JPH0727812A - Insulation diagnosing device - Google Patents

Abstract

PURPOSE:To provide an insulation diagnosing device for electrical facilities with which a deteriorated part can be specified. CONSTITUTION:An insulation diagnosing device is constituted of an arithmetic processing section 19 which inputs the outputs of zero-phase current transformers 14 connected to feeders 12 branched from a bus constituting an electric power system to a band-pass filter 18 and an intermittently arc-grounding high-frequency current to a frequency detecting means 22, calculates an intermittently arc-ground point from a detected frequency and the constant of the electric power system, and finds the feeder having the highest output value by comparing the multiple outputs of the filter 18 with each other. Since the section 19 always compares the output of the filter 18 with numerical values in (n) stages, an intermittently arcing ground point can be always specified and insulation diagnosis can be always performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulation diagnostic device for a power system, and more particularly to an insulation diagnostic device for constantly monitoring insulation of an electric work and calculating an insulation deterioration ground fault point.

[0002]

2. Description of the Related Art Insulation deterioration of a power cable gradually progresses and eventually leads to a ground fault. In general, the following two cases are common as the mechanism of progress of insulation deterioration. First, in the first case, a current starts to leak from a damaged or deteriorated portion of the power cable coating or the conductor supporting insulator, and damage or deterioration progresses due to heat, pressure, ions, etc. generated by the leak current. . The second case is a case where, as seen in a cable or the like, a dielectric breakdown occurs at once after water penetrates into an insulator in a tree shape, but thereafter the insulation is restored. The latter is called an intermittent arc light ground fault, and it is difficult to detect the ground fault occurrence point. However, recent electrical equipment is
There is a demand for a technique for detecting an intermittent arc light ground fault current in a live state.

Conventionally, a switchgear is provided between the neutral point of the ground voltage transformer (hereinafter abbreviated as GPT) and the ground,
When the circuit is closed during normal operation and opened during insulation deterioration diagnosis, a DC voltage is applied to both electrodes of the switchgear, and the leakage current from electrical equipment to the ground is measured, and the result exceeds a predetermined reference value. Had to stop the electrical equipment and individually inspect the power line for insulation deterioration.

Further, in Japanese Patent Laid-Open No. 4-42726,
The ground fault section is judged by extracting the ground fault signal by detecting the zero-phase current with each of the reference line voltage signal and the line voltage signals for the other two phases, and detecting the ground fault phase from that phase. The point cannot be detected.

[0005]

In the prior art, after the insulation deterioration is detected, the power equipment is stopped, and then each part is separated and the insulation resistance of each part is measured again. The effort required to maintain the equipment was large. Furthermore, in the event of a ground fault, a high voltage is generated between the GPT neutral point and the ground, so it is not possible to install an insulation monitoring device at all times and perform measurements, and carry out regular short-term diagnostics. However, it was difficult to cope with the rapidly progressing insulation deterioration and to estimate the ground fault point during the intermittent arc light ground fault.

An object of the present invention is to provide an insulation diagnostic apparatus capable of safely and constantly monitoring insulation deterioration without stopping power equipment and identifying a ground fault point when an intermittent arc light ground fault occurs.

[0007]

In order to achieve the above object, in an insulation diagnostic device for diagnosing insulation of an electric work by detecting a zero-phase current of a power system, a high frequency detected from each of a plurality of feeders. Frequency detecting means for detecting the frequency of the current, a bandpass filter for extracting the high frequency current and extracting the power system frequency component, and calculating the intermittent arc light ground fault point from the output of the frequency detecting means and the constant of the power system. The insulation diagnosis device is provided with an arithmetic processing unit that compares a plurality of outputs of the bandpass filter to obtain a feeder having the maximum output value.

A bandpass filter for extracting the power system frequency component of the zero-phase current detected from each of the plurality of feeders, and the output of the bandpass filter is compared with N stepwise set levels to obtain N levels. The insulation diagnosis apparatus may be provided with an arithmetic processing unit for dividing into stages.

