JPH1114688A - Insulation monitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an insulation monitor which monitors insulation deterioration of an electric line surely, from the comparison between the variation of the leakage current value of a second-class grounding conductor, and the variation of a current value depending on a resistance component of a superposed frequency of each feeder obtained by converting a superposed voltage into a voltage to ground. SOLUTION: A leakage current value flowing in a second-class grounding conductor is measured by an Io measuring circuit 2, and a superposed voltage supplied from a superposed voltage supplying circuit is converted into a voltage to ground and a current value depending on a resistance component of a superposed frequency of a feeder 11 is measured by an Ir measuring circuit 3. An Ir mismeasurement judging circuit 4 utilizes that the magnitude of a variation by the insulation deterioration of an electric line differs from that of a variation depending on a facility apparatus 13, and judges whether or not the current value measured by the Ir measuring circuit 3 is mismeasurement, on the basis of the variations of the current values measured by both measuring circuits.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an insulation monitoring device.

[0002]

2. Description of the Related Art In this type of insulation monitoring apparatus, particularly, there are two methods for measuring the insulation deterioration of a low-voltage path: the Io method and the Ir method.
There is a method. Hereinafter, these measurement principles will be briefly described.

In the Io system, a current Io flowing through a second-class ground line due to a commercial frequency component on a low-voltage piezoelectric path is detected by a current transformer. Assuming that currents flowing through the ground line by the commercial frequency are I _C1 , I _R1 , I _C2 , and I _R2 ,

[0004]

Io = I _R1 + I _R2 + I _C1 + I _R2 On the other hand, Ir method superimposes a different low-frequency voltage and the commercial frequency in the low-pressure path to the two ground lines, I _C current flowing through the ground line by the low-frequency voltage, only the detection I _R current of I _R current I do. _Assuming that the currents flowing through the ground line due to the low-frequency voltage are _IgC1 , _IgC2 , _IgR1 , and _IgR2 ,

[0005]

## _EQU2 ## Ir = I _gR1 + I _gR2 I _r detector utilizes the Ir scheme of the above two methods, constantly monitors the circuit of the insulation deterioration, an alarm path leakage current due to the insulation resistance (I _R component) exceeds a set value It is configured to emit.

Further, as described in, for example, Japanese Patent Application Laid-Open No. 6-337278, there is also a type in which this alarm is transmitted to an alarm receiving unit provided at the far end of the electric circuit. By the way, for those branched to the second-class grounding line and the feeder via the power transformer, for example, the above-described Ir method is used, and in each of the branched feeders, the resistance of the superimposed frequency converted to the ground voltage is used. The insulation state is monitored by measuring the component current.

[0007]

However, such an insulation monitoring device sometimes makes an erroneous measurement when a leakage current having a superimposed frequency is generated from the equipment. For example, the insulation resistance of the equipment to which a certain feeder supplies power is 1 MΩ,
Assume that the ground voltage is 200V. The superimposed voltage is 0.
It is assumed that the frequency is 5 V and 20 Hz. In this case, the current of 20 Hz measured by this feeder is

[0008]

## EQU3 ## 0.5 / 1M = 0.5 μA. To convert this to ground voltage, the measured value is

[0009]

## EQU4 ## 0.5 μ × (200 / 0.5) = 0.2 mA This is the case where the measurement is correct. However,
If this equipment is a motor that runs at 20 Hz,
A leakage current of 20 Hz occurs. This current value is

[0010]

## EQU5 ## 200 / 1M = 200 μA. The insulation monitoring device recognizes this 20 Hz current value as a current due to the superimposed voltage. For this reason, this is converted to the earth voltage, and the measured value is

[0011]

## EQU6 ## 200 μ × (200 / 0.5) = 80 mA This is a case where erroneous measurement is performed. As described above, when there is a device that generates a leakage current of a superimposed frequency, an erroneous measurement occurs and the reliability is poor.

An object of the present invention is to provide an insulation monitoring device for monitoring an insulation state of an electric circuit by superimposing a voltage on a second type ground line of a power transformer. It is an object of the present invention to provide an insulation monitoring device capable of judging the state of an electric circuit and reliably monitoring the insulation state of an electric circuit.

[0013]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides an electric circuit formed by branching into a second type ground line and a feeder to which a load is connected at one end through a power transformer. An insulation monitoring device for monitoring an insulation state of a first type grounding line, wherein a leakage current flowing through the grounding line when a voltage having a frequency different from the commercial frequency is superimposed on the second type grounding line is measured.
Measuring means, and converting the superimposed voltage to a ground-to-ground voltage,
A second measuring means for measuring the current value of the resistance component of the feeder at the frequency of the superimposed voltage; a change amount of the current value measured by the first measuring means; and a current measured by the second measuring means. The gist of the present invention is to include a determining means for comparing the amount of change in the value with the value to determine the insulation deterioration of the electric circuit.

