JP2000028671A - Insulation detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an insulation detector where a device configuration is simpler than an igr insulation detector (a current component caused by the unbalance of insulation resistance against ground), manufacturing cost is made low, and the insulation deterioration of an electric path to be monitored can be detected accurately. SOLUTION: An insulation detector is provided with power supply terminals 10T and 10S for receiving power supply from a T-phase electric circuit 2T and an S-phase electric circuit 2S, a ground terminal 10E that is connected to a ground line 8 of a Type 3 installation construction, a differential amplifier 17 for outputting the differential voltage between the power supply terminal 10T and the grounding terminal 10E being connected to the T-phase electric circuit, and a CPU 22 for detecting insulation deterioration based on the value of the vector sum by performing the discrete Fourier transformation of a leakage current i0 and a voltage signal from the differential amplifier 17 and extracting only the vector component, that is in phase with the reference vector from the leakage current vector with the voltage signal as a reference vector. By obtaining only a current component (igr) caused by the unbalance of the vector component that is in phase with the reference vector is obtained from a leakage current vector, only the current component (igr) caused by the unbalance of the insulation resistance against the ground can be obtained so that the leakage current i0 is detected without being affected by the leakage current component (igc) caused by the unbalance of the capacitance against the ground.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulation detector for detecting insulation deterioration of a single-phase three-wire circuit.

[0002]

2. Description of the Related Art Conventionally, an insulation detector constantly measures this leakage current (i0) by utilizing the property that the leakage current of an electric circuit to be monitored flows back to a ground wire of a second-class grounding work. There is an i0 insulation detector that emits an abnormality detection signal when a predetermined change occurs. FIG. 6 shows a configuration of a conventional i0 insulation detector, and is a grounding wire of a second-class grounding construction in which a middle line (S-phase wire) of a single-phase three-wire circuit, which is a circuit to be monitored, is grounded. 61
A current transformer (CT) 62 for detecting a leakage current is attached to the power supply, and the detected leakage current i0 is amplified and rectified by an amplification rectifier circuit 63.
The signal is output to the alarm determination circuit 64. Alarm judgment circuit 64
Is a warning level alarm value (15 m) preset in the alarm value setting circuit 65 from the detected current value from the amplification rectifier circuit 63.
A) and the warning level warning value (50 mA) are compared. When the current value is higher than the warning level warning value, the warning warning display lamp is lit, and when the current value is higher than the warning level warning value, the warning warning display lamp is lit. At the same time, an alarm signal is output to a transmitter or a transmitter that automatically transmits the monitoring result. i
0 The insulation detector detects the capacitances C1, C
This is applied when 2 is always small, and when insulation is reduced, the leakage current i0 of the monitored circuit becomes large. Therefore, in FIG. 6, by always measuring the magnitude of the leakage current i0 flowing through the ground wire 61 of the second-class grounding work, it is possible to detect a decrease in the insulation of the electric circuit to be monitored.

However, the leakage current i0 in the AC circuit is
Is the current component igr based on the ground insulation resistances Rg1 and Rg2.
(= Ig1 + ig2) and the current component igc (= ic1 + ic2) based on the ground capacitances C1 and C2, so that insulation monitoring may not be possible simply by changing the leakage current i0. In other words, the i0 insulation detector cannot distinguish whether the change in the leakage current i0 is due to the imbalance between the ground insulation resistances Rg1 and Rg2 or the imbalance between the ground capacitances C1 and C2. An increase in the leakage current i0 due to an imbalance between the capacitances C1 and C2 may be erroneously detected as a decrease in insulation. Therefore, in order to deal with such a problem, the commercial frequency (for example, 50
Hz) and a low frequency (for example, 10 Hz) different from that of the second type grounding work is sent to the ground line of the second-class grounding work as a monitoring signal, and the monitoring signal flowing back to the second grounding work through the ground impedance is separated and detected. Thus, an igr insulation detector that constantly measures only the current component igr based on the ground insulation resistance is used.

