JPH0731049A - Method and apparatus for measuring primary current of zero-phase current transformer - Google Patents

Abstract

PURPOSE:To allow correction of the current transformation ratio of ZCT and the input resistance of a relay while eliminating the influence of zero-phase current of the power supply frequency component by measuring the primary current of the ZCT in a ground relay provided for a high or low voltage line while connecting a load. CONSTITUTION:A ZCT 5 and a ground relay 8 are provided for a line connected with a load 3 and a test line 13 is disposed at the detecting section of the ZCT while being connected with a correcting current generator 10. A correction factor for a gain correcting circuit 26 under a state where the load current has no effect is set using one bandpass filter 24 arranged in a zero-phase current transformer primary current measuring unit 20 whereas the variation in the zero-phase current due to the ZCT is detected using the other bandpass filter 23.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides an unknown zero-phase current transformer (hereinafter referred to as ZCT) installed on a high-voltage or low-piezoelectric path with unknown current ratio and input resistance value of a relay or the like. The present invention relates to a correction method and a correction device, and particularly to a zero-phase current transformer primary current measurement device, in particular, in a state where power is supplied to a load, Z
TECHNICAL FIELD The present invention relates to a method and a measurement device that enable control information for CT to be obtained.

[0002]

2. Description of the Related Art In private power receiving equipment, etc., a low-voltage path is provided for a high-voltage path via a transformer, etc., and a high-voltage air switch and a ground fault relay are arranged on the high-voltage path. Therefore, a zero-phase current transformer is provided in the high-pressure air switch to cope with an accident on a high-voltage path, and information such as insulation deterioration on the high-voltage path is obtained. In the general power receiving equipment, as shown in FIG. 4, a switch 2 and a ZCT 5 are arranged between a power source 1 and a load side 3, and a high voltage is provided by a ground fault relay connected to the ZCT 5. It is possible to measure the zero-phase current of an electric circuit. Then, by using the information of the zero-phase current measured by the ground fault relay, the state of leakage or insulation deterioration on the high-voltage path is detected, and if an accident occurs on the high-voltage path, the switch 2 is activated. To be able to use means such as stopping power supply.

Further, the information on the zero-phase current obtained by the ZCT can also be used to obtain the data of the leakage current which causes the insulation deterioration in the high piezoelectric path and other accidents. It is necessary to set information such as the current transformer ratio and the input resistance of the ground fault relay for the zero-phase current transformer primary current measuring device. However, the current ratio of the zero-phase current transformer provided in the high-pressure air switch and the input resistance of the ground fault relay can be easily known in the case of a newly installed device, but the existing power Unless otherwise specified, equipment and the like cannot immediately know such information. In addition, the current ratio of the zero-phase current transformer and the input resistance of the ground fault relay, etc. differ depending on the manufacturer, model, etc. It is required to have it as the basic data for measuring the phase current. Therefore, in order to know the characteristics of the unknown ZCT, ground fault relay, etc., for example, a correction device configured as shown in FIG. 5 is used.

In the example shown in FIG. 5, ZCT5
The test line electric circuit 13 is arranged in parallel to the electric circuit with respect to the detection unit, and the correction current generator 1 is connected to the test line electric circuit 13.
0a is connected. Then, the switch 2 is turned off, and the comparative commercial frequency current is supplied from the correction current generator 10a to the test line circuit 13 in a state where no current is supplied to the load side, and the input resistance R end portion of the ground fault relay is connected. A means for measuring the voltage, inversely converting the detected value, and detecting the primary current of the ZCT 5 from the relationship between the input resistance and the current as shown in the graph of FIG. 6 is used. In the example shown in the graph of FIG. 6, the ZCT primary current is estimated on the basis of the value of the input resistance end voltage, with the ZCT primary current on the horizontal axis and the input resistance end voltage of a ground fault relay or the like on the vertical axis. You can As mentioned above, in order to know the characteristics of ZCT and ground fault relay,
When trying to detect the ZCT under load, due to the imbalance of the capacitance between the load and the earth,
In many cases, zero-phase current is constantly flowing. Therefore, since the correction in the load state becomes inaccurate due to the influence of the zero-phase current of the power supply frequency, it is possible to measure the relationship between the ZCT primary current and the voltage at the input resistance end of the ground fault relay in the power failure state. Will be needed.

