JP6897933B2 - High-voltage insulation monitoring device and high-voltage insulation monitoring method - Google Patents

Description

The present invention relates to a high-voltage insulation monitoring device and a high-voltage insulation monitoring method for detecting a decrease in insulation of a high-voltage distribution line.

In high-voltage power receiving equipment, it is common to install a switch (partitioned switch) at the receiving point from the distribution system and combine the switch with a ground relay to protect the ground fault. The ground relay performs a cutoff operation by a switch when a ground fault accident that exceeds the set values of the zero-phase voltage and the zero-phase current occurs. Further, in the ground relay, the load current value for protecting the rated breaking capacity of the switch is obtained from the current transformer (CT) inside the switch.

As a method for detecting a ground fault, a method using a zero-phase voltage taken out from a zero-phase voltage detector (ZPD) in a switch or a zero-phase current taken out from a zero-phase current transformer (ZCT) is used. (See, for example, Patent Document 1). The insulation resistance value at the time of a ground fault is 0 to several tens of kΩ, and a zero-phase current of about 100 mA is detected.

On the other hand, when the cause of the ground fault is gradually deteriorated due to equipment pollution, there is a period when the insulation resistance is slightly reduced before the accident. When this is detected, it is necessary to detect a high resistance of about several MΩ, that is, a zero-phase current of several mA. However, where the zero-phase current is ideally zero, when the load current becomes large, an error of about several mA occurs in the zero-phase current transformer (ZCT), so it is not possible to detect a zero-phase current of several mA. difficult. Therefore, in Patent No. 5972097 (Patent Document 2), the applicant has proposed a technique for correcting the error of the zero-phase current due to the influence of the load current of each phase. This makes it possible to detect insulation deterioration with high accuracy.

Japanese Unexamined Patent Publication No. 6-284559 Japanese Patent No. 5972097

However, in the technique of Patent Document 2, when the characteristics of the zero-phase current transformer (correction coefficient of the equation) are obtained, the balance of the three-phase load is changed while the combination of the load currents of each phase is zero. The relationship between the phase load current and the zero-phase current is being sought. That is, it is necessary to measure the load current and zero-phase current of each phase while controlling the load, and the correction coefficient cannot be obtained when an "arbitrary" load is connected to the switch. Therefore, in order to obtain the correction coefficient, it is necessary to measure the new switch before installation or to separate the existing switch from the circuit. In particular, when performing the above measurement with an existing switch, there is a problem that a power failure is always accompanied.

Therefore, an object of the present invention is a high-voltage insulation monitoring device and a high-voltage insulation monitoring device capable of obtaining the characteristics of a zero-phase current transformer without causing a power failure even with an existing switch and performing highly accurate insulation deterioration detection. It is to provide an insulation monitoring method.

In order to solve the above problems, a typical configuration of the high-voltage insulation monitoring device according to the present invention includes a zero-phase transformer that detects a zero-phase current and a transformer that detects a load current of each phase. It is a high-voltage insulation monitoring device that is connected to a switch to detect a decrease in insulation of a high-voltage distribution line. It uses the load current of each phase and the characteristics of the zero-phase sequence current, and is zero due to the influence of the load current of each phase. It is equipped with a correction unit that corrects the zero-phase current so as to suppress the error of the phase current, and an insulation reduction detection unit that detects the insulation deterioration of high resistance based on the corrected zero-phase current. Measure the load current and zero-phase current of each phase at least four times with the load current flowing, and multiply the load current of each phase by the correction coefficient to define the zero-phase current error. Using one of the measured values of the above as the reference value, the load current of each phase for the remaining three times and the difference between the zero-phase current and the reference value are used to obtain the correction coefficient, which is an unknown number in the equation, and the correction coefficient is used as the equation. It is characterized in that an error is obtained by applying it.

According to the above configuration, the correction coefficient can be obtained with an arbitrary load connected. Therefore, even with an existing switch, the characteristics of a zero-phase current transformer can be obtained without causing a power failure.

The high-voltage insulation monitoring device may further include a microground fault detection unit that detects a large decrease in insulation in a short period of time by using the measured value of the zero-phase current for one cycle.

According to the above configuration, it is possible to detect a microground fault which is a short-time accident such as a tree contact or a discharge property, and it is possible to perform comprehensive ground fault detection.

The high-voltage insulation monitoring device may further include a phase detector that detects the phase rotation direction of the three-phase alternating current from the phase of the load current of each phase.