FIG. 7 shows the configuration of an igr insulation detector.
2, a low frequency monitoring signal is superimposed on a commercial current and injected into a monitoring target electric circuit on the transformer secondary side (low voltage side) through a ground line 71 by an oscillator 73 incorporated in the injection transformer 72, and the monitoring target electric circuit is provided. , A leakage current i0 returning to the ground line 71 of the second-class grounding work is detected by a current transformer (CT) 74 for detection, amplified by an amplifier 75, and then separated and extracted by a filter 76 for a monitoring signal component. Further, this signal component is synchronously detected by the signal of the oscillator 73 by the synchronous detection circuit 77 and output to the alarm determination circuit 78. The alarm determination circuit 78
When the current value of the input monitoring signal is compared with the warning level warning value (15 mA) and the warning level warning value (50 mA) preset in the warning value setting circuit 79, and the current value is equal to or higher than the warning level warning value Is a warning lamp,
When the alarm level is equal to or higher than the alarm level alarm value, the alarm lamp is turned on, and an alarm signal is output to a transmitter or an alarm device that automatically transmits the monitoring result. The igr insulation detector controls the phase and the like of the monitoring signal injected into the commercial current to control the current component igr due to the unbalance between the ground insulation resistances Rg1 and Rg3 and the unbalance between the ground capacitances C1 and C3. Since the current component igc can be distinguished from the current component igc, only the current component igr of the leakage current i0 due to the imbalance between the ground insulation resistances Rg1 and Rg3 can be constantly measured to perform high-precision insulation monitoring. However, in the case of a sound circuit without large insulation capacitances C1 and C3 and no insulation deterioration in the monitored circuit, the current component igc of the current component igc due to the unbalance of the ground capacitances C1 and C3 included in the leakage current i0. The ratio is the ground insulation resistance Rg1
, Rg3, the current component igr is significantly larger than that of the current component igr, so that only the current component igr caused by the imbalance between the ground insulation resistances Rg1 and Rg3 is extracted by using the filter 76 and the synchronous detection circuit 77. And the detection error tends to increase. To prevent this, a capacitance suppressing circuit is provided to suppress the ineffective component.

[0005]

As described above, in the igr insulation detector, a monitor signal having a frequency different from the commercial frequency is injected into the commercial current through the ground line 74, and the monitor signal is returned to the ground line 74 through the ground impedance. Since the current signal igr due to the imbalance between the ground insulation resistances Rg1 and Rg3 of the leakage current i0 can be constantly measured by separately extracting and detecting the signal for use, the insulation with higher accuracy than the i0 insulation detector is obtained. Monitoring is possible. However, the igr insulation detector includes an injection transformer 72 for superposing and injecting a low-frequency monitoring signal on a commercial current, and a leakage current i0 of a monitored circuit.
A filter 76 for separating and extracting a monitoring signal component from the
It is necessary to include a synchronous detection circuit 77 for synchronously detecting the separated and extracted monitoring signal component, a capacitance suppressing circuit for suppressing an ineffective component caused by ground capacitances C1 and C3 of the monitored circuit, and the like. The structure and control method are more complicated than the i0 insulation detector, and the manufacturing cost is high. On the other hand, the i0 insulation detector is simpler in configuration and control method than the igr insulation detector, and has the advantage of lower manufacturing cost. However, as described above, the ground insulation resistances Rg1 and Rg1
Since the change in the leakage current i0 due to the unbalance of g2 and the leakage current i0 due to the unbalance between the ground capacitances C1 and C2 cannot be distinguished, the leakage due to the unbalance between the ground capacitances C1 and C2 cannot be distinguished. There is a possibility that an increase in the current i0 may be erroneously detected as insulation deterioration, and the detection accuracy is poor. The present invention has been made in view of the above circumstances, and has as its object to provide an insulation detector which has a simpler device configuration than the igr insulation detector, has a lower manufacturing cost, and can detect insulation deterioration of a monitored circuit with high accuracy. Is to provide.