However, since the number of power receiving equipments for private use is very large, when it is attempted to obtain information such as the ZCT current-changing ratio and the input resistance of the ground fault relay for all of those equipments, the investigation and There is a problem that the measurement work is complicated and requires a lot of labor. However, in the conventional power receiving equipment for private use, since there is no information such as the ZCT current ratio or the input resistance of the ground fault relay in advance, it is necessary to obtain data such as the characteristics of the zero-phase current transformer for each of the equipment. , Efforts such as conducting surveys and measurement work.

[0006]

SUMMARY OF THE INVENTION The present invention is a conventional ZCT as described above.
It solves the problem of obtaining information such as the current change ratio and the input resistance of the ground fault relay. It is easy to measure the ZCT primary current for the ZCT etc. arranged in the high-voltage or low-voltage circuit under load connection. The purpose of the present invention is to provide a method and an apparatus capable of performing such a measurement, and in particular, it is possible to measure a zero-phase current due to insulation deterioration in a circuit without knowing the current-changing ratio or characteristics of the ZCT or ground fault relay. The purpose is to provide a device for doing so.

[0007]

The present invention relates to a zero-phase current transformer provided in a ground fault relay installed in a high-voltage or low-piezoelectric path, in which a ZCT current ratio, an input resistance of the ground fault relay, and the like are set. The present invention relates to a method for obtaining information for correction and a zero-phase current transformer primary current measuring device. In the present invention,
With respect to the zero-phase current flowing in the measuring part of the zero-phase current transformer, a current of a frequency component different from the power supply frequency is caused to flow from the correction current generator, and a zero-phase current transformer primary current measuring device for measuring the zero-phase current is provided. A method of detecting a current of a frequency component different from the power source frequency component and correcting the current ratio of the zero-phase current transformer and the input resistance of a relay is used. Further, in the present invention, the zero-phase current transformer primary current measuring device includes a second bandpass filter used for correction and a first bandpass filter used for measuring zero-phase current, After providing a means for switching through the changeover switch and correcting the current ratio of the zero-phase current transformer,
A mechanism for processing the information of the zero-phase current transformer is configured through the first bandpass filter, and the value obtained by detecting the current of the frequency component different from the power source frequency component by using the second bandpass filter is set to zero. The control coefficient of the phase current transformer primary current measuring device is set, and the primary current of the zero phase current transformer at the measured frequency can be measured by using the circuit of the first bandpass filter.

In addition to the above construction, in the present invention, a correction current generator is integrally incorporated in the zero-phase current transformer primary current measuring device, and the current ratio of the zero-phase current transformer, the input of the relay, etc. It is also possible to configure a detection circuit that uses the second bandpass filter and a device that supplies power from the correction current generator only when detecting resistance.

As described above, a means for causing a current different from the power supply frequency from the test line circuit to flow to the ZCT primary side together with the zero-phase current to the ZCT detector is provided to correct the zero-phase current transformer primary current measuring device. By configuring means for measuring through different bandpass filters at the time of measurement and at the time of measurement, Z
A device that is not affected by the CT primary current can be obtained. Then, by correcting the control value of the zero-phase current transformer primary current measuring device using the current component flowing in the test line circuit, it is possible to set the control information for the zero-phase current transformer primary current measuring device, The control information once stored is the ZC
It can be arbitrarily used for power receiving equipment provided with T and the like.

