JPH01221680A - Detecting method for insulating condition - Google Patents

Abstract

PURPOSE:To always monitor in a hot-line state an insulating condition for an electric machine and a cable by detecting a traveling-wave generated due to a corona discharge or a partial discharge, with sensors which are installed in an electrical base point and each transmission path for an electric power. CONSTITUTION:A low frequency current consisting of a power source frequency and its harmonic frequency, and the traveling-wave current generated with the corona discharge or the partial discharge are induced in each winding, and an inductive reactance of a 1st winding M1 is made to be small for the low frequency and large for a pulse. Therefore, a flux variation by a magnetomotive force of the low frequency current iE is extinguished almost completely but the one by the magnetomotive force of the pulse current caused by the traveling-wave (ip) passing through is not extinguished. So, only a signal generated with the traveling-wave passing through can be obtained from both terminals of a 2nd winding M2. Also with sensors SR for deciding a deteriorating phase, which are inserted in each phase of capacitors CT arranged in a bus LP, a discriminating signal for the deteriorating phase can be obtained by discriminating which phase the traveling-wave will pass through. Further, the traveling-wave is made to pass through to the same direction even if any phase or any part within the system is deteriorated, thereby the base signal for that direction can be obtained by a sensor SF on a common line.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for detecting an insulation state, and more particularly to a method for identifying a defective insulation portion of a power transmission path.

[Conventional technology]

In general, local insulation failures may occur in buried power cables and power equipment connected to them due to various factors.

Causes of such insulation failures include mechanical external forces, chemical changes in the insulation material, and so-called water trees, but 80% of serious accidents are caused by such insulation deterioration. Therefore, various insulation testing methods have been proposed.

An example of this is a method in which the power transmission system is periodically brought into a power outage state. First, in the method of testing by applying a DC voltage to the line, the first step is to measure partial discharge, the second step is to measure dielectric relaxation due to residual voltage, discharge current, and residual charge, and the third step is to measure the dielectric relaxation phenomenon due to residual voltage, discharge current, and residual charge.
Examples include measuring insulation performance by potential attenuation and leakage current.

On the other hand, in the method of testing by applying AC voltage to the line,
The first method includes measurement of partial discharge, and the second method includes measurement of dielectric relaxation phenomenon due to dielectric loss tangent l.

Apart from this, there is a method of testing the power transmission path in a live state by using a portable measuring device.

[Problem that the invention seeks to solve]

However, among the conventional detection methods described above, those that periodically put the power transmission system in a power outage state require time to measure each line in sequence, and
- There are restrictions on the locations that can be measured due to power outages. For this reason, even if the insulation condition deteriorates over time, there is a problem in that it is impossible to know the trend and it is impossible to take preventive measures.

On the other hand, the method of inspecting the power transmission path in a live state using a portable measuring device not only requires human labor for preparation work and measurement, but also has the problem that it is difficult to ensure safety and requires skill for measurement. There is.

The present invention has been made in view of the above-mentioned matters, and a technical object thereof is to provide a method for detecting the insulation state of power equipment and power cables that can constantly monitor the insulation state of the power cable in a live wire state. .

[Means for solving problems]

In order to solve the above technical problem, the present invention employs the following method in a transmission system having one or more power transmission paths.

That is, when the insulation performance of the power transmission path deteriorates, traveling waves generated due to corona discharge or partial discharge that occur in that region are detected by the electrical reference point and the sensor S attached to each power transmission path. do.

The sensor S has a linear BH characteristic in which magnetomotive force and magnetic flux density have a substantially proportional relationship, and has a ring-shaped core K whose magnetic permeability is substantially constant from a low frequency range to a high frequency range. It is formed by winding a first winding Ml and a second winding M2, and detects the insulation state by measuring a signal from the second winding M2.

[Effect]

When an insulation defect occurs in a power transmission path, corona discharge or partial discharge occurs at that location.

Then, a traveling wave is generated due to this discharge and travels in both directions on the line from the defective part. Therefore, by detecting the direction of this traveling wave, it is possible to identify the transmission path where the insulation performance has deteriorated.

As a method of detecting the direction of the traveling wave, the traveling direction of the traveling wave at a specific (reference) point of the common bus line, which is an electrical reference point, and the traveling direction of the traveling wave on each power transmission path taken out from the common bus line. By comparing the phase with that, it is also possible to identify the defect position.

