JP4506959B2 - Insulation monitoring device - Google Patents

Description

  The present invention relates to an insulation monitoring device, and more particularly to a technique for measuring an insulation resistance value in order to monitor an insulation state of an electric circuit.

  A method of monitoring the insulation state of the distribution system by the magnitude of the leakage current is widely used. However, with the spread of electronic devices, the leakage current that flows through the capacitance of noise filters becomes larger than the leakage current that flows through the insulation resistance, and the leakage current is the vector sum of the capacitance component and the resistance component. It is difficult to judge whether the insulation state is good or not just by monitoring.

  In order to make it easier to judge the quality of the insulation state, it is effective to obtain only the component that flows through the insulation resistance by removing the capacitance component contained in the leakage current. A method of calculating the insulation resistance from the signal voltage value and the resistance leakage current value due to the signal voltage, by applying the signal for use and extracting the applied frequency component from the detected leakage current as the resistance leakage current due to the signal voltage Has been proposed (see, for example, Patent Document 1).

  However, since the application device for the insulation resistance monitoring signal and the band pass filter are required, the device becomes large and expensive, the application signal is superimposed on the main circuit, the load equipment malfunctions, the application signal Because it is unavoidable to suppress the frequency to a low frequency of 20 Hz or less and a low voltage of about 2 V or less, the input / output conversion loss of the injection transformer at a low frequency is increased and the applied signal leakage current is reduced to several tens μA or less. There are drawbacks such as that the measurement accuracy of the insulation resistance cannot be increased due to an increase in the input / output conversion loss of the detection ZCT.

  In order to solve the above-mentioned problems, several methods have been proposed in which no signal voltage is applied to the circuit under measurement.

  One of these methods that does not apply the signal voltage is a resistance leakage due to the phase relationship between the harmonic leakage current vector and the harmonic ground voltage vector at the representative order of the harmonic component contained in the leakage current and ground voltage of the circuit under test. A method of obtaining an insulation resistance by obtaining a current and dividing a harmonic voltage value of a representative order by this resistance leakage current value (see, for example, Patent Document 2).

In another method in which the signal voltage is not applied, the simultaneous measurement is performed based on the scalar amounts of the harmonic leakage current component and the harmonic ground voltage component in the two representative orders of the harmonic component included in the leakage current and the ground voltage of the circuit under test. An insulation resistance component is obtained by an equation, and the quality of the insulation state is judged by this magnitude. According to this, since a band-pass filter and a phase shift correction device are not required, the device can be miniaturized (see, for example, Patent Document 3).
JP-A-1-143971 Japanese Patent Laid-Open No. 6-043196 JP 2003-177154 A

  However, in the example of Patent Document 2, a device that corrects a phase shift of either or both of a band-pass filter for both a leakage current circuit and a voltage circuit, a leakage current detection zero-phase current transformer, and a ground voltage detection transformer. It is difficult to connect the lead-out wiring to the insulation deterioration point when detecting the ground voltage required for calculating the insulation resistance value. There is a problem that it must be a place away from the location where the leakage current is generated, and the detected ground voltage contains only a harmonic component attenuated to about several percent of the theoretical value. There are drawbacks such as the fact that the harmonic component value cannot be obtained correctly and the measurement accuracy of the insulation resistance is lowered.

  Also, the example of Patent Document 3 has a drawback that the measurement accuracy of the insulation resistance is lowered because the harmonic component value of the ground voltage cannot be obtained correctly as in the above example.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an insulation monitoring device that enables a small, inexpensive, and highly accurate insulation resistance value measurement.

