WO2024062653A1

WO2024062653A1 - Live wire diagnostic system and live wire diagnostic method

Info

Publication number: WO2024062653A1
Application number: PCT/JP2023/009569
Authority: WO
Inventors: 淳額賀; 深大佐藤
Original assignee: 株式会社日立産機システム
Priority date: 2022-09-22
Filing date: 2023-03-13
Publication date: 2024-03-28
Also published as: JP2024046467A

Abstract

This diagnostic device compares the frequency characteristics of a current transformer at the start of the operation and the frequency characteristics of the current transformer after the start of the operation, and, when an amount of change thereof has exceeded a prescribed threshold value, detects deterioration of ground insulation of a device.

Description

Live line diagnostic system and live line diagnostic method

The present invention relates to a live line diagnostic system and a live line diagnostic method.

High-voltage equipment such as switchboards, switchgear, and switching equipment are used for a long period of time after being installed, and as a result, deterioration over time such as a decline in insulation performance may occur. It is generally known that partial discharge occurs when the insulation performance of power equipment deteriorates. If electrical discharge (hereinafter also referred to as partial discharge) repeatedly occurs inside power equipment, it may lead to insulation breakdown, which may lead to disasters such as fire. Therefore, in order to safely operate power equipment, it is important to detect the insulation performance of equipment.

Normally, when measuring insulation resistance, the load (electrical equipment) is disconnected, i.e., a power outage is assumed, and an insulation tester is installed in the circuit to measure the resistance.

Further, Patent Document 1 discloses a technique for detecting insulation resistance shown below. Specifically, a low-frequency signal is injected into the ground wire of the device using an injection transformer, and this signal voltage flows through the insulation resistance and ground capacitance, and the current that returns to the ground wire is detected by the current transformer. A method is used in which the insulation resistance of the electrical circuit is measured by extracting only the leakage current component of the measurement low-frequency signal using a filter and then detecting only the insulation resistance component using a synchronous rectifier.

In this method, the measurable insulation resistance value is determined by the noise voltage of the filter following the current transformer and the magnitude of the noise voltage included within the passband.

Japanese Patent Application Publication No. 3-209177

In conventional insulation resistance measurements, resistance is measured while the equipment is in a power outage state, which causes the equipment to be unable to operate during that period, resulting in a reduction in equipment availability.

Furthermore, the method of injecting a low frequency signal using a transformer in order to measure in a live line state as disclosed in Patent Document 1 has a problem in that the measurable resistance value is limited by noise in the filter section.

Therefore, an object of the present invention is to provide a live line diagnostic system that can detect the insulation state inside a device with high accuracy in a live line state.

A live line diagnostic system according to one aspect of the present invention is a live line diagnostic system for diagnosing the state of ground insulation of equipment in a live line state, the system including a first current transformer provided on the input side of a power line of the equipment. and a second current transformer provided on the output side of the power line of the device, and a processing section that is connected to the first current transformer and the second current transformer and performs a predetermined process. a diagnostic device, and the processing unit measures the outputs of the first current transformer and the second current transformer, respectively, at the start of operation of the device, and determines the output of the first current transformer. A first frequency characteristic and a second frequency characteristic of the second current transformer are obtained, a first ratio of the first frequency characteristic and the second frequency characteristic is determined as an initial value, and the process After operation of the device, the section measures the outputs of the first current transformer and the second current transformer, and determines the third frequency characteristic of the first current transformer and the third frequency characteristic of the second current transformer. Obtain each fourth frequency characteristic of the current transformer, determine a second ratio of the third frequency characteristic and the fourth frequency characteristic, and calculate the amount of change of the second ratio from the first ratio. The method is characterized in that deterioration of the ground insulation of the device is detected when the value exceeds a predetermined threshold value.

According to one aspect of the present invention, in a live line diagnostic system, the insulation state inside a device can be detected with high accuracy in a live line state.

FIG. 2 is a schematic diagram showing the device configuration of the live line diagnostic system of the present embodiment. FIG. 3 is a vector diagram showing components of leakage current of the device. It is a figure which shows the calibration of a current transformer. FIG. 3 is a schematic diagram showing changes in output characteristics of a current transformer. FIG. 3 is a schematic diagram showing a direct comparison of frequency characteristics. FIG. 5 is a diagram showing a diagnostic algorithm corresponding to FIG. 4; FIG. 3 is a schematic diagram showing diagnosis using differential signals. FIG. 6 is a diagram showing a diagnostic algorithm corresponding to FIG. 5;

Embodiments of the present invention will be described below with reference to the drawings. Note that in each drawing, the same components are designated by the same reference numerals, and detailed explanations of overlapping parts will be omitted.

