JPH0526908A - Detecting circuit for current of protective relay - Google Patents

Abstract

PURPOSE:To obtain a detecting circuit of a current of a protective relay which conducts detection of the current with high precision and, in addition, can make the whole processing operation fast by enabling execution of other arithmetic processings in the course of A/D conversion by sampling for detection of the current. CONSTITUTION:A comparator circuit 11 provided with an amplitude determining circuit for an input signal and outputting an A/D conversion processing instruction signal to an arithmetic processing circuit 9 only when the input signal is larger than a prescribed value is interposed between an input terminal of an A/D conversion circuit 8 and the arithmetic processing circuit 9, and an input processing wherein execution of A/D conversion is controlled to be made or not according to an output value of the comparator circuit 11 and other arithmetic processings are executed within the time when an A/D conversion processing is not executed is conducted. An A/D converter of which the processing speed is low and which is inexpensive is used for the A/D converter 8 for inputting a current and the same high-speed processing as executed when high-speed A/D conversion is used is conducted, while the function of a protective relay can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection relay current input circuit for inputting a circuit current by an A / D conversion circuit.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram showing a current detection circuit of a conventional protection relay. In the figure, reference numeral 1 denotes an electromagnetic contactor that controls the opening and closing of electric power of a load device 2, for example, an electric motor.
Between the electromagnetic contactor 1 and the load device 2, a current transformer 3 for detecting the circuit current of each of the three phases is interposed. Each current transformer 3 has a resistor 6 for converting its output current into a voltage.
Further, they are respectively connected to the A / D conversion circuit 8 via the diode 7 that bypasses the reverse current of the current transformer 3. The A / D conversion circuit 8 converts the output signal of the current transformer 3 into an A / D signal.
It is converted into a digital signal.

Each A / D conversion circuit 8 is connected to an arithmetic processing circuit 9 via a digital output line 8a. The arithmetic processing circuit 9 has a function of protecting the load device 2 according to conditions such as a current signal. Arithmetic processing circuit 9 and A
A control line 8b for supplying a control signal from the arithmetic processing circuit 9 to the A / D converter 8 is connected between the / D conversion circuits 8. The arithmetic processing circuit 9 drives the relay 10 by the output signal.

The relay 10 is connected to the coil 1a of the electromagnetic contactor through its normally closed contact 10a. A normally closed push button switch 5 for demagnetizing the electromagnetic contactor, a normally open push button switch 4 for exciting the electromagnetic contactor, and an auxiliary contact 1b of the electromagnetic contactor are sequentially connected to the coil 1a of the electromagnetic contactor.

The conventional protection relay current detection circuit configured as described above operates the load device 2 in the following manner. First, the push button 4 is operated to operate the electromagnetic contactor coil 1
A is excited and the electromagnetic contactor 1 is operated. Then, electric power is supplied to the load motor via the current transformer 3 to operate the load.

The output of the current transformer 3 is converted by a resistor 6 and a diode 7 into a voltage signal half-wave rectified with respect to the primary current of the current transformer 3. Under the control of the arithmetic processing circuit 9, the A / D conversion circuit 8 performs sampling at intervals sufficiently shorter than the cycle of the load current waveform and performs A / D conversion every time. A / D
For the conversion, sampling is repeated for a period equal to or longer than the cycle of the load current waveform, and the A / D conversion data for the number of repetitions is supplied to the arithmetic processing circuit 9 via the conversion output line 8a.

The arithmetic processing circuit 9 calculates a circuit current by calculating a load current at that time from a plurality of A / D converted data. The arithmetic processing circuit 9 performs a predetermined determination process on this circuit current and stops the operation of the load device 2. When the condition for protecting the device is obtained, the output relay 10 is driven to open the output contact 10a, and the electromagnetic contactor 1 is stopped.

[0008]

As described above, the conventional current detection circuit for the protection relay has a function of detecting the circuit current A for detecting the circuit current.
Since the / D conversion must be performed every sampling cycle, the A / D conversion process must be performed at a high speed in order to detect the current with high accuracy. Moreover, if the A / D conversion process is performed at a high speed during the current detection period, there is a problem that other protection processing functions of the arithmetic processing circuit 9 are significantly deteriorated.

The present invention has been made in view of the above points, and it is possible to perform current detection with high accuracy and to perform other arithmetic processing during A / D conversion by sampling for current detection. A current detection circuit for a relay is provided.

[0010]

According to the present invention, there is provided a current transformer for detecting a circuit current, a converter circuit for half-wave rectifying the output of the current transformer, and an A / D converter for converting the output of the converter circuit. An A / D converter, and an arithmetic circuit for arithmetically processing the output of the A / D converter, which is obtained by repeatedly A / D-converting the circuit current at a constant sampling period equal to or longer than the period of the load current into digital data. In a current detection circuit of a protection relay including a relay that protects a load device by the output of the arithmetic processing circuit, a magnitude determination circuit of an input signal is provided, and an A / D conversion processing command is issued only when the input signal is larger than a predetermined value. A current detection circuit for a protection relay, wherein a comparator circuit for outputting a signal to an arithmetic processing circuit is interposed between an input terminal of an A / D conversion circuit and the arithmetic processing circuit.

