiliary CTs 2a and 2b are connected to the R phase and the T phase, respectively, and the S phase is an adder circuit 10 configured by hardware. Since the current signal is generated, the number of parts can be reduced and the cost can be reduced while maintaining the reliability of the protection operation in the CPU 7.

  Next, a three-phase overcurrent protection relay according to Embodiment 2 of the present invention will be described with reference to FIG. FIG. 2 is a configuration diagram of the three-phase overcurrent protection relay according to the second embodiment of the present invention. The second embodiment is different from the first embodiment in the position where the adder circuit is connected. 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, the outputs of the branched R-phase and T-phase first and second auxiliary CTs 2a and 2b are respectively sent as S-phase signals via the fourth and fifth filter circuits 3a1 and 3b1. The data is input to an adder circuit 10 configured by hardware to be generated. The output of the adder circuit 10 is input to the detection circuit 4.

  According to the three-phase overcurrent protection relay of the second embodiment, in addition to the same effects as those of the first embodiment, the signal input to the adder circuit 10 is routed through the fourth and fifth filter circuits 3a1, 3b1. Therefore, the accuracy of the generated S-phase signal can be improved.

1a, 1b Main circuit CT
2a, 2b, 2c Auxiliary CT
3a, 3b, 3c, 3a1, 3b1 Filter circuit 4 Detection circuit 5 A / D converter 6 Multiplexer 7 CPU
10 Adder circuit

Claims (3)

An auxiliary CT that measures the current in the main circuit;
A detection circuit that receives an output of the auxiliary CT and detects a current value of the main circuit;
A three-phase overcurrent protection relay including an output of the detection circuit via an A / D converter and a multiplexer and a CPU for performing a protection operation;
The auxiliary CT is for two phases,
In the remaining phases, the output of each auxiliary CT is branched and input to an adder circuit configured by hardware to generate a signal, and a three-phase overcurrent protection relay.   The three-phase overcurrent protection relay according to claim 1, wherein a filter circuit for cutting noise is connected to each output side of the auxiliary CT.   The three-phase overcurrent protection relay according to claim 1 or 2, wherein the CPU has a 2 out of 3 function.

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