JP7193939B2 - Insulation monitor - Google Patents

Description

The present invention relates to improving the measurement accuracy of an insulation monitoring device.

As an insulation monitoring device for monitoring whether a distribution system maintains a normal insulation state, there is a fundamental wave active component method (hereinafter referred to as an Ior method). The Ior type insulation monitoring device inputs the leakage current of the monitored circuit from the zero-phase current transformer ZCT, extracts the fundamental wave leakage current Io that is the same as the commercial frequency, and from the phase difference (θ) with the captured voltage, An effective leakage current Ior of the phase-to-ground voltage and the in-phase component is calculated. From the change in this value, deterioration of wiring and equipment is judged and preventive maintenance is performed.
Patent Literature 1 discloses an example of an Ior-type insulation monitoring device.

JP 2011-149959 A

An example of a conventional insulation monitoring device is shown in FIG. Leakage current is detected by a zero-phase current transformer 102 provided in the wiring 101 of the distribution system and input to the insulation monitoring device 100 . In the insulation monitoring device 100 , the leakage current is converted into a voltage by the burden resistor 111 , amplified by the operational amplifier 114 , and converted into a digital value by the AD converter 115 . The CPU 116 removes the harmonic component from the AD-converted leakage current value by calculation to calculate the fundamental wave active component (Io). Calculate the active leakage current (Ior).

FIG. 6 shows an AD conversion image when the maximum input and the minute input are input to the AD converter 115 in the insulation monitoring device of FIG. When the maximum input is input, the resolution of the AD converter (2*th power) can be fully used, but when the input is minute, only a part of the resolution of the AD converter can be used, so the leakage current However, it was not possible to capture minute changes in , and it was not possible to improve the measurement accuracy.

In addition to 1000 turns, there are products with various numbers of turns, such as 2000 turns and 3000 turns. there was a case.

In addition, in the insulation monitoring device, since the current to be measured is small, the measurement accuracy of minute leakage current may not be stable. The cause of this is thought to be the influence of noise and offset voltage, and it is common to insert a capacitor as a means of suppressing the influence of noise and the like. However, inserting a capacitor causes a signal delay and affects the accuracy of the effective leakage current Ior. Therefore, it is not an effective means for the Ior type insulation monitoring device, and it is difficult to improve the accuracy of minute leakage current measurement. .

SUMMARY OF THE INVENTION It is an object of the present invention to provide an insulation monitoring device capable of measuring even a minute leakage current with stable accuracy without affecting the effective leakage current Ior.

In order to solve the above problems, the present invention is characterized by providing a plurality of load resistors in the measurement circuit of the insulation monitoring device and automatically switching the load resistors according to the magnitude of the leakage current to be measured.

To give an example of the "insulation monitoring device" of the present invention,
An insulation monitoring device for monitoring the insulation state of an electric circuit by inputting a leakage current from a zero-phase current transformer and calculating a fundamental wave active component leakage current, wherein the leakage current from the zero-phase current transformer is supplied. a load resistor switch for switching connection of the plurality of load resistors; an amplifier for amplifying the voltage of the load resistors; an AD converter for AD-converting the output of the amplifier; A leakage current value is obtained from the output of the load resistor, and a measurement processing unit for switching connection of the load resistors by the load resistor switching switch, wherein the measurement processing unit is connected to one of the plurality of load resistors. A current sampled value is compared with a predetermined reference value, and if the sampled value is equal to or greater than the predetermined reference value, the sampled value is stored; if the sampled value is smaller than the predetermined reference value, calculating a burden resistance value at which the magnitude of the input of the AD converter becomes larger than the value when the one burden resistance is connected , creating a switching signal for switching the plurality of burden resistances, and switching the burden resistance to It is characterized by storing a sampling value of the connected leakage current.

According to the present invention, even a minute leakage current can be measured with stable accuracy without affecting the effective leakage current Ior.
In addition, products with various input ranges can be handled by the same equipment, and measurement accuracy that is not affected by the difference in the number of turns of the zero-phase current transformer ZCT can be ensured.

