JPH07119778B2 - Insulation resistance measurement method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for measuring insulation resistance of an electric circuit, and more particularly to a phase error correction means for detecting a monitor signal at that time.

(Prior Art) In order to detect insulation line resistance for converting high-voltage electricity into low-voltage electricity and transmit it to a required device in advance, and to promptly find a trouble in the electricity path to supply a stable power, a second conventional method is used. It is common to have an insulation monitoring device as shown in the figure.

In this device, a low-impedance low-frequency oscillator 5 is inserted into one of the low-voltage secondary electric lines 2 and 3 of a transformer transformer 1, for example, a second-class grounding earthing line 4 provided in the electric line 3 to connect the electric lines 2, 3
A measuring AC signal is applied between the earth and the ground, and a monitoring signal from the low frequency oscillator 5 leaking through the insulation resistance Ro and the electrostatic capacitance Co between the electric line and the ground is applied to the ground line. It is extracted by the combined zero-phase AC device 6, and this is input to the control unit 8 via the filter 7 that passes only the monitoring signal.

Since this control unit has a built-in synchronous detection circuit, a part of the output of the low frequency oscillator 5 is input as a synchronous signal for this purpose.

The operation of this device will be described below.

The low frequency oscillator 5 is applied to the electric line and flows through the insulation resistance Ro and the electrostatic capacitance Co between the electric line and the ground and the ground wire 4
_Let the leakage currents that return to be I _R and I _C , respectively.

Since the relationship between this current and voltage has a phase difference of θ as shown in Fig. 3, if the in-phase component of the low-frequency oscillator output, I _R = || cos θ, is found, the current flowing through the insulation resistance Ro I _R can be calculated, and the value of insulation resistance Ro can be obtained from this value. In this case, in order to accurately derive the insulation resistance Ro, it is necessary to accurately measure the phase difference θ between the circulating leakage current value and the measurement signal.

However, in the above-mentioned configuration, the phase characteristics of the zero-phase current transformer 6 and the filter 7 greatly change due to temperature change or aging change, so that even if the phase angle θ is first accurately grasped, There has been a drawback that an error occurs with the progress of and it becomes impossible to accurately detect the insulation resistance value.

That is, if the phase is deviated, the in-phase component of the leakage current flowing back to the ground line 4 becomes || cos (θ +), and I _R cannot be correctly detected.

(Object of the Invention) The present invention has been made in order to eliminate the above-mentioned drawbacks in the conventional method for measuring the insulation resistance of electric circuits and the like. It is an object of the present invention to provide an insulation resistance measuring method that enables accurate insulation resistance measurement regardless of changes over time.

(Summary of the Invention) In the present invention, in order to achieve this object, the phase error in the measurement system is always detected, and the calculation result is corrected based on this result.

In this case, in order to detect a phase error, two signal lines are passed through the zero-phase current transformer, one of which is energized with the low-frequency signal oscillator output and a switch means is inserted. The switch means is inserted in the other signal line and the current flowing in the ground line is made to flow in the opposite direction, so that the switch means inserted in the two signal lines is closed to zero. A structure in which a low frequency signal is directly applied to a phase current transformer to detect the phase difference between the phase of the output current of the measurement system and the initial set value, and the calculated value or calculation process is corrected based on this result. Is.

(Example) Hereinafter, the present invention will be described in detail based on illustrated examples.

FIG. 1 is a block diagram showing an embodiment of an insulation resistance measuring apparatus according to the present invention, and the same reference numerals as those in FIG. 2 mean the same elements.

That is, 1 is a transformer, 2 and 3 are low-piezoelectric paths, and one of them 3 is connected to a grounding wire 4 that has been subjected to type 2 grounding work. The output of the secondary coil of the zero-phase current transformer is input to the control circuit 8 via the filter 7, and is connected to the current transformer 6 as a comparison signal of the synchronous detection circuit of the section. The zero-phase current transformer of the insulation resistance measuring device connected so as to input a part of the output, and the signal line 9 having both ends connected to the output end of the low-frequency oscillator 5 and the zero-phase current transformer 5 Two signal lines, that is, a ground line 4 passing through and a signal line 10 connected in parallel are passed through.

In addition, the switch means 11 and 12 are connected to the two signal lines 9 and 10.
Is connected in series, and a current adjusting resistor 13 is connected to the signal line 9 and the other signal line 10 is passed through the zero-phase current transformers so that the current flowing in the opposite direction to the ground line 4 is reversed. Let

The operation of the insulation resistance measuring device configured as described above will be described.

