JPH07209366A - Insulation monitor for isolated neutral wiring line - Google Patents

Abstract

PURPOSE:To monitor the ground impedance stably without feeding a high monitoring current to an isolated neutral line by inserting a series circuit of a pair of resistors between a pair of lines connected with the secondary of an insulating transformer. CONSTITUTION:A series circuit 12 is connected between the lines 5, 6 connected with the secondary coil 4 of an insulating transformer 2. The circuit 12 comprises a pair of resistors R1, R2 having resistances high enough to restrict the current flow sufficiently lower than the ground fault current being monitored. Means 19 for detecting the current flowing through a monitoring power supply 13 comprises a resistor R3 for detecting current and the voltage across the resistor R3 is applied to a low-pass filter 24 passing the frequency component of the power supply 13 and lower frequency components. Output from the low-pass filter 24 is passed through a DC converter circuit 25 to a subtractor circuit 26. Output from the subtractor circuit 26 is amplified 27 and fed through a buffer 28 to a comparator circuit 29 which makes a comparison with a predetermined voltage and delivers a level discrimination output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-ground wiring type electric circuit insulation monitoring apparatus.

[0002]

2. Description of the Related Art Safety standards for hospital electrical equipment are stipulated in Japanese Industrial Standards JIS T 1022. If a ground fault current flows in an electric line and the power is cut off, there is a risk of seriously impairing medical care. It is stipulated that the outlet circuit in the medical room where the equipment is used is of the non-grounded wiring system, and an insulation monitoring device is provided on the power supply side of the non-grounded electric circuit. This insulation monitoring device is a method of measuring and monitoring the ground impedance of the electric circuit, and the alarm device installed in it is a ground fault that flows when one of the ungrounded electric circuits is connected to the ground with a low-impedance conductor. It is said that it must operate when the current value becomes 2 mA.

A typical prior art is Japanese Patent Publication No. 1-16088.
In this prior art, for example, 50 Hz
An auxiliary voltage source for applying an auxiliary voltage having a frequency, for example, 55 Hz, which is slightly separated from the frequency between the neutral point of the non-grounded electric path and the ground, and applying a voltage substantially equal to the earth voltage of the electric path. , A current detector for detecting a current flowing between the neutral point and the ground, and a current limiter for keeping the current flowing through the human body at 2 mA or less even if the human body comes into contact with the non-grounded circuit in series. Connected and configured.

[0004]

In such a prior art, the current limiter keeps the current between the neutral point and the ground to be 2 mA or less for the purpose of monitoring. It is presumed that it is configured to constantly pass a certain amount of current, and therefore the monitored current is large, which impairs the insulation of the non-grounded circuit.

An object of the present invention is to provide an insulation monitoring device for an electric line of an ungrounded wiring system, which can monitor the impedance to ground stably and does not require a large monitoring current to flow in the ungrounded electric line. It is to be.

Another object of the present invention is to provide a non-ground wiring type electric circuit insulation monitoring device which can simplify the circuit configuration.

[0007]

According to the present invention, an insulating transformer whose primary input is supplied with AC power, a pair of electric lines connected to the secondary output of the insulating transformer, and a pair of electric lines connected between the pair of electric lines. , A series circuit composed of a pair of resistors having a large resistance value so as to flow a current sufficiently smaller than a predetermined ground fault current value of the ground fault current to be monitored flowing between each electric path and the ground, A monitoring power supply, which is interposed between the mutual connection point of the pair of resistors and ground, and provides an AC voltage having a frequency different from that of the AC power supply, a capacitor connected in series to the monitoring power supply, and the monitoring. Current detecting means for detecting an alternating current flowing in the power supply for power supply, and means for level-discriminating the detection output of the current detecting means by the predetermined ground fault current value, between any of the electric paths and the ground,
The predetermined ground fault at the frequency of the AC power supply between the first impedance seen from the monitoring power supply when there is a DC resistance having the predetermined ground fault current value and any of the electric paths and ground. Second viewed from the monitoring power supply at the frequency of the monitoring power supply when there is a capacitance that is a current value
It is a non-ground wiring type electric circuit insulation monitoring apparatus, wherein the resistance value of the pair of resistors and the electrostatic capacitance of the capacitor are selected so that the impedance becomes equal.

