JPH10307163A - Residual current detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a residual current detector capable of accurately detecting residual current with an especially simple and cheap constitution simultaneously detecting and responding to various accidents in a residual current detector detecting the current value of the residual current detected with a residual current transformer. SOLUTION: The output signal line 10 of a residual current meter 1 arranged on lines 100u, 100V, 100W of three-phase alternating current is connected to input terminals 2a, 2b of an operator amplifier 2 constituted of a current-voltage converter circuit. By this, the residual current flowing in the lines 100U, 100V and 100W can be accurately detected with a simple and cheap constitution and without using a fine and expensive apparatus such as a microampere meter and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zero-phase current detecting device for detecting a current value of a zero-phase current detected by a zero-phase current transformer. The present invention relates to a zero-phase current detection device that can be used.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional zero-phase current detecting device of this type. FIG. 4 shows an overall circuit configuration diagram of a conventional zero-phase current detection device. In FIG. 1, a conventional zero-phase current detecting device includes three-phase AC power lines 100U and 100U.
V, 100 W zero-phase current transformer 1
And an ammeter 7 connected directly to the output signal line 10 of the zero-phase current transformer 1 or via the protection relay circuit 6. This ammeter 7 is connected to the output signal line 10
Are connected to the input terminals 6a of the protection relay circuit 6 and are connected to the zero-phase current transformer 1 in series.

The protection relay circuit 6 includes a zero-phase voltage detector 12
The protection relay circuit 6 receives the detection voltage V11 and the detection current I from the zero-phase current transformer 1.
Based on (1), a control to open or shut off the contact 110 of the AC load switch 100 is performed. The zero-phase voltage detector 124 is connected to each of the three-phase AC power lines 100U, 100V, 100W on the load side of the AC load switch 100 via a fuse 120, zero-phase capacitors 121, 122, and a transformer 123. Configuration. The AC load switch 100 is controlled by the protection relay circuit 6 to turn on the contact 112 to supply a current to a tripping coil 111 from a control driving power supply (not shown), and to excite the tripping coil 111 to excite the tripping coil 111. The contact 110 is in a trip open or cutoff state.

Next, the operation of the conventional zero-phase current detecting device based on the above configuration will be described with reference to FIG. First, the current I1 detected from the zero-phase current transformer 1 is input to the protection relay circuit 6 via the output signal line 10, and the protection relay circuit 6 connects the load resistance 61 and the primary winding of the transformer 62 to each other. By adding the detected current I1 to the combined impedance Z formed by the parallel circuit, a primary voltage V10 is generated in the primary winding, and the primary voltage V10 is determined based on the winding ratio of the transformer 62 with respect to the primary voltage V10. A secondary voltage V20 is induced.
This secondary-side voltage V20 is filtered through a band-pass filter 63 to remove harmonic noise components, and the fundamental wave 50 Hz or 60 Hz
Hz, the protection control unit 64 detects the zero-phase current I0.

The protection relay circuit 6 also receives the detection voltage V11 from the zero-phase voltage detector 124 and outputs the zero-phase current I
The zero-phase voltage V0 is detected in the same manner as the zero detection operation. Based on the detected zero-phase current I0 and zero-phase voltage V0, the protection controller 64 calculates a phase difference between them, detects a ground fault direction based on the phase difference, and detects a ground fault section. Then, the trip opening or breaking operation of the AC load switch 100 is controlled.

As described above, when a ground fault has occurred in a high-voltage customer, the protection relay circuit 6 detects this fault, shuts off the AC load switch 100 disposed at the responsible demarcation point, and disconnects the other. In addition to preventing accidents affecting customers, the accidents will be eliminated on the premises of the high-voltage customers where the accident occurred.

[0007]

Since the conventional zero-sequence current detecting device is constructed as described above, one of the main elements for detecting the ground fault is the zero-sequence current I0.
There was a problem that it was not possible to detect at what level of the zero-phase current I0 the three-phase alternating current lines 100U, 100V, and 100W were flowing at the time of detection. That is,
The zero-phase current I0 detected by the protection relay circuit 6 is used as data for determining the occurrence of a ground fault in the protection relay circuit 6, and if it is not determined that a ground fault has occurred, its numerical value level is specifically determined. Cannot be detected and confirmed.

When the current value of the zero-phase current I0 increases, various accidents such as a ground fault accident occur specifically. The cause is caused by high-voltage electrical equipment (for example, a high-voltage cable, Deterioration of insulation of a transformer or the like, or contact of foreign matter with a distribution line, and the like. As a preventive measure for these various accidents, insulation resistance is regularly detected. However, it is a large-scale inspection work, and the limit is about once a year. Has not been effective.