[0009]

With this structure, the above-mentioned object can be achieved by the present invention by the following operations. Generally, in a power system, if three phases are unbalanced, a zero-phase current flows, and therefore a system abnormality can be found by detecting the zero-phase current.
The intermittent arc light ground fault is characterized in that the continuation of the ground fault is short, but the current is high frequency. The detected zero-phase current is amplified by high frequency to detect the frequency. Although it is difficult to measure the peak value, many means such as measuring the time between zero crossings are used for detecting the high frequency. This frequency is a function of the stray capacitance of the power system and the inductance determined by the distance between the measurement point and the intermittent arc light ground fault point, and the relationship between the frequency and the distance can be determined. Therefore, the intermittent arc light ground fault point can be determined from the frequency.

When a high frequency current is amplified and input to a band pass filter for extracting the power system frequency component,
The peak value of the output is proportional to the peak value of the high frequency current. Therefore, when there are a plurality of feeders, it is possible to specify the feeder having the intermittent arc light ground fault by obtaining each output value and selecting the feeder having the maximum value from the output values.

Further, normally, the value of the fundamental frequency component output from the bandpass filter is obtained, and the zero-phase current generated due to the insulation deterioration is compared with that which is classified into n stages in advance, thereby diagnosing the always isolated state. You can

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention and a configuration example of an electric equipment 2 as a target thereof. First, in the figure, the target electric equipment 2 is a power receiving unit 10 connected to a commercial power source or an in-house generator, a bus bar 11 connected to the power receiving unit 10,
It is composed of a plurality of feeders 12 drawn from the bus bar 11, a circuit breaker 13 for the feeders 12, and a zero-phase current transformer 14. Power is supplied to the load 15 using a power cable at the tip of the feeder 12.

Insulation monitoring device 1 according to an embodiment of the present invention
Is an amplifier 17 for taking in the zero-phase current signal 16 of the zero-phase current transformer 14 provided for each feeder 12 of the electric equipment 2 and amplifying the zero-phase current signal 16, and a bandpass filter for inputting the output signal thereof. 18 and the same zero-phase current signal 16
And a high-frequency amplifier 21 for amplifying the signal 16 including a harmonic, a frequency detecting means 22 for inputting the output signal thereof, an output signal of the band-pass filter 18, and
An arithmetic processing unit 19 which takes in a signal from the frequency detecting unit 22 and performs an operation for specifying a ground fault point at the time of intermittent arc light ground fault, a detection signal 30 indicating a feeder whose insulation is deteriorated by an output from the arithmetic processing unit 19, and an intermittent arc light ground fault. The display unit 20 is configured to display a diagnosis result in response to a detection signal 31 that specifies a ground fault point at time.

FIG. 2 shows an example of the temporal change of the zero-phase current when the insulation of the cable deteriorates. Generally, when cable insulation deteriorates, zero-phase current increases with time. Zero-phase current reaches a value I ₂ which is predetermined, zero-phase current because breaker 13 is opened at the stage in front of the I ₁ reaching I ₂ by the protective device, insulation deterioration in electrical equipment maintainer If it is possible to inform the occurrence of the power generation, sudden power supply interruption can be avoided. The zero-phase current I ₂ for opening the circuit breaker 13 by the protection device is generally about 200 milliamperes, and the zero-phase current is several tens of milliamperes in order for the maintenance personnel of the electric equipment to deal with it with a margin. _It is necessary to perform maintenance work at time t ₁ when it becomes ₁ . Therefore, the insulation monitoring device needs to be able to detect a zero-phase current of about several milliamperes. Therefore, in the zero-phase current transformer 14 of the insulation monitoring apparatus in this embodiment, the number of turns of the secondary winding is increased so that it can detect up to 2 milliamperes, which has higher sensitivity than a normal one.