Further, the present invention is characterized in that the frequency of the power source for monitoring is set to a value which is in the vicinity of a declining value which is an integral fraction of the frequency of the AC power source and which is different from the declining value.

According to the present invention, the current detecting means is provided with a current detecting resistor connected in series to the monitoring power source and a voltage across the current detecting resistor to filter the frequency of the monitoring power source. A circuit for converting the output of the filter into a direct current, a subtracting means for subtracting a predetermined voltage from the output from the direct current converting circuit, and an amplifying means for amplifying the output of the subtracting means.

Still further, according to the present invention, the current detecting means is supplied with a voltage between both ends of the current detecting resistor connected in series with the monitoring power source and the current detecting resistor, and filters the frequency of the monitoring power source. It is characterized by including a filter, a circuit for converting the output of the filter into a direct current, and an analog / digital conversion means for converting the output of the direct current conversion circuit into a digital value with higher resolution as the output level increases.

[0011]

According to the present invention, a series circuit composed of a pair of resistors is provided between a pair of electric paths to which the secondary output of the insulating transformer is connected, and a neutral point which is a connection point of the pair of resistors and a neutral point. A configuration in which a monitoring power supply for applying an AC voltage is connected to the ground, that is, the ground, and a current having a frequency of the monitoring power supply flowing through the monitoring power supply is detected by a current detection means to discriminate the detected current level. Therefore, by selecting the resistance value of each of the pair of resistors to be a sufficiently large value, the current flowing to the human body when the human body comes into contact with the ungrounded electric circuit that is the secondary output of the insulating transformer is
For example, the safety is maintained at 150 μA or less, and since such a current value is small, the insulation of the non-grounded circuit is not deteriorated. The above 150 μA is a ground fault current value to be monitored, for example, 2 mA. Is a sufficiently small value.

According to the invention, the monitoring power supply applies an AC voltage between the neutral point and the ground, and a DC resistance component and a DC resistance component which are real components of the ground impedance between each of the two non-grounded circuits and the ground. Insulation can be monitored by the capacitance, which is an imaginary component.

Further, according to the present invention, it is possible to monitor the respective ground impedances between the two respective non-grounded electric paths which are the secondary outputs of the insulating transformer and the ground,
That is, it is possible to monitor not only the insulation deterioration between one non-grounded circuit and the ground, but also the insulation deterioration between both ungrounded circuits and the ground.

According to the present invention, a common current detecting means and a level discriminating means are provided in order to monitor the insulation by the direct current resistance and the electrostatic capacitance, whereby the circuit structure can be simplified. There is. Therefore, the resistance values of the pair of resistors and the capacitance of the capacitor are selected so that the first impedance and the second impedance are equal.

The frequency of the power supply for monitoring is set to a value near the frequency of the system power supply, for example, a diminishing frequency of an integral fraction of 60 Hz or 50 Hz, and a value different from the diminishing frequency. For example, when the frequency of the AC power source is selected to be 60 Hz, the diminishing frequency is 1/3 times that 20
Approximately 19 Hz or 21 Hz, which is close to Hz,
The respective values are the same when the frequency of the AC power supply is 50 Hz. If the frequency of the AC voltage of the monitoring power supply is selected to be the same as or close to the secondary output voltage of the isolation transformer, that is, the frequency of the system power supply, the AC voltage of the monitoring power supply and the output of the system power supply Is a problem, and there is a risk that the detected current will fluctuate due to the occurrence of a beat due to the phase shift, and therefore the frequency of the AC voltage of the monitoring power supply and the frequency of the AC power supply must be sufficiently separated. If the frequency of the power supply for monitoring is selected to be high, noise may be emitted to the outside. Therefore, it is preferable that the frequency of the power supply for monitoring is lower than the frequency of the AC power supply. The beat is prevented from occurring by shifting the frequency from the value obtained by dividing the frequency by an integer.

Further in accordance with the present invention, the isolation transformer 2
With the next output voltage, the ground fault current value to be monitored, for example, the fact that the ground current resistance of 50 mA or less, which is 2 mA described above, is level discriminated and an alarm is generated. In addition, the ground capacitance due to the stray capacitance due to the long installation of the electric path has the same ground impedance of 50K at the system power frequency of 60Hz or 50Hz.
Ω is 0.053 μF or 0.063 μF, and is configured to generate an alarm when the capacitance to the ground or more is exceeded.