[0006]

According to a first aspect of the present invention, a neutral point for a secondary side of a power distribution transformer is grounded by a grounding wire of a second-class grounding construction. The S-phase electrical circuit is pulled out from the neutral point on the secondary side of the
An insulation detector for detecting deterioration of insulation of a distribution line that supplies power to a load with three wires together with a three-phase circuit and a T-phase circuit based on a leakage current i0 flowing through a ground line of the second-class grounding work. A pair of power terminals for receiving power supply from the T-phase circuit and the S-phase circuit, a ground terminal connected to the ground wire of the third kind installation work, and a side connected to the R-phase circuit or the T-phase circuit. When a differential amplifier that outputs a differential voltage between the power supply terminal and the ground terminal, and discrete Fourier transform of the leakage current i0 and the voltage signal from the differential amplifier, and the voltage signal is used as a reference vector. And an arithmetic processing unit for extracting only a vector component having the same phase as the reference vector from the leakage current vector, obtaining a vector sum thereof, and detecting insulation deterioration based on the value. According to a second aspect of the present invention, in the insulation detector according to the first aspect, the arithmetic processing unit determines whether or not the vector sum is on a positive side area of a real axis on a complex plane.
It is characterized in that it is determined on which side of the phase circuit or the T-phase circuit the insulation deterioration has occurred.

As described above, according to the first aspect of the present invention, the leakage current i0 and the voltage signal from the differential amplifier, that is, the difference voltage between the ground line of the third type installation work and the R-phase circuit or the T-phase circuit are set. And a discrete Fourier transform, and extracting only the vector component having the same phase as the reference vector from the leakage current vector when the voltage signal is used as the reference vector, and calculating the vector sum thereof. Since only the current component (igr) caused by the imbalance of the ground can be extracted, the leakage current i0 (ig) is not affected at all by the leak current component (igc) caused by the imbalance of the ground capacitance.
r) can be detected, and insulation deterioration of the electric circuit to be monitored can be detected with high accuracy. Further, by detecting the signal of the leakage current i0 and the signal of the above-mentioned difference voltage and performing discrete Fourier transform, respectively, it is possible to measure only the fundamental wave component of both signals and detect the insulation deterioration, so that the detection can be performed with high reliability. it can. Also, in order to extract only the current component (igr) caused by the imbalance of the ground insulation resistance from the leakage current i0, an injection transformer for injecting a monitoring signal, a filter for separating and extracting the monitoring signal component from the leakage current i0, etc. Because it is not necessary to use the device, the device configuration can be simplified compared to the igr insulation detector.
Manufacturing costs are reduced. Also, as described in claim 2,
By providing a function that can determine which side of the R-phase circuit and the T-phase circuit has caused the insulation deterioration, it becomes easier to specify the location where the insulation deterioration has occurred, so that the insulation restoration work can be performed early.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the embodiments shown in the accompanying drawings. FIG. 1 is a schematic circuit diagram showing an example of an embodiment of the present invention. Reference numeral 1 denotes a distribution transformer, reference numeral 2 denotes a single-phase three-wire distribution line that is an electric circuit to be monitored, and reference numeral 3 denotes an insulation detector according to the present invention provided to detect an abnormality in the insulation level of the distribution line 2. It is. In the power distribution system shown in the figure, the secondary side (low voltage side) neutral point 2P of the transformer 1 is grounded via the grounding wire 4 of the second-class grounding work, and from there, the neutral line of the distribution line 2 is provided. The S-phase circuit 2S is drawn out, and the S-phase circuit 2S and the R-phase and T-phase circuits 2R,
Power is supplied to the load by three lines T. Insulation detector 3
Is supplied with power (100 VAC) from the distribution line 2 via a pair of branch lines 5S, 5T connected to the S-phase electric circuit 2S and the T-phase electric circuit 2T of the distribution line 2. Reference numeral 6 denotes branch lines 5S and 5T and power supply terminals 10S and 10T of the insulation detector 3.
It is a connector (outlet) that connects the power supply lines 7S and 7T drawn from the power supply line. The connector 6 has a power terminal 6
S, 6T and a ground terminal 6E are provided. Connector 6
The grounding terminal 6E is grounded via a grounding wire 8 for the third-class grounding work.
Is connected to the ground wire 9 drawn from the ground terminal 10E. An AC / DC power supply 1 is provided inside the insulation detector 3.
1, amplification circuit 12, first low-pass filter (LPF) 1
3, the first A / D converter 14, the voltage dividing circuit 15, the contact switch 16, the differential amplifier 17, the second low-pass filter (LP
F) 18, second A / D converter 19, A / D conversion timing control circuit 20, clock circuit 21, CPU 22, RO
M23, etc. are provided. AC / DC power supply 11
Are branch lines 5S, 5T, power supply lines 7S, 7T from the distribution line 2.
The AC power supplied to the power supply terminals 10S and 10T is converted into a direct current, and the power is suppressed to a predetermined voltage to supply power to various IC circuits in the insulation detector 3. The amplification circuit 12 amplifies the leakage current i0 detected by the detection current transformer (CT) 24 attached to the ground wire 4 of the second-class grounding work, and outputs it to the first LPF 13. The first LPF 13 is
The input current from the amplifier circuit 12 is supplied to the first A / D converter 14 by passing only a current component having a predetermined frequency or less (for example, 50 Hz or less). First A / D converter 14
Converts the signal input from the first LPF 13 into a digital signal and supplies the digital signal to the CPU 22.

