JP2008198046A - Carrier transmission system for insulation monitoring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carrier transmission system of an insulation monitoring device for transmitting a carrier through a low voltage cable installed in a power reception facility for private use, and for preventing the influence of a noise by superimposing a non-sinusoidal alternating currents on a low voltage cable as a carrier. <P>SOLUTION: A CT6 for detection and a CT7 for carrier superimposition are arranged in a B type ground line 5 of a low voltage cable for private use, and a system for superimposing a non-sinusoidal AC voltage signal is used for an AC voltage signal to be superimposed on the low voltage cable as the carrier. Also, the carrier reception part of a notification unit 20 selects and receives a basic wave which is generated in the low voltage cable from the carrier and the frequency components of each higher harmonic wave, and when one frequency being received cannot be received, the reception frequency is successively selected so that resistivity to the noise of the low voltage cable can be increased. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an insulation monitoring apparatus installed in a private power receiving facility, in which a non-sinusoidal alternating current is superimposed on a low piezoelectric path as a carrier wave in a carrier system using an existing low piezoelectric path as a carrier wave information transmission path. The present invention relates to a carrier wave transmission system of an insulation monitoring device that uses a fundamental wave and each harmonic component generated in a low piezoelectric path as carrier wave frequency components, and noise of the low piezoelectric path can reduce the influence on the carrier wave.

In general, a power receiving facility is installed on a high-voltage distribution line from a supply substation (distribution substation), and power is supplied to each demand section of the private power receiving facility by converting it into a low-voltage current using a transformer. There is a route. In general industrial parks or the like, for example, a means for constantly monitoring the insulation state as disclosed in Japanese Patent Application Laid-Open No. 7-27799 is used.
In the above-mentioned conventional example, the detector superimposes a sinusoidal alternating current as a carrier wave on the low piezoelectric path by means of a carrier injection transformer (CT) provided on the B type ground line of the low piezoelectric path of the private electrical equipment, and toward the notification device. A method of transmitting information on the insulation state of the electric circuit is used (for example, see Patent Document 1).
JP-A-7-27799

In the leakage detection device of the conventional example, as described with reference to FIG. 9, the CT 6 for detection and the CT 7 for carrier wave superposition are arranged on the B-type ground line 5 provided in connection with the low piezoelectric path 3. Then, these two types of CT are connected to the oscillation circuit and the input circuit of the detector 10a, and based on the signal input from the detection CT 6, the insulation level of the detected electric circuit is set to “normal”, “ Represented by “caution” and “warning” signals, the carrier wave superimposing CT 7 of the detector 10 a superimposes a sinusoidal alternating current carrier wave on the low piezoelectric path to transmit the information. Then, by transmitting by changing the frequency according to the transmission information, the receiving device 20a that receives the information determines the content of the transmitted information from the information of the superimposed frequency (hereinafter, “ Multi-frequency method ”is used.
For example, as the frequency of the carrier wave, 1477 Hz is selected when insulation is normal, 1336 Hz is selected when insulation is cautioned, and 1209 Hz is selected when insulation is cautioned, and used as a signal of each frequency.

  However, when using the insulation monitoring method as described above, in recent years, as electrical equipment connected to the feeder line, semiconductor applied equipment such as inverters has increased, so there are many types of noise in electrical circuits. Is becoming more frequent. And since the noise has increased in many cases, the following failure has occurred in the performance of the device that detects the information on the electric circuit.

For example, it has been recognized that a failure that occurs when the conventional detection means is used is exemplified below.
a: Occurrence of carrier wave abnormality: In the frequency band close to the carrier wave frequency, due to the increase of electric circuit noise, carrier wave transmission becomes impossible (hereinafter referred to as “carrier wave abnormality”), resulting in an inconvenient situation where the device loses its function. To do.
b: Occurrence of false alarms: Since the detection device uses a method for judging transmission information from frequency components, the frequency with which false alarms occur due to noise mixed in the carrier wave band and unnecessary dispatch is required for security personnel Becomes higher.
c: Multi-information transmission is difficult: When transmission information such as heavy ground fault and detector operation important for security management is added, it is necessary to increase the transmission / reception frequency. However, increasing the transmission / reception frequency makes it more susceptible to electrical circuit noise, making it difficult to transmit multiple information.