That is, to explain an example of the action with reference to FIG.
Traveling wave current generated by insulation deterioration at a point passes through all sensors. Here, with the direction of the traveling wave passing through the sensor SF provided near the capacitor C provided on the first common bus LP as a reference, and looking at the traveling wave current passing through the sensor (S) provided on each cable (L), the corresponding Only the sensor (Sl) of the cable (Ll) where the insulation has deteriorated will detect the traveling wave in the opposite direction.

Similarly, if the direction of the traveling wave passing through the sensor SG located between the second common bus LG and the ground GND is taken as a reference, let's look at the traveling wave current passing through the sensor (S) provided on each cable (L). and the cable (Ll) where the insulation deterioration occurred
Only the sensor (S4) detects the traveling wave in the opposite direction.

Therefore, the signals detected by these sensors S are
By measuring with , the location of insulation failure becomes clear.

As a sensor (signal discriminator) for detecting traveling waves, the annular core K may be formed of, for example, an amorphous metal containing cobalt as a main component.

Then, as shown in FIG. 3(A), a cable (L) serving as a power transmission path is wound around the annular core K. Cable (L)
A low frequency current and a high frequency current are flowing through the core K, and a magnetomotive force is generated in the core K due to this.

The first winding Ml and the second winding M2 act as a secondary coil for the cable (primary coil) (L), so depending on this magnetomotive force, an electromotive force is generated in the first @ wire M1, or both ends thereof are Because of the short circuit, a current flows through the annular core to cancel out the changes in the magnetic flux inside.

Here, the annular core has a high magnetic permeability, the permeability is approximately constant from the low frequency range to the high frequency range, both the residual magnetism and the coercive force are small, and the magnetomotive force and the magnetic flux density have a substantially proportional relationship. Since it has the BH characteristic of the line type, the first winding M
! The inductive reactance of is small for low frequencies and large for high frequencies.

Therefore, the low frequency component is canceled out and only the high frequency component is obtained from the second winding M2.

Incidentally, in practice, the detected wire 4 only needs to be inserted into the core L as shown in FIG. 3(B).

The material of the annular core is, for example, cobalt (Go).
) Iron (Fe) Silicon (Si) Boron (B) Molybdenum (
Mo) Made of nickel (Ni), formula % () (where a-r indicates the percentage of each component element, a = 50
~90, b=t~10, c=5~20, d=O~20,
e=0 to 20, f=1 to 5, and the sum of a=f is 1
Set to 00. ) is displayed.

In addition, for the annular core, for example, a ribbon of a cobalt-based amorphous alloy is used to form a toroidal core at a temperature of 150°C.
A desired magnetic permeability can be obtained by performing heat treatment at a temperature of .degree. C. to 450.degree. C. for 5 to 180 minutes. In this case, it is preferable to perform the heat treatment in a direct current magnetic field or an alternating current magnetic field from the viewpoint of uniformity of performance, and more stable performance can be obtained if the heat treatment is performed in a nitrogen atmosphere.

Note that the first @ wire Ml and the second @ wire M2 may be divided into separate windings, or the first @ wire M1 and the second winding M2 may partially be used in common.

In addition, the core may be, for example, 602 made by Bakum Shemerce, which is a ribbon of cobalt-based amorphous alloy.
5F can be used.

In addition to the above-mentioned sensors, there are other sensors for detecting traveling waves.
Depending on the nature of the energy to be transmitted, a passing wattmeter or the so-called S
Applications such as a WR meter can also be considered.

〔Example〕

Embodiments of the present invention will be explained based on FIGS. 1 to 9.

First, the applicant confirmed that when an insulation failure occurs in a power transmission path, corona discharge or partial discharge occurs in the relevant part, and traveling waves are generated in the transmission path due to these discharges. did.

Hereinafter, in explaining a method for detecting an insulation state, a description will be given starting from a device that detects an insulation defect in a power transmission path based on the traveling wave.

AC power supply A first supplies power to substation 1, and in this substation 1, power is supplied to the t#th transmission line via transformer TI and circuit breaker Bl.
, i bus, and F, and this first common bus LF' is grounded (GIIO) via a capacitor C.

A ring-shaped sensor SF is attached to the line between the capacitor C and the ground section so as to surround it, and the output signal from this sensor SF becomes a signal at a reference point provided on the common bus bar.

The first common bus line LP is provided with a circuit breaker B2. Circuit breaker B3
, a power transmission cable 1, a cable L2, and a cable L3 are connected via a circuit breaker B4, and annular sensors St and S2.83 are attached to these cables so as to surround the cables. The cable Ll is extended to the electricity demand location 2.