Further, the intermediate terminal 1 in the output signal line 10 of the zero-phase current transformer 1 does not pass through the protection relay circuit 6.
In the case where the configuration in which Oa and 10b are connected is adopted, there is a problem that the protection relay circuit 6 cannot perform an accident detection operation accurately and reliably. That is, the protection relay circuit 6
In order to detect the zero-phase current I0, the primary voltage V10 induced on the basis of the combined impedance Z formed by the parallel circuit of the burden resistor 61 and the primary winding of the transformer 62.
Therefore, if the ammeter 7 is connected to the intermediate terminals 10a and 10b of the output signal line 10, the combined impedance Z will change, and an accurate zero-phase current I0 cannot be detected. There is a problem that the relay circuit 6 cannot properly cope with various accidents and malfunctions.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is possible to accurately detect a zero-phase current with a simple and inexpensive configuration, and to detect and cope with various accidents with a high-precision zero-phase current. It is an object of the present invention to provide a zero-phase current detection device that can detect the current.

[0011]

The zero-phase current detecting device according to the present invention connects an input terminal of an operational amplifier to an output signal line of a zero-phase current transformer for detecting a zero-phase current of three-phase alternating current. The operational amplifier converts an input current value input from an input terminal into a voltage value and outputs the voltage value, and detects a zero-phase current based on the output voltage value. As described above, in the present invention, by connecting the output signal line of the zero-phase current transformer provided in the three-phase AC electric wire to the input terminal of the operational amplifier having the current-voltage conversion circuit configuration, A zero-phase current flowing in a road can be detected with high accuracy using a simple and inexpensive configuration without using a precise and expensive device such as a microampere meter.

Further, in the zero-phase current detecting device according to the present invention, a zero-phase current transformer is incorporated in the AC load switch if necessary, and an input terminal of the operational amplifier is connected to the zero-phase current transformer. And a protection relay circuit that drives and controls the AC load switch. Thus, in the present invention, by connecting the input terminal of the operational amplifier between the output signal line of the zero-phase current transformer and the protection relay circuit,
The protection relay circuit can accurately and reliably detect various accidents and normally control the drive of the AC load switch, while detecting the zero-phase current with high accuracy.

Further, the zero-phase current detecting device according to the present invention includes a zero-phase current calculating unit for calculating and detecting the zero-phase current based on the current ratio of the zero-phase current transformer, if necessary. is there. As described above, in the present invention, since the zero-phase current calculation unit calculates the zero-phase current based on the current ratio of the zero-phase current transformer, the zero-phase current is manufactured with a different current ratio for each manufacturer. The zero-phase current can be accurately calculated according to the zero-phase current transformer.

Further, the zero-phase current detecting device according to the present invention compares the detected zero-phase current with a predetermined threshold value as required, and based on the comparison result, determines the characteristic of the three-phase AC related to the zero-phase current. Is to be detected. As described above, in the present invention, a predetermined threshold value is set, and the threshold value is compared with the detected zero-phase current to compare the state of the three-phase AC power line and various devices connected to the power line. Accordingly, the accident can be predicted and diagnosed before various accidents occur.

Further, the zero-phase current detecting device according to the present invention converts the detected zero-phase current into a digital signal as necessary, and Fourier-transforms the zero-phase current of the digital signal to be included in the zero-phase current. To detect higher harmonics.
As described above, in the present invention, since the zero-phase current to be digitized is Fourier-transformed to detect the harmonic, the harmonic can be detected together with the zero-phase current.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment of the Present Invention) Hereinafter, a zero-phase current detecting device according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is an overall circuit configuration diagram of the zero-phase current detection device according to the present embodiment, and FIG. 2 is a detailed block configuration diagram of an arithmetic control unit in the zero-phase current detection device shown in FIG.