To achieve the above object, the insulation monitoring device of claim 1, a ground voltage detecting means for detecting a ground voltage of the measured three-phase alternating current circuit, the leakage may to earth from the measured three-phase alternating current circuit Harmonic leakage current detecting means for detecting a leakage current component value of a predetermined order in the harmonic component included in the current, a reference phase indicating a phase with respect to a detection reference time at a predetermined order of the ground voltage, and a predetermined order of the leakage current A phase detection unit that detects a phase difference from a reference phase indicating a phase with respect to a detection reference time in the phase, and a phase relationship between the leakage current and the ground voltage in a predetermined order detected by the phase detection unit. circuit ground insulation resistance R and ground conductance .omega.C (omega is 2 [pi] f, f is the fundamental frequency, C is the capacitance of the leakage current) and ωCR calculating means for calculating the value of the product ωCR with, A ground voltage V detected by serial ground voltage detecting means, and the leakage current component value I _gn given order n detected (n is a multiple of 3) by the harmonic leakage current detecting means was calculated by the ωCR calculating means ωCR Is given to a predetermined relational expression R = F (V, I _gn , ωCR) for deriving the ground insulation resistance R, and the ground insulation resistance calculation means for calculating the ground insulation resistance R and the ground insulation resistance calculation means Output means for outputting information on the insulation state of the circuit under test based on the calculated ground insulation resistance R.

According to a second aspect of the present invention, there is provided the insulation monitoring apparatus according to the first aspect, wherein the output means is the ground insulation calculated by the ground insulation resistance calculating means as information relating to the insulation state of the three-phase AC circuit to be measured. Displaying, recording, external output or reporting that the resistance R has become a predetermined value or less, or that the resistance leakage current value calculated based on the ground insulation resistance R has become a predetermined value or more ; At least one of the ground insulation resistance value R and the resistance leakage current value is classified into at least two areas such as a safety area and a dangerous area according to the magnitude, and is displayed, recorded, externally output or notified. It is characterized by doing either or both.

The insulation monitoring device according to claim 3, in the invention of claim 1 or 2, wherein the ground insulation resistance calculation means, ground voltage V according to claim 1, leakage current component value I _gn, based ωCR following formula,
R = (V / I _gn ) × ((1+ (ωCR) ² ) ^0.5 × (1+ (nωCR) ² ) ^0.5 ― (1+ (ωCR) ² ) ^0.5 ) / (1+ (nωCR) ² ) ^0.5 )
Or
R = (V / I _gn ) × ((1+ (ωCR) ² ) ^0.5 / (1+ (nωCR) ² ) ^0.5 ) / ((1 / (1+ (ωCR) ² ) ^0.5 ) + (1 / (1+ (nωCR) ² ) ^0.5 ))
Is used as the relational expression R = F (V, I _gn , ωCR).

  The present invention configured as described above uses the ground voltage scalar quantity of the circuit to be measured and the scalar quantity of the harmonic component included in the leakage current, the leakage current n-order harmonic component, n-order ground admittance, and calculation formula induction. The most important feature is to obtain the insulation resistance from the relationship between the nth-order theoretical harmonic component of the ground voltage used as the medium in the stage and the harmonic first-order virtual leakage current used as the medium in the calculation formula stage. To do.

  According to the insulation monitoring device of the present invention, since the signal voltage applying device is unnecessary, it can be made small and inexpensive. Also, since it depends only on the harmonic component of the voltage to be measured and the leakage current of the circuit to be measured, and not on the harmonic component of the voltage that is difficult to detect in the actual circuit, the insulation resistance value of the electric circuit is highly accurate and economical. Can be measured automatically.

  Therefore, it is easy to accurately detect changes over time in insulation deterioration and issue an alarm, and it is possible to prevent accidents by making it possible to perform inspection and maintenance in advance.

  Hereinafter, preferred embodiments of an insulation monitoring apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

The present invention, the leakage current component value I _gn and insulation resistance R and ground conductance EnuomegaC (n in any order n in harmonic components included in the leakage current I _g to the ground from the circuit under test is an integer, omega = 2 [pi] f , f is the fundamental frequency, C is the first and the relational expression, the leakage current component value at order n of the above representation of the n-th theoretical ground voltage E _n using n-th ground admittance Y _n consisting of capacitance) I _gn , nth-order ground admittance Y _n , ground voltage V, harmonic primary virtual leakage current component I _g1, harmonic primary ground admittance Y ₁ consisting of insulation resistance R and ground conductance ωC, and nth-order theoretical it is to provide a method and an insulation monitoring device for calculating the insulation resistance R without depending on the harmonic component values of the voltage to ground by solving a second equation which represents the ground voltage E _n as simultaneous equations.