At the electricity demand location 2, a sensor S4 is attached to the cable L1, and is connected to the second common bus LG via a circuit breaker B5.

The second common bus line LG is grounded (G
ND) has been done. A ring-shaped sensor SG is attached to the line between the capacitor C and the ground so as to surround it, and the output signal from this sensor SG becomes the signal at the reference point of the second common bus line LG.

The second common bus LG has a circuit breaker B6. A power transmission cable L4 and a cable L5 are connected via a circuit breaker B7, and a ring-shaped senna S5. S6 are respectively attached to surround these cables.

The cable L4 is connected to the electric motor M, and the cable L5 is connected to the transformer T2.

Said Senna St, S2. The output signal of S3 is input to the scan circuit 10 and divided in time series, and then sent to the direction comparison circuit 1.
! and is compared with the signal from the sensor SF.

This comparison result is input to the data transmission circuit 12.

On the other hand, the sensor S5. The output signal of S6 is input to the scan circuit 20 and divided in time series, and then sent to the direction comparison circuit 2.
1ζ is input and compared with the signal from the sensor SG. This comparison result is input to the data transmission circuit 22.

The respective signals of the data transmission circuit 12 and the data transmission circuit 22 are input to the measurement section 33, and these signals are first sent to the scan circuit 3! After being input into the system and chronologically formatted, the data is input to the high-speed data storage circuit 32 and also to the alarm/display circuit 33.

The high-speed data storage circuit 32 is a personal computer 34
It is now connected to the computer and data can be exchanged.

A CRT 36 and a printer 37 are connected to the personal computer 34 to display test results. The specific hardware of the high-speed data storage circuit 32 will be explained based on FIG. Peak detection PS1 connected to detect the maximum value of the output signal A of 20 MIIZ connected in parallel with this peak detection PS
/D converter AD, a memory board MB which stores the respective output signals of these peak detection PS and A/D converter AD and has a capacity of 2B.

A personal computer 34 that sends and receives signals to and from the memory board MB, and a printer 35 as an output device are connected as shown in the figure.

Next, the operating principle of the sensor S and the operating principle of the circuit will be explained.

As shown in FIG. 5, the sensor S has a substantially constant magnetic permeability from low to high frequencies, small residual magnetism and coercive force, and a linear B-H characteristic as shown in FIG. Core K made of cobalt-based amorphous gold and white
It is constructed by winding a coil around. As shown in FIG. 3, this coil consists of a first @ wire Ml wound around the core K in a short circuit, and a second winding M2 with both ends open. The core has a width of 10"9, an inner diameter of 1501.j and a height of 31. The number of turns of the first winding M-1 is 3, and the number of turns of the second winding M2 is 10. be.

With such a configuration, it is possible to distinguish between the frequency of the power source, a low frequency current that is a harmonic thereof, and the traveling wave current associated with the above-mentioned corona discharge or partial discharge. As a result of experiments on the sensitivity of the sensor S having such a configuration, it was possible to detect a corona discharge charge amount of about 20 PC.

Figure 2 shows an example of implementation on a line transmitting three-phase alternating current.
Here, the traveling speed V of the traveling wave is: ■=[(magnetic permeability x permittivity)'/'') ] -'.

Here, since the dielectric constant of the polyethylene insulator is four times that of air, the propagation speed in the transmission path is about 1/2 of the speed of light, so Vl;k is about 150III/μs. Since the traveling wave thus passes through the core at high speed, a sharp pulsed magnetomotive force is generated. Each winding is induced by a low frequency current that is the frequency of the power supply and its harmonics, as well as a traveling wave current associated with the above-mentioned corona discharge or partial discharge, but the inductive reactance of the first winding M1 is becomes small, and becomes large for pulses. Therefore, is the magnetomotive force of the low frequency current iE?
Although this magnetic flux change can be almost completely canceled out, the magnetic flux change due to the magnetomotive force of the pulse current caused by the passage of the traveling wave ip remains uncancelled.

Therefore, only the signal accompanying the passage of the traveling wave can be obtained from both terminals of the second @ line M2.

In addition, it is possible to determine which phase the traveling wave passes through using a degraded phase determination sensor SH inserted into each phase of the capacitor CT installed on the bus LP, and obtain a signal for determining the degraded phase. Furthermore, the sensor SF connected to the common line of the capacitor CT
No matter which phase deteriorates or which part of the system deteriorates, the traveling wave passes in the same direction, so that it is possible to obtain a signal that serves as a reference for the direction of the traveling wave.