According to the above configuration, it is possible to automatically set the phase rotation direction when obtaining the characteristics of the zero-phase current transformer. Further, by detecting the phase rotation direction at a predetermined timing such as when the power is turned on or periodically, it is possible to automatically respond to the change in the phase rotation direction.

Further, a typical configuration of the high-pressure insulation monitoring method according to the present invention is connected to a switch provided with a zero-phase current transformer that detects a zero-phase current and a current transformer that detects a load current of each phase. Detects the zero-phase current of the high-voltage distribution line, detects the load current of each phase of the high-voltage distribution line, and uses the load current of each phase and the characteristics of the zero-phase sequencer to zero due to the influence of the load current of each phase. A high-voltage insulation monitoring method that detects a decrease in insulation of high resistance based on the corrected zero-phase current after correcting the zero-phase current so as to suppress the error of the phase current. For an equation that defines the zero-phase current error by measuring the load current and zero-phase current of each phase at least four times with the load current flowing through the switch, and multiplying the load current of each phase by a correction coefficient. Using one of the four measurement values as the reference value and using the difference between the load current and zero-phase current of each phase of the remaining three times and the reference value, the correction coefficient, which is an unknown number in the equation, is obtained, and the correction coefficient is obtained. Is characterized by finding the error by applying to the equation.

According to the method of the above configuration, the correction coefficient can be obtained with an arbitrary load connected. Therefore, the characteristics of the zero-phase current transformer can be obtained without causing a power failure to the existing equipment. It should be noted that the components corresponding to the technical idea in the high-voltage insulation monitoring device described above and their description thereof can also be applied to the high-voltage insulation monitoring method.

According to the high-voltage insulation monitoring device or the high-voltage insulation monitoring method according to the present invention, it is possible to suppress the error of the zero-phase current due to the influence of the load current of each phase and perform highly accurate insulation deterioration detection. In particular, since the correction coefficient can be obtained with an arbitrary load connected, the characteristics of a zero-phase current transformer can be obtained even with an existing switch without causing a power failure.

It is a block diagram which shows the schematic structure of the high voltage insulation monitoring apparatus. It is a graph which shows the relationship between the load current in a three-phase equilibrium state, and the level of a zero-phase current before and after correction. It is a block diagram which shows the schematic structure of the high voltage insulation monitoring apparatus which concerns on 2nd Embodiment. It is a figure explaining the difference between the insulation deterioration detection explained in 1st Embodiment and the fine ground fault detection added in 2nd Embodiment. It is a block diagram which shows the schematic structure of the high voltage insulation monitoring apparatus which concerns on 3rd Embodiment.

[First Embodiment]
The first embodiment of the high-voltage insulation monitoring device and the high-voltage insulation monitoring method according to the present invention will be described. FIG. 1 is a block diagram showing a schematic configuration of a high-voltage insulation monitoring device. The high-voltage insulation monitoring device 10 includes a switch 20 (classified switch) provided on the high-voltage distribution line L1 of the distribution system that supplies electricity from the substation to the demand destination, and a switch 20 in response to the occurrence of a ground fault. It is provided with a ground relay relay 30 that shuts off by the above, and a display unit 50 that notifies the occurrence of a ground fault or the like.

The switch 20 includes a zero-phase voltage detector 22 (ZPD) that detects the zero-phase voltage of the high-voltage distribution line L1, a zero-phase current transformer 24 (ZCT) that detects the zero-phase current of the high-voltage distribution line L1, and a high voltage. It has a current transformer 26 (CT) for detecting the load current of each phase of the distribution line L1 and a current transformer 28 (VT) for an instrument. The switch 20 is provided at a power receiving point from a power distribution system in a high-voltage power receiving facility. As the zero-phase voltage detecting device 22, for example, a capacitor-type zero-phase voltage detecting device that detects the zero-phase voltage by synthesizing the ground voltage of each phase can be used.

In the ground relay 30, the zero-phase voltage detected by the zero-phase voltage detection device 22 and the zero-phase current detected by the zero-phase transformer 24 are set from the viewpoint of protection coordination with the distribution system. Determine if the voltage and zero-phase current set values are exceeded. When it is determined that the zero-phase voltage and the zero-phase current exceed the set value, it is determined that a ground fault has occurred. Then, the ground relay 30 determines the phase of the zero-phase voltage-zero-phase current, determines whether it is a ground fault on the power supply side or a ground fault on the load side, and if it is a ground fault on the load side, the switch 20 Performs the shutoff operation by. As a result, the high-voltage distribution line L1 is cut off by the switch 20.