At any order n in harmonics first relational expression contained in the leakage current I _g, the leakage current component value I _gn, from a theoretical ground voltage E _n and the insulation resistance R and ground conductance nωC in order n shown by comprising ground admittance _{Y n I gn = Y n ×} E n ................................................... formula (1)
Guide as a basis.
Y _n = ((1 / R) ² + (nωC) ² ) ^0.5 …………… Formula (2)
= (1+ (nωCR) ² ) ^0.5 × (1 / R) ............ Formula (3)
Substituting equation (3) into equation (1), I _gn = (1+ (nωCR) ² ) ^0.5 × (1 / R) × E _n ... equation (4)
E _n = (I _gn × R) / (1+ (nωCR) ² ) ^0.5 obtained from this ......... Formula (5)
Is the first relational expression.

The second relational expression harmonic primary voltages to ground E ₁ as shown in (b) of FIG. 1, the theoretical ground voltage E _n in any order n in harmonics, harmonic primary and n E ₁ = ((I _g1 / I _gn ) + (Y _n / Y ₁ )) × E obtained by multiplying the next leakage current component ratio by the sum of the harmonic first order and nth order ground admittance component ratio _n ............ Formula (6)
Guide as a basis.
Since the harmonic primary ground voltage E ₁ in the equation (6) can be regarded as almost equal to the ground voltage V, E ₁ ≈V ……………………………… (7)
Y ₁ = (1+ (ωCR) ² ) ^0.5 × (1 / R) ............ Formula (8)
I _g1 = Y ₁ × E ₁ ≈ (1+ (ωCR) ² ) ^0.5 × (V / R) ...... Formula (9)
Y _n = (1+ (nωCR) ² ) ^0.5 × (1 / R) ............ Formula (10)
Therefore, substituting the formulas (7) to (10) into the formula (6) and rearranging them results in V = (((1+ (ωCR) ² ) V + I _gn · R (1+ (nωCR) ² ) ^0.5 ) / (I _gn · R (1+ (ωCR) ² ) ^0.5 )) E _n ......... Formula (11)
E _n = (I _gn · R (1+ (ωCR) ² ) ^0.5 obtained from this ) V / ((1+ (ωCR) ² ) V + I _gn · R (1+ (nωCR) ² ) ^0.5 ) ............ Formula (12)
Is the second relational expression.

R = (V / I _gn ) × ((1+ (ωCR) ² ) ^0.5 × (1+ (nωCR) ² ) ^0.5 obtained by solving the equations (5) and (12) as simultaneous equations — (1+ (ωCR) ² ) ^0.5 ) / (1+ (nωCR) ² ) ^0.5 ) Equation (13)
Is an equation for calculating the insulation resistance value R.

Theoretically ground voltage E _n harmonics primary voltages to ground E ₁ second relational expression of harmonic order n, as shown in the (B) 1, harmonics primary and n next ground admittance component ratio And E _n = ((Y ₁ / Y _n ) − (I _gn / I _g1 )) E _1, which is obtained by multiplying the difference between the first harmonic and the n-th order leakage current component ratio ( ₁ ) 14)
Can be guided as a basis.

E _n = (((1+ (ωCR) ² ) ^0.5 obtained by substituting Equation (10) from Equation (7) into Equation (14) and rearranging. ) / ((1+ (nωCR) ² ) ^0.5 )) V-I _gn · R / (1+ (ωCR) ² ) ^0.5 ............ Formula (15)
Becomes another second relational expression, and R = (V / I _gn ) × ((1+ (ωCR) ² ) ^0.5 / (1+) obtained by solving the equations (5) and (15) as simultaneous equations. (NωCR) ² ) ^0.5 ) / ((1 / (1+ (ωCR) ² ) ^0.5 ) + (1 / (1+ (nωCR) ² ) ^0.5 )) Equation (16)
Is another formula for calculating the insulation resistance value R.