Therefore, there are various methods for modulating and transmitting the carrier wave according to the transmission information while avoiding the above-mentioned disadvantageous state. Next, an amplitude modulation method (hereinafter referred to as “solution”) used as a means for solving the problem. An example of “ASK method” will be described.
In order to avoid the disturbance of the signal to be transmitted and to modulate and transmit the carrier wave according to the transmission information by using the modulation method, the detection information is transmitted as a patterned intermittent wave as shown in FIG. A scheme can be used. In the case of the intermittent carrier wave shown in FIG. 10, the duration of each signal is
D signal (separator signal): 0.75 seconds,
S signal (short signal): 0.25 seconds
L signal (long signal): 0.5 seconds
O signal (no signal): 0 and 25 seconds are set, and each signal is oscillated by repeating ON and OFF as described in FIG. 11 according to a predetermined pattern for each signal. A transmission means is used.
Then, according to the information to be transmitted, transmission is performed by changing the intermittent information in the information field in the pattern as shown in FIG. 11, and the receiving side uses a method for judging the transmission information from the intermittent pattern of the information field. There is.

However, when a method of modulating and transmitting such a carrier wave according to transmission information is used, the following problem that needs to be solved arises.
That is, as a problem in the case of using the modulation method, the electric circuit noise increases in a frequency band close to the carrier frequency, so that the carrier wave cannot be transmitted due to the noise. There are an increasing number of cases where it cannot be performed well.

  The present invention relates to an insulation monitoring device installed in a power receiving facility for private use, in which a non-sinusoidal alternating current is superimposed on a low piezoelectric path as a carrier wave in a carrier wave method using an existing low piezoelectric road as a carrier wave information transmission path. The present invention relates to a device that uses a fundamental wave and each harmonic component generated in an electric circuit as carrier wave frequency components, and can reduce the influence of noise on a low piezoelectric circuit or the carrier wave.

According to the present invention, information on the insulation state of the low piezoelectric path detected by the detection CT is arranged by arranging a CT for detection and a CT for superimposing a carrier wave on a type B ground line of the low piezoelectric path of the private power receiving facility. A detector having a function of transmitting the AC voltage signal superimposed on the low piezoelectric path from the carrier superimposing CT as a carrier wave modulated according to the insulation state of the low piezoelectric path through the low piezoelectric path;
The present invention relates to an insulation monitoring device configured to be combined with an alarm device having a function of receiving the carrier wave superimposed on the low piezoelectric path and outputting an alarm.
The invention of claim 1 uses a method of superimposing a non-sinusoidal AC voltage signal on the AC voltage signal superimposed on the low piezoelectric path as the carrier from the detector,
In the carrier wave receiver of the reporting device, it has a function to select and receive the fundamental wave generated in the piezoelectric path lower than the carrier wave and the frequency components of each harmonic,
For some reason, when one of the frequencies being received becomes unreceivable, the reception frequency is sequentially selected to receive a carrier wave, and the resistance to noise of the low piezoelectric path is enhanced.

The invention of claim 2 uses the continuous non-sinusoidal AC voltage as a carrier wave, changes the frequency of the carrier wave according to the insulation state of the electric circuit, and uses the method of transmitting information in the insulation monitoring device.
Only when the non-sinusoidal AC voltage used as the carrier wave is selected from the frequency components of the fundamental wave and each harmonic generated in the electric circuit, and the carrier receiving unit of the notification device receives two or more frequency components. The accuracy of the received information can be ensured by determining the signal as a carrier wave.

  According to a third aspect of the present invention, in the carrier wave receiver of the notification device according to the first aspect, a current flowing from the low piezoelectric path to the ground through a carrier wave detecting capacitor is detected as a carrier wave signal.

  In the present invention, unlike the conventional method in which only a single frequency component generated in a low piezoelectric path is used as a carrier wave in a conventional insulation monitoring device by a sine wave AC carrier wave, a large number of frequency components generated in the electric path by the carrier wave are used. Is used. Therefore, when the reception state of one frequency deteriorates, other frequencies can be selectively used, so that the state in which a carrier wave cannot be normally transmitted is dramatically reduced.

Also, in the conventional method, especially in the continuous wave method, processing of extra information due to false alarms has been a big problem, but multiple frequency components are selected from the fundamental wave component and the harmonic component of the carrier wave generated in the electric circuit. Since only a case where the signal can be received is determined as a signal by a carrier wave, the false alarm is drastically reduced.
In addition, compared with the conventional system, the present system hardly exhibits an increase in the size of the receiving circuit and can exhibit the feature that the circuit is not complicated.