However, the zero-phase current signal 16 has a waveform in which harmonics and noise are superimposed on the waveform of the fundamental frequency.
In this device, since a region in which the waveform component of the fundamental frequency is small must be handled, the performance required of the bandpass filter 18 is about Q = 5 with the fundamental frequency at the center. The zero-phase current signal 16 is amplified to a predetermined level by the amplifier 17, and the fundamental frequency component is extracted by the bandpass filter 18 and then input to the calculation unit 19. The calculation unit 19 identifies the cable in which the insulation deterioration has occurred and estimates the degree of the insulation deterioration based on the input signal.

Even if the insulation deterioration does not occur, the zero-phase current flows in each feeder because the stray capacitances of each phase constituting the feeder are not uniform. If an insulation deterioration state occurs in a specific feeder in this state, the current vector flowing in the feeder becomes large due to the ground fault current. The zero-phase current vectors of the other feeders are in the opposite direction compared to the insulation deterioration feeder. Therefore, to identify the deterioration feeder,
The magnitude and direction of each zero-phase current may be detected. Insulation deterioration is almost always caused by deterioration of the entire feeder, and there is no need to detect the deterioration position.

FIG. 3A shows an example of the intermittent arc light ground fault current waveform, and FIG. 3B shows the relationship between the peak current of the high frequency current applied to the bandpass filter 18 and the maximum value of the bandpass filter output. This is an example. The amplifier 17 and the bandpass filter 18 receive the peak of the high frequency current input as shown in FIG. 3B when the high frequency current of 10 times or more the bandpass frequency as shown in FIG. 3A is applied. The maximum value of the current and the output of the bandpass filter 18 is
There is a proportional relationship. Therefore, in the arithmetic processing section 19, the effective value of each bandpass filter 18 output is calculated,
It suffices to detect the feeder having the maximum value, and further to detect that the direction of the feeder current is in the opposite direction as compared with other feeders.

Next, the degree of insulation deterioration is determined by comparing the absolute value of the zero-phase current of the insulation deterioration feeder specified by the calculation result in the above-described calculation processing unit 19 with n stepwise reference current values. It can also be determined. A signal 30 specifying the insulation deterioration feeder and a signal 31 indicating the degree of insulation deterioration of the feeder in n steps are displayed by the arithmetic processing unit 19 on the display unit 2.
The display unit 20 displays the name or number of the feeder having insulation deterioration and the degree of insulation deterioration of the feeder in n stages.

Next, a means for identifying the ground fault point of the intermittent arc light ground fault current will be described. Fig. 4 shows the relationship between the intermittent arc light ground fault current waveform and the cable length to the ground fault point. FIG. 4A shows a ground fault current waveform, and A, B and C attached to the waveforms in the figure show the cable length up to the ground fault point as shown in FIG. 4B. . The longer the cable length to the ground fault point, the lower the vibration frequency of the ground fault current.

Since the zero-phase current signal 16 is generated due to the flow of the intermittent arc light ground fault current, the frequency detecting means 22 detects the oscillation frequency of the ground fault current after amplifying the signal by the high frequency amplifier 21. In order to transfer the frequency characteristics of the zero-phase current transformer 14 to a high frequency (normally 50 KHz to 1 MHz), it is necessary to reduce the load on the zero-phase current transformer 14, and therefore, the high-frequency amplifier 21 generates a small signal current. It is amplified to reduce the input impedance of the zero-phase current transformer 14.

An intermittent arc light ground fault simulation test was carried out and the following phenomenon was discovered. (1) The intermittent arc light ground fault current is the stray capacitance (Cb) on the bus side.
And total capacitance of stray capacitance (Cx) of other feeders Ct = C
Depends on b + Cx. (2) If the total cable length of the ground fault feeder is M (Km) and the distance to the ground fault point is M ₁ (km), the intermittent arc light ground fault current depends on M ₁ . (3) The resonant frequency of the intermittent arc light ground fault current is inversely proportional to the square of Ct * L. Where L is the reactance of the cable. (4) The peak value of the intermittent arc light ground fault current is proportional to the square of Ct and inversely proportional to the square of M ₁ .