Referring to FIG. 1, the device configuration of the live line diagnostic system of Example 1 will be described.
A current transformer 2 is provided on the entrance side of an electric circuit on a panel 1 such as a switchboard. A variable impedance 3 and a variable capacitor 4 are arranged in parallel in the current transformer 2. A current transformer 5 is provided on the outlet side of the electrical circuit of the panel 1. A variable impedance 6 and a variable capacitor 7 are also arranged in parallel with the current transformer 5. A voltage divider 13 is arranged on the entrance side of the electric circuit of the panel 1.

Current transformer 2 and current transformer 5 are connected to diagnostic device 100, which includes a processing unit that performs predetermined processing. Here, the processing unit has a Fourier transform unit 8, a signal storage and comparison operation unit 9, a calibration circuit 10, a difference processing unit 12, and switches 15 and 16.

The processing section switches the switches 15 and 16 to output the output signals of the current transformer 2 and the current transformer 5 to the calibration circuit 10 or the Fourier transform section 8, the signal storage/comparison calculation section 9, and the difference processing section 12, respectively. control so that

The current transformer 2 and the current transformer 5 are installed outside the power line 11 so as to be electrically insulated from the internal wiring of the device. The processing unit of the diagnostic device 100 detects deterioration of the ground insulation of the equipment in a live line state.

The equipment in the panel 1 can be divided into resistance Ra and capacitance Ca. If the equipment in the panel 1 is in a normal state, the leakage current ΔIa from the equipment is extremely small, and the earth insulation resistance of the equipment is several GΩ or more. When the current Iar flowing through the resistance Ra of the device and Iac flowing through the capacitance Ca are shown in the vector diagram shown in FIG. 2, the leakage current ΔIa is represented by a composite vector of Iar and Iac.

At this time, if the insulation resistance Ra decreases due to equipment deterioration or dirt, the leakage current ΔIa increases and the vector angle δ decreases. When the inflow current to the entrance of the electric circuit of the panel 1 is Ia, and the outflow current from the outlet is Ia', the leakage current ΔIa is expressed as ΔIa=Ia-Ia'. Therefore, it is possible to detect leakage current ΔIa from the difference between the output signals of current transformer 2 and current transformer 5.

However, because the leakage current is a very small current, noise that flows into the signal detected by the current transformer has a significant effect on the measurement accuracy. In order to detect this very small current, it is necessary to reduce the effects of noise as much as possible. Because common mode noise flows into both current transformer 2 and current transformer 5, theoretically the leakage current component can be extracted by calculating the difference between the output signals of current transformer 2 and current transformer 5.

However, in reality, each current transformer has its own output characteristics, and due to differences in output characteristics, the output signal will differ even for the same input signal. Therefore, when extracting a minute signal, there is a high possibility that the signal will be buried in error components if only the difference processing is performed.

Therefore, in the first embodiment, as shown in FIG. 3, the current transformers 2 and 5 are calibrated at at least two types of current values (I1, I2) smaller than the rated current at the time of starting up the equipment. to match the output characteristics of current transformer 2 and current transformer 5. This minimizes the influence of noise on the differential signal. Here, in FIG. 3, the horizontal axis is the input current I, and the vertical axis is the transformer output V.

In this way, in the first embodiment, the current transformer is Calibration of current transformer 2 and current transformer 5 is performed using a plurality of current values to make the output characteristics of current transformer 2 and current transformer 5 uniform.

Next, a method for determining a change in insulation resistance of a device will be described with reference to FIGS. 4 and 5.

For the output signals from current transformer 2 and current transformer 5 whose output characteristics have been made uniform through the above calibration, the frequency characteristics of each individual signal are held as initial values at the start of operation. When a leakage current occurs inside the panel 1 of the device due to insulation deterioration, the impedance of the panel 1 changes and the ground resistance value decreases.

As a result, board 1 exhibits characteristics close to a low-pass filter (LPF). Therefore, the frequency characteristics of the output signal of the current transformer 2 and the frequency characteristics of the current transformer 5 differ due to the insertion of the panel 1 between them. Specifically, in the current transformer 5, the high frequency component decreases (see FIG. 4).

First, a method for determining a change in insulation resistance of a device will be described with reference to FIGS. 4 and 6.

The determination method in FIG. 4 is based on the ratio of the frequency characteristics of current transformer 2 and the frequency characteristics of current transformer 5 at the initial value at the start of operation, and the ratio of the frequency characteristics of current transformer 2 and the frequency characteristic of current transformer 5 after the start of operation. This method compares the ratio of frequency characteristics.

The advantage of this determination method is that by using the ratio as an evaluation function and comparing the ratio of frequency characteristics at the start of operation and after the start of operation, changes in the absolute amount of the signal due to factors other than deterioration factors can be offset.

The evaluation algorithm will be explained with reference to FIG.
First, before starting operation, the current transformers 2 and 5 are calibrated to align the output characteristics of the current transformers 2 and 5 at a current value smaller than the rated current (step 601 ).