[0010]

The zero-phase current transformer primary current measuring method and apparatus of the present invention will be described with reference to the illustrated example. The example shown in FIG. 1 shows a means for supplying a correction current to the ZCT of the measuring apparatus of the present invention, in which a switch 2 is arranged in an electric path connecting a power source 1 and a load 3, and the switching is performed. The ZCT 5 is arranged corresponding to the container 2. A test line circuit 13 is provided in the circuit in which the ZCT 5 is arranged, and the oscillator 1 shown in FIG.
The signal output from 2 causes a correction current having a frequency different from the frequency flowing from the constant current generating circuit 11 to the electric circuit to flow. Moreover, in the ZCT 5 shown in FIG. 1, the output terminals 6 and 6a are connected to the ground fault relay 8 and the test line circuit 1
The other terminals 7 and 7 a provided on the reference numeral 3 are connected to the correction current generator 10. In the detection circuit based on ZCT5 shown in FIG. 1, a known value It flows from the correction current generator with respect to an unknown current value Io flowing through the electric path, so that the two currents Io and It The combined current is made to be detected by ZCT5.

Then, when performing the correction work for the zero-phase current transformer primary current measuring device, by detecting only the It component from the ZCT secondary side current component, the influence of the Io component is eliminated, The current ratio of the zero-phase current transformer and the input resistance of the relay etc. can be corrected. At the time of this correction, the current value I output from the correction current generator
Since the t component is known, the work of setting the correction coefficient in the zero-phase current transformer primary current measuring device can be easily performed. Further, after performing the correction work of the zero-phase current transformer primary current measuring device, the unknown current value Io is measured by detecting only the Io component using the zero-phase current transformer primary current measuring device. You can

In the present invention, a zero-phase current transformer primary current measuring device having a configuration as shown in FIG. 2 is constructed. In the zero-phase current transformer primary current measuring device 20, the input circuit 21 is connected to the terminals 6 and 6a of the input portions Z1 and Z2 for the input resistance R of the ground fault relay 8, and the input circuit 21 and the amplifier are connected. Two band-pass filters 23 and 24 are arranged in parallel to 22 and the signals from the two band-pass filters are transmitted to the gain correction circuit 26 via the changeover switch 25. Further, the RMS converter 27, the output circuit 30, and the display 32 are connected to the gain correction circuit 26 so that the information of the current detected by the ground fault relay 8 can be displayed. The oscillator 12 oscillates a power supply frequency and a frequency different from a harmonic of the power supply frequency, and the constant current generating circuit 1
In No. 1, the constant current is always applied regardless of the impedance of the test current circuit. In addition, the current flowing from the constant current generating circuit 11 is basically used only during correction, and the current value is, as a general rule, set to be equal to or less than the operating value of the ground fault relay or the like.

In each of the circuits provided in the zero-phase current transformer primary current measuring device 20, the input circuit 21 is an input circuit for the voltage at the input terminal of the ground fault relay in order to reduce the influence on the ground fault relay. It has high impedance and low reactance, and a protection circuit against abnormal voltage is installed. Further, the amplifier 22 is used to amplify the input signal to a required level. 2 arranged in parallel with the output circuit of the amplifier 22
The one bandpass filters 23 and 24 are configured as members having the same gain, and the first bandpass filter 23 is used to detect the current to be measured.
Used to pass the measured current frequency (commercial frequency). Further, the second bandpass filter 24 is used for correction and is configured to have a function of passing the frequency component of the oscillator.

A gain correction circuit 26, which is connected to the two bandpass filters via a changeover switch 25, constitutes a gain adjustment circuit for correcting the ZCT current-changing ratio and the input resistance of a relay or the like. . At the time of the correction, a current from the oscillator is made to flow to the ZCT primary side, the magnitude of the output voltage from the bandpass filter 24 is adjusted, and the current value flowing from the constant current generating circuit is adjusted so that the display current of the display matches. Circuit. Further, the RMS converter 27 detects the effective value of the signals output from the two bandpass filters. When the RMS converter is configured as a simple type, it is an absolute value detection type. Further, the display 32 is used to display the ZCT primary current and the current value of the constant current generating circuit. The output circuit 30 outputs the detection value to a monitor such as a recorder connected to the output terminal 31.