Further in accordance with the present invention, the current detecting means comprises:
Has a resistance for current detection connected in series to the power supply for monitoring,
The voltage across the current generated by the current flowing through the current detecting resistor is applied to the filter so that the voltage corresponding to the ground impedance is detected, and the output of the filter is converted by the subtracting means into a DC converter circuit, for example, a full-wave rectifier circuit and a smoothing circuit. By converting the DC voltage into a direct current, and subtracting a predetermined voltage from the output of the DC conversion circuit, the impedance to ground is higher than the high resistance value of the pair of resistors for obtaining the neutral point. Even if is relatively small, level discrimination can be easily performed.

Further, according to the invention, when the current detecting means is realized by a processing means such as a microcomputer, the output obtained by converting the output from the filter into a direct current by the direct current converting circuit has a higher resolution as the output level is higher. By using the analog / digital conversion means for converting into a digital value by means of the analog / digital conversion means, level discrimination is facilitated even if the ground impedance is relatively small compared to the high resistance value of the pair of resistance values in order to obtain a neutral point. It will be possible to do.

[0019]

1 is a block diagram showing the overall construction of an embodiment of the present invention. RMS value from commercial AC power supply 1
Electric power of 0V is given to the primary coil 3 of the isolation transformer 2. The frequencies f1 and f2 of the commercial AC power supply 1 are f1 = 50
Hz or f2 = 60 Hz. Isolation transformer 2 of 2
The output of the next coil 4 is supplied from electric lines 5 and 6 to electric equipment 7 such as hospitals and clinics. The electric paths 5 and 6 are of a non-grounded wiring system, and the electric impedances Z1 and Z2 between the electric paths 5 and 6 and the ground 8 are measured and monitored by the insulation monitoring device 9 according to the present invention. The output voltage of the secondary coil 4 of the insulating transformer 2 has an effective value of 100V.

When the ground impedance of the electric path 5 is Z1 as described above, when the human body 10 contacts the other electric path 6 and the electric path 6 is grounded, the secondary coil 4 of the insulating transformer 2 to the electric path 5, A ground fault current indicated by reference numeral I1 flows through the ground impedance Z1, the ground 8, the human body 10 and the electric path 6. When the value of this ground fault current is such that the value of the ground fault current flowing when one of the ungrounded electric circuits is connected to the ground by a low impedance conductor becomes 2 mA, the insulation monitoring device of the present case Reference numeral 9 gives an alarm by the alarm means 11. The ground impedance Z1 or Z2 at which such an alarm operation is performed is 50 kΩ (= 100 V).
/ 2 mA).

A series circuit 12 is connected between the electric paths 5 and 6 which are the outputs of the secondary coil 4 of the insulating transformer 2. This series circuit 12 is composed of a pair of resistors R1 and R2, and has a large resistance value so that only a current sufficiently smaller than the ground fault current value of 2 mA to be monitored, for example, 150 μA flows. In this specification, reference numerals of resistors and capacitors may represent their resistance values and capacitances. In this example, R1 = R2 = 2 MΩ.

FIG. 2 is an equivalent circuit diagram of the electric circuit shown in FIG. The monitoring power source 13 includes a connection point 14 which is a neutral point of the pair of resistors R1 and R2 of the series circuit 12 and a ground 8.
Is intervened between. The monitoring power supply 13 is a commercial AC power supply 1 that is the system power supply, and thus an insulation transformer 2.
It is a power supply that outputs an AC voltage having a frequency f3 different from the output of the secondary coil 4. The frequency f3 of the monitoring power supply 13 is set to a value that is close to the diminishing value of the frequencies f1 and f2 of the commercial alternating-current power supply 1 that is an integral fraction thereof, and is different from the diminishing value. In this embodiment, the decreasing value is the commercial AC power supply 1
Is 1/3 of the frequencies f1 and f2, and the frequency f3 of the monitoring power supply 13 is, for example, 21 Hz or 1 as described above.
It is 9 Hz. The output voltage of the monitoring power supply 13 has an effective value of 12V. A capacitor C1 is also connected in series to the monitoring power supply 13. The capacitance of the capacitor C1 is set to 0.03 μF as described later.