In each of the drawings, the zero-phase current detecting apparatus according to the present embodiment is a zero-phase current detecting apparatus for detecting a zero-phase current I0 flowing through three-phase AC power lines 100U, 100V, and 100W in a service line from a distribution line. Output signal line 1 of current transformer 1
00 and the protection relay circuit 6 for driving and controlling the AC load switch 100 disposed in the electric wire 100U, 100V, 100W, the current value of the detected current I1 transmitted from the output signal line 10. Are connected in series to input terminals 2a and 2b of an operational amplifier 2 for converting the voltage to a voltage value.
Is a configuration for calculating the zero-phase current I0. The connection of the operational amplifier 2 is made directly to the connection terminal between the zero-phase current transformer 1 and the protection relay circuit 6 or through a connector. The protection relay circuit 6 receives the detection voltage from the zero-phase voltage detector 124 to calculate the zero-phase voltage V0 as in the conventional device shown in FIG. 4, and detects the detection current transmitted from the output signal line 10. I1 is input, the zero-phase current I0 is calculated, and the trip coil 111 is excited based on the calculation results to perform trip opening or breaking drive control of the AC load switch 100.

The arithmetic control unit 3 includes an anti-aliasing filter 31, an A / D converter 32, a band-pass filter 33, a basic effective value operation unit 34, and an effective value operation unit 3.
5, an average value calculation unit 36, a maximum value storage unit 37, and a current transformation ratio calculation unit 38. In addition, the arithmetic control unit 3
Is a comparison operation unit 39 for comparing the zero-phase current I0 output from the current transformation ratio operation unit 38 with the threshold value of the accident prediction limit set and input by the key input unit 4, and a time period for which this comparison result is set in advance. Time storage unit 391 that stores when the time has exceeded
And an alarm output unit 392 that issues an alarm when the preset time is exceeded. Zero-sequence current I0 from the current transformer ratio calculator 38 and excess time storage 39
1 and the respective outputs of the alarm output unit 392 are respectively output to the display unit 5, and the display unit 5 is configured to output and display on the display screen 52 under the control of the display control unit 51.

Next, the operation of the zero-phase current detecting device according to this embodiment based on the above configuration will be described. First, when the AC load switch 100 is turned on, the three-phase AC
When U, 100V, 100W are in the live state, the zero-phase current transformer 1 is connected to the electric lines 100U, 100V, 100W.
When the current balance between W changes and a zero-phase current I0 flows, the zero-phase current I0 is detected and a detected current I1 corresponding to the current transformation ratio is output. The detected current I1 is supplied to the input terminals 2a and 2b of the operational amplifier 2.
And the input terminals 2a and 2b can be regarded as being in a short-circuit state (Imaginary Shot-circuit), so that the zero-phase current is attenuated with no load (that is, the input impedance is "0"). And also supplied to the protection relay circuit 6.

The protection relay circuit 6 calculates a zero-phase current I0 based on the detected current I1 supplied in the same manner as in the conventional device shown in FIG. 4 and based on an output voltage V1 from the zero-phase detector 124. The AC load switch 100 is tripped or cut off based on the results of these calculations. Various accidents that occur in the premises of the high-voltage customers who connect the AC load switch 100 to the power lines 100U, 100V, and 100W can prevent the spillover accidents from affecting other high-voltage customers and also eliminate the various accidents that have occurred. be able to.

In the trip or cutoff drive control of the AC load switch 100 based on the detection of various accidents by the protection relay circuit 6, the operational amplifier 2 controls the supplied detection current I1.
And outputs it to the arithmetic and control unit 3. The converted voltage V1 is determined by the current I1
U, 100 V, and 100 W, since the current value corresponds to the current ratio of the zero-phase current transformer 1 with respect to the zero-phase current I0 flowing through 100 W,
This voltage value is also a value proportional to the zero-phase current I0.

The arithmetic control unit 3 removes a frequency component higher than the sample frequency from the converted voltage V1 with an anti-aliasing filter 31, and then converts the voltage V1 into an A / D converter 32.
Is converted into a digital signal, and the converted digital signal is transmitted in parallel to a basic effective value computing unit 34 via a band-pass filter 33 and to an effective value computing unit 35, an average value computing unit 36, and a maximum storage unit 37. Enter This A / D
The converter 32 samples the analog value voltage V1 into a discrete signal by a sample and hold circuit, holds only the magnitude of the amplitude of the discrete signal, and converts the held analog value into several discrete signals by a quantizer. The discrete amplitude is converted into a binary code of "1" / "0" by an encoder.

The band-pass filter 33 passes only a basic waveform of a digital signal, for example, a component of a commercial frequency of 50 Hz or 60 Hz, and a basic effective value calculator 34 converts the digital signal of the basic waveform from the zero-phase current transformer 1. An effective value is calculated for the basic waveform of the output detection current I1. In addition, the effective value calculator 35 outputs the digital signal output from the A / D converter 32 from the zero-phase current transformer 1 for all of the basic waveform (for example, the commercial frequency component) and the distortion waveform (the high frequency component). The effective value of the detected current I1 is calculated. Further, the digital signal output from the A / D converter 32 is calculated as an average value of the digital signal by the average value calculation section 36 and stored in the maximum value storage section 37 as the maximum value of the digital signal.