Formula (13) or Formula (16) is
R = F (V, I _gn , ωCR) ……………… Formula (17)
This indicates that the measurement does not depend on the harmonic component of the ground voltage that is susceptible to attenuation.

The ground voltage V is given by the voltage measurement circuit, and the harmonic n-th order component I _gn of the leakage current is given by a method such as Fourier expansion of the leakage current detected by the zero-phase current transformer, so that the remaining ωCR is the measured circuit. It shows that the insulation resistance value R can be calculated if given as a specific numerical value.

When the circuit under test is a single-phase AC circuit, ωCR can be expressed as follows.
The electrostatic capacitance component I _gc and the resistance component I _gr of the leakage current are I _gc = ωCV (18)
I _gr = V / R ……………… Formula (19)
And I _gc / I _gr = (ωCV) / (V / R) = ωCR
ωCR = I _gc / I _gr ……………… Formula (20)
As described above, ωCR is expressed as a ratio of the capacitance component I _gc and the resistance component I _gr of the leakage current.

For the circuit to be measured is a three-phase alternating current circuit, for the leakage current detected by the ZCT is a vector sum of each phase leakage current, harmonics 3 m (m is an integer) of the leakage current in the following non Since the magnitude and phase depend on the imbalance of each phase admittance, and the ratio of the capacitance component and the resistance component cannot be obtained, ωCR is obtained at the harmonic 3 m order where all three phases are in phase. .
The capacitance component I _gcn and the resistance component I _grn of the leakage current in the harmonic 3 m-th order are I _gcn = 3 m ωCE _n (Equation 21)
I _grn = E _n / R ......... Formula (22)
I _gcn / I _grn = (3 m ωCE _n ) / (E _n / R) = 3 m ωCR
ωCR = (I _gcn / I _grn ) / (3 m ) (23)
As,? Cr is expressed as a value obtained by dividing the capacitance component I _gcn the ratio of the resistance component I _grn leakage current in order 3m of.

The ratio of the capacitance component I _gcn of the leakage current, that is, the resistance component I _grn , is obtained from the increasing tendency of the even-order harmonic component value calculated when the leakage current is Fourier-expanded.

  In many loads, even harmonic components are detected in the leakage current.

  FIG. 2 is a distribution diagram showing the leakage current harmonic component of the lamp load circuit, and the presence of even-order harmonic component values is recognized.

  Even in an experiment in which a ground simulation circuit consisting of a known resistance and capacitance is connected to a three-phase AC circuit that uses an inverter as a power source, depending on the presence of even-order leakage current harmonic components and the magnitude of the ground capacitance There is a tendency for the leakage current harmonic component to increase with the order.

  FIG. 3 shows harmonic component values of leakage current in two types of experiments conducted by changing the admittance of the ground simulation circuit.

  Black circles in FIG. 3 represent even harmonic components obtained by Fourier expansion of the leakage current when a ground simulation circuit is connected in parallel with a resistance of 150 kΩ and a capacitance of 0.047 μF, and a three-phase distorted AC voltage is applied. Expressed in order of order, only the 3n-th order (n is an integer) in which the leakage current of each phase of the three phases is in phase is extracted from even-orders.

  The white circles in FIG. 3 represent a ground simulation circuit having a resistance of only 75 kΩ, and the leakage current when a three-phase distorted wave AC voltage is applied is Fourier-expanded to represent even-order harmonic components in order. Only the next (n is an integer) is extracted and described.

  These even-order harmonic leakage current groups show an increasing tendency as the order increases as shown by the solid line in FIG. 3 when the ground capacitance exists, and when the capacitance is not included in FIG. As shown by the broken line, it is a flat straight line having no gradient.

  In this way, even-order harmonic leakage current groups are linear according to the increase in order, and when there is no capacitance, the even-order harmonic ground voltage is increased against the increase in order. Therefore, ωCR can be obtained by the method described below.