The current detecting means 19 for detecting the current flowing through the monitoring power source 13 includes a current detecting resistor R3 interposed in series between the monitoring power source 13 and the ground 8.

In the current detecting means 19 for detecting the alternating current flowing through the monitoring power source 13, the voltage across the current detecting resistor R3 is given to the low pass filter 24 as shown in FIG. Frequency f of power supply 13 for
3 and lower frequency components are filtered and passed, that is, the cutoff frequency fc1 of the low-pass filter 24.
Is equal to the frequency f3 of the monitoring power supply 13. The output of the low-pass filter 24 is supplied to the DC conversion circuit 25, where the output of the low-pass filter 24 is converted into DC, and the output V1 thereof is supplied to the subtraction circuit 26. Subtraction circuit 26
Then, a predetermined voltage V2 is subtracted from the output voltage V1 from the DC conversion circuit 25, and the output (=
V1-V2) is amplified by the amplifier circuit 27, and the buffer 28
Is applied to one input of the comparison circuit 29 via. In the comparison circuit 29, the output of the buffer 28 and the predetermined voltage V
3 is compared. As a result, when one of the ungrounded electric circuits 5 and 6 is connected to the ground 8 with a low-impedance conductor, the value of the ground fault current flowing becomes 2 mA. A level discrimination output is obtained, which causes the drive circuit 31 to output the alarm means 11
Drive the buzzer 32 of the acoustically and the lamp 33
A visual alarm is displayed by.

If the insulation of at least one of the ground impedances Z1 and Z2 is lowered and the ground fault current value 2 mA at which an alarm is to be generated becomes (a) the DC resistance is lowered, or (b) the electrostatic resistance is lowered. In either case (a) or (b) when the capacity becomes large, in order to enable the subsequent current detection means 19 to generate an alarm, the resistance is set as follows. The resistance values of R1 and R2 and the capacitance of the capacitor C1 are selected. The resistance value of the current detection resistor R3 is the resistance values of the resistors R1 and R2 and the frequencies f1 and f of the AC power source 1 of the capacitor C1.
It is sufficiently small compared to the reactance at 2 and can be ignored. For example, R3 = 150 kΩ.

In the equivalent circuit of FIG. 2, the resistors R1 and R2 are
The combined resistance R12 of

[0027]

[Equation 1]

The reactance X1 of the capacitor C1 at the frequency f3 of the monitoring power supply 13 is

[0029]

[Equation 2]

It is Therefore, the ground impedance Z
When either one of Z1 and Z2 is short-circuited, the combined impedance Z11 viewed from the monitoring power supply 13 is as shown in FIG.

[0031]

[Equation 3]

In the above case (a), that is, in the case where any of the ground impedances Z1 and Z2 is a DC resistance having a predetermined ground fault current value of 2 mA, the monitoring power supply 1
The first impedance Z12 viewed from 3 is obtained with reference to FIG. This DC resistance R20 is 50 kΩ (=
100 V / 2 mA). Such DC resistance R20
Is present as the ground impedance, the first impedance Z12 viewed from the monitoring power supply 13 is expressed by Equation 4.

[0033]

[Equation 4]

In the above-mentioned case (b), the monitoring power supply 13 when there is an electrostatic capacity between the electric paths 5 and 6 at the frequency f1 or f2 of the AC power supply 1 and which has the predetermined ground fault current value of 2 mA. The second impedance Z13 viewed from the monitoring power supply 13 at the frequency f3 of 1 is obtained with reference to FIG. When the frequency of the AC power supply 1 is f1 = 60 Hz, and the electrostatic capacity that gives a ground fault current value of 2 mA is C2, the reactance X2 of the electrostatic capacity C2 is expressed by Equation 5.

[0035]

[Equation 5]

When the ground impedance Z1 or Z2 consists of such an electrostatic capacitance C2, the reactance X3 by the electrostatic capacitance C2 at the frequency f3 of the monitoring power supply 13 is obtained.
Is shown in Equation 6.