Problems, configurations, and effects other than those described above will be clarified by the following description of the embodiments.

1 shows an overall block diagram of an insulation monitoring device of Example 1. FIG. FIG. 2 shows a block configuration diagram of a CPU of the insulation monitoring device of Example 1. FIG. 4 shows a processing flow diagram of the insulation monitoring device of the first embodiment. FIG. 4 shows an example of a voltage waveform sampled in the insulation monitoring device of Example 1. FIG. 1 shows an overall configuration diagram of an example of a conventional insulation monitoring device; FIG. An image of conventional AD conversion is shown.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. In addition, in each drawing for describing the embodiments, the same component is given the same name and reference numeral, and the repeated description thereof is omitted.

FIG. 1 shows the overall configuration of an insulation monitoring device according to Example 1 of the present invention.
FIG. 1 shows the overall configuration of an insulation monitoring device that has a plurality of burden resistances in a measurement circuit and has a function of automatically switching the burden resistance value according to the magnitude of the current to be measured.

In FIG. 1, reference numeral 101 denotes wiring for measuring leakage current in a distribution system, reference numeral 102 denotes a zero-phase current transformer ZCT, and reference numerals 103 and 104 denote input signal lines from the zero-phase current transformer. Reference numeral 121 denotes a measuring transformer (VT), and reference numeral 122 denotes an input signal line from the measuring transformer. A leakage current from the zero-phase current transformer 102 and a measured voltage from the measuring transformer 121 are input to the insulation monitoring device 100 .

In the insulation monitoring device 100, reference numeral 111 denotes a rated burden resistance, reference numerals 112 and 113 denote switching burden resistances, and reference numeral 117 denotes a burden resistance switching switch for switching the burden resistance. Further, reference numeral 114 denotes an operational amplifier (amplifier), reference numeral 115 denotes an AD converter, reference numeral 116 denotes a CPU, and reference numeral 118 denotes a voltage input circuit.

The outline of the operation of the insulation monitoring device 100 is as follows. The zero-phase current flowing in the wiring 101 of the distribution system is transformed by the zero-phase current transformer 102 and input to the insulation monitoring device through the input signal lines 103 and 104 . The input current signal (leakage current) is converted into a voltage by an optimum combination of load resistors 111, 112, and 113, and the operational amplifier 114 amplifies the signal. The signal is input to the AD converter 115 and converted into a digital value. Based on the digital value indicating the leakage current value and the voltage signal input by the voltage input circuit 118, the CPU 116 performs calculations to calculate the fundamental wave leakage current Io and the fundamental wave effective component leakage current Ior. The optimum combination of the load resistors 111 , 112 , 113 is switched by switching the load resistor switch 117 with a switching signal generated by the CPU 116 .
In FIG. 1, a plurality of load resistors 111, 112, and 113 are arranged and switched by the load resistor selector switch 117. However, digital resistors are used as the load resistors, and the resistance values of the digital resistors are changed according to the switching signal from the CPU 116. may be configured to change

FIG. 2 shows a block configuration diagram of a CPU related to the insulation monitoring device of the first embodiment.

A signal from the AD converter 115 and a voltage signal from the voltage input circuit 118 are input to the input unit 206 . Leakage current value measuring section 201 obtains a sampled value of the input signal from the AD converter corresponding to the leakage current value. When switching to the rated load resistor, the comparison unit 202 compares the leakage current value and a predetermined reference value stored in the storage unit 203, for example, a leakage current value of 50% of the rating (50% of the input voltage range of the AD converter). Leakage current value corresponding to %). If the leakage current value is greater than or equal to the predetermined reference value, the sampling value measured by the leakage current value measurement section 201 is stored in the sampling value storage section of the storage section 203 . If the leakage current value is smaller than the predetermined reference value, the comparison result signal is output to switching signal generator 204 . Switching signal generating section 204 calculates an optimum burden resistance value based on the comparison result signal from comparing section 202 and outputs a switching signal for switching to the optimum burden resistance to burden resistance switching switch 117 . Note that when the rated burden resistance is switched to the optimum burden resistance, the sampling value measured by the leakage current value measurement unit 201 is stored in the sampling value storage unit of the storage unit 203 . Leakage current measurement unit 201 , comparison unit 202 , and switching signal generation unit 204 constitute measurement processing unit 200 .

