JPH09121440A - Protective relay - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize the fail safe function of an analog circuit against abnormality without increasing the burden on a processing circuit. SOLUTION: The analog circuit of a protective relay is doubled by providing an analog circuit 21 in parallel with another analog circuit 15 and whether the difference between the outputs of the circuits 15 and 21 is equal to or smaller than a prescribed value is discriminated by means of an amplifier circuit 22 and a window comparator 23. When the difference is larger than the prescribed value, the output of a processing circuit 17 is inhibited by means of a NAND gate 24 interposed between the processing circuit 17 and an auxiliary relay 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protective relay preferably used as an overcurrent relay against a short circuit or overvoltage.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing an electrical configuration of a typical prior art overcurrent relay 1. The secondary current of the current transformer 3 interposed in the bus bar 2 is input to the overcurrent relay 1. The secondary current is converted into a voltage waveform by the conversion resistor 4 and then input to the analog circuit 5.

The analog circuit 5 is realized by a diode bridge, an RC integrating circuit, etc., and full-wave rectifies and smoothes the input voltage waveform and outputs it. The output of the analog circuit 5 is
After being converted into a digital value in the analog / digital converter 6, it is input to the processing circuit 7 realized by a microcomputer or the like. The processing circuit 7 compares the input digital value with a predetermined threshold value, and when the threshold value or more is exceeded, the relay coil 9 of the auxiliary relay 8 is excited and the relay switch 10 is turned on. As a result, the circuit breaker (not shown) interposed in the bus bar 2 shuts off.

[0004]

In the above-mentioned prior art,
When an abnormality occurs in the analog circuit 5 and the output thereof exceeds the threshold value, the processing circuit 7 derives an erroneous output, and the circuit breaker operates to cause a power failure.

As a countermeasure against such a problem, it may be considered that the analog circuit 5 is duplicated, its output is digitally converted, and then compared by the processing circuit 7. However, in such a configuration, the original threshold value determination operation of the processing circuit 7 and the comparison operation of the output of the analog circuit 5 are added, and there is a problem that the determination takes too long and the software becomes complicated. . On the other hand, there is a demand for activating the circuit breaker promptly when an overcurrent occurs, for example, within 50 msec.

An object of the present invention is to provide a protective relay capable of promptly detecting an abnormality in an analog circuit and preventing an erroneous output.

[0007]

A protective relay according to the present invention rectifies and smoothes an input waveform by a first analog circuit,
A protective relay that converts the output voltage of the first analog circuit into a digital value in a digital circuit, compares it with a predetermined first threshold value, and drives the breaker to be cut off when the output voltage exceeds the first threshold value. A second analog circuit configured in the same manner as the first analog circuit and provided in parallel, an output voltage of the first analog circuit and a second analog circuit.
Of the analog circuit, and a determination circuit that determines whether or not the difference between the two is within a predetermined second threshold, and the determination circuit that responds to the determination result of the determination circuit. When it is outside the threshold value of, a blocking means for blocking the cutoff output from the digital circuit to the breaker is included.

According to the above structure, the existing analog circuit is duplicated, and the judgment circuit for judging whether or not any one of the outputs is abnormal is driven by the circuit breaker. Provided separately from the digital circuit,
The blocking means interposed between the digital circuit and the circuit breaker is operated according to the result of the determination.

Therefore, an abnormality in the analog circuit can be detected promptly without increasing the load on the software of the digital circuit, and erroneous output from the digital circuit can be surely prevented.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Regarding one embodiment of the present invention,
The following is a description based on FIGS. 1 to 3.

FIG. 1 is a block diagram showing an electrical configuration of an overcurrent relay 11 which is a protective relay according to an embodiment of the present invention. The secondary current of the current transformer 13 interposed in the bus bar 12 is input to the overcurrent relay 11. After the secondary current is converted into a voltage waveform in the conversion resistor 14,
It is input to the analog circuit 15 which is the first analog circuit.

