JPH07128387A - Insulation monitor for line of isolated neutral wiring system - Google Patents

Abstract

PURPOSE:To provide an insulation monitor for the line in an isolated neutral wiring system in which the ground impedance can be detected positively while preventing dielectric deterioration during measurement. CONSTITUTION:Ground impedances Z1, Z2 are formed between the lines 5, 6 of isolated neutral wiring system and the earth 8a. The insulation monitor comprises impedance elements Z3, Z4 and a resistor RA connected between the lines 5, 6 and the earth 8b, an amplifier 14 and a rectifying/smoothing circuit 15 for detecting the currents flowing through the impedance elements Z3, Z4, switching elements 11, 12 for selecting the line 5 or 6, sample & hold circuits 16, 17 for sampling detection values related to the lines 5 or 6, an adder circuit 18, a subtractor circuit 19, and a circuit 21 for comparing an output signal from the subtractor circuit 19 with a predetermined reference level set at a reference circuit 22.

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 when any one wire of the ungrounded electric circuit is connected to the ground with a low impedance conductor. It is specified to operate when the current value becomes 2 mA or more.

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 by the human body at 2 mA or less even if the human body contacts 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 a configuration in which a certain amount of current is constantly applied is made, 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 a non-grounded wiring type insulation monitoring apparatus capable of reliably detecting ground impedance and preventing insulation deterioration during measurement.

[0006]

According to the present invention, there is provided an insulating transformer having a primary input side to which AC power is supplied, a first electric line and a second electric line connected to a secondary output side of the insulating transformer, and Detecting the sum of the impedance element connected between the first electric path or the second electric path and the ground, the current flowing through the impedance element, and the current flowing through the resistance capacitance formed between the first electric path or the second electric path and the ground. For detecting the current, a switch means for selecting either the first electric path or the second electric path as a current source flowing through the impedance element, and a first electric current output from the current detecting means when the first electric path is selected. Computation means for adding the detection value and the second detection value output from the current detection means when the second electric circuit is selected, and the output from the computation means and a predetermined reference level are compared. A path of the insulation monitoring device ungrounded wiring system, characterized in that it comprises a comparing means for it.

The present invention is also characterized in that the impedance element includes a series circuit or a parallel circuit composed of a resistor and a reactance element.

Further, according to the present invention, an offset means for canceling a DC component of a signal and an offset level generating means for generating an offset level of the offset means are provided between the current detecting means and the comparing means. Prepare,
The power supply of the offset level generating means is supplied from the secondary output side of the isolation transformer.

According to the present invention, the arithmetic means includes first and second sampling means for sampling the output from the current detecting means in synchronization with the switching operation of the switch means, and the first sampling means. And an adding means for adding the output from the second sampling means.

[0010]

According to the present invention, the primary input side is provided with an insulating transformer, and the secondary output side of this insulating transformer is connected to the first electric path and the second electric path to thereby connect the non-grounded wiring. By forming an electric path of the method and connecting an impedance element between the first electric path or the second electric path and the ground, when an insulation failure occurs between the first electric path or the second electric path and the ground. A ground fault current will flow through the impedance element. At this time, it is preferable to use a high impedance element having a value of, for example, about 1 MΩ, which can prevent insulation deterioration during measurement.

When the impedance element is connected to the first circuit, a ground fault current flows through the ground impedance between the second circuit and the ground, while the impedance element is connected to the second circuit. In this case, the ground fault current flows through the ground impedance between the first electric path and the ground. Therefore, the switch means selects either the first electric path or the second electric path as the current source flowing through the impedance element, and the current detecting means detects the current flowing through the impedance element, whereby the first electric path and the second electric path are detected. Both of the insulation defects can be detected.

Further, the ground fault current flowing when the first electric path is selected is measured as the first detection value, and the ground fault current flowing when the second electric path is selected is measured as the second detection value. The first detection value and the second detection value obtained in this way are added to calculate a total value of these values, and the total value is treated as an index of insulation evaluation. It is possible to evaluate the electric circuit evenly. Then, by comparing the total value with a predetermined reference level and determining the insulation failure of the first electric path or the second electric path when the total value exceeds a predetermined reference level, for example, an alarm is issued and used. It is possible to notify a person of danger such as electric leakage.

More specifically, FIG. 1 is a circuit diagram for explaining the principle of the present invention. In FIG. 1A, one end of a resistor R for detecting a ground fault current is connected to a first electric path 5. FIG. 1B shows a case where one end of the resistor R for detecting the ground fault current is connected to the second electric path 6.