If the order A component of the harmonic even-order leakage current is I _gA , the order B component is I _gB , and the ground voltage of the order A and the order B is E _AB , then I _gA = E _AB × (1+ (AωCR) ² ) ^0.5 / R .... Formula (24)
I _gB = E _AB × (1+ (BωCR) ² ) ^0.5 / R Equation (25)
I _gB / I _gA = (1+ (BωCR) ² ) ^0.5 / (1+ (AωCR) ² ) ^0.5 Formula (26)
Rearranging equation (26), ωCR = ((I _gB ² -I _gA ² ) / (B ² I _gA ² -A ² I _gB ² )) ^0.5 ... Equation (27)
ΩCR is obtained as follows.

In practical use, Equation (27) is calculated between as many even orders as possible, and the average value is adopted, or the harmonic even-order leakage current group is calculated using a statistical method such as the least squares method as follows: I _g = a (x−1 + B
(I _g : even-order harmonic leakage current after statistical processing, a: gradient, x: even-order harmonic order, b: virtual leakage current in order 1)
By using as many even-order leakage current groups as possible (for example, calculating an average value of a plurality of ωCRs) ) The ωCR calculation error can be reduced.

  Note that some of the harmonic even-order leakage current components may have a value that protrudes compared to other order components, but this value is calculated due to the time width when the leakage current is time-division sampled. Since it is considered to occur, it is excluded from the application to the calculation for obtaining ωCR.

The ratio of ωCR, that is, the capacitance component I _{gcn of the} leakage current and the resistance component I _grn can also be obtained by determining the phase angle of the ground voltage and the leakage current.

FIG. 4 is a vector diagram showing the relationship between the ground voltage, the phase angle Φ of the leakage current, the leakage current resistance component I _gr, and the capacitance component I _gc .

  When the circuit under test is a single-phase AC circuit, the phase angles Φ and ωCR can be obtained from the ground voltage and the leakage current.

The ground voltage and leakage current from the effective power W obtained by integrating the product of the multi-point sampling instantaneous value of the ground voltage and the multi-point sampling instantaneous value of the leakage current and the apparent power VA which is the product of the effective value of the ground voltage and the effective value of the leakage current. Φ = cos ⁻¹ (W / VA) ............ Formula (28)
Can be obtained as follows.
I _gc / I _gr = tanΦ ............ Formula (29)
Therefore, from the equations (20) and (29), ωCR = tanΦ = tan (cos ⁻¹ (W / VA)) ............ Equation (30)
ΩCR is obtained as follows.

When the circuit to be measured is a three-phase AC circuit, the phase angle of the ground voltage and the leakage current is obtained at the harmonic 3 m-th order ( m is an integer) that is in phase with all three phases.

Harmonic components of ground voltage are often only attenuated in magnitude, and cannot be applied to obtain active power or apparent power, but leakage current components of the same order as the harmonic representative order component of ground voltage Therefore , the phase angle Φ _n with the harmonic component of the leakage current can be obtained by the following method.

The phase angle Φ _n of the ground voltage and leakage current in the harmonic 3 m order is the difference between the phase angle of the ground voltage and leakage current obtained by Fourier expansion of the ground voltage and leakage current with respect to the detection reference point.

但し

ωＣＲ＝ｔａｎΦ_n／３ｍ＝ｔａｎ（ｔａｎ^-1（ｂ_V／ａ_V）―ｔａｎ^-1（ｂ_I／ａ_I））／３ｍ …………式（３２）
のように求めることができる。

However,

ωCR = tan Φ _n / 3 m = tan (tan ⁻¹ (b _V / a _V ) −tan ⁻¹ (b _I / a _I )) / 3 m ............ formula (32)
Can be obtained as follows.

  An error may occur in the calculated value of the equation (32) due to the attenuation of the harmonic component value of the ground voltage. Therefore, in practical use, the equation (32) is calculated in as many orders as possible, By adopting the average value, the ωCR calculation error can be reduced.

  The insulation resistance can be calculated by substituting ωCR obtained by Expression (27), Expression (30), or Expression (32) into Expression (13) or Expression (16).

For a three-phase alternating current circuit, it calculates the insulation resistance only in harmonic 3 m th component of the leakage current.