The present invention further includes a current transformer for detecting a circuit current, a conversion circuit for half-wave rectifying the output of the current transformer, and an A / D converter for A / D converting the output of the conversion circuit. An arithmetic circuit for arithmetically processing the output of the A / D converter in which the circuit current is repeatedly A / D converted into digital data at a constant sampling period equal to or longer than the period of the load current; In a protection relay current detection circuit including a relay that protects a load device by an output, an A / D converter uses an A / D converter only when an input signal is larger than a predetermined value according to a control signal from an arithmetic processing circuit.
It is a current detection circuit of a protection relay having a comparator function of outputting a conversion processing command signal to the arithmetic processing circuit.

[0012]

According to the current detection circuit of the protection relay according to the present invention, since the reference voltage close to 0 voltage is provided together with the A / D conversion circuit and the comparator has a comparator function to judge the comparison with the input signal, the comparator judgment means When it can be determined in advance that the signal is ON, the A / D conversion result is set to 0 without performing the A / D conversion. Then, during the current detection period, other current information can be input to the arithmetic processing circuit without requiring a predetermined circuit A / D conversion process. Therefore, the total A / D conversion processing time can be shortened, and during that time, other processing can be performed in parallel with the A / D conversion processing.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a current detection circuit of a protection relay according to an embodiment of the present invention. Note that FIG.
The same parts as those of the conventional one shown in FIG. In the current detection circuit of this protection relay, the output of the A / D conversion circuit 8 is supplied to the arithmetic processing circuit 9 via the A / D conversion output line (digital output line) 8a, and the comparator circuit via the comparator output line 11a. 11 outputs are supplied. The comparator 11 compares the input signal VIN with a predetermined reference voltage VREF and outputs it when the input signal VIN> reference voltage VREF. That is, one terminal of the comparator 11 is connected to the wiring portion between the diode 7 and the A / D converter 8, and the other terminal of the comparator 11 is connected to the reference power supply 12 which is the reference for determining the input signal. ing.

Incidentally, like the conventional one shown in FIG. 4,
The resistor 6 converts the output current of the current transformer 3 into a voltage, and the diode 7 bypasses the reverse current of the current transformer 3 that detects the circuit current to half-waveform the output voltage and A / D-converts it. Circuit 8
Is A / D-converts the output signal of the current transformer 3 into a digital signal, and the arithmetic processing circuit 9 protects the load according to the result of the A / D conversion.

The arithmetic processing circuit 9 and the A / D conversion circuit 8 are also provided.
A control line 8b for supplying a control signal from the arithmetic circuit to the A / D converter 8 is connected between them. The arithmetic processing circuit 9
The output signal drives the relay 10.

Further, the relay 10 is also similar to the conventional one shown in FIG. 4 through the normally closed contact 10a, and the electromagnetic contactor 1 is provided.
Of the electromagnetic contactor 1 connected to the coil 1a.
A normally-closed push button switch 5 for demagnetizing, a normally-open push button switch 4 for exciting the electromagnetic contactor 1, and an auxiliary contact 1b of the electromagnetic contactor 1 are sequentially connected.

According to the current detection circuit of the protection relay configured as described above, the main circuit current is half-wave rectified by the action of the converter 2, the resistor 6 and the diode 7, as shown in FIG. Is converted into a voltage waveform signal (1.). That is, in order to process this voltage waveform signal (1.) and calculate the circuit current, a period that is sufficiently shorter than the period of the voltage waveform signal (1.) over a period equal to or longer than the period of the voltage waveform signal (1.). Therefore, it is necessary to input data, and the detection cycle ΔT and the current detection period T are set to the sizes shown in FIG. 2, for example.

That is, FIG. 2 is a characteristic diagram showing the sampling timing of the A / D conversion processing for the input signal waveform and the processing time of the arithmetic processing circuit 9 for the A / D conversion processing. In FIG. 2, VREF is a comparator reference. Is a voltage, and ΔT is a detection cycle, that is, a sampling cycle of A / D conversion, which is set sufficiently shorter than the cycle of the load current waveform. T is a current detection period and is set to a length equal to or longer than the cycle of the load current waveform. Further, the A / D conversion processing time of the arithmetic circuit indicates a period during which the arithmetic processing circuit is operating for controlling the A / D conversion circuit 8.

Next, the A / D conversion process will be described with reference to the flow chart of the current detection process shown in FIG. The starting point of the flow chart is the start point of the current detection period, and the comparison output 11a of the comparator 11 is first input to the arithmetic processing circuit 9 to perform level determination.