On the other hand, the voltage dividing circuit 15
1 and the power terminals 10S and 10T of the insulation detector 3, and the S-phase circuit 2S and the T-phase circuit 2 of the distribution line 2.
The two supply voltages from T are each reduced to a predetermined value or less and output to the contact switch 16. The contact switch 16 is C
The voltage dividing circuit 15 is operated by a control signal from the PU 22.
The contact is switched so that one of the two outputs from is selected and input to the differential amplifier 17. The differential amplifier 17 has one output voltage of the voltage dividing circuit 15 selected by the contact switch 16 and the voltage (third-class ground voltage) E3 of the ground terminal 10E.
Is input. The differential amplifier 17 is connected between the voltage of the power supply terminals 10S and 10T output from the voltage dividing circuit 15 and the ground terminal 1
The voltage difference from the voltage E3 of the second LPF 18 is amplified.
Output to The second LPF 18 allows the current from the differential amplifier 17 to pass only a current component having a predetermined frequency or lower (for example, 50 Hz or lower) and supplies the current to the second A / D converter 19. The second A / D converter 19 converts the signal input from the second LPF 18 into a digital signal and supplies the digital signal to the CPU 22. The first and second A / D converters 14 and 19 perform sampling at the same timing with each other according to a control signal from the A / D conversion timing control circuit 20. The CPU 22 is a main control device of the insulation detector 3 and operates in synchronization with a clock signal supplied from the clock circuit 21. A program executed by the CPU 22 is written in the ROM 23, and the CPU 22 executes the first A / D converter 14 and the contact switch 1 according to the program.
6, monitoring the insulation state of the distribution line 2 while controlling the second A / D converter 19, the A / D conversion timing control circuit 20, etc.
The result is output from the output port 24. Output port 2
4 is connected to a conventional transmitter or notifier for automatically transmitting the monitoring result.