When operating the zero-phase current transformer primary current measuring apparatus of the present invention constructed as described above, the following steps a to d are taken to perform the zero-phase current transformer primary current measuring apparatus. Make the adjustment work. a: By switching the changeover switch 25 to the second bandpass filter 24, the bandpass filter 24 causes the RMS converter 27 to generate a constant current generating circuit even when a current such as a power supply frequency and harmonics is flowing to the ZCT primary side. The signal of is transmitted. b: By connecting the correction current generator, the current of the constant current generating circuit flows on the ZCT primary side. c: Adjusted by the gain correction circuit 27 so that the display of the display 32 matches the current value flowing to the ZCT primary side by the correction current generator. As a result, the correction of the ZCT current-changing ratio and the ground-fault relay input resistance without the influence of the power supply frequency is completed. d: The changeover switch 25 is changed over to the first bandpass filter 23. And bandpass filter 2
The function of 3 makes it possible to measure the ZCT primary current at the measured frequency.

As described above, as an example of performing the correction work by switching the bandpass filter of the zero-phase current transformer primary current measuring device and operating the gain correction circuit, a current of 20 mA at 20 Hz from the correction current generator. The band pass filter 24 can be configured to correspond to 20 Hz. Further, the bandpass filter 23 is configured to correspond to a commercial frequency of 50 Hz,
Be able to measure zero-phase current in the circuit that feeds the load. Then, for example, by adjusting the display so as to be 20 mA at 20 Hz through the bandpass filter 24 in the step c, the zero-phase current transformer primary current measurement device is used to perform correction. In the measurement using the bandpass filter 23, the zero-phase current can be measured with the gain correction circuit set to 50 Hz and the volume fixed. Therefore, in the zero-phase current transformer primary current measuring device of the present invention, the ZCT
For a circuit whose unknown current ratio or input resistance of the ground fault relay is unknown, insulation degradation etc. can be measured using the zero-phase current transformer primary current measuring device corrected as described above. It will be possible. In the embodiment of the present invention, the two bandpass filters 23 and 24 and the changeover switch 25 are separately provided, and the means for changing over the circuit is constituted by the changeover switch. In the above device, the mechanism of the device can be simplified by switching the pass frequency band of one band pass filter to the measured current or the frequency band of the correction current generator.

The device of the present invention configured as described above can be applied to both a high voltage circuit and a low voltage circuit, but as shown in FIG. 3, terminals 6 and 6a for a ground fault relay and By using the ZCT 5 provided with the terminals 7 and 7a for the test line electric circuit, it can be applied to any ZCT. Then, using the ZCT as shown in FIG. 3, a terminal is connected to the input circuit of the zero-phase current transformer primary current measuring device, and another terminal of the ZCT is connected to the terminal of the correction current generator. By connecting, the primary current of ZCT can be easily measured.

Further, in the zero-phase current transformer primary current measuring device of the present invention, as shown in FIG. 2, the correction current generator 10 and the zero-phase current transformer primary current measuring device 20 are provided as separate devices. Although it is possible to configure it, in order to improve the operability of the zero-phase current transformer primary current measurement device, a circuit for the correction current generator is installed inside the zero-phase current transformer primary current measurement device. The method of using the circuit of the correction current generator can be used only when the volume of the gain correction circuit is corrected integrally. Then, by setting a correction coefficient in the zero-phase current transformer primary current measuring device in the gain correction circuit for a circuit whose ZCT characteristics and the like are unknown, when performing subsequent insulation deterioration detection, It is possible to easily perform the measurement operation using the information set in the gain correction circuit without performing the correction operation.