Under the conditions of FIG. 2, initially the input signal VIN <
It becomes the reference voltage VREF and the output of the comparator 11 is in a non-existent state. At this time, the arithmetic processing circuit 9 does not perform the A / D conversion processing, but performs the other processing of the protection relay. At the end of the process, the current value data is set to 0, and the process returns to the current detection process. After that, the number of times of repetition during the current detection period is determined, and if the number of times has not reached the specified number, the current detection starts again.

Next, at the comparator input, the input signal V
When IN> reference voltage VREF, there is an output from the comparator, so this is judged and A / D conversion processing is executed. After the A / D conversion process is completed, the current value data is
It is input to the data of the D conversion result and the determination process of the number of repetitions is performed. If the number of repetitions is less than or equal to the specified value, the current detection process is restarted and repeated.

When the number of times of repetition reaches the specified value, the processing is completed and the current detection processing flow is ended. However, the repeat detection cycle during the current detection period must be kept constant,
It is necessary to set the processing time of other implementation processing to be the same as the A / D conversion processing time.

As described above, in the current detection circuit of the protection relay, the current signal is 0 during about 1/2 of the current detection period.
During this period, it is not necessary to perform A / D conversion that takes a long processing time. That is, the arithmetic processing circuit 9 only needs to perform the determination processing of the input signal of the comparator 11 which is completed in a short time, and utilizes the time difference generated between the determination processing of the input signals of the respective comparators 11 in the conventional current. It is possible to perform another detection process that cannot be performed by the detection circuit.

As a result, it is possible to prevent the processing and operation of the A / D conversion circuit 8 and the arithmetic processing circuit 9 from being deteriorated, to detect the current with high accuracy, and to perform the A / D by sampling for the current detection. Other arithmetic processing is sufficiently performed during D conversion.

In the embodiment, the A / D converter and the comparator are separate circuits, but the A / D converter having the comparator function by the control signal can be used to switch the control signal. Good as a thing. Further, the arithmetic processing circuit may be processed by a microcomputer.

In the embodiment, the case where the main circuit current is a three-phase current in a three-phase load has been described, but the main circuit current may be a circuit for one phase. Further, it goes without saying that the present invention can be applied to a current detection circuit other than the current detection circuit of the protection relay.

[0027]

As described above, according to the current detection circuit of the protection relay of the present invention, the comparator circuit is connected in parallel to the current signal A / D conversion circuit section, and the output data is A / D converted. Control the execution of the
Since the other processing is performed during the period when the D conversion is not performed, the A / D converter having a low processing speed can be used to make the apparatus inexpensive, and the current of the conventional protection relay can be obtained within the same processing time. It is possible to improve the circuit function by enabling more processing than the detection circuit.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a current detection circuit of a protection relay according to an embodiment of the present invention.

FIG. 2 is a current waveform diagram showing a current detection state of the embodiment.

FIG. 3 is a flowchart at the time of current detection processing of the same embodiment.

FIG. 4 is a circuit diagram showing a current detection circuit of a conventional protection relay.

[Explanation of symbols]

1. Electromagnetic contactor 2. Loader 3. Current transformer 6. Resistor 7. diode 8. A / D converter 9. Arithmetic processing circuit 10. Relay 11. comparator 12. Reference power supply

Claims (2)

[Claims] 1. A current transformer for detecting a circuit current, a conversion circuit for half-wave rectifying the output of the current transformer, an A / D converter for A / D converting the output of the conversion circuit, and the circuit. An arithmetic circuit for arithmetically processing the output of the A / D converter, which converts the current into digital data by repeatedly A / D converting it at a constant sampling cycle that is at least the cycle of the load current, and a load by the output of the arithmetic processing circuit. A protection relay current detection circuit including a relay for protecting a device includes an input signal magnitude determination circuit, and outputs an A / D conversion processing command signal to an arithmetic processing circuit only when the input signal is larger than a predetermined value. A current detection circuit for a protection relay, wherein a comparator circuit is interposed between an input terminal of an A / D conversion circuit and the arithmetic processing circuit. 2. A current transformer for detecting a circuit current, a conversion circuit for half-wave rectifying the output of the current transformer, an A / D converter for A / D converting the output of the conversion circuit, and the circuit. An arithmetic circuit for arithmetically processing the output of the A / D converter, which converts the current into digital data by repeatedly A / D converting it at a constant sampling cycle that is at least the cycle of the load current, and a load by the output of the arithmetic processing circuit. In a current detection circuit of a protection relay including a relay for protecting the device,
The / D converter has a comparator function of outputting an A / D conversion processing command signal to the arithmetic processing circuit only when the input signal is larger than a predetermined value in accordance with a control signal from the arithmetic processing circuit. Protection relay current detection circuit.