The ground relay 30 includes a memory 32 that stores the measured values of the zero-phase current and the load current of each phase, an FFT analysis unit 34, a correction unit 36 that corrects the zero-phase current, and several MΩ before the occurrence of the ground fault. It has an insulation reduction detection unit 38 that detects a high resistance insulation reduction.

The insulation degradation detection unit 38 detects a high resistance insulation degradation based on the zero-phase current corrected by the correction unit 36. The correction unit 36 and the insulation deterioration detection unit 38 are configured by hardware such as an electric circuit, but are not limited to this, and may be configured by software such as a program, or they. It may be composed of a combination of both.

The display unit 50 displays a display notifying that a ground fault has occurred and a display notifying that a several MΩ insulation deterioration has occurred before the ground fault occurred. As the display unit 50, for example, a magnetic reversal display or the like can be used, and in addition, an indicator lamp such as an LED lamp or an LED display can be used. When an indicator light, an LED display, or the like is used, for example, a power source such as a solar cell or a rechargeable battery is provided, and power is supplied to the display unit 50 from the power source.

Next, the correction process by the correction unit 36 described above will be described in detail. First, the effect of the load current on the zero-phase current, which is the output of the zero-phase current transformer 24, will be described, and then the actual correction procedure will be described.

The ground relay 30 stores each output signal from the zero-phase voltage detection device 22, the zero-phase current transformer 24, the current transformer 26, and the instrument transformer 28 in the memory 32 for a certain period of time. The FFT analysis unit 34 performs FFT analysis on the data stored in the memory 32, and extracts the zero-phase current of the frequency line having the maximum output level and the load current of each phase. The frequency line at which the output level is maximized is determined by the output of the instrument transformer 28. The instrument transformer 28 is used as a power source for the ground relay, but since the output is always stable, it can also be used for determining the frequency line. The instrument transformer 28 may be built in the switch 20 or may be externally attached.

The output of the zero-phase current _transformer 24 is the zero-phase current I ZCT, and the output of the current transformer 26 attached to each phase line is the load currents I _U , _IV , and I _W. The zero-phase current I _ZCT is represented by the following equation (1) by the respective load currents I _U , _IV , and I _W.
I _ZCT = I _U + _IV + I _W ... (1)
In the case of a three-phase equilibrium state, I _ZCT = 0 originally. Therefore, when a zero-phase current is generated even in a three-phase equilibrium state (I _ZCT ≠ 0), the cause is the influence of the load current.

FIG. 2 is a graph showing the relationship between the load current in the three-phase equilibrium state and the level of the zero-phase current before and after the correction. According to the above-mentioned measurement results, as shown in FIG. 2, the level of the zero-phase current (waveform A1) before correction increases in proportion to the load current. However, the level of the zero-phase current due to the influence of the load current is about 2 mA even when the load current is 25 A. Normally, the ground relay 30 detects a zero-phase current of 100 mA or more flowing with a ground fault resistance of 10 kΩ or less to determine a ground fault, so a load current of about 2 mA affects the detection of a normal ground fault. There are few things.

However, when it is necessary to detect an accurate zero-phase current in a high resistance insulation reduction of several MΩ, it is necessary to detect a zero-phase current of about 1 mA as the zero-phase current due to the insulation reduction, so that the load current becomes The effect on the zero-phase current is a major obstacle to detection. Therefore, in order to perform highly accurate insulation deterioration detection, it is necessary to eliminate or mitigate the influence of the load current.

In the case of the three-phase equilibrium state, the zero-phase current is theoretically zero. Therefore, the reason why the load current affects the zero-phase current is due to the characteristics of the zero-phase current transformer 24. Therefore, in order to correct the zero-phase current, it is necessary to acquire each load current from the current transformer 26 and to grasp the characteristics of the zero-phase current transformer 24.