[0037]

[Equation 6]

Therefore, the second impedance Z13 seen from the monitoring power supply 13 at the frequency f3 of the monitoring power supply 13
Is expressed by Equation 7.

[0039]

[Equation 7]

When the current detecting means 19 is a DC resistance having the ground impedance Z1 or Z2 having a predetermined ground fault current of 2 mA, and has a capacitance C2 having the predetermined ground fault current value of 2 mA. In any of the cases (a) and (b), the first impedance Z11 is used in common to enable the level discrimination operation.
And the second impedance Z13 are equal to each other, that is, Z11 = Z13 (8) holds, the resistance values of the resistors R1 and R2 and the electrostatic capacitance of the capacitor C1 are selected. In this embodiment, the resistance R
1 and R2 are selected to have a high resistance value of 2 MΩ in order to prevent electric shock, and therefore the combined resistance R12 is 1 MΩ, and when the frequency f1 of the commercial AC power supply 1 is 60 Hz, the predetermined ground fault current value is 2 mA. Reactance X2 of Equation 5 =
50 kΩ (= 100 V / 2 mA), so C
2 = 0.053 μF, so this capacitance C
2, the frequency f3 of the monitoring power supply 13 (= 21H
The reactance X3 in z) is 150 kΩ. Therefore, when the value of the capacitor C1 is calculated so that the above-mentioned formula 8 is satisfied, that is, the first impedance Z11 shown in the formula 3 and the second impedance Z13 shown in the formula 7 are equal, C1 = 0. It becomes 03 μF. At this time, X1 = 265 kΩ, Z11 = Z13 = 1034 k
Ω.

FIG. 4 is an electric circuit diagram showing a specific configuration of the monitoring power supply 13 and the like. AC / D for the electric circuits 5 and 6
A C converter 36 is connected, and positive and negative DC voltages of 15 V are output to the output lines 34 and 35, and the DC power supplies electric power to the electric circuit of the insulation monitoring device 9.

The monitoring power supply 13 is connected via the line 40 to
A sinusoidal wave having a frequency f3 = 21 Hz is oscillated and derived, and the frequency can be finely adjusted by the variable resistors VR4 and VR5.

FIG. 5 is an electric circuit diagram showing a specific structure of the low-pass filter 24. A current detecting resistor R3 is connected between the line 41 connected to the ground 8 and the chassis 38 of the insulation monitoring device 9 of the present invention, and a noise blocking capacitor C30 is connected in parallel to the resistor R3. Capacitor C30 is, for example, 0.01 μF. The low pass filter 24 includes a buffer 43 and a total of three stages of operational amplifiers 4.
4, 45, 46, including resistors R22, R23 and capacitors C31, C32, C33, resistors R24, R25 and capacitors C34, C35, C36 and resistor R
26, R27 and capacitors C37, C38, C39
The cutoff frequency fc1 is determined by the following, and its selectivity Q = 1.3 × 3, and the component of the frequency f3 of the monitoring power supply 13 is derived from the line 47.

FIG. 6 is an electric circuit diagram showing a specific electrical structure subsequent to the low pass filter 24. The signal derived from the low-pass filter 24 via the line 47 is given to the DC conversion circuit 25, and full-wave rectified by the full-wave rectification circuit 51 including the operational amplifiers 49 and 50 and the diodes D7 and D8. The full-wave rectified output is smoothed by the smoothing circuit 52 and converted into a direct current.

The DC output is given from line 53 to one input of operational amplifier 54 which constitutes subtraction circuit 26. A predetermined voltage V3 of, for example, 1 to 2V is applied from the reference voltage generating circuit 55 to the other input of the operational amplifier 54 via the line 56. Thus the operational amplifier 5
The voltage (V1-V2) is derived from 4 to the line 57. Thus, the small voltage (V1-V2) is applied to the amplifier circuit 27.
It is amplified with high gain. In this way, in the amplifier circuit 27,
From the output voltage V1 of the low pass filter 24 to the reference voltage V2
Is subtracted and amplified, the ground impedances Z1 and Z2 depend on the ground impedances Z1 and Z2 in the amplifier circuit 27 even if the ground impedances Z1 and Z2 are smaller than the resistance values of the resistors R1 and R2 of the series circuit 12. It becomes possible to easily amplify and detect the current flowing through the current detecting resistor R3, and prevent the saturation of the amplifier circuit 27. Due to the function of the capacitor C41 connected to the line 67, abrupt fluctuation of the output of the amplifier circuit 27 is suppressed.