The signals from these detection layers may be sent out in time series by the scan circuit as in the embodiment described above, but if there is sufficient signal transmission capacity, parallel processing may be performed.

The traveling wave exhibits a frequency spectrum similar to that of discharge noise and has energy over a wide frequency range, but it may exhibit a frequency distribution peculiar to corona discharge due to poor insulation, and unnecessary bands may be restricted to prevent external noise. In order to improve the S/N ratio with respect to noise, it is effective to limit the band using a bandpass filter.

When we experimented using a bandpass filter in this way, we found that the frequency range to be detected was from 20KH2 to 200KH2.
Mt [Z preferably from 300 KHz to 50 MIIZ
.

More preferably, good results were obtained when it was set between 300 KH2 and 5 Mn2. The specific passing frequency must be optimized for each case using a spectrum analyzer or the like. As for this filter, of course, in addition to the single tuning type described above, a multi-point tuning type comb filter can be used.

Next, the results of an experiment in which the sensor shown in FIG. 3 was used in the circuit shown in FIG. 1 to detect a traveling wave caused by corona discharge due to deterioration of the cable insulation will be described with reference to FIG. 6. In the graph, J is the signal characteristic line of the sensor SF provided on the cable, and Q is the signal characteristic line of the sensor S1 provided on the bus bar.

If the cable is defective, the traveling waves will travel in both directions, but
Since the traveling wave current passes through the sensor SF and the sensor S1 in opposite directions, the phases of J and Q are substantially opposite to each other. This reveals the presence of a traveling wave, ie, a defect in the cable.

Next, actual measured waveforms will be explained based on FIGS. 8 and 9.

FIG. 8 shows a case where a traveling wave is generated far away from the measurement point, and the traveling wave reflected by a terminal load such as an electric motor appears periodically.

Incidentally, although it is possible to observe the pulses associated with corona discharge as they are, since they occur in an extremely short period of time, it may be difficult to capture them. Therefore, by inserting a resonant circuit into the pulse detection circuit, it is possible to easily capture the pulse. FIG. 9 shows waveforms when such a circuit is used, where Jl is a pulse associated with corona discharge, and this pulse then excites the resonant circuit to exhibit a damped waveform J2 of a specific frequency.

Note that the dimensions, shape, and material of the core are not limited to those in the embodiments described above, and can of course be changed as appropriate depending on the detection conditions.

〔Effect of the invention〕

According to the present invention, when the insulation performance of the power transmission path deteriorates, traveling waves generated due to corona discharge or partial discharge that occur at that location are installed at the electrical reference point and each power transmission path, respectively. Since the sensor S detects the signal and the signal from the second winding M2 wound around the sensor S is measured, the insulation state of the electric equipment and the cable can be constantly monitored in a live state.

Furthermore, when an abnormality occurs in the insulation state, the location can be specified.

Therefore, insulation defects can be detected at a minor stage, and accidents caused by insulation defects can be prevented.

[Brief explanation of the drawing]

Figures 1 to 9 show embodiments of the present invention; Figure 2 is an overall block diagram; Figure 2 is a circuit diagram of the senna portion; Figure 3 (A)CB'') is a front view of the senna. , Figure 4 is a BH characteristic diagram of the core used in the sensor, Figure 5 is its frequency characteristic diagram, Figure 6 is a graph diagram showing the detection results of traveling waves, and Figure 7 is a graph diagram showing the detection results of traveling waves.
The figure is a block diagram of the signal processing circuit, and FIGS. 8 and 9 are graphs of measurement results. ! ...Substation, 2.Electricity demand location, 3.Measurement section, St, S2. S3. S4. S5. S6. SF...Sensor, M! ... 1st winding, M2
...2nd @ line, K...core, C
, CT? ...Capacitor, P...Insulation deterioration point. Figure 3 (A) (B) Figure 4 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] (1) In a transmission system that has one or more power transmission paths, when the insulation performance of the power transmission path deteriorates, the traveling waves generated due to corona discharge or partial discharge that occur in that area are measured using electrical standards. Detection is performed by sensors S attached to each point and each power transmission path. A first winding M1 and a second winding M2, both ends of which are short-circuited, are wound around an annular core K whose winding is approximately constant, and the insulation state is determined by measuring the signal from the second winding M2. A method for detecting an insulation state, the method comprising: detecting an insulation state;