Hereinafter, the operation of the insulation detector 3 will be described. The insulation detector 3 connects the power lines 7S, 7T and the ground line 9 to the power terminals 6S, 6T and the ground terminal 6E of the connector 6, respectively, and connects the detection current transformer 24 to the ground line 4 of the second-class grounding. Is attached and connected to the amplifier circuit 12, the operation is started by turning on a power switch of an operation panel (not shown). At that time, as an initial setting process, the CPU 22 first switches the contacts with the voltage dividing circuit 15 sequentially by the contact switch 16 and supplies the contacts from the S-phase circuit 2S and the T-phase circuit 2T of the distribution line 2 via the voltage dividing circuit 15. These two voltages are input to the differential amplifier 17 one by one. As a result, the voltage of the S-phase circuit 2S and the third-class ground voltage E
3 and the difference voltage between the voltage of the T-phase circuit 2T and the third type ground voltage E3 are sequentially output, and the respective signals are passed through the second LPF 18 and the second A / D converter 19 to the CPU 22.
Supplied to The CPU 22 compares the two signals, and selects the contact having the larger difference voltage by the contact switch 16. In this case, since the S-phase circuit 2S of the distribution line 2 is grounded by the ground wire 4 of the second-class grounding work, the difference voltage between the voltage of the S-phase circuit 2S and the third-class ground voltage E3 is extremely small. The contact on the T-phase side of the voltage dividing circuit 15 is selected. That is, the contact switch 16 is connected to the branch line 5 regardless of whether the branch line 5 is connected to the secondary side circuit 2S and 2T of the transformer 1 or to the case where the branch line 5 is connected to 2S and 2R. It is provided in consideration of convenience so that a signal can be input. After performing the initial setting process, the CPU 22 detects the current by the detection current transformer 24 attached to the ground wire 4 of the second-class grounding work, and detects the amplification circuit 12, the first LPF 13, and the first A / D converter. 14 and the value of the leakage current i0 supplied from the distribution line 2 through the power line 7T and the ground line 9, the voltage dividing circuit 15, the differential amplifier 17, and the second LPF 1
8, a single-phase voltage input through the second A / D converter 19,
That is, based on the value of the difference voltage between the voltage of the T-phase electric circuit 2T and the third type ground voltage E3, insulation deterioration is detected by the operation described below.

The sampling operation of the leakage current i0 and the difference voltage and the operation of the CPU 22 will be described with reference to the waveform diagram shown in FIG. Here, the first and second A / D converters 1
Assume that the A / D conversion is performed simultaneously at 4,19. As shown in the figure, the signal frequency is set to 50 Hz, and 8
If sampling is performed once, a time window of one cycle T, that is, a time window of 20 ms is provided, and a discrete Fourier transform (DFT) operation is performed on the sampled value in the time window by the following equation (1). Thus, the effective value and phase of the signal frequency can be obtained.

[0012]

(Equation 1) The CPU 22 performs the discrete Fourier transform on both the leakage current i0 and the difference voltage signal. Then, FIG. 2A →
As shown in (B) → (C), the window is shifted by the time length of one sampling cycle. Here, the voltage signal (difference voltage)
Considering the i0 vector using the sampling data of (i) as a reference vector, it can be expressed as shown in FIG. Note that the subscript <vtl> indicates a vector quantity. This figure illustrates a vector addition formula of i0 <vtl> = igr <vtl> + igc <vtl>, and the first and second terms on the right side of the formula use the symbols shown in FIG. When,
Each is expressed as igr <vtl> = ig1 <vtl> + ig2 <vtl> igc <vtl> = ic1 <vtl> + ic2 <vtl>. Therefore, the leakage current i0 in FIG. 1 is i0 <vtl> = ig1 <vtl> + ig2 <vtl> + ic1 <vtl> + ic2
<vtl> is a vector addition expression.

In the case of the i0 insulation detector, ig1 <vtl> and ig2
<vtl> and ic1 <vtl> and ic2 <vtl> cancel each other out because the directions of their vectors are different from each other by 180 °.
It will not be detected as 0 <vtl>. However, the unbalanced component is the ground capacitance C1 of the R-phase and T-phase circuits 2R and 2T,
Since it occurs due to C2, it has a different phase from the single-phase voltage vector. Therefore, if only igr <vtl> is extracted from i0 <vtl>, the influence of igc <vtl> can be avoided.
Therefore, after performing the initial setting process, the CPU 22 detects a signal of the leakage current i0 and the signal of the difference voltage, performs a discrete Fourier transform on both signals, and obtains i0 <vtl> when the voltage signal is used as a reference vector. , A vector component having the same phase as that of the reference vector is extracted, the sum of the extracted components is used as a leakage current i0 <vtl> component, and based on the value, the insulation deterioration of the distribution line 2, which is the electric circuit to be monitored, is detected.