The storage unit 203 includes a reference value storage unit that stores a predetermined reference value, a sampling value storage unit that stores a sampling value of leakage current, and the like, and stores necessary data. Fundamental wave leakage current computing section 205 computes fundamental wave leakage current Io and fundamental wave effective component leakage current Ior from the sampling value of the leakage current and the voltage signal input from voltage input circuit 118 , and outputs them to storage section 203 . The CPU 116 further includes a display unit 206 that displays the calculation result of the fundamental wave active component leakage current Ior, a communication unit 208 that exchanges data with a host device, and a control unit 209 that controls the entire system.

In addition, in order to correspond to the zero-phase current transformer ZCT with a large maximum input of leakage current to be measured, a burden resistance having a value smaller than the rated burden resistance is provided, and the comparison result of the comparison unit 202 is that the sampling value is If it is sufficiently larger than a predetermined reference value and is in a saturated state, it may be configured to switch to that burden resistance.

Next, the processing flow of the insulation monitoring device shown in FIG. 1 will be explained using FIG.

When the insulation monitoring device starts the measurement process (S301), first, the load resistor 111 for rating is connected, and the input signal corresponding to the leakage current is sampled (S302). The comparison unit 202 determines whether a predetermined reference value, for example, a leakage current value is 50% or more of the rated value from the sampled data (S303). If it is 50% or more, the sampling value is stored in the storage unit 203 (S306). If it is 50% or less, the switching signal generating unit 204 calculates an appropriate burden resistance to generate a switching signal, and the burden resistance switching switch 117 switches to an appropriate burden resistance (S304). Then, the input signal corresponding to the leakage current in the switched burden resistor is sampled again (S305), and the sampled value is stored in the storage unit 203 (S306). Based on the stored sampled values, the sampled values are corrected by a coefficient linked to the value of the burden resistance (S307), and the calculation process ends (S308). After that, the fundamental wave leakage current calculation unit 205 performs calculation processing of the fundamental wave leakage current Io and the effective component fundamental wave leakage current Ior.

Assuming that the rated burden resistance is α, the burden resistor may be selected as 10α for an input with a leakage current value of 10%, and 5α for an input with a leakage current value of 20%. As an example of a combination of burden resistances, α, 5α (five times), and 10α (10 times) can be set, but the range may be further expanded. If the maximum input leakage current is large and corresponds to saturation, a value such as α/5 (1/5) or α/10 (1/10) may be used.

FIG. 4 shows an example of a voltage waveform input to the AD converter 115 in the case of a minute leakage current in the insulation monitoring device shown in FIG. In FIG. 4, reference numeral 401 denotes the voltage waveform input at the rated load resistor in S302, and reference numeral 402 denotes the voltage waveform input in S305 when the appropriate load resistor is switched in S304.
With the voltage waveform 401, only part of the resolution (2* power) of the A/D converter can be used, and small signal changes cannot be measured. can be measured. By increasing the input voltage of the AD converter, the quantization error of the AD converter can be reduced.

According to this embodiment, the leakage current value is obtained from the rated burden resistor, and when the leakage current value is small, the optimum burden resistance is selected. , and a wide range of AD converter resolutions can be used. Therefore, minute changes in leakage current can be captured, and measurement accuracy can be improved.

In addition, since no capacitor is inserted as a means for suppressing the influence of noise or the like, even a minute leakage current can be measured with stable accuracy without affecting the fundamental wave active component leakage current Ior.