The intermittent arc light ground fault phenomenon is a resonance vibration waveform of L and C of the cable, and the current and its frequency are generally
It is expressed by the following formulas 1 and 2.

[0023]

## EQU1 ## I = K ₁ * V / (√ (L / C)) I: current, C = Ct, voltage of V = C, K ₁ = coefficient

[0024]

## EQU2 ## f = K ₂ / (2π * (√ (L * C)) f: frequency, C = Ct, K ₂ = coefficient On the other hand, if the cable length to the ground fault is M ₁ , then L is
It is expressed by the following equation.

[0025]

Equation 3] _{L = K 3 * M 1 K} 3 = Equation 4 from the coefficient Equations 2 and 3 by the cable is guided.

[0026]

## EQU4 ## M ₁ = K / ((2πf) ² * C) K = coefficient Therefore, after the zero-phase current is detected by the zero-phase current transformer 14, its frequency is detected, and the arithmetic processing unit 19 calculates the equation 4 The distance to the ground fault can be estimated by calculation.

A signal indicating the feeder in which the intermittent arc light ground fault current specified by the above calculation result flows and the position estimation result of the ground fault occurrence point of the feeder is sent from the calculation unit 19 to the display unit 20 and displayed. In the section 20, the name or number of the feeder in which the intermittent arc light ground fault has occurred due to the insulation deterioration and the position thereof are displayed by the cable length. The maintenance staff of the electric equipment makes an immediate repair or a plan of repair according to the contents of the display device.

[0028]

As described above, according to the present invention, the intermittent arc light ground fault point can be estimated for each feeder, and the insulation deterioration can be constantly diagnosed.

[Brief description of drawings]

FIG. 1 shows the configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a change over time of a zero-phase current due to insulation deterioration.

FIG. 3 is a diagram showing output characteristics of a bandpass filter when (a) an intermittent arc light ground fault current waveform and (b) an intermittent arc light ground fault current are input.

FIG. 4 is a diagram showing (a) the relationship between the intermittent arc light ground fault current waveform and the cable length up to the ground fault point, and (b) the relationship between the cable length up to the ground fault point and the intermittent arc light ground fault current frequency. .

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulation monitoring apparatus 2 Electric equipment 10 Power receiving section 11 Bus 12 Feeder 13 Circuit breaker 14 Zero-phase current transformer 15 Load 17 Amplifier 18 Band pass filter 19 Calculation processing section 20 Display section 21 High frequency amplifier 22 Frequency detecting means

Claims (4)

[Claims] 1. An insulation diagnostic device for diagnosing insulation of an electric work by detecting a zero-phase current of a power system, and a frequency detecting means for detecting a frequency of the zero-phase current detected from a feeder, and the frequency detecting means. An insulation diagnosis apparatus comprising an arithmetic processing unit for calculating an intermittent arc light ground fault point from the output of the electric power system and a constant of the electric power system. 2. An insulation diagnostic device for diagnosing insulation of an electric work by detecting a zero-phase current of a power system, and frequency detection means for detecting a frequency of the zero-phase current detected from each of a plurality of feeders. A bandpass filter for inputting the zero-phase current and extracting the power system frequency component, and calculating an intermittent arc light ground fault point from the output of the frequency detecting means and a constant of the power system and comparing a plurality of outputs of the bandpass filter. An insulation diagnosis device comprising an arithmetic processing unit for obtaining a feeder having the maximum output value. 3. A band pass for extracting the power system frequency component of the zero phase current detected from each of a plurality of feeders in an insulation diagnosis device for diagnosing insulation of an electric work by detecting a zero phase current of the power system. An insulation diagnosis apparatus comprising: a filter; and an arithmetic processing unit that compares the output of the band pass filter with N levels set in stages and divides the output into N stages. 4. The insulation diagnostic device according to claim 1, wherein the feeder is an insulated cable.