  The calculation of the expression (13) or the expression (16) is performed for as many orders as possible, and the accuracy of calculating the insulation resistance is improved by a method of adopting the average value.

However, among the plurality of calculated values, some of the orders resulting in a calculation result that is far from other orders are excluded from the application to the calculation for obtaining the insulation resistance. The reason for the exclusion described above is that the calculation result is far from the other component orders. It is because it ends up.
Exclusion judgment methods such as excluding those with the standard deviation value exceeding the set value in the calculated value group may be excluded, but the selected order with the largest and smallest calculation results are excluded. A practically sufficient result can be obtained by using the average value of the calculation results in the remaining orders as the insulation resistance.

FIG. 5 is a diagram showing the input to the circuit under test and the insulation monitoring device. The insulation resistance R and the ground capacitance C forming the ground admittance of the circuit under test 1 are parallel to the ground. flowing leakage current Ig ₀ through the earth and transformer secondary side ground line 2 of TR.

The insulation monitoring device 6 receives the secondary output Ig of the leakage current Ig ₀ detected by the zero-phase current transformer 3 installed in the circuit under test 1 and the ground voltage V detected from the ground voltage existence phase.

  FIG. 6 is a block diagram showing an embodiment of the insulation monitoring apparatus of the present invention. In FIG. 6, reference numeral 6 denotes a monitoring device, which is composed of the following units. Reference numeral 3 denotes a leakage current detection zero-phase current transformer shown in FIG. 5, and the secondary output line 4 is input to the input unit 41 together with the ground voltage detection line 5. Reference numeral 51 denotes a power supply unit that supplies an operating voltage to the inside of the monitoring device. A / D conversion unit for converting to a digital value, 6b is a Fourier transform unit for extracting harmonic components of leakage current, 6c is a sampling and digital conversion instruction for the A / D conversion unit 6a, and the obtained digital value Is stored in the storage unit 6d and is an arithmetic processing unit for calculating an insulation resistance and a resistance leakage current by the method of the above embodiment. The arithmetic processing unit 6c also outputs an insulation resistance value and a resistance leakage current value, which are calculation results, to an output unit 6g described later.

  The output unit 6g gives the result obtained by the arithmetic processing unit 6c as visual information such as a display, a voice notification such as a buzzer, or a remote notification to the host device 10 through communication as information on the insulation state of the circuit under test. It is an output part for performing. The setting unit 6e gives a judgment value for alarm output and the like, and outputs the output value to the output unit 6a or the host device 10 when the calculated value of the insulation resistance or resistance leakage current reaches the set value. The output means is a visual display by a display device, a sound notification such as a buzzer, a notification and a recording of a calculation result and an abnormality occurrence time. The above-described alarm judgment value can be set and the alarm holding state can be canceled from the host device 10.

  The storage unit 6d or the host device 10 can continuously store the calculation results, and can be used for continuous recording of the insulation state, continuous monitoring of the progress of insulation deterioration, and retroactive checking.

  The arithmetic processing unit 6c calculates the resistance leakage current and outputs the value together with the insulation resistance value and the resistance leakage current value to the output unit 6g to display on the insulation resistance value indicator or the like or a buzzer. It is good also as a target of alarm output, such as.

  In addition, any one of insulation resistance, resistance leakage current, and capacitance leakage current is classified into at least two areas such as a safety area and a dangerous area depending on its magnitude, and is displayed, recorded, externally output or notified. You may make it do.

It is a relationship figure which shows the relationship of the ground voltage in the harmonic primary and n order for demonstrating the Example by this invention. It is a distribution map which shows the even-order harmonic component value group of the leakage current in a three-phase alternating current simulation circuit. It is a distribution map of the leakage current harmonic component in an actual load. It is a relationship figure which shows the phase angle of a ground voltage and a leakage current, and the relationship between a leakage current resistance component and an electrostatic capacitance component. It is a circuit diagram which shows the leakage current circuit and the input method to an insulation monitoring apparatus. It is a block diagram which shows the structure of the insulation monitoring apparatus by embodiment of this invention. It is explanatory drawing of the insulation monitoring system by a prior art (for example, patent document 1). It is explanatory drawing of the insulation monitoring system by a prior art (for example, patent document 2). It is explanatory drawing of the insulation monitoring system by the conventional Example (for example, patent document 3).