First, when the switch means 11 and 12 inserted into the two signal lines newly provided are both opened, the operation of this device is the second.
Since there is no difference from the conventional one shown in the figure, its explanation is omitted.

Next, considering the case where the switch means 12 in which the signal line 10 is inserted is closed, this signal line has an insulation resistance Ro and a capacitance of the electric path.
The leakage component of the low frequency signal that flows to the ground via Co will flow.

This leakage current originally flows back to the ground line 4, but if a signal line is connected in parallel with this, it will flow equally into the signal line 10 and the ground line.

Moreover, since the signal line 10 penetrates the zero-phase current transformer in the opposite direction to the ground line 4, they cancel each other out, resulting in the leakage current being output to the secondary coil of the zero-phase current transformer 6. do not do.

When the switch means of the other signal line 9 is closed in this state, a signal from the low frequency signal oscillator 5 flows and a low frequency signal component is output to the secondary coil of the zero-phase current transformer 6 and passes through the filter 7. To the control circuit 8.

Therefore, if the control circuit 8 compares the signal with the signal from the low-frequency signal oscillator 5, the amount of phase delay due to the zero-phase current transformer 6 and the filter 7 can be detected.

That is, the signal derived via the signal line 9 has no cause for causing a phase delay other than the zero-phase current transformer 6 and the filter 7, and assuming that the amount of these phase delays is zero, the signal leaks back through the electric path. Since the component is zero, the phase difference between the two signals to be compared in the control circuit 8 should be zero, and the phase difference generated between the two is that generated by the zero-phase current transformer 6 and the filter 7. Can be regarded as

After the phase difference is obtained in this way, the switch means of each of the signal lines 9 and 10 is opened to perform the same operation as in the conventional method described above.
An accurate insulation resistance value can be obtained by performing the calculation | cos (θ +) and substituting the previously obtained value into this to calculate I _R.

In addition, in the calculation at this time, the value obtained by the conventional method || c
Subtracting the value obtained by the above-mentioned means from the phase angle (θ +) at os (θ +), that is, (θ +)-=
It will be apparent that θ may be obtained from the equation θ.

The resistor 13 inserted in the signal line 9 is for setting the current, and the signal level output to the zero-phase current transformer is set by this resistance value. Therefore, the output level of the control circuit 8 can also be monitored. At the same time, changes in the gains of the zero-phase current transformer 6 and the filter 7 can also be monitored.

By correcting the calculation in the control circuit 8 based on these data, a more accurate insulation resistance value can be obtained.

Therefore, if the above-mentioned phase correction work is repeated intermittently, it is possible to always eliminate the measurement error due to temperature change or secular change.

Further, it is possible to automatically perform such correction work.

In the above-described embodiments, the case of the single-phase two-wire electric circuit has been shown, but it is obvious that the single-phase three-wire electric circuit, the three-phase three-wire electric circuit, and the like can be widely applied.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing a conventional insulation resistance measuring device, and FIG. 3 is a vector diagram showing the relationship between current and voltage. 1 …… transformer, 2,3 …… electric circuit, 4 …… ground wire, 5 …… low frequency signal oscillator, 6 …… zero-phase current transformer, 7 …… filter, 8 …… control circuit, 9 and 10 ...... Signal lines, 11 and 12 ...... Switch means, 13 ...
…Resistor.

Claims (3)

[Claims] 1. A measurement, wherein a low frequency signal voltage for measurement different from a commercial frequency is applied to an electric line through a ground wire of a transformer, and the current is returned to the ground wire by a zero-phase current transformer coupled to the ground wire. In the method of deriving the leakage component of the low frequency signal for use in calculating the insulation resistance value of the electric circuit from this leakage component,
A signal line partially connected in parallel to the ground line is coupled to the zero-phase current transformer in a direction opposite to that of the ground line to cancel the leakage component at the output end of the zero-phase current transformer. At the same time, the signal line to which the low-frequency signal or another low-frequency signal is applied is pierced through the zero-phase current transformer to detect the phase error of the leakage component extraction system of the low-frequency signal for measurement. Insulation resistance measuring method characterized by. 2. The means for calculating the insulation resistance of the electric circuit from the leakage component extracts the effective component proportional to the insulation resistance value of the electric circuit by synchronously detecting the leakage component with the low frequency signal. The insulation resistance measuring method according to claim 1, which is characterized. 3. The insulation resistance measuring method according to claim 1 or 2, wherein a switch means is provided for each of the two signal lines, and the switch means is opened and closed as necessary.