  The configuration of the apparatus of the present invention will be described according to the illustrated example. In the circuit diagram illustrated in FIG. 1, the detector 10 and the notification device 20 for detecting leakage and transmitting information for superimposing a signal carrier wave on the low piezoelectric path with respect to the low piezoelectric path 3 of the private power receiving equipment. And a detection CT 6 for detecting the insulation state of the low piezoelectric path. The low piezoelectric path 3 is provided to the high piezoelectric path 1 via a transformer 2, and supplying low-voltage power from the low piezoelectric path 3 to each device on the demand side is a conventional technique. It is configured in the same way as general power supply equipment.

  A second type grounding wire (B type grounding wire) 5 is connected to the grounding electrode 5a for the low piezoelectric path 3, and the B type grounding wire 5 is superposed on the detection CT 6 of the detector 10 and the carrier wave. CT7 for each are arrange | positioned, and are connected to each circuit of the detector 10. FIG. Then, information relating to the insulation of the low piezoelectric path obtained from the CT 6 for detection is processed by the detector 10, and the information relating to the insulation of the low piezoelectric path detected is superimposed on the low piezoelectric path 3 as a carrier wave via the CT 7 for carrier wave superposition, This is transmitted to the reporting device 20 connected to the low piezoelectric path 3. The notification device 20 processes the transmitted signal and displays it on a display device or the like, or transmits information from an output circuit to a remote information collection center through a telephone line or the like. .

The detector 10 detects the insulation state of the low piezoelectric path by the low piezoelectric path insulation detection circuit 11 based on the information obtained from the detection CT 6, and transmits the detected result to the CPU 12. Processes according to the set information processing program. Then, the information as a result of the processing is transmitted from the external input / output circuit 15 to the device that receives arbitrary information connected to the outside via the external input / output terminal 16.
The information processed by the CPU 12 is transmitted to the amplifier 14 through the oscillation circuit 13 and transmitted from the carrier wave superimposing CT 7 to the low piezoelectric path 3 through the B-type grounding line 5.

  The carrier wave detection circuit 21 provided in the notification device 20 is supplied with a carrier wave transmitted from the detector 10 via the low piezoelectric path 3, and the information processed by the carrier wave reception circuit 22 is processed by the CPU 23 to be displayed. 24 is output as information to be displayed. The information processed by the CPU 23 is transmitted through the data transmission / reception circuit 25 from the connection terminal 26 to an external receiving facility via a telephone line or the like.

  In order to explain the characteristics of information processing by each processing circuit described in the block diagram of FIG. 1 and the apparatus provided with the circuit, the low-piezoelectric path insulation detection circuit 11 of the detector 10 is detected by the detection CT 6. Based on the signal, an operation of detecting the insulation state of the low piezoelectric path is performed, and the information is transmitted to the CPU 12. The CPU 12 controls the transmission frequency or intermittent pattern of the carrier wave and the entire detector according to the insulation state of the low piezoelectric path 3. Then, if necessary, the external input / output circuit 15 is used to input external temperature, information that may affect the electrical equipment, alarms, etc. A control signal is transmitted to the oscillation circuit 13 through the control circuit.

The information processed by the CPU 12 is processed as information directed to the amplifier 14 via the oscillation circuit 13. In the oscillation circuit 13, two types of signal output methods can be used. The information processed by the CPU 12 is transmitted from the amplifier 14 through the B-type grounding wire 5 to the notification device 20 from the low piezoelectric path 3.
The oscillation circuit 13 can output the processed information using one of two types of signals, a multi-frequency system and a modulation system (ASK system).

For example, the following signal processing method can be appropriately employed.
a: Multi-frequency method: The CPU controls the oscillation frequency according to the type of information to be transmitted. b: Modulation method (ASK method): The CPU controls the intermittent pattern of the carrier wave according to the type of information to be transmitted.
The signal processing method shown in the above example is selected and applied to the insulation monitoring device. In the amplifier to which the information is transmitted, the signal output from the oscillation circuit is subjected to power amplification and transmitted to the carrier wave superimposing CT 7.