_{The zero-phase current error I ZCT_e} caused by the influence of each load current is as follows using the correction coefficients α, β, γ (ZCT characteristic vector) representing the influence of the vectors I _U , _IV , and I _{W of each load current.} It is represented by the equation (2).
I _{ZCT_e} = α ・ I _U + β ・_IV + γ ・ I _W・ ・ ・ (2)
I _{ZCT_e:} Zero-phase current error I _U , _IV , I _W : Load current of each phase α, β, γ: Correction coefficient

This equation (2) is an equation that defines the error of the zero-phase current due to the influence of each load current. Here in the prior application (Japanese Patent No. 5972097), by applying a load current of the three sets of each phase load balancing is different while maintaining the remaining zero-phase current to zero, 6-way simultaneous equations (I _U, I _V, Since I _W is a vector, it becomes 6 elements instead of 3 elements).

However, the zero-phase current that can be acquired by the switch 20 of the local equipment includes the zero-phase current due to the residual component and the insulation resistance of the equipment. These components are indistinguishable from the output generated by the influence of the load current, and their magnitude is indefinite. Equation (3) shows the relationship between the zero-phase current and the load current in the field measurements.
I _{ZCT_e} = α ・ I _U + β ・_IV + γ ・ I _W + I _OO + I _OR・ ・ ・ (3)
α, β, γ: Correction coefficient I _{ZCT_e} : Zero-phase current error I _U , _IV , I _W : Load current of each phase I _OO : Residual zero-phase current I _OR : Zero-phase current formula due to insulation resistance of local equipment In (3), since _IOO and _IOR are unknown variables, it is not possible to solve the 6-element simultaneous equation.

Therefore, the correction unit 36 performs the processing as follows. According to the knowledge obtained from the verification in the actual field, the insulation resistance value of the equipment on the consumer side measured at the latest inspection is sufficiently high, and if it is within a few days after the inspection, the temporal fluctuation of the residual amount will be. Small enough to be ignored. Similarly, the temporal fluctuation of the insulation resistance value is negligibly small. Therefore, on _{the assumption that IOO} and _IOR are constants rather than variables, the equations obtained by substituting the reference values from the remaining three equations are subtracted from the remaining three equations, with one of the four measured values as the reference value. to clear the _{I OO} and _{I OR} by. Then, the following equation (4) is obtained.
_{(I ZCT_N -I ZCT_0) = α} (I U_N -I U_0) + β (I V_N -I V_0) + γ (I W_N -I W_0) ··· (4)
α, β, γ: Correction coefficient I _{ZCT_N} : Zero-phase current at any time point N (N = 1-3)
I _{ZCT_0:} reference value to the selected zero-phase current _{I U_N, I V_N, I W_N} : each phase of the load at any point in time N current _{I U_0, I V_0, I W_0} : each phase of the load current selected reference value

Equation (4) is undefined components _{I OO,} since it does not include the _{I OR,} it is possible to solve the 6-way simultaneous equations. In this way, the indefinite component can be canceled and the correction coefficient can be obtained by using the measured values of the load current and the zero-phase current at the four time points where the balance of the load current is different.

The measured values of the load current and the zero-phase current for four times can be appropriately selected from the measured values analyzed by FFT a plurality of times. As a criterion for selecting 4 doses, those having a significant difference are preferable. Any one of the four doses may be used as the reference value, but for example, one having a zero-phase current I _{ZCT_N} close to the average can be used. As an example of data accumulation, 60 seconds (3,000 cycles) are accumulated with a cycle rate of 0.02 seconds. Then, for example, data for about 2 seconds is FFT-analyzed to obtain a measured value for one time.

_{The value of IOO_N} + _{IOR_N} can be determined from the equation (3) using the values of the correction coefficients α, β, and γ obtained as described above. _{Then, by substituting the load currents I U_N} , _{IV_N} , and I _{W_N} of each phase at the time of actual correction into the equation (3), the error I _{ZCT_e} of the zero-phase current can be obtained. Then, as in the following equation (5), the corrected zero-phase current I ₀ (estimated value) is _{obtained by subtracting the error I ZCT_e from the zero-phase current I ZCT_N} (measured value) at the time of the correction. Can be done.
I ₀ = I _{ZCT_N-} I _{ZCT_e} ... (5)
I ₀ : Zero-phase current after correction I _{ZCT_N} : Zero-phase current at an arbitrary time point N (time point to be corrected) I _{ZCT_e} : Error of zero-phase current

As shown in FIG. 2, according to this correction, the corrected zero-phase current (waveform A2) is about 0.2 mA, regardless of the load current value, as compared with the uncorrected zero-phase current (waveform A1). stable. 0.2mA corresponds to the zero-phase current flowing with a ground fault resistance of 20MΩ. Since the zero-phase current after correction is closer to 0.0 mA than the zero-phase current before correction, it can be seen that the effect of the load current is mitigated by the correction.