The effective value calculated by the basic effective value calculating unit 34 and the effective value calculated by the effective value calculating unit 35, the average value calculated by the average value calculating unit 36, and the maximum value stored in the maximum value storage unit 37. Is input to the current transformer ratio calculator 38. The current transformer ratio calculator 38 converts the zero-phase current transformer 1 input from the key input unit 4 in advance.
To calculate the zero-phase current I0. The current ratio of the zero-phase current transformer 1 is different depending on the maker of the zero-phase current transformer or the switch, and the adopted numerical value is previously input from the key input unit 4 to the current ratio calculator 38. Is input to The current transformer ratio calculator 38 stores the inputted current transformer ratio adopted for each manufacturer (not shown).
And the various current transformation ratios can be displayed on the display unit 5 and selected by the key input unit.

The effective value, the average value, and the maximum value of the zero-phase current I 0 calculated by the current ratio calculating unit are displayed on the display screen 52 by the display control of the display control unit 51. In addition, the zero-phase current I calculated based on the effective value including the basic waveform and the distorted waveform
By displaying 0 on the display unit 5, the true effective value can be confirmed even when the zero-phase current is distorted. In addition, when there is a difference between the effective value of only the basic waveform and the effective value including the basic waveform and the distorted waveform, the degree of distortion of the waveform can be confirmed, and phenomena that cause various accidents, such as harmonics, etc. It can be used as a material for diagnosing factors other than insulation deterioration.

Each value calculated by the current ratio calculating unit 38 is also input to a comparison calculating unit 37,
Reference numeral 7 compares the monitoring limit value of the zero-phase current I0 input from the key input unit 4 with each of the input values, and based on the comparison result, stores the maximum value of the excess time in the excess time storage unit 391.
, And also stores the number of times, time, and the like. Further, the excess is output to the display unit 5 via the alarm output unit 292 as an alarm to the outside based on the comparison result. This display can be arbitrarily read out later from the storage unit and displayed.

(Another Embodiment of the Present Invention) A zero-phase current detecting device according to another embodiment of the present invention will be described below with reference to FIG. FIG. 3 is a detailed block configuration diagram of an arithmetic control unit in a zero-phase current detection device according to another embodiment.

In the figure, a zero-phase current detecting device according to another embodiment has a zero-phase current transformer 1, an operational amplifier 2, and a key input unit 4, similarly to the embodiment device shown in FIGS. And the display unit 5 in common, and the circuit configuration of the arithmetic control unit 3 is different. The arithmetic control unit 3 performs a fast Fourier transform process on the digital signal converted by the A / D converter 32 in addition to the configuration shown in FIG. 2 to calculate a fundamental component and a harmonic component. And a harmonic current content calculator 380 for calculating the content of the harmonic component current with respect to the calculated fundamental current. The display unit displays the calculated harmonic current content. 5, and when the content rate of the harmonic current becomes a predetermined value or more, an alarm is output from the alarm output unit 390 to the display unit 5 to be displayed or notified.

Next, a description will be given of a harmonic search operation of the harmonic search device based on the above configuration. As in the first embodiment, the detected current I1 induced by the zero-phase current transformer 1 is supplied to the operational amplifier 2, and is also supplied to the protection relay circuit 6 via the operational amplifier 2 in a no-load state. Is supplied. The operational amplifier 2 converts the detection current I1 into a voltage V1, and this voltage V1 is applied to the anti-aliasing filter 31.
And is converted into a digital signal by the A / D converter 32. Based on the detected current of the digital signal, the fast Fourier transform unit 340 performs a fast Fourier transform process to calculate each component of the fundamental current and the harmonic current. From the fundamental current and the harmonic current, a harmonic current content calculating unit 38
0 calculates the harmonic current content, which is the ratio of the nth harmonic to the effective value of the fundamental wave.

The display unit 5 displays this harmonic current content rate as a digital value. When the alarm output unit 390 becomes a predetermined value or more, an alarm sound such as a buzzer (not shown) is generated to notify the operator. Notify. The alarm output unit 390 can generate the alarm sound by changing the loudness of the alarm sound according to the magnitude of the harmonic current content. Also, the alarm output unit 39
The numerical value of the harmonic current content of a predetermined value based on 0 may be set arbitrarily.