The carrier wave from the detector 10 transmitted through the low piezoelectric path 3 is input to the carrier wave detection circuit 21 in the notification device 20, and the information processed by the carrier wave reception circuit 22 is transmitted to the CPU 23.
The CPU 23 controls carrier wave reception status, reception information determination, reception frequency control, alarm type determination, and overall reporting device, and transmits the processed information to the display 24 as necessary. Then, based on the signal output from the CPU, the operation state of the apparatus is determined, the lighting of the indicator lamp is performed by the analyzed signal, and the operation of the information such as notifying the operator is performed. . Information can be sent to the data transmission / reception circuit 25 through the telephone circuit 26 by a signal from the CPU 23.

To further explain the role of each circuit in the reporting device 20 and the operation of information processing,
* In the carrier wave detection circuit 21, the current flowing through the capacitor C to the ground is detected by a current transformer or the like.
* The carrier wave applied from the detector 10 to the electric circuit is received, and in the case of the multi-frequency system, the signal processing based on the configuration is performed to prevent false alarms and the like.

Explanation of carrier wave detection method (common to both multi-frequency and modulation systems):
In the conventional method, the reporting device detects the carrier wave by detecting the ground voltage generated in the electric circuit by the carrier wave and the voltage between point A and point B, as in the example shown in FIG.
In this method, as described above, the voltage generated by the carrier wave has a property of decreasing as the harmonic order increases, and as the harmonic order increases, the received signal becomes smaller and difficult to receive. The carrier wave signal current flowing to the ground through the carrier wave detection capacitor is detected by the carrier wave detection unit 21 of the reporting device 20 from the point A provided on the electric circuit.
This scheme can minimize the effect of decreasing voltage as the harmonic order increases.

Next, another example of the configuration of the receiving circuit in this apparatus will be described.
* Example of receiver circuit configuration:
(Multi-frequency circuit configuration)
Next, FIG. 3 illustrates a configuration of a receiving circuit using a band-pass filter with variable pass frequency (hereinafter referred to as “variable fo BPF”). In this circuit diagram, the carrier wave output from the carrier wave detection unit uses a high-pass filter (hereinafter referred to as “HPF”) 31 and a low-pass filter (hereinafter referred to as “LPF”) 32 to reduce noise in unnecessary frequency bands, The carrier wave is input to the variable Fo type BPF 33.
The carrier wave separated by the variable Fo type BPF 33 is converted into a digital signal by the A / D converter 34 and sent to the CPU 35 to determine the reception frequency.
In this circuit, when it is desired to further improve the reception performance, a lock-in amplifier or the like having a high frequency discrimination capability is used instead of the variable Fo type BPF 33.

Next, the operation of the circuit shown in FIG. 3 will be described.
The CPU controls the variable Fo-type BPF so as to sequentially change the reception frequency of the fundamental wave and the harmonic wave of the carrier wave according to a predetermined carrier wave frequency. For example, as in the case of receiving the fundamental wave and the fifth harmonic, the CPU determines that the information received from two or more frequency components is a carrier signal from the transmission side.
If the frequency being received becomes unreceivable (for any reason), the reception frequency is changed in order, the frequency that can be received is searched, and an operation that can receive two or more frequency components is performed. Do.

* Configuration example of a device using a plurality of variable Fo type BPF circuits:
In the above description of the present invention, the operation of a device using one variable Fo-type BPF circuit has been described. However, a high-performance receiving circuit is configured by always configuring the device to receive a plurality of frequencies. be able to.

Circuit configuration of another example of modulation method:
FIG. 4 illustrates the configuration of a receiving circuit using a variable Fo type BPF circuit. In this circuit example, the carrier wave output from the carrier wave detection unit is passed through the HPF and LPF to reduce noise in unnecessary frequency bands, and the carrier wave is input to the variable Fo-type BPF 33.
The carrier wave separated by the variable Fo-type BPF 33 becomes a patterned intermittent signal from which the carrier frequency component is removed by the rectifying / smoothing circuit 36, and the intermittent signal is converted into a digital signal by the A / D converter. , The intermittent pattern is determined by sending it to the CPU 35, and the type of transmission information is determined.