First, referring to FIG. 1A, the insulating transformer 2
AC power source 1 such as commercial AC power is connected to the primary coil 3 of the above, and the first electric path 5 and the second electric path 6 are connected to the secondary coil 4 of the insulating transformer 2 to form a non-ground wiring type electric path. Is forming. Further, the first electric line 5 and the second electric line 6
It is assumed that the insulation failure occurs in the first electric path 5 and the ground impedance Z1 of the first electric path 5 and the ground impedance Z2 of the second electric path 6 are formed. At this time, assuming that the voltage generated in the secondary coil 4 is V, the currents flowing in the ground impedances Z1 and Z2 are i1 and i2, respectively, and the current flowing in the resistor R is i3, Z1 · i1 + Z2 · i2 = V (1) Z1 · i1 + R · i3 = 0 (2) i1 = i2 + i3 (3) The following three expressions hold. When the current i3 is obtained from these equations and the absolute value | Va | of the voltage Va generated across the resistor R is further obtained, the following equation (4) is obtained.

[0015]

[Equation 1]

On the other hand, in FIG. 1B, when one end of the resistor R is connected to the second electric path 6, Z1 · i1 + Z2 · i2 = V (5) Z2 · i2- is used by using Kirchhoff's law. R · i3 = 0 (6) Three expressions of i1 = i2 + i3 (7) hold. When the current i3 is obtained from these equations and the absolute value | Vb | of the voltage Vb generated across the resistor R is further obtained, the following equation (8) is obtained.

[0017]

[Equation 2]

Then, by adding | Va | and | Vb |, from equations (4) and (8),

[0019]

[Equation 3]

Is calculated.

Next, the combined impedance Z1 · Z2 / (Z1 + Z2) of the ground impedances Z1 and Z2 is plotted on the horizontal axis, and the sum of absolute values of the voltages Va and Vb | Va | + | V.
The voltage V = 100 of the secondary coil 4 with b |
FIG. 2 shows the result of graphing the equation (9) under the condition of V and resistance R = 1 MΩ. As shown in FIG. 2, the total value | Va | + | Vb | is 10 when the combined impedance is 0Ω.
It shows a curve where the total value | Va | + | Vb | monotonously decreases as the combined impedance increases from 0V. Therefore, when either the first electric line or the second electric line is connected to the ground by a conductor having a low impedance, the value of the ground fault current flowing becomes, for example, 2 mA, and an insulation failure alarm is issued. , The combined impedance is 100V / 2mA = 50kΩ
And the total value | Va | + | Vb | at this time is 95.
Since it is 2 V, by setting this value to the reference level of the alarm, it becomes possible to reliably detect even if the insulation failure occurs in either the first electric path or the second electric path.
In addition, in the above description, even if the resistor R for detecting the ground fault current is an impedance element, it can be similarly applied.

Further, since the impedance element includes a series circuit or a parallel circuit composed of a resistance element and a reactance element, the ground impedances Z1 and Z of each electric path are provided.
2 has not only a pure resistance component but also a reactance component that changes the phase of the ground fault current, that is, when the DC resistance to ground of each circuit is extremely high but the capacitance to ground is low, causing insulation failure. Therefore, it is possible to surely detect.

Explaining in detail below, for example, the phase of the current due to the reactance component X1 of the ground impedance Z1 (= R1 + j · X1, j is an imaginary unit) of the first electric path deviates from the phase due to the resistance component R1 by 90 degrees. Become. For example, when the reactance component X1 is capacitive, the current phase advances 90 degrees.

At this time, when the impedance element for detecting the ground fault current is only the pure resistance component R, the absolute value | Vb | of the voltage generated across the impedance element is
Compared to the value when there is no reactance component of the ground impedance Z1, | R + R1 + j · X1 | / (R + R1)
However, even if the reactance component X1 increases, it does not change much.

On the other hand, when the impedance element for detecting the ground fault current has not only the pure resistance component R but also the reactance component X, the absolute value | Vb | of the voltage generated across the impedance element is the reactance of the ground impedance Z1. Compared to the value when there is no component, | R + R1 + j
・ (X + X1) | / | R + R1 + j · X | increases, so that it becomes sensitive to changes in the reactance component X1. Therefore, the impedance element for detecting the ground fault current includes a series circuit or a parallel circuit consisting of a resistance and a reactance element, so that even if the ground capacitance of each circuit is low and insulation failure occurs, it can be detected reliably. can do.