As described above, the leakage current i0 flowing through the ground line 4 of the second-class grounding work is treated as a vector amount i0 <vtl>,
By extracting only the current components igr <vtl> caused by the ground insulation resistances Rg1 and Rg2 from i0 <vtl> and detecting insulation deterioration, the influence of the leakage current components Igc caused by the ground capacitances C1 and C2 is completely eliminated. Since it is possible to detect the leakage current i0 (igr) without receiving it, it is possible to detect the insulation deterioration of the monitored circuit with high accuracy. Also, the leakage current i0
By performing the discrete Fourier transform by detecting the signal of the differential voltage and the differential voltage, the insulation deterioration can be detected by measuring only the fundamental wave component of both signals, so that the detection can be performed with high reliability. In other words, the higher the frequency of the signal, the lower the impedance due to the effect of the high-frequency component of the signal, so that the ground insulation resistances Rg1 and Rg2 apparently decrease, and the current component due to the unbalance between the ground insulation resistances Rg1 and Rg2. Although the measurement error of igr increases, an accurate measurement value can be obtained by measuring only the fundamental component of the signal. On the other hand, in the conventional i0 insulation detector, the insulation deterioration of the monitored circuit is detected based only on the scalar amount of the leakage current i0.
There is a possibility that an increase in the leakage current i0 due to the unbalance of the above is erroneously detected as insulation deterioration.

Further, according to the present invention, by comparing the phase of a voltage signal serving as a reference vector with the phase of a current component igr <vtl> caused by imbalance between ground insulation resistances Rg1 and Rg2, a single-phase three-wire system is obtained. R-phase circuit 2R and T-phase circuit 2 of distribution line 2
It is possible to determine on which side of T the insulation degradation has occurred. That is, in the complex plane shown in FIG. 4, the current component i due to the unbalance between the ground insulation resistances Rg1 and Rg2 is obtained.
If the gr vector is in the positive region of the real axis, it can be determined that insulation deterioration has occurred on the electric circuit on the side that supplies power to the insulation detector 3, that is, on the T-phase electric circuit 2T in this example.
If the vector of the current component igr is in the negative side region of the real axis, insulation degradation occurs on the side of the circuit opposite to the side supplying the reference current to the insulation detector 3, that is, in this example, on the side of the R-phase circuit 2R. It can be determined that it has occurred. In the above embodiment, the power of the insulation detector 3 is supplied from the S-phase electric circuit 2S and the T-phase electric circuit 2T of the distribution line 2, but the power is supplied from the S-phase electric circuit 2S and the R-phase electric circuit 2R. It may be. In this case, if the vector of the current component igr is in the positive region of the real axis, it can be determined that insulation deterioration has occurred on the R-phase electric circuit 2R side. Further, in the above-described embodiment, the leakage current i0 and the voltage signal are converted into digital signals using dedicated A / D converters 14 and 19, respectively. For example, as shown in FIG. After the voltage signal is multiplexed by the multiplexer 31 and then alternately input to the A / D converter 33 via the sample and hold circuit 32, one A / D
The D converter 33 can convert the two signals into digital signals. However, in this case, since the sampling timing of the i0 signal and the voltage signal do not coincide with each other, it is necessary to perform a discrete Fourier transform on the i0 signal and the voltage signal, and then perform time correction to temporally match the two values.