* The signal processing operation in the circuit of FIG.
The CPU performs an operation of selecting a frequency at which a carrier wave can be normally received by giving a command to the variable Fo-type BPF 33 and sequentially changing the passing frequency when reception becomes impossible at the currently used frequency.
For example, if the fundamental wave cannot be received due to electric circuit noise while the fundamental wave is normally received, the frequency of the third harmonic component that can receive the intermittent pattern normally is selected and used. Perform the operation.

* Carrier frequency selection function:
Signal transmission by an intermittent signal is a technical means that exhibits the feature that transmission in a narrow occupied band is possible. Therefore, the problem can be solved by providing a function of switching the carrier frequency using this characteristic.

* Configuration example using a plurality of variable Fo BPF circuits:
In the above description of the present invention, the operation of a device using one variable Fo-type BPF circuit has been described. However, a high-performance receiving circuit is configured by always configuring the device to receive a plurality of frequencies. be able to.

* Means for solving the problems of the conventional scheme: In order to solve the problems of the conventional carrier scheme, the following measures should be taken.
: Form of the carrier wave superimposed on the electric circuit: The carrier wave superimposed on the electric circuit is a sine wave AC voltage in the conventional method, but in this method, a non-sine wave AC is superimposed.

* To explain the voltage generated in the electric circuit when non-sinusoidal alternating current is superimposed,
If each frequency of the fundamental wave of the carrier wave is a square wave of ω and the peak value is E, the harmonic component included in the voltage waveform generated in the electric circuit is an odd harmonic component as represented by the following equation. It decreases as the harmonic order increases.
V = 4E / π (sinωt + sin3ωt / 3 + sin5ωt / 5... +
……… + sinNωt / N)

* Frequency distribution of the voltage generated in the circuit due to the superimposed voltage:
According to the previous equation, the frequency distribution of the voltage generated in the electric circuit is as shown in FIG. 5 below, where the effective value of the fundamental wave is E1 and each frequency of the fundamental wave is ω. Voltages of odd harmonic components such as frequency ω and angular frequencies 3ω, 5ω are generated.

* The following method can be used for information transmission when the multi-frequency method is used. For example,
a: A non-sinusoidal alternating current is superimposed as a carrier wave.
b: Similar to the conventional method, the frequency is changed according to the transmission information.
c: On the receiving side, the fundamental wave and harmonic component voltages generated by the non-sinusoidal AC generated in the electric circuit are detected as shown in the graph of FIG.
For example, when two or more frequencies are received, such as when a fundamental wave and a fifth harmonic are received, it is determined that the signal is a carrier wave from the transmission side.
It is considered possible to use the method as described above.
If the frequency being received becomes unreceivable (for some reason), the reception frequency is sequentially changed to search for a receivable frequency and adjust so that two or more frequency components can be received. .
For example, if only the frequency component of the fundamental wave can be received, it is determined as noise.

Measures to be taken when transmission information changes during the information transmission:
Transmission information changes (for example, change from normal insulation to warning)
As shown in FIG. 7, when the frequency of the fundamental wave of the carrier wave changes from ω to ω1, when two or more frequency components are received, it is determined that the signal is a carrier wave from the transmission side.

An example of information transmission by the modulation method used in the present invention will be described by taking the ASK method as an example.
a: A non-sinusoidal alternating current is superimposed as a carrier wave.
b: Like the conventional method, information is transmitted by intermittently transmitting a carrier wave.
c: Reception is the same as the intermittent pattern wave of each harmonic from the fundamental wave of the carrier wave according to the ASK system, and therefore there is a property that the intermittent pattern does not change even if any frequency component is received. Therefore, using this property, the reception frequency is selected and used as necessary.
The above aspects are possible.
And, for example, when the fundamental wave cannot be received due to electric circuit noise while the fundamental wave is normally received, as shown in FIG. 8, the third harmonic component that can normally receive the intermittent pattern can be obtained. Select the frequency to use.

Next, in addition to the above-described configurations, application examples of this method will be further described. The following method can be adopted.
(1) Ground return type power line carrier system:
As described in this example, this method can be used for a carrier wave method using a carrier voltage superimposed between a power line and the ground, such as a low piezoelectric path insulation monitoring device.
(2) Power line carrier system:
In addition to the ground return type power line carrier system, it can also be used for a system in which a carrier wave is superimposed between power line lines to transmit information.

  In the present invention, signal waves having various waveforms such as a square wave, a trapezoidal wave, a triangular wave, and a peak clip wave of a sine wave can be used as the carrier wave waveform injected into the electric circuit.