[0031]

As described above, according to the present invention, the output signal line of the zero-phase current device provided in the three-phase AC electric wire is connected in series to the input terminal of the operational amplifier having a current-voltage conversion circuit configuration. By connecting to zero, there is an effect that the zero-phase current flowing in the electric wire can be detected with high accuracy using a simple and inexpensive configuration without using a precise and expensive device such as a microampere meter. Further, if this connection is made by a connector, connection to an existing circuit can be easily made, and diagnostic workability at the time of inspection can be improved. Also, in the present invention, by connecting the input terminal of the operational amplifier between the output signal line of the zero-phase current transformer and the protection relay circuit, various kinds of accidents can be accurately and reliably detected by the protection relay circuit and the There is an effect that the zero-phase current can be detected with high accuracy while normally controlling the drive of the load switch. Further, in the present invention, since the zero-phase current calculation unit calculates the zero-phase current based on the current ratio of the zero-phase current transformer, the zero-phase current manufactured by each manufacturer has a different current ratio. There is an effect that the zero-phase current can be accurately calculated according to the phase current transformer.
Further, in the present invention, by setting a predetermined threshold value, and comparing the threshold value with the detected zero-phase current to detect the state of the three-phase AC electric wire and various devices connected to the electric wire. This has the effect that an accident can be predicted and diagnosed before various accidents occur. Further, in the present invention, since the zero-phase current to be digitized is Fourier-transformed to detect the harmonic, there is an effect that the harmonic can be detected together with the zero-phase current.

[Brief description of the drawings]

FIG. 1 is an overall circuit configuration diagram of a zero-phase current detection device according to a first embodiment of the present invention.

FIG. 2 is a detailed block configuration diagram of an arithmetic control unit in the zero-phase current detection device shown in FIG.

FIG. 3 is a detailed block configuration diagram of an arithmetic control unit in a zero-phase current detection device according to another embodiment of the present invention.

FIG. 4 is an overall circuit configuration diagram of a conventional zero-phase current detection device.

FIG. 5 is a detailed block diagram of a protection relay circuit in the conventional zero-phase current detection device shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Zero-phase current transformer 2 Operational amplifier 2a, 2b Input terminal 3 Operation control part 4 Key input part 5 Display part 6 Protection relay circuit 7 Ammeter 10 Output signal line 10a, 10b Intermediate terminal 31 Anti-aliasing filter 32 A / D converter Reference Signs List 33 band pass filter 34 basic effective value calculation unit 35 effective value calculation unit 36 average value calculation unit 37 maximum value storage unit 38 current conversion ratio calculation unit 39 comparison calculation unit 51 display control unit 52 display screen 61 burden resistance 62 transformer 63 band pass Filter 64 Protection control unit 100 AC load switch 100U, 100V, 100W Electric line 110 Contact 111 Trip coil 112 Contact 120 Fuse 121, 122 Zero-phase capacitor 123 Transformer Zero-phase detector 340 Fast Fourier transform unit 380 Harmonic current Content calculation unit 390, 92 alarm output unit 391 over time storage unit

Claims (5)

[Claims] An input terminal of an operational amplifier is connected to an output signal line of a zero-phase current transformer for detecting a zero-phase current in a power line, and the operational amplifier converts an input current value input from the input terminal into a voltage value. A zero-phase current detection device, which converts and outputs the zero-phase current based on the output voltage value. 2. The zero-phase current detecting device according to claim 1, wherein the zero-phase current transformer is built in an AC load switch, and an input terminal of the operational amplifier is connected to the zero-phase current transformer. A zero-phase current detection device, which is connected in series between a switch and a protection relay circuit that drives and controls the AC load switch. 3. The zero-phase current detection device according to claim 1, further comprising a zero-phase current calculation unit that calculates and detects a zero-phase current based on a current ratio of the zero-phase current transformer. A zero-phase current detection device, characterized in that: 4. The zero-phase current detecting device according to claim 1, wherein the detected zero-phase current is compared with a predetermined threshold value, and a three-phase current related to the zero-phase current is determined based on the comparison result. A zero-phase current detecting device for detecting phase alternating current characteristics. 5. The zero-phase current detecting device according to claim 1, wherein the detected zero-phase current is converted into a digital signal, and the zero-phase current of the digital signal is Fourier-transformed to obtain a zero signal. A zero-phase current detecting device for detecting a harmonic contained in a phase current.