In such a configuration, the amount of change in the current value measured by the first measuring means and the amount of change in the current value measured by the second measuring means change almost equally when the insulation is deteriorated. In the case of the load leakage current, the amount of change in the current value measured by the second measuring means is significantly increased.
The determination means can surely monitor the insulation deterioration of the electric circuit based on these change amounts.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram for explaining a configuration of an insulation monitoring device according to an embodiment of the present invention. In the figure, reference numeral 1 denotes an insulation monitoring device, which is an Io measuring circuit (2) for measuring a leakage current value Io of a second type ground wire.
And an Ir measuring circuit (3) for measuring a resistance component current value Ir obtained by converting a resistance component current value of a superimposed frequency of the feeder line to a ground voltage, and a change amount of the Io value and an Ir measurement circuit by the Io measurement circuit (2). An Ir erroneous measurement discrimination circuit (4) for judging whether or not the change in the Ir value is due to the insulation deterioration of the electric circuit based on the change in the Ir value due to (3).
In the present embodiment, the insulation monitoring circuit 1
An external alarm output circuit (5) for issuing an external alarm when the Ir value measured by the measurement circuit (3) exceeds a set value, an Ir display circuit (6) for displaying the measured Ir value, and transmitting this information to an external device. An Ir transmission circuit (7) for transmission is provided.

Here, when a voltage is superimposed on the second type ground line (10) of the power transformer (9) at a frequency other than the commercial frequency (superimposed frequency) by the superimposed voltage supply circuit (8),
(The superimposed voltage is usually 1 V or less.) An electric circuit (14) is generated. Then, the second class ground line current detection device (12
-1), the second-class ground wire (1) of the power transformer (9)
0) is detected, and the second current is detected by the I0 measurement circuit (2).
The leakage current value Io of the seed ground wire is measured. Also, the power transformer (9) is operated by the feeder current detecting device (12-2).
Of the feeder line (11) branched from the
The detection circuit (3) measures the resistance component current value Ir obtained by converting the resistance component current value of the superimposed frequency of the feeder line to the ground voltage. The Ir erroneous measurement determination circuit (4) outputs I0
The second type ground line (1) measured by the measurement circuit (2)
The change amount of the Io value of the feeder line (11) measured by the Ir measurement circuit (3) is monitored and compared, and the change amount of the Ir value of the feeder line (11) measured by the Ir measurement circuit (3) is monitored. It is determined whether or not the Ir value of 11) is a correct measurement value.

Next, the principle of determination by the Ir erroneous measurement determination circuit (4) will be described in detail with reference to the drawings. FIG.
FIG. 4 is a diagram showing the relationship between the Io value and the Ir value as a vector.
In the figure, the resistance component current of the superimposed frequency is Ir (1
5) If the capacitor component current is Ic (16), the measured Io value is the combined current Io (17).

FIG. 3 is a diagram showing the relationship between the measured Io value and the amount of change in the Ir value when the leakage current increases due to insulation deterioration. In the figure, when the current of the superimposed frequency is Ir and the resistance component current of the superimposed frequency increases to Ir '(18) due to insulation deterioration, the measured Io value increases to Io' (20). The change amount at that time is “Ir ′ (18) −Ir” (19),
(Io ′ (20) −Io) (21), and the difference between these changes is “Ir ′ (18) −Ir” (1) at the maximum.
9).

FIG. 4 shows the equipment (13) of FIG.
Is, for example, the amount of change in the Ir value measured by the Ir measurement circuit (3) when the inverter is operated at the superimposed frequency, and the Io measurement circuit (2) when the Ir value is assumed to be a current due to the superimposed voltage. FIG. 5 is a diagram showing a relationship between the amounts of change in the theoretical value of Io which will be measured by the method.

In FIG. 1, when the equipment (13) operates at the superimposed frequency, a leakage current at the superimposed frequency occurs. When the insulation state of the equipment (13) is normal, this leakage current is a very weak current. However, since the Ir measurement circuit (3) measures a current value converted to a ground voltage,
A current value at least 100 times the actual current value is measured. At this time, the Ir value measured by the Ir measurement circuit (3) is Ir ′
In (22), the change amount of Ir is “Ir ′ (22) −Ir”.
(24).