Next, to explain the effectiveness of this method and the characteristics of its configuration,
(1) Reduction of carrier abnormality:
Unlike the conventional method that uses only a single frequency band, this method uses a large number of frequency components generated in the electric circuit by a carrier wave. When the reception state of one frequency deteriorates, the other frequency is changed. Since it can be selectively used, the state in which the carrier wave cannot be normally transmitted (hereinafter referred to as “carrier wave abnormality”) is drastically reduced.
(2) Reduction of false alarms:
In the conventional system, especially when using the multi-frequency system, unnecessary dispatch of security personnel due to false alarms has been a big problem. Thus, false alarms are dramatically reduced.
In addition, in the modulation system, error control can be performed to eliminate almost all false reports.
(3) Simple configuration:
Even if this system is compared with the conventional system, there is almost no increase in the size of the receiving circuit, and the circuit is not complicated.
The above features can be exhibited.

It is a block diagram which shows the structure of the processing circuit provided in the apparatus of this invention. It is explanatory drawing of the circuit of a carrier wave transmission means. It is explanatory drawing of the receiving circuit of a multifrequency system. It is explanatory drawing of the receiving circuit of an ASK system. It is explanatory drawing of the fundamental wave and harmonic voltage which arose in the electric circuit by the carrier wave. It is explanatory drawing of the carrier wave reception band of a multi-frequency system. It is explanatory drawing of a carrier wave reception band when the carrier frequency of a multi-frequency system changes. It is explanatory drawing of the carrier wave receiving method of an ASK system. It is explanatory drawing of the circuit of a carrier wave transmission means. It is explanatory drawing of the intermittent carrier wave of an ASK system. It is explanatory drawing of the kind of alarm of ASK system, and the intermittent pattern of a carrier wave.

Explanation of symbols

1 high voltage path, 2 transformer, 3 low voltage path,
5 Class B ground wire, 6 CT for detection, 7 CT for carrier wave superposition,
10 detector, 11 low piezoelectric path insulation detection circuit, 12 CPU,
13 oscillation circuit, 14 amplifier, 15 external input / output circuit.
20 Reporter, 21 Carrier detection circuit, 22 Carrier reception circuit,
23 CPU, 24 display, 25 data transmission / reception circuit,
31 HPF, 32 LPF, 33 variable fo type BPF,
34 A / D conversion circuit, 35 CPU, 36 Rectification / smoothing circuit.

Claims (3)

Place the CT for detection and CT for superimposing the carrier wave on the Class B ground wire of the low piezoelectric path of the power receiving equipment for private use.
Information on the insulation state of the low piezoelectric path detected by the detection CT is used as a carrier wave obtained by modulating an alternating voltage signal superimposed on the low piezoelectric path from a carrier superposition CT according to the insulation state of the low piezoelectric path. A detector having a function of transmitting via a low piezoelectric path;
In the insulation monitoring device configured to receive the carrier wave superimposed on the low piezoelectric path and configured in combination with a notification device having a function of outputting an alarm,
The AC voltage signal superimposed on the low piezoelectric path as the carrier from the detector uses a method of superimposing a non-sinusoidal AC voltage signal,
In the carrier wave receiver of the reporting device, it has a function to select and receive the fundamental wave generated in the piezoelectric path lower than the carrier wave and the frequency components of each harmonic,
An insulation monitoring device characterized in that when one of the frequencies being received cannot be received for some reason, the reception frequency is sequentially selected to receive a carrier wave, and the resistance to noise of the low piezoelectric path is enhanced. Carrier system. In the insulation monitoring device that uses a continuous non-sinusoidal alternating voltage as a carrier wave, changes the frequency of the carrier wave according to the insulation state of the electric circuit, and transmits information,
The non-sinusoidal AC voltage used as the carrier wave is selected from frequency components of the fundamental wave and each harmonic generated in the electric circuit,
Only when the carrier receiving unit of the reporting device receives two or more frequency components, by determining that the signal is a carrier wave,
2. The carrier system for an insulation monitoring apparatus according to claim 1, wherein accuracy of received information can be ensured.   2. The carrier system for an insulation monitoring device according to claim 1, wherein the carrier wave receiving unit of the reporting device detects a current flowing from the low piezoelectric path through a carrier wave detecting capacitor to the ground as a carrier wave signal.

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