Further, by providing an offset means for canceling the DC component of the signal between the current detecting means and the comparing means and an offset level generating means for generating the offset level of the offset means, the current detecting means is provided. When the value of the ground fault current detected by the means includes a DC component and a fluctuation component, only the fluctuation component can be amplified to improve the measurement sensitivity, and the saturation of the amplifier due to the DC component can be prevented. . Furthermore, when the AC power supplied to the isolation transformer fluctuates, the value of the ground fault current detected by the current detection means also fluctuates accordingly, but the power source of the offset level generation means is the secondary output of the insulation transformer. By being supplied from the side, the offset level also changes according to the voltage fluctuation of the AC power. Therefore, the output from the offset means cancels the influence of the voltage fluctuation of the AC power, and a signal with a good S / N ratio can be obtained.

Further, the arithmetic means is synchronized with the switching operation of the switch means, and first and second sampling means for sampling the output from the current detecting means, the output from the first sampling means and the second sampling means. By including an adding unit for adding the outputs from the current detection unit and the first detection value output from the current detection unit at the time of connection with the first electric line, and the current detection unit at the time of connection with the second electric line. The addition operation with the second detection value can be easily realized.

[0028]

FIG. 3 is a block diagram showing the overall construction of an embodiment of the present invention. The insulation monitoring device for the non-grounded wiring type circuit is, for example, 100 V effective value from the commercial AC power supply 1.
Isolation transformer 2 in which the AC power is supplied to the primary coil 3
, Electric paths 5, 6 respectively connected to the secondary coil 4 of the insulating transformer 2, impedance elements Z3, Z4 and a resistance RA connected between the electric path 5 or between the electric path 6 and the ground 8b, and an impedance element Z3, An amplifier 14 and a rectifying / smoothing circuit 15 for detecting a current flowing through Z4,
The switching elements 11 and 12 for selecting either the electric path 5 or the electric path 6 as a current source flowing through the resistor RA and the impedance element Z3 or Z4, and the detection value Va output from the rectifying / smoothing circuit 15 when the electric path 5 is selected are A sample and hold circuit 16 for sampling, and a sample and hold circuit 1 for sampling the detection value Vb output from the rectifying and smoothing circuit 15 when the electric path 6 is selected.
7, a timing generation circuit 10 for generating control timing pulses for the switching elements 11 and 12 and the sample and hold circuits 16 and 17, and an adder circuit 1 for adding the outputs of the sample and hold circuits 16 and 17.
8, a subtraction circuit 19 for canceling the DC component of the signal from the addition circuit 18, a reference circuit 20 for generating an offset level of the subtraction circuit 19, an output signal from the subtraction circuit 19 and a reference circuit 22. A comparison circuit 21 for comparing with a predetermined reference level, a meter circuit 23 for quantitatively displaying the output signal from the subtraction circuit 19, and an acoustic alarm 25 such as a buzzer based on the judgment result of the comparison circuit 21.
And a drive circuit 24 for driving an optical alarm 26 such as a lamp.

The electric lines 5 and 6 are connected to an electric equipment 7 provided in a hospital, a clinic, etc. on the basis of the non-grounded wiring system, and insulation failure is equivalently provided between the electric line 5 and the ground 8a. A ground impedance Z1 is formed, while a ground impedance Z2 equivalently representing insulation failure is formed between the electric path 6 and the ground 8a. Further, a transformer 27 is connected to the electric paths 5 and 6, and a DC voltage P smoothed through a rectifying / smoothing circuit 28 is supplied as a power source of the reference circuit 20.

Next, the operation will be described. When only the switching element 11 is turned on by the timing generation circuit 10, the ground path current ia is formed in the path of the electric path 5, the impedance element Z3, the switching element 11, the resistor RA, the ground 8b, the ground 8a, the ground impedance Z2, and the electric path 6.
Flows. At this time, a voltage signal of ia × RA is generated at both ends of the resistor RA, the voltage signal is amplified by the amplifier 14, the voltage signal is smoothed by the rectifying / smoothing circuit 15, and the envelope of the signal is detected. Va can be obtained. The detected value Va is sampled by the sample hold circuit 16 whose timing is controlled by the timing generation circuit 10 and held for a predetermined time.