The signal on the line 67 is supplied to one input of the operational amplifier 59 of the comparison circuit 29 via the buffer 28. The other input of the operational amplifier 59 is supplied with the voltage V3 corresponding to the discrimination level from the resistors R64 and R65 forming the discrimination level setting circuit 60. Operational amplifier 59
Indicates that the voltage at the discrimination level voltage V3 or more corresponding to the predetermined ground fault current value of 2 mA is applied to the line 2 in the buffer 2
When applied from 8 to the operational amplifier 59, a high level signal is derived to make the transistor TR3 of the drive circuit 31 conductive. As a result, the relay coil 63 of the relay 62 is
Is excited, the relay contact 64 becomes conductive, an alarm sound is generated from the buzzer 32 of the alarm means 11, and an alarm lamp 33 is also generated.
Lights up and a visual display is made. The output of the amplifier circuit 27 via the line 67 is given to the meter circuit 68, and the meter 69 is driven.

FIG. 7 is a block diagram showing the overall construction of another embodiment of the present invention. This embodiment is similar to the previous embodiment, and corresponding parts bear the same reference numerals. It should be noted that in this embodiment, the output of the DC conversion circuit 25 is given to the analog / digital conversion means 87 to be digitized, and the signal representing the digital value is given to the processing circuit 91 realized by a microcomputer or the like to perform arithmetic processing. Then, the alarm operation by the buzzer 32 or the lamp 33 is performed.

FIG. 8 shows an analog / digital conversion means 87.
It is a figure which shows the resolution of. DC output level from the DC conversion circuit 25, and therefore analog / digital conversion means 8
As the input level of 7 is higher, the resolution is increased by converting the digital value for each smaller level difference ΔV. As a result, the ground impedances Z1 and Z2 become equal to the resistance R of the series circuit 12.
It is possible to reliably measure and monitor the ground impedances Z1 and Z2 even if the impedances are relatively small as compared with 1 and R2. The processing circuit 91 is realized by a microcomputer or the like as described above, and the analog / digital conversion means 8 is provided.
Each output of 7 is stored in a memory, and when the digital value exceeds a predetermined ground fault current value of 2 mA to be monitored, an alarm means including a buzzer 32 and a lamp 33 is activated.

Instead of the low-pass filter 24, a band-pass filter or the like for extracting and filtering the component of the frequency f3 of the monitoring power supply 13 may be used.

[0050]

As described above, according to the present invention, a neutral point obtained by a series circuit composed of a pair of resistors and a ground, which is a ground, are provided between a pair of electric paths connected to the secondary output of an insulating transformer. During this period, an AC voltage having a frequency different from the frequency of the system power supply, which is the secondary output of the isolation transformer, is applied from the monitoring power supply, and the AC current is detected by the current detection means to discriminate the level. It is possible to stably detect the insulation impedance between the ungrounded electric path connected to the secondary side of the insulation transformer and the ground, and increase the resistance value of the pair of resistors so that the human body comes into contact with the electric path. Even if the ground fault current value to be monitored is, for example, 2 m
It is possible to prevent the risk that a current exceeding A flows.

According to the present invention, the current detection is performed by selecting the resistance value of the pair of resistors and the capacitance of the capacitor so that the first impedance and the second impedance viewed from the monitoring power supply become equal. The means and the level discriminating means can both monitor the insulation due to the DC resistance and the electrostatic capacitance between the electric path and the ground, and the configuration can be simplified.

Further, according to the present invention, the frequency of the monitoring power supply is set to a value which is close to the decrement value of the integral power of the AC power supply which is the system power supply and is different from the decrement value. Does not cause the detection current to become unstable, and there is no risk of noise being generated outside.

Further, according to the present invention, even if the ground impedance is smaller than the high resistance value of each of the pair of resistors for obtaining the neutral point, the subtraction circuit can detect the impedance and the insulation monitoring by the amplification circuit can be performed. You will be able to do it accurately.