There are various types of zero-phase current transformers ZCT, such as those with windings of 1000 turns, 2000 turns, and 3000 turns. By connecting the insulation monitoring devices shown in FIGS. 1 and 2 to ZCTs with different numbers of turns, the load resistance can be automatically switched according to the number of turns of the ZCT. Even when connected, leakage current can be sampled with the same accuracy as a 1000-turn zero-phase current transformer.

In order to obtain the absolute value of the effective fundamental wave leakage current Ior, information on the number of turns of the winding is required. For this purpose, the ZCT format including the information on the number of turns may be input in advance.

According to this embodiment, it is possible to ensure measurement accuracy that is not affected by the difference in the number of turns of the zero-phase current transformer ZCT.

DESCRIPTION OF SYMBOLS 100... Insulation monitoring device 101... Wiring of a distribution system 102... Zero-phase current transformer ZCT
Reference numerals 103, 104: Input signal line from zero-phase current transformer 111: Rated burden resistor 112, 113: Switching burden resistor 114: Operational amplifier (amplifier)
115...AD converter 116...CPU
117... Burden resistance changeover switch 118... Voltage input circuit 121... Measurement transformer (VT)
122...Input signal line from measuring transformer 200...Measurement processing unit 201...Leakage current value measuring unit 202...Comparing unit 203...Storage unit 204...Switching signal generating unit 205...Fundamental wave leakage current calculating unit 206...Input unit 207... Display unit 208 Communication unit 209 Control unit 401 Voltage waveform input from rated load resistor 402 Voltage waveform input from switching load resistor

Claims (6)

In an insulation monitoring device that monitors the insulation state of an electric circuit by inputting a leakage current from a zero-phase current transformer and calculating a fundamental wave active component leakage current,
a plurality of burden resistors supplied with leakage current from the zero-phase current transformer;
a burden resistance changeover switch for switching connection of the plurality of burden resistances;
an amplifier that amplifies the voltage of the burden resistor;
an AD converter that AD converts the output of the amplifier;
A measurement processing unit that obtains a leakage current value from the output of the AD converter and switches connection of the burden resistance by the burden resistance switching switch,
The measurement processing unit compares a sampled value of leakage current obtained by connecting one of the plurality of burden resistors to a predetermined reference value, and if the sampled value is equal to or greater than the predetermined reference value, a load resistor value that stores the sampled value, and when the sampled value is smaller than the predetermined reference value, the magnitude of the input of the AD converter becomes larger than the value when the one load resistor is connected; is calculated to create a switching signal for switching the plurality of burden resistors, and a sampling value of leakage current connecting the switched burden resistors is stored. The insulation monitoring device of claim 1,
The insulation monitoring device, wherein the measurement processing unit corrects the sampling value by a predetermined coefficient according to the burden resistance when the burden resistance is switched from the one burden resistance. The insulation monitoring device of claim 1,
The measurement processing unit
a leakage current value measuring unit that obtains a sampling value of the leakage current;
a comparison unit that compares the sampling value of the leakage current with the predetermined reference value;
When the sampling value is smaller than the predetermined reference value, the load resistance value is calculated so that the magnitude of the input of the AD converter becomes larger than the value when the one load resistor is connected, and the load resistance is calculated. a switching signal creation unit that creates a switching signal for switching the resistance;
An insulation monitoring device comprising: The insulation monitoring device of claim 1,
An insulation monitoring device comprising a storage unit for storing the predetermined reference value and the sampling value. The insulation monitoring device of claim 1,
the burden resistor is a digital resistor;
An insulation monitoring device, wherein a digital resistance value of the burden resistor is changed by a switching signal from the measurement processing unit. The insulation monitoring device of claim 1,
An insulation monitoring device that calculates a fundamental wave leakage current Io and a fundamental wave active component leakage current Ior based on a leakage current value and a voltage signal of an electric circuit.

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