On the other hand, when only the switching element 12 is turned on by the timing generation circuit 10, the electric path 6, the impedance element Z4, the switching element 12, and the resistor R
A ground fault current ib flows through a route of A, ground 8b, ground 8a, ground impedance Z1, and electric path 5. At this time, a voltage signal of ib × RA is generated at both ends of the resistor RA, the voltage signal is amplified by the amplifier 14, the voltage signal is smoothed by the rectifying / smoothing circuit 15, and the envelope of the signal is detected.
The detection value Vb can be obtained. The detected value Vb is sampled by the sample hold circuit 17 whose timing is controlled by the timing generation circuit 10 and held for a predetermined time.

In this way, the detected value Va held by the sample hold circuit 16 and the detected value Vb held by the sample hold circuit 17 are input to the adder circuit 18, and the total value | V
a | + | Vb | is obtained. The two detection values Va,
Since Vb is detected at different timings, there is no influence of the phase, and absolute value addition is performed.

The signal output from the adder circuit 18 is input to the subtractor circuit 19, the DC component is canceled by the offset level set by the reference circuit 20, and only the fluctuation component of the signal is emphasized. And is amplified at a predetermined amplification rate. The rectifying and smoothing circuit 2 is used as the power source of the reference circuit 20.
Since the DC voltage P from 8 is supplied, the voltage fluctuation of the AC power supplied to the isolation transformer and the offset level fluctuate in phase with each other, and as a result, the output of the subtraction circuit 19 cancels each other out. .

The output signal from the subtraction circuit 19 is input to the comparison circuit 21 and is compared with the predetermined reference level set by the reference circuit 22 in magnitude. For example, if the predetermined reference level is set to a value corresponding to 95.2 V shown in FIG. 2 and the output signal of the subtraction circuit 19 is smaller than this value, the combined impedance of the ground impedances Z1 and Z2 is larger than 50 kΩ. Therefore, it is determined that there is no insulation failure in the electric paths 5 and 6. On the other hand, the subtraction circuit 19
If the output signal of is higher than this value, the combined impedance of the ground impedances Z1 and Z2 is 50 kΩ or less, and it is determined that insulation failure has occurred in the electric paths 5 and 6.

When the comparison circuit 21 determines that insulation failure has occurred in the electric lines 5 and 6, an insulation failure signal is transmitted to the drive circuit 24 to cause the audible alarm 25 to generate a warning sound or an optical alarm. A warning light is displayed on the device 26 to notify the user or doctor. In order to display the degree of insulation failure in analog, the output signal from the subtraction circuit 19 is the meter circuit 23.
Is displayed quantitatively by.

FIGS. 4 and 5 are circuit diagrams showing a specific structure of the insulation monitoring apparatus shown in FIG. First, in FIG. 4, the impedance element Z3 connected to the electric path 5 is formed of a series circuit of a resistor R11 and a capacitor C11. For example, the resistor R11 has a resistance of 680 kΩ and a capacitor C11.
11 is preferably set to 3900 pF. This is because when the power supply frequency f is 60 Hz, the capacitor C1
1 reactance X11 is 1 / (2π ・ 60 ・ 3900)
pF) = 680 kΩ, which is about the same as the resistance R11 and the series impedance is | R11 + j · X11.
This is because the impedance becomes as high as | = 1 MΩ.
As a result, it is possible to detect with high sensitivity without lowering the insulation of the electric path 5 and even if the ground impedances Z1 and Z2 are capacitive. The same applies to the impedance element Z4 connected to the electric path 6, in which the resistance R12 is 680 kΩ and the capacitor C12 is 39.
It is preferably set to 00 pF.

For the switching elements 11 and 12, it is preferable to use a semiconductor relay incorporating a light emitting diode in order to improve the insulation, and the transistors TR1 and TR2 are responded to in response to the control signals SA and SB from the timing generation circuit 10.
By turning on the built-in light emitting diode,
The semiconductor relay turns on or off.

The other ends of the switching elements 11 and 12 are connected to each other and connected to one end of the resistor RA. The other end of the resistor RA is connected to the ground 8b. The resistance value of the resistor RA is selected to be about 1/10 of that of the impedance elements Z3 and Z4, that is, about 100 kΩ. Switching element 1
When a ground fault current flows through the resistor RA due to conduction of either one of 1 and 12, and a voltage signal is generated across the resistor RA,
It is amplified by the amplifier 14 and supplied to the rectifying / smoothing circuit 15 shown in FIG. A noise absorbing capacitor is connected in parallel to both ends of the resistor RA.