Here, if it is assumed that Ir ′ (22) measured by the Ir measuring circuit (3) is a current generated by the superimposed voltage, the theory of Io that should be measured by the Io measuring device (2) The value should be I'o (23), and the amount of change should be (I'o (23) -Io) (25). However, the actual Ir value is the measured Ir '
Since it is 1/100 or less of (22), the Io value actually measured by the Io measuring device (2) is much smaller than I′o, and the amount of change in the measured Io value is almost zero. Should be close to zero.

That is, when the Ir value measured due to actual insulation deterioration increases, the leakage current Io of the second type ground wire of the power transformer measured at the same time also increases substantially in the same manner as the change amount of the Ir value. I do. However, when a leakage current of the superimposed frequency occurs, the measured Ir value is measured as a value that is much larger than the actual leakage current because the actual leakage current value is converted to a ground voltage. Therefore, the measured I
The amount of change in the r value is much larger than the amount of change in Io measured at the same time. From this, the Ir erroneous measurement determination circuit (4) measures the leakage current of the second type ground line (10).
o value change and each feeder (1
The insulation state can be monitored by monitoring and comparing the amount of change in the leakage current Ir of the resistance component of the superimposed frequency of 2-1..., 12-n).

As described above, the Ir erroneous measurement determination circuit (4) monitors and compares the amount of change of Io and the amount of change of Ir.
If the theoretical value of o greatly differs from the actually measured Io value, it is determined that the Ir value measured by the Ir measurement circuit (3) is an erroneous measurement.

Further, the Ir erroneous measurement discriminating circuit (4) informs the external alarm output circuit (5), the Ir value display circuit (6) and the Ir value that the Ir value measured by the Ir measuring circuit (3) is erroneous measurement.
The value is transmitted to the value transmission circuit (7). This prohibits the external alarm output circuit (5) from outputting an alarm to the outside. Also, the I value displayed by the Ir value display circuit (6)
The r value is displayed in a different expression from that in which a normal measured value is displayed, or the Ir value transmitted to an external device by the Ir value transmission circuit (7) is transmitted in a different expression from the case in which a normal measured value is transmitted. . In this way, the insulation state can be reliably monitored even from an external or remote location.

[0025]

As described above, according to the present invention, the insulation state of the electric circuit formed by branching to the second type ground line and the feeder having one end connected to the load via the power transformer is monitored. A first measuring means for measuring a leakage current flowing through the grounding line when a voltage having a frequency different from the commercial frequency is superimposed on the second type grounding line; A second measuring unit that converts the current value of the resistance component of the feeder at the frequency of the superimposed voltage into a voltage between the superimposed voltages, a change amount of the current value measured by the first measuring unit, and a second measurement Means for comparing the amount of change in the current value measured by the means with the means for determining insulation deterioration of the electric circuit, the amount of change in the current value obtained from the first measurement means and the second measurement means. Monitoring of electrical circuit insulation deterioration based on the It can be.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of an insulation monitoring device according to a first embodiment of the present invention.

FIG. 2 shows a leakage current value I of a second-class ground line in FIG.
FIG. 9 is a diagram for explaining a relationship between the current value Ir and a superimposed voltage converted into a voltage between the ground and a resistance component of a superimposed frequency of each feeder.

FIG. 3 is a diagram for explaining the relationship between Io and Ir when the leakage current increases due to insulation deterioration of the electric circuit in FIG. 1;

FIG. 4 is a diagram for explaining a relationship between Ir and a theoretical value of Io which changes in relation to the equipment (13) in FIG. 1;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Insulation monitoring device, 2 ... Io measurement circuit, 3 ... Ir measurement circuit 4 ... Ir erroneous measurement discrimination circuit, 8 ... Superimposed voltage supply circuit, 9 ...
Power transformer 10 ... Second class ground wire, 11 ... Feeder

Claims (2)

[Claims] 1. An insulation monitoring device that branches through a power transformer into a second-class ground wire and a feeder to which a load is connected at one end, and monitors an insulation state of a formed electric circuit,
A first measuring means for measuring a leakage current flowing through the ground line when a voltage having a frequency different from a commercial frequency is superimposed on the second type ground line, and converting the superimposed voltage into a voltage between ground and A second measuring means for measuring the current value of the resistance component of the feeder at the frequency of the superimposed voltage; and a change amount of the current value measured by the first measuring means and measured by the second measuring means. A determination unit for comparing the amount of change in the current value to determine insulation deterioration of the electric circuit. 2. The method according to claim 1, wherein when a current is generated by a load connected to the feeder, the determination unit determines a change amount of the current value measured by the second measurement unit and the change amount of the current value measured by the first measurement unit. 2. The insulation monitoring device according to claim 1, wherein the amount of change in the current value is compared to determine whether or not the change is due to insulation deterioration of the electric circuit.