As described above, the correction unit 36 can correct the zero-phase current affected by the load current to a level at which highly accurate insulation deterioration detection is possible. Therefore, the insulation deterioration detection unit 38 can determine the corrected zero-phase current and detect the insulation deterioration of high resistance (several MΩ) with high accuracy.

In particular, in the present invention, the correction unit 36 uses one of the measured values for four times as a reference value, and uses the load current of each phase for the remaining three times and the difference between the zero-phase current and the reference value to form an equation. The correction coefficient, which is an unknown number, is being obtained. As a result, the correction coefficient can be obtained with an arbitrary load connected. Therefore, even with the existing switch 20, the characteristics of the zero-phase current transformer 24 can be obtained without causing a power failure.

Further, since it is possible to detect the insulation deterioration of high resistance with high accuracy even for the existing switch 20, it is not necessary to purchase a new switch 20, and the ground relay 30 according to the present invention can be used. The cost of introduction can be reduced.

[Second Embodiment]
A second embodiment of the high-voltage insulation monitoring device and the high-voltage insulation monitoring method according to the present invention will be described. The same reference numerals are given to the overlapping parts of the first embodiment and the description, and the description thereof will be omitted.

As described in the first embodiment, in order for the correction unit 36 to correct the zero-phase current, it is necessary to accumulate the data of the cycle for a certain period of time while performing the FFT analysis. When a general-purpose microcomputer is used to construct an apparatus at low cost, the calculation load becomes heavy if FFT is continuously performed. However, since the decrease in insulation resistance due to equipment contamination gradually progresses with the passage of time, it is not necessary to constantly monitor it, and it is not practical to perform it periodically (for example, take in for several seconds every few minutes and perform FFT analysis). It is enough.

However, in the configuration of the first embodiment, long-term insulation deterioration can be detected, but short-term accidents such as tree contact and discharge property cannot be detected. Therefore, in the present embodiment, the configuration is added so that a short-time accident can be detected.

FIG. 3 is a block diagram showing a schematic configuration of the high-voltage insulation monitoring device according to the second embodiment. In the ground relay 30 shown in FIG. 3, in addition to the insulation deterioration detecting unit 38, a fine ground fault detecting unit 40 that detects a large insulation deterioration in a short time and in a short cycle is provided.

A zero-phase current is input from the zero-phase current transformer 24 to the microground fault detection unit 40. The insulation resistance value at the time of a ground fault is 0 to several tens of kΩ, and the micro ground fault detection unit 40 detects a zero-phase current of about 100 mA. Therefore, FFT analysis is not required for the micro-ground fault detection unit 40 to detect the zero-phase current, and the micro-ground fault can be detected by using the measured value of the zero-phase current for one cycle.

FIG. 4 is a diagram for explaining the difference between the insulation deterioration detection described in the first embodiment and the microground fault detection added in the second embodiment. As shown in FIG. 4A, the insulation reduction detection has a larger detectable insulation resistance value than the microground fault detection, and can detect a megaohm-order insulation deterioration due to equipment contamination. On the other hand, the time required for detection is long, and it is not possible to detect an accident for a short time. Micro-ground fault detection has a shorter detection time than insulation deterioration detection, and can detect short-time accidents such as tree contact and discharge. On the other hand, the detectable resistance value is lower than the insulation reduction detection.

Then, as shown in FIG. 4 (b), a high resistance range of 0.04 to 3 MΩ can be detected by insulation deterioration detection, and a short time range of 0.02 seconds or more can be detected by microground fault detection. can do. As described above, according to the configuration of the present embodiment, it is possible to detect both a decrease in insulation resistance due to equipment contamination and a microground fault that is a short-term accident such as tree contact or discharge, and is a comprehensive ground. Entanglement detection can be performed.

[Third Embodiment]
A third embodiment of the high-voltage insulation monitoring device and the high-voltage insulation monitoring method according to the present invention will be described. The same reference numerals are given to the overlapping parts of the first embodiment and the description, and the description thereof will be omitted.

The effect of the load current on the zero-phase current transformer 24 differs depending on the phase rotation direction (phase order) of the three-phase alternating current. Therefore, it is necessary to input the phase rotation direction to the correction unit 36 at the time of correction.