The timing generation circuit 10 includes a timer IC 1
6A and 6B, the control signal SA and SB shown in (1) and (2) of FIG.
A pulse with a duty of 50% is generated. On the other hand, the control signal SB is the time constant circuit of the resistor R13 and the capacitor C13,
The waveform is shaped by the NAND element IC2, the NOT element IC3, etc., and the sampling signal SC is generated.
T element IC5, resistor R14, capacitor C14, NAN
Waveform is shaped by D element IC6, NOT element IC7, etc.
A sampling signal SD is created. The power supply circuit 40
Supplies DC voltage + VC, -VC as a power source for each circuit.

Next, referring to FIG. 5, the voltage signal generated across the resistor RA is amplified by the amplifier 14 to, for example, an amplification factor of 1.
Is amplified by and is input to the rectifying / smoothing circuit 15. The rectifying / smoothing circuit 15 includes diodes D1 and D2, an operational amplifier IC8.
It has a full-wave rectifier circuit made up of, for example, a smoothing circuit made up of a capacitor C15, a resistor 15, an operational amplifier IC9, etc., and smoothes the voltage signal to detect the envelope of the signal.

The sample and hold circuit 16 has an analog switch SW1 which is opened and closed by a sampling signal SC.
, Sampling capacitor C16, operational amplifier IC
And has a function of holding the voltage value charged in the sampling capacitor C16 by conducting the analog switch SW1 for a predetermined time even after the analog switch SW1 is cut off. Similarly, the sample hold circuit 17 includes an analog switch S that opens and closes according to the sampling signal SD.
It is composed of W2, a sampling capacitor C17, and an operational amplifier IC11.

The signals held by the sample and hold circuits 16 and 17 are input to the adder circuit 18 including the operational amplifier IC12 and added, and the total value of the detected values Va and Vb is calculated.

The subtracting circuit 19 has a subtracter including the IC 14 and a non-inverting amplifier including the IC 15, and cancels the DC component of the signal from the adding circuit 18 based on the offset level output from the reference circuit 20. After that, the remaining fluctuation component is amplified at a predetermined amplification rate. The reference circuit 20 is shown in FIG.
And a resistor series circuit for dividing the DC voltage P supplied from the rectifying / smoothing circuit 28 shown in FIG. 4, and a buffer IC 13 for amplifying the offset level set by the resistor series circuit with an amplification factor of 1. .

The output of the subtraction circuit 19 is input to the comparison circuit 21 and the meter circuit 23 through a low pass filter composed of a resistor R16 and a capacitor 18. The meter circuit 23 includes a buffer IC 17 and a meter M1 that analog-displays its output.

The comparison circuit 21 is the power supply circuit 4 shown in FIG.
A resistor series circuit that divides the DC voltage + VC supplied from 0, and a comparator IC16 that compares the reference level set by the resistor series circuit and the output of the subtraction circuit 19 with each other.
Have and. When the output of the subtraction circuit 19 becomes higher than the reference level, the comparator IC16 outputs a high level signal, the transistor TR3 of the next drive circuit 24 becomes conductive, and the relay RL1 operates. Based on the output of the relay RL1, the acoustic alarm 25 such as a speaker and the optical alarm 26 such as a lamp shown in FIG. 3 operate to notify the user or the like of insulation failure.

FIG. 6 is a timing chart showing the operation of the insulation monitoring apparatus shown in FIGS. 3, 4 and 5. The timing generation circuit 10 generates a pulse having a cycle of 10 seconds and a duty of 50%, and the control signal S shown in FIG.
When A becomes high level, only the switching element 11 becomes conductive, the ground fault current ia flows through the impedance element Z3 and the resistor RA, and a voltage signal of ia × RA is generated at both ends of the resistor RA. When the voltage is amplified by the amplifier 14 and the voltage signal is smoothed by the rectifying / smoothing circuit 15, FIG.
The detection signal Q1 shown in is obtained. Next, the sampling signal SC shown in FIG. 6 (5) is supplied from the timing generation circuit 10 to the sample hold circuit 16, and the detection signal Q1 is sampled at the rising time thereof to detect the detection value Va.
Is held for a predetermined time.