Further, according to the present invention, the output of the filter is given to the analog / digital conversion means, and the higher the output level, the higher the resolution, and the higher the resolution, the more the analog / digital conversion means is converted into the digital value. Therefore, even if the ground impedance is relatively small compared to the high resistance value of the pair of resistors for obtaining the neutral point described above, it becomes possible to accurately and accurately discriminate the level of the ground impedance. .

[Brief description of drawings]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of the embodiment shown in FIG.

FIG. 3 is a vector diagram for explaining impedance seen from a monitoring power supply 13 related to ground impedances Z1 and Z2.

FIG. 4 is a specific electric circuit diagram showing a monitoring power supply 13 and a configuration related thereto.

5 is an electric circuit diagram showing a specific configuration of a low pass filter 24. FIG.

FIG. 6 is a DC conversion circuit 25, a subtraction circuit 26, and an amplification circuit 2
7 is an electric circuit diagram showing a specific configuration of a buffer 28, a comparison circuit 29, and the like.

FIG. 7 is a block diagram showing the overall configuration of another embodiment of the present invention.

8 is a diagram for explaining the resolution of the analog / digital conversion means 87. FIG.

[Explanation of symbols]

 1 Commercial AC Power Supply 2 Insulation Transformer 3 Primary Coil 4 Secondary Coil 5,6 Electric Circuit 8 Earth 9 Insulation Monitoring Device 10 People 13 Monitoring Power Supply 14 Neutral Point 24 Low Pass Filter 25 DC Conversion Circuit 26 Subtraction Circuit 27 Amplification Circuit 28 Buffer 29 Comparison Circuit 31 Drive Circuit 32 Buzzer 33 Lamp Z1, Z2 Ground Impedance R1, R2 Resistance R3 Current Detection Resistance C1 Capacitor

Claims (4)

[Claims] 1. An insulating transformer having AC power supplied to a primary input, a pair of electric paths connected to a secondary output of the insulating transformer, and a pair of electric paths connected between the electric paths and a ground. The series circuit consisting of a pair of resistors having a large resistance value so as to pass a current sufficiently smaller than the predetermined ground fault current value of the ground current to be monitored, and the pair of resistors in the series circuit are mutually connected. A monitoring power supply that is interposed between the point and ground and that provides an AC voltage having a frequency different from that of the AC power supply; a capacitor that is connected in series to the monitoring power supply; and an AC current that flows in the monitoring power supply. Current detecting means for detecting, and means for level-discriminating the detection output of the current detecting means based on the predetermined ground fault current value, between any of the electric paths and the ground, the predetermined ground fault current value and DC resistance When there is a capacitance between the first impedance as seen from the monitoring power supply when any of the above is present and any one of the electric paths and the ground, and which has the predetermined ground fault current value at the frequency of the AC power supply. The non-grounded wiring, wherein the resistance value of the pair of resistors and the capacitance of the capacitor are selected so that the second impedance viewed from the monitoring power supply at the frequency of the monitoring power supply becomes equal. System electric circuit insulation monitoring device. 2. The frequency of the power supply for monitoring is set to a value which is near a diminished value of an integral fraction of the frequency of the AC power supply and is different from the diminished value.
A non-grounded wiring type electric circuit insulation monitoring device. 3. The current detecting means includes a current detecting resistor connected in series to the monitoring power source, a filter for applying a voltage across the current detecting resistor, and a filter for filtering the frequency of the monitoring power source, and a filter. 3. The circuit according to claim 1, further comprising: a circuit for converting the output of the above into a direct current, a subtracting means for subtracting a predetermined voltage from the output from the direct current converting circuit, and an amplifying means for amplifying the output of the subtracting means. Non-grounded wiring circuit insulation monitoring device. 4. The current detecting means includes a current detecting resistor connected in series to the monitoring power source, a filter for applying a voltage across the current detecting resistor and filtering the frequency of the monitoring power source, and a filter. 2. The circuit according to claim 1, further comprising: a circuit for converting the output of the DC converter into DC, and an analog / digital converter for converting the output of the DC converter into a digital value with higher resolution as the output level increases. Insulation monitoring device for ground wiring type electric circuits.