[0016]

As described above, according to the present invention, the following excellent effects can be exhibited. The insulation detector according to the first aspect of the present invention detects only the leakage current component caused by the imbalance of the ground insulation resistance without being affected by the leakage current component caused by the imbalance of the ground capacitance. Because it is possible to detect the insulation deterioration of the electric circuit to be monitored more accurately than the conventional i0 insulation detector, and to extract only the current component due to the unbalance of the ground insulation resistance from the leakage current. In addition, since it is not necessary to use an injection transformer for injecting a monitoring signal or a filter for separating and extracting a monitoring signal component from leakage current as in the case of the igr insulation detector, the device configuration is simpler than that of the igr insulation detector. Production cost is reduced. According to the second aspect of the present invention, the insulation detector of the first aspect is provided with a function of determining which side of the R-phase circuit and the T-phase circuit has the insulation deterioration. Since it is easy to identify the location where the occurrence of the insulation has occurred, the insulation restoration work can be performed at an early stage.

[Brief description of the drawings]

FIG. 1 is a schematic circuit diagram illustrating an example of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a signal sampling operation in the embodiment of the present invention.

FIG. 3 is a diagram showing a leakage current vector (i0 <vtl>) and a current component vector (igr <vtl>) resulting from an imbalance in insulation resistance to ground.
FIG. 4 is an explanatory diagram showing a relationship between a leakage current component vector (igc <vtl>) caused by an imbalance in ground capacitance.

FIG. 4 is an explanatory diagram of a criterion for determining which side of an R-phase circuit or a T-phase circuit has caused insulation deterioration.

FIG. 5 is a main part circuit diagram showing another embodiment of the present invention.

FIG. 6 is a schematic circuit diagram of a conventional i0 insulation detector.

FIG. 7 is a schematic circuit diagram of an igr insulation detector.

[Explanation of symbols]

1 Distribution transformer, 2 single-phase three-wire distribution line, 2P neutral point, 2S S-phase circuit, 2R R-phase circuit, 2T T-phase circuit, 3 Insulation detector, 4 Grounding wire for second-class grounding , 5
S branch line, 5T branch line, 6 connector, 6E ground terminal, 6S power terminal, 6T power terminal, 7S power line,
7T power line, 8 ground wire for 3rd class grounding, 9 ground wire, 10E ground terminal, 10S power terminal, 10T
Power supply terminal, 11 AC / DC power supply, 12 amplifier circuit, 1
3 first low-pass filter, 14 first A / D converter, 1
5 voltage divider circuit, 16 contact switches, 17 differential amplifier,
18 second low-pass filter, 19 second A / D converter, 20 A / D conversion timing control circuit, 21 clock circuit, 22 CPU, 23 ROM.

Claims (2)

[Claims] 1. A secondary side neutral point of a distribution transformer is grounded by a ground wire of a second-class grounding construction, an S-phase electrical path is drawn out from the transformer secondary-side neutral point, and an R-phase electrical path outside of the S-phase electrical path. And T
An insulation detector for detecting insulation deterioration of a single-phase three-wire distribution line that supplies power to a load with three wires together with a phase electric circuit based on a leakage current flowing through a ground wire of the second-class grounding work, A pair of power terminals for receiving power supply from the phase or T-phase circuit and the S-phase circuit, a ground terminal connected to the ground wire of the type 3 installation work, and a connection to the R-phase circuit or the T-phase circuit. A differential amplifier that outputs a differential voltage between the power terminal and the ground terminal on the other side, discrete Fourier transforms the leakage current and the voltage signal from the differential amplifier, and converts the voltage signal to a reference vector. And an arithmetic processing unit for extracting only a vector component having the same phase as the reference vector from the leakage current vector obtained when the sum is obtained, obtaining a sum of the vectors, and detecting insulation deterioration based on the value. . 2. The arithmetic processing unit determines whether the R-phase circuit or the T-phase circuit has insulation degradation depending on whether or not the vector sum is on the positive side of the real axis on a complex plane. The insulation detector according to claim 1, wherein the insulation detector detects whether or not there is a difference.