On the other hand, when the control signal SA shown in FIG. 6 (1) becomes low level and the control signal SB shown in FIG. 6 (2) becomes high level, only the switching element 12 becomes conductive and the impedance elements Z4 and Z4. When the ground fault current ib flows through the resistor RA and a voltage signal of ib × RA is generated across the resistor RA, the voltage signal is amplified by the amplifier 14 and the voltage signal is smoothed by the rectifying / smoothing circuit 15. The detection signal Q2 shown in 4) is obtained. Next, the sampling signal SD shown in (6) of FIG. 6 is supplied from the timing generation circuit 10 to the sample hold circuit 17, the detection signal Q2 is sampled at the rising time thereof, and the detection value Vb is held for a predetermined time. Although the detection signals Q1 and Q2 are shown separately for easy understanding, both are signals output from the rectifying / smoothing circuit 15 and are superimposed on each other.

In this way, the detected value Va when the impedance element Z3 is energized and the detected value Vb when the impedance element Z4 is energized are detected for each cycle of the timing generation circuit 10, and are provided at a stage subsequent to the sample hold circuits 16 and 17. The total value | Va | + | Vb |
Is calculated.

[0049]

As described in detail above, according to the present invention, the insulation deterioration during the measurement is prevented, and the total value of the first detection value regarding the first electric path and the second detection value regarding the second electric path is evaluated for insulation. Therefore, it is possible to equally comprehensively evaluate the symmetric first electric path and the second electric path. Then, by comparing the total value with a predetermined reference level,
It is possible to reliably determine the insulation failure of each electric circuit.

Even when the ground impedance of each electric path includes a reactance component, it is possible to reliably detect the insulation failure.

Since the S / N ratio of the ground fault current detection signal is improved, highly reliable insulation determination can be performed.

[Brief description of drawings]

FIG. 1 is a circuit diagram for explaining the principle of the present invention.

FIG. 2 is a graph showing a relationship between a total voltage value | Va | + | Vb | and a combined impedance of ground impedances Z1 and Z2.

FIG. 3 is a block diagram showing the overall configuration of an embodiment of the present invention.

FIG. 4 is a circuit diagram showing a specific configuration of the insulation monitoring device shown in FIG.

5 is a circuit diagram showing a specific configuration of the insulation monitoring device shown in FIG.

6 is a timing chart showing the operation of the insulation monitoring device shown in FIGS. 3, 4, and 5. FIG.

[Explanation of symbols]

 1 Commercial AC Power Supply 2 Insulation Transformer 3 Primary Coil 4 Secondary Coil 5 and 6 Electrical Circuit 7 Electrical Equipment 8a and 8b Grounding 10 Timing Generation Circuit 11 and 12 Switching Element 14 Amplifier 15 Rectifying and Smoothing Circuit 16 and 17 Sample and Hold Circuit 18 Adder Circuit 19 Subtraction circuit 20, 22 Reference circuit 21 Comparison circuit 23 Meter circuit 24 Drive circuit 25 Acoustic alarm 26 Optical alarm Z1, Z2 Ground impedance Z3, Z4 Impedance element RA Resistance

Claims (4)

[Claims] 1. An insulating transformer to which AC power is supplied to a primary input side, a first electric line and a second electric line connected to a secondary output side of the insulating transformer, a first electric line or a second electric line, and grounding. An impedance element connected between the impedance element and a current detecting unit for detecting a sum of a current flowing through the impedance element and a current flowing through a resistance capacitance formed between the first electric path or the second electric path and the ground; A switch means for selecting either the first electric path or the second electric path as a current source flowing through the impedance element, a first detection value output from the current detecting means at the time of selecting the first electric path, and a second electric path Computation means for adding the second detection value output from the current detection means at the time of selection, and comparison means for comparing the output from the computation means with a predetermined reference level are provided. A non-ground wiring type electric line insulation monitoring device. 2. The insulation monitoring device for a non-grounded wiring type electric line according to claim 1, wherein the impedance element includes a series circuit or a parallel circuit including a resistance and a reactance element. 3. An offset means for canceling a DC component of a signal and an offset level generating means for generating an offset level of the offset means are provided between the current detecting means and the comparing means, 2. The insulation monitoring apparatus for a non-grounded wiring type electric circuit according to claim 1, wherein the power supply of the offset level generating means is supplied from the secondary output side of the insulation transformer. 4. The computing means synchronizes with a switching operation of the switch means, and first and second sampling means for sampling an output from the current detecting means, and an output from the first sampling means. 2. An insulation monitoring device for a non-grounded wiring type electric line according to claim 1, further comprising: an addition unit for adding the outputs from the second sampling unit.