Next, at the start of operation, the outputs of current transformer 2 and current transformer 5 are measured to obtain frequency characteristics (step 602). Specifically, the frequency characteristics of the output signals of the current transformers 2 and 5 are acquired by the Fourier transform unit 8 and the signal storage/comparison calculation unit 9, and the output signals of the current transformers 2 and 5 are obtained by obtaining the frequency characteristics of the output signals of the current transformers 2 and 5. is stored as a frequency component.

Next, the ratio of the frequency characteristics of current transformer 2 and current transformer 5 is calculated (step 603), and the above ratio is set as an initial value (step 604).

Next, after the start of operation, the signals of current transformer 2 and current transformer 5 are acquired to acquire frequency characteristics (step 605). Next, the ratio of the frequency characteristics of current transformer 2 and current transformer 5 is calculated (step 606).

Next, it is determined whether the amount of change in the above ratio (after operation has started) from its initial value exceeds a threshold value (step 607). If the amount of change in the above ratio from its initial value exceeds the threshold value, a warning of a drop in resistance is issued (step 608). If the amount of change in the above ratio from its initial value does not exceed the threshold value, the process returns to step 605.

Although the fundamental frequency of the power line 11 is a commercial frequency wave, it also contains harmonic components. When the insulation resistance of equipment has not deteriorated, the ground resistance is so large that it can be considered almost infinite. Therefore, the frequency components of the currents flowing through current transformer 2 and current transformer 5 are equal. Although the high frequency component of the intensity is small, changes in the high frequency component can also be evaluated by taking the ratio.

In the initial state, the ratio of the frequency characteristics of current transformer 2 and current transformer 5 is close to 1. This ratio is stored as an initial value. When the insulation resistance of equipment deteriorates and leakage current occurs, the grounding resistance decreases.

The impedance of the equipment changes, and high-frequency components leak through the capacitive components of the equipment, causing the equipment to act as an LPF. This reduces the high-frequency components in the frequency characteristics of current transformer 5. At the same time, a change also appears in the ratio between current transformer 2 and current transformer 5, and if the value of current transformer 5 is used as the numerator, the high-frequency components of the ratio value will decrease. A comparison is made with the initial value of the ratio, and if frequency components exceeding the threshold value are generated, an alarm is issued to warn of an abnormality in the insulation resistance.

The current transformer 2 and the current transformer 5 are installed outside the power line 11, and are electrically insulated from the wiring inside the panel 1, so that the current transformer 2 and the current transformer 5 are connected even when the line is live. The output signal of is detectable. By analyzing this output signal, the state of insulation deterioration of the panel 1 in the live wire state can be determined with high accuracy.

Next, with reference to FIGS. 5 and 8, another method for determining a change in insulation resistance of a device will be described.

The determination method shown in FIG. 5 is a method of directly comparing the initial frequency characteristics (at the start of operation) and the frequency characteristics after an elapsed time (after the start of operation) of the same current transformer 5.

The evaluation algorithm will be explained with reference to FIG.
First, before starting operation, current transformer 2 and current transformer 5 are calibrated to make the output characteristics of current transformer 2 and current transformer 5 the same at a current value smaller than the rated current (step 801 ).

Next, at the start of operation, the output of the current transformer 5 is measured to obtain frequency characteristics (step 802). Specifically, the frequency characteristics of the output signal of the current transformer 5 are acquired by the Fourier transform section 8 and the signal storage/comparison calculation section 9, and the output signal of the current transformer 5 is stored as a frequency component.

Next, the output of the current transformer 5 is set to an initial value (step 803). Next, after the start of operation, the signal of the current transformer 5 is acquired and the frequency characteristics are acquired (step 804).

Next, it is determined whether the amount of change from the initial value of the frequency characteristic (after the start of operation) exceeds a threshold value (step 805). If the amount of change from the initial value of the frequency characteristic exceeds the threshold value, a warning of a decrease in resistance is issued (step 806). If the amount of change from the initial value of the frequency characteristic does not exceed the threshold, the process returns to step 804.

Example 2 will be described with reference to FIG.
As shown in FIG. 7, in the second embodiment, in the configuration of the first embodiment, the difference signal between the current transformer 2 and the current transformer 5 is acquired by the difference processing section 12 (see FIG. 1), and this difference signal is used. The frequency characteristics at the start are held as initial values.

Then, insulation deterioration is measured by comparing the frequency characteristics of the output signal after the start of operation and detecting that the amount of change exceeds a threshold value.

According to the above embodiment, the live line diagnostic system is capable of highly accurately detecting the insulation state inside the device in a live line state.