The analog circuit 15 is composed of a diode bridge, an RC integrator circuit, etc., and converts the input voltage waveform shown in FIG. 2 (a) into a full-wave rectified signal as indicated by reference numeral α1 in FIG. 2 (b). Smooth and output. The output voltage V1 of the analog circuit 15 is converted into an 8-bit digital value at a sampling frequency of, for example, 240 Hz in an analog / digital converter 16, and then input to a processing circuit 17 realized by a microcomputer or the like. .

Therefore, for example, when the alternating current flowing through the bus bar 12 is 60 Hz, the voltage shown in FIG. 2 (a), as indicated by a triangle, is added to the waveform shown by reference numeral α1 in FIG. 2 (b). Four data items are sampled per one cycle T of the waveform. The processing circuit 17 sets the sampled digital value in a predetermined period, for example, 1
The average value is obtained over a period of 2 seconds, and when the average value becomes equal to or larger than a value corresponding to a preset first preset threshold current, for example, 2 A, it is determined that an overcurrent state exists.

The processing circuit 17 degausses the relay coil 19 of the auxiliary relay 18 when the digital value of the output voltage V1 is less than the value corresponding to the settling current, that is, when it is not in the overcurrent state. The relay switch 20 is cut off, and the circuit breaker (not shown) interposed in the bus bar 12 is in a conductive state. On the other hand, when the digital value of the output voltage V1 is equal to or more than the value corresponding to the settling current, that is, when the processing circuit 17 is in the overcurrent state, the processing circuit 17 excites the relay coil 19, whereby the relay switch 20 becomes conductive, The circuit breaker interposed in the bus bar 12 shuts off.

In the present invention, an analog circuit 21 which is a second analog circuit is provided to the existing relay system configured as described above, and the analog circuit is duplicated and the amplification which constitutes the determination circuit is performed. A circuit 22, a window comparator 23, and a NAND gate 24 as a blocking means are provided.

The analog circuit 21 is the analog circuit 1
5 and outputs an output voltage V2 as indicated by reference numeral α2 in FIG. 2B, for example.

The amplifier circuit 22 comprises a differential amplifier 25, input resistors 26 and 27, and a feedback resistor 28. Output voltage V from each of the analog circuits 15 and 21
1, V2 are input to the inverting input terminal and the non-inverting input terminal of the differential amplifier 25 via the input resistors 26 and 27, respectively. A feedback resistor 28 is interposed between the output terminal of the differential amplifier 25 and the inverting input terminal. Therefore, the differential amplifier 25 outputs the output voltage VS corresponding to the difference between the output voltages V1 and V2 with the gain set by the resistors 26 to 28.

The output voltage VS is input to the inverting input terminal and the non-inverting input terminal of the pair of comparators 31 and 32 constituting the window comparator 23, respectively. A predetermined high level voltage VH is input to the non-inverting input terminal of the comparator 31, whereas a predetermined low level voltage VL is input to the inverting input terminal of the comparator 32. The output from the comparators 31 and 32 is the output resistance 3
It is supplied to one input of the NAND gate 24 via 3, 34. The output of the processing circuit 17 is input to the other input of the NAND gate 24 via the line 29, and the output of the NAND gate 24 is connected to one input of the relay coil 19. The other input of the relay coil 19 is connected to the high level power supply line 30.

Further, the output resistors 33 and 34 and the NAN
A connection point 35 with one input of the D gate 24 is connected to a power supply line 37 of high level VH via a pull-up resistor 36, and a light emitting diode 38 and a resistor 3 are connected.
It is connected to the high level power supply line 40 via 9.

Therefore, the amplifier circuit 2 shown in FIG.
When the output voltage VS of 2 is above the voltage VL and below VH, that is, before the time t1, that is, when the difference between the output voltages V1 and V2 is relatively small, the comparator 3
1 and 32 respectively derive high level outputs. As a result, the connection point 35 becomes high level as shown in FIG. 3B, and the output from the processing circuit 17 becomes NAN.
The output is inverted as it is through the D gate 24 and is output. When the output voltage V1 is equal to or higher than the value corresponding to the settling current, the output of the processing circuit 17 becomes high level and the relay coil 19 becomes When excited, the breaker of the bus bar 12 is cut off.