Explanation of symbols

V: Ground voltage E _{n of the} circuit to be measured Theoretical ground voltage I _{g at the} n-th harmonic: Leakage current I _{g1 of the} circuit to be measured: Virtual leakage current I at the first harmonic _gn : Leakage current R at the nth harmonic: Insulation resistance C: Ground-to-ground capacitance nωC: Ground conductance Y at the nth harmonic: ₁ ... Ground admittance at the first harmonic Y _n ... Ground admittance in the n-th order harmonic φ ... Phase angle between ground voltage and leakage current φ _n ... Phase angle between the ground voltage and leakage current in n-order harmonic W ... Active power VA ... Apparent power 1 ... Circuit under test 2 ... Transformer secondary side ground line 3 ... Zero phase current transformer 4 ... Zero phase current input part 5 ... Ground voltage input part 6 ... Insulation resistance measuring device 6a ... A / D conversion unit 6b ... Fourier transform unit 6c ... Arithmetic processing unit 6d ... storage unit 6e ... setting unit 6g ... output unit 10 ... host device

Claims (3)

A ground voltage detecting means for detecting a ground voltage of the three-phase AC circuit to be measured;
A harmonic leakage current detecting means for detecting a leakage current component value of a predetermined order in the harmonic components included in the leakage current to ground from the measured three-phase alternating current circuit,
Phase detection means for detecting a phase difference between a reference phase indicating a phase with respect to a detection reference time in a predetermined order of the ground voltage and a reference phase indicating a phase with respect to a detection reference time in a predetermined order of the leakage current;
Based on the phase relationship between the leakage current and the ground voltage in a predetermined order which is detected by said phase detecting means, the ground insulation resistance R and ground conductance .omega.C (omega is 2πf of the circuit to be measured, f is the fundamental of the leakage current ΩCR calculating means for calculating the value of the product ωCR with the frequency, C is capacitance) ,
The ground voltage V detected by the ground voltage detection means, the leakage current component value I _{gn of} the predetermined order n (n is a multiple of 3) detected by the harmonic leakage current detection means, and the ωCR calculated by the ωCR calculation means To the predetermined relational expression R = F (V, I _gn , ωCR) for deriving the ground insulation resistance R, and the ground insulation resistance calculation means for calculating the ground insulation resistance R;
Output means for outputting information on the insulation state of the circuit under test based on the ground insulation resistance R calculated by the ground insulation resistance calculation means;
An insulation monitoring device comprising: The output means, as information on the insulation state of the three-phase AC circuit to be measured, indicates that the ground insulation resistance R calculated by the ground insulation resistance calculation means has become a predetermined value or less, or based on the ground insulation resistance R Displaying, recording, external output or reporting that the resistance leakage current value calculated in the above has reached a predetermined value or more, and at least one of the ground insulation resistance value R and the resistance leakage current value , 2. The insulation monitoring apparatus according to claim 1, wherein one or both of display, recording, external output and notification are performed by dividing into at least two areas such as a safety area and a dangerous area depending on the size of the area. . The ground insulation resistance calculation means, ground voltage V according to claim 1, leakage current component value I _gn, the following equation based on? Cr,
R = (V / I _gn ) × ((1+ (ωCR) ² ) ^0.5 × (1+ (nωCR) ² ) ^0.5 ― (1+ (ωCR) ² ) ^0.5 ) / (1+ (nωCR) ² ) ^0.5 )
Or
R = (V / I _gn ) × ((1+ (ωCR) ² ) ^0.5 / (1+ (nωCR) ² ) ^0.5 ) / ((1 / (1+ (ωCR) ² ) ^0.5 ) + (1 / (1+ (nωCR) ² ) ^0.5 ))
Is used as the relational expression R = F (V, I _gn , ωCR). 3. The insulation monitoring apparatus according to claim 1, wherein:

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