It is known that the phase rotation direction is determined by the phase voltage phase with a device generally called a phase detector. However, the switch 20 may not have a built-in sensor for detecting the phase voltage. Therefore, in the present embodiment, the phase rotation direction is determined using a part of the data used in the first embodiment.

FIG. 5 is a block diagram showing a schematic configuration of the high-voltage insulation monitoring device according to the third embodiment. The ground relay 30 shown in FIG. 5 includes a phase detector 42 that detects the phase rotation direction of three-phase alternating current from the phase of the load current of each phase, in addition to the insulation drop detection unit 38.

The phase detector 42 receives the processing data of the FFT analysis unit 34 and determines the phase rotation based on the phase of the load current of each phase. If the equipment is in a power-charged state, at least the transformer no-load current and the cable charging current of the power receiving equipment flow, so that the phase rotation can be determined.

According to the above configuration, the phase rotation direction can be automatically set when the characteristics of the zero-phase current transformer 24 are obtained. Further, by detecting the phase rotation direction at a predetermined timing such as when the power is turned on or periodically, it is possible to automatically respond to the change in the phase rotation direction.

Finally, the aforementioned embodiments are exemplary and the scope of the invention is not limited thereto. The above-described embodiment can be variously changed. For example, some components may be deleted from all the components shown in the above-described embodiment, and the components according to different embodiments may be appropriately combined. Is also good.

The present invention can be used as a high-voltage insulation monitoring device and a high-voltage insulation monitoring method for detecting a decrease in insulation of a high-voltage distribution line.

L1 ... High-voltage distribution line, 10 ... High-voltage insulation monitoring device, 20 ... Switch, 22 ... Zero-phase voltage detector, 24 ... Zero-phase current transformer, 26 ... Current transformer, 28 ... Instrument transformer, 30 ... Ground Interference electric power, 32 ... Memory, 34 ... FFT analysis unit, 36 ... Correction unit, 38 ... Insulation deterioration detection unit, 40 ... Micro ground fault detection unit, 42 ... Phase detector, 50 ... Display unit

Claims (4)

A high-voltage insulation monitoring device that detects a decrease in insulation of a high-voltage distribution line by connecting to a switch equipped with a zero-phase current transformer that detects the zero-phase current and a current transformer that detects the load current of each phase. ,
A correction unit that corrects the zero-phase current so as to suppress an error of the zero-phase current due to the influence of the load current of each phase by using the load current of each phase and the characteristics of the zero-phase current transformer.
It is equipped with an insulation degradation detector that detects insulation degradation of high resistance based on the corrected zero-phase current.
The correction unit
With the load current flowing through the switch, the load current of each phase and the zero-phase current were measured at least four times.
For the equation that defines the error of the zero-phase current by multiplying the load current of each phase by the correction coefficient.
Using one of the four measured values as a reference value, and using the load current of each of the remaining three times and the difference between the zero-phase current and the reference value, the correction coefficient, which is an unknown number in the equation, is obtained.
A high-voltage insulation monitoring device characterized in that an error is obtained by applying the correction coefficient to the equation. The high-voltage insulation monitoring device further
The high-voltage insulation monitoring device according to claim 1, further comprising a microground fault detecting unit that detects a large decrease in insulation in a short period of time by using the measured value of the zero-phase current for one time. The high-voltage insulation monitoring device further
The high-voltage insulation monitoring device according to claim 1 or 2, further comprising a phase detector that detects the phase rotation direction of three-phase alternating current from the phase of the load current of each phase. Connect to a switch equipped with a zero-phase current transformer that detects the zero-phase current and a current transformer that detects the load current of each phase.
Detects the zero-phase current of the high-voltage distribution line and
The load current of each phase of the high-voltage distribution line is detected, and the load current is detected.
Using the load current of each phase and the characteristics of the zero-phase current transformer, the zero-phase current is corrected so as to suppress the error of the zero-phase current due to the influence of the load current of each phase.
A high-voltage insulation monitoring method that detects high-resistance insulation degradation based on the corrected zero-phase current.
When correcting the zero-phase current
With the load current flowing through the switch, the load current of each phase and the zero-phase current were measured at least four times.
For the equation that defines the error of the zero-phase current by multiplying the load current of each phase by the correction coefficient.
Using one of the four measured values as a reference value, and using the load current of each of the remaining three times and the difference between the zero-phase current and the reference value, the correction coefficient, which is an unknown number in the equation, is obtained.
A high-voltage insulation monitoring method characterized in that an error is obtained by applying the correction coefficient to the equation.

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