On the other hand, as shown after the time t1, the output voltage V1 becomes higher than the output voltage V2,
When the output voltage VS becomes higher and becomes higher than the voltage VH, the comparator 31 derives a low level output. As a result, the connection point 35 becomes low level, and the processing circuit 17
The output from is blocked by the NAND gate 24 and the light emitting diode 38 is turned on. Similarly, when the output voltage V2 becomes higher than the output voltage V1, the output voltage VS becomes lower, and when the output voltage V2 becomes lower than the voltage VL, the comparator 32 derives a low level output, and the NAND
The gate 24 cuts off the output of the processing circuit 17, and
The light emitting diode 38 lights up.

In this way, when the difference between the output voltages V1 and V2 becomes large, it is determined that an abnormality has occurred in one of the analog circuits 15 and 21, and the processing circuit 17 of the processing circuit 17 via the NAND gate 24 determines. The output is cut off to prevent erroneous output, and the light emitting diode 38 is turned on to notify the occurrence of abnormality.

The comparator 3 for the output voltage VS
Table 1 shows the outputs from 1, 32 and the connection point 35.

[0024]

[Table 1]

Thus, the overcurrent relay 1 according to the present invention
1, the analog circuit is duplicated by using the analog circuits 15 and 21 to prevent erroneous output from the processing circuit 17 to the auxiliary relay 18 to improve reliability, and the reliability is improved by an analog / digital converter. 16 and processing circuit 1
An amplifier circuit 22 provided separately from the digital circuit composed of 7
Since it is realized by the window comparator 23, the load on the software of the processing circuit 17 does not increase, and the occurrence of abnormality can be detected promptly.

The present invention is not limited to the overcurrent relay in which the secondary current of the current transformer 13 is input, but can be implemented in an overvoltage relay in which a voltage waveform is input from the transformer.

[0027]

As described above, the protective relay according to the present invention rectifies and smoothes the input waveform by the first analog circuit,
A protective relay that converts the output voltage of the first analog circuit into a digital value in a digital circuit, compares it with a predetermined first threshold value, and drives the breaker to be cut off when the output voltage exceeds the first threshold value. In (2), a second analog circuit is provided to duplicate the analog circuit, and a determination circuit provided separately from the digital circuit determines whether or not there is an abnormality in the two analog circuits.

Therefore, in order to realize the fail safe by duplicating the analog circuit and improve the reliability, the abnormality of the analog circuit is promptly detected without increasing the load on the digital circuit, and the fail safe operation is performed. It can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electrical configuration of an overcurrent relay according to an embodiment of the present invention.

FIG. 2 is a waveform diagram for explaining an operation of an analog circuit in the overcurrent relay.

FIG. 3 is a waveform diagram for explaining the operation of a window comparator in the overcurrent relay.

FIG. 4 is a block diagram showing an electrical configuration of a typical prior art overcurrent relay.

[Explanation of symbols]

 11 Overcurrent Relay (Protective Relay) 12 Busbar 13 Current Transformer 14 Conversion Resistor 15 Analog Circuit (First Analog Circuit) 16 Analog / Digital Converter (Digital Circuit) 17 Processing Circuit (Digital Circuit) 18 Auxiliary Relay 21 Analog Circuit (Second analog circuit) 22 Amplifier circuit (judgment circuit) 23 Window comparator (judgment circuit) 24 NAND gate (blocking means) 25 Differential amplifier 31 Comparator 32 Comparator 38 Light emitting diode

Claims (1)

[Claims] 1. An input waveform is rectified and smoothed by a first analog circuit, and an output voltage of the first analog circuit is converted into a digital value by a digital circuit, and then compared with a predetermined first threshold value. A protective relay configured to drive a circuit breaker to shut off when the voltage exceeds a first threshold value. A second analog circuit configured in the same manner as the first analog circuit and provided in parallel, and a first analog circuit. Comparing the output voltage of the second analog circuit with the output voltage of the second analog circuit, in response to the determination result of the determination circuit for determining whether the difference between the two is within a predetermined second threshold, And a blocking means for blocking a breaking output from the digital circuit to the breaker when the difference is outside the second threshold.