[0019]

Since the present invention uses the zero-phase current transformer primary current measuring device constructed as described above, the ZC
It is possible to measure the primary current of T in the load connection state without being affected by the zero-phase current of the power supply frequency, and it is not necessary to measure the electric path in a power failure state as in the case of the conventional device. Further, in the present invention, a means for flowing a current different from the power supply frequency from the test line circuit to the ZCT primary side together with the zero-phase current is provided to the ZCT detection section, and the zero-phase current transformer primary current measurement device is corrected. By configuring means for measuring through different bandpass filters at the time of measurement, it is possible to obtain a device that is not affected by the current to be measured. Then, the control information for the zero-phase current transformer primary current measurement device is set by correcting the control value in the gain correction circuit of the zero-phase current transformer primary current measurement device using the current component flowing in the test line circuit. The control information once stored can be arbitrarily used for the power receiving equipment provided with the ZCT or the like, and the current ratio of the zero-phase current transformer and the input resistance of the relay or the like can be known. Without doing so, it is possible to easily perform the operation of detecting insulation deterioration and the like in a high voltage and low piezoelectric path.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a schematic configuration of a measuring apparatus of the present invention.

FIG. 2 is a circuit diagram of a zero-phase current transformer primary current measuring device of the present invention.

FIG. 3 is an explanatory diagram of a ZCT to which the present invention can be applied.

FIG. 4 is an explanatory view showing a measuring device using a general ZCT.

FIG. 5 is an explanatory diagram showing a conventional correction means.

FIG. 6 is a graph showing the relationship between the ZCT primary current and the input resistance end voltage of the ground fault relay.

[Explanation of symbols]

1 power supply, 2 switch, 3 load, 5 zero-phase current transformer (ZCT), 8 ground fault relay, 10 correction current generator, 11 constant current generation circuit, 12
Oscillator, 13 Test line circuit, 20 Zero-phase current transformer Primary current measuring device, 21 Input circuit, 23/24
Band pass filter, 25 selector switch,
26 gain correction circuit, 27 RMS converter,
30 output circuits, 32 display.

Claims (4)

[Claims] 1. A zero-phase current transformer provided in a ground fault relay or the like installed in a high-voltage or low-piezoelectric path, wherein a correction current generator supplies power to a zero-phase current flowing in a measurement part of the zero-phase current transformer. A zero-phase current transformer primary current measuring device that measures a zero-phase current by passing a current having a frequency component different from the frequency, detects a current having a frequency component different from the power-supply frequency component, and transforms the zero-phase current transformer. A zero-phase current transformer primary current measurement method characterized by correcting the input resistance of a ratio, relay, etc. 2. The zero-phase current transformer primary current measuring device comprises:
A means for switching the second bandpass filter used at the time of correction and the first bandpass filter used at the time of measuring the zero-phase current through a changeover switch is provided, and the current ratio of the zero-phase current transformer, etc. After the setting of, the mechanism for processing the information of the zero-phase current transformer is configured through the first bandpass filter, and the second bandpass filter is used to configure the frequency component different from the power source frequency component. A control coefficient of the zero-phase current transformer primary current measuring device is set according to the value of detected current, and the primary current of the zero-phase current transformer is measured using the circuit of the first bandpass filter. Claim 1
The zero-phase current transformer primary current measurement method described in. 3. The zero-phase current transformer primary current measuring device comprises:
A means for switching the second bandpass filter used at the time of correction and the first bandpass filter used at the time of measuring the zero-phase current through a changeover switch is provided, and the current ratio of the zero-phase current transformer, etc. After setting, the means for processing the information of the zero-phase current transformer through the first bandpass filter and the current of the frequency component different from the power source frequency component by using the second bandpass filter. Provide a means to set the control coefficient of the zero-phase current transformer primary current measuring device according to the detected value, and a means to display the detected current-change ratio of the zero-phase current transformer and the input resistance information of the relay etc. Zero-phase current transformer primary current measuring device characterized by. 4. A zero-phase current transformer primary current measuring device is integrally incorporated with a correction current generator, and only when correcting a current ratio of a zero-phase current transformer or an input resistance of a relay or the like. The zero-phase current transformer primary current measuring apparatus according to claim 3, wherein power is supplied from a detection circuit using the bandpass filter of No. 2 and a correction current generator.