1 Panel 2 Current transformer on the power input side 3 Variable impedance 4 Variable capacitance 5 Current transformer on the power output side 6 Variable impedance 7 Variable capacitance 8 Fourier transform section 9 Signal storage/comparison calculation section 10 Calibration circuit 11 Power line 12 Difference processing Section 13 Voltage divider 14 Switch 15 Switch 100 Diagnosis device

Claims

A live line diagnostic system that diagnoses the condition of ground insulation of equipment in a live line state,
a first current transformer provided on the input side of the power line of the device;
a second current transformer provided on the output side of the power line of the device;
a diagnostic device that is connected to the first current transformer and the second current transformer and includes a processing section that performs predetermined processing;
The processing unit includes:
When the device starts operating, the outputs of the first current transformer and the second current transformer are measured, and the first frequency characteristic of the first current transformer and the second current transformer are determined. obtain the second frequency characteristics of the device,
Determining a first ratio of the first frequency characteristic and the second frequency characteristic as an initial value,
The processing unit includes:
After the equipment starts operating, the outputs of the first current transformer and the second current transformer are measured, and the third frequency characteristic of the first current transformer and the second current transformer are determined. obtain the fourth frequency characteristic of the device,
determining a second ratio between the third frequency characteristic and the fourth frequency characteristic;
A live line diagnostic system, wherein deterioration of the ground insulation of the device is detected when the amount of change of the second ratio from the first ratio exceeds a predetermined threshold.
The processing unit includes:
Before starting the operation of the equipment, the first current transformer and the second current transformer are calibrated so that the first output characteristic of the first current transformer and the second current transformer are calibrated. The live line diagnostic system according to claim 1, wherein the live line diagnostic system matches the second output characteristic of the flow device.
The processing unit includes:
The live wire according to claim 2, wherein the calibration is performed using a plurality of current values smaller than a rated current to match the first output characteristic and the second output characteristic. Diagnostic system.
A first variable impedance and a first variable capacitor are arranged in parallel in the first current transformer,
A second variable impedance and a second variable capacitor are arranged in parallel in the second current transformer,
The processing unit includes:
Performing the calibration using a plurality of the current values by adjusting the first variable impedance, the first variable capacitor, the second variable impedance, and the second variable capacitor, respectively. The live line diagnostic system according to claim 3.
The processing unit includes:
The first frequency characteristic, the second frequency characteristic, the third frequency characteristic, and the fourth frequency are determined using a difference signal between the outputs of the first current transformer and the second current transformer. The live line diagnostic system according to claim 1, characterized in that the characteristics are determined respectively.
The first current transformer and the second current transformer are
installed outside the power line so as to be electrically insulated from internal wiring of the device;
The processing unit includes:
The live line diagnostic system according to claim 1, wherein deterioration of the ground insulation of the device is detected in the live line state.
A live line diagnostic system that diagnoses the condition of ground insulation of equipment in a live line state,
a current transformer provided in the power line of the device;
a diagnostic device that is connected to the current transformer and includes a processing section that performs predetermined processing;
The processing unit includes:
When the device starts operating, the output of the current transformer is measured to determine a first frequency characteristic of the current transformer as an initial value,
The processing unit includes:
After the start of operation of the device, measure the output of the current transformer to determine a second frequency characteristic of the current transformer,
A live line diagnostic system, wherein deterioration of the ground insulation of the device is detected when the amount of change of the second frequency characteristic from the first frequency characteristic exceeds a predetermined threshold.
The current transformer is
installed outside the power line so as to be electrically insulated from internal wiring of the device;
The processing unit includes:
8. The live line diagnostic system according to claim 7, wherein deterioration of the ground insulation of the device is detected in the live line state.
A live line diagnostic method for diagnosing the state of ground insulation of equipment in a live line state, the method comprising:
A first current transformer is provided on the input side of the power line of the device,
a second current transformer is provided on the output side of the power line of the device;
When the device starts operating, the outputs of the first current transformer and the second current transformer are measured, and the first frequency characteristic of the first current transformer and the second current transformer are determined. respectively obtaining second frequency characteristics of the device;
determining a first ratio between the first frequency characteristic and the second frequency characteristic as an initial value;
After the equipment starts operating, the outputs of the first current transformer and the second current transformer are measured, and the third frequency characteristic of the first current transformer and the second current transformer are determined. obtaining respective fourth frequency characteristics of the device;
determining a second ratio between the third frequency characteristic and the fourth frequency characteristic;
detecting deterioration of the ground insulation of the device when the amount of change of the second ratio from the first ratio exceeds a predetermined threshold;
A live wire diagnostic method characterized by having the following.
Calibrating the first current transformer and the second current transformer before starting operation of the device;
matching a first output characteristic of the first current transformer with a second output characteristic of the second current transformer by the calibration;
10. The live-line diagnostic method according to claim 9, further comprising: