JP2020148579A - Single-shot earth fault detector - Google Patents

Abstract

To provide a single-shot earth fault detector which separates a single-shot earth fault and a noise from each other to detect a single-shot earth fault alone, finds a degraded part or a surge entrance part in the stage of generation of a single-shot earth fault, and predicts and displays/warns a position where a cable failure is highly likely to occur for precaution.SOLUTION: A single-shot earth fault detector 1 includes: a converter 11 for measuring a current flowing in a ground line 24 of a sheath 23 of every high-pressure power cable line 20; an integration circuit 12 for integrating the current and converting the current into the charge amount; a determination circuit 13 for determining at least a predetermined amount alone of the charge amount; and a display 14 for displaying the result and/or a warning device. A single-shot earth fault having a pulse-shaped discharge in the high-pressure power cable 21 and another noise such as an opening/closing surge or a lightning surge are separated and the single-shot earth fault alone is detected. The detected single-shot earth fault is displayed or a warning to the single-shot earth fault alone is issued. In that way, it becomes possible to predict a cable failure due to a complete earth fault current before the failure actually happens.SELECTED DRAWING: Figure 1

Description

According to the present invention, in a high-voltage power cable used in a factory or the like, even if a failure occurs due to dielectric breakdown due to natural deterioration or the like, a complete ground fault does not occur at once, and one quarter of a single commercial frequency. It is known in part that it stays in a ground fault with a degree of waveform, and this ground fault (hereinafter referred to as a single ground fault) is detected and it is preliminarily detected before the cable develops into a full-scale electrical failure. It is related to a single-shot ground fault detection device that predicts and displays.

Most of the power systems in which high-voltage power cables are used are distributed in non-grounded systems or high-resistance grounded systems, and even if insulation breaks occur due to deterioration of the high-voltage power cables, ground faults at commercial frequencies are immediately generated. It does not develop into a failure in which the current continues, and the insulation is temporarily restored with a single ground fault current that has a waveform about one-fourth of the commercial frequency, and then the single ground fault is repeated before full-scale operation. It is known in part that it leads to a typical ground fault.

This phenomenon occurs in the case of non-grounded systems, etc., because there is a phase difference between the ground fault current and voltage, and it is difficult for the ground fault to continue, and the main material of the high-voltage power cable is a cross-linked polyethylene cable (CV or The reason is that it is composed of a CVT cable) and is difficult to carbonize immediately, the dielectric strength is high when the diameter of the break hole is small, and the insulation is restored when foreign matter such as moisture is blown off. ..

Even if a high-voltage power cable fails, dielectric breakdown due to mechanical stress such as cutting of insulation will develop into a complete ground fault at once.

For this reason, this phenomenon is a phenomenon that occurs mainly in cases such as destruction due to insulation deterioration even in a cable failure, and does not apply to all failures including failures such as cable disconnection.

On the other hand, in high-voltage power cables (mainly 6.6 kV and 3.3 kV class CVs and CVT cables), partial discharge detection and insulation resistance have been attempted to predict deterioration of the high-voltage power cables in advance. Various methods for predicting deterioration of high-voltage power cables such as measurement have been tried. However, it is difficult to detect a weak signal in the field, and even if it deteriorates to some extent, it is not a decision to replace the high-voltage power cable, and it is usual to continue using it.

Until now, the single-shot ground fault phenomenon was not generally known because the CV cable makes a small clicking sound even if the insulation breaks down due to insulation deterioration due to insulation deterioration or intrusion surge. This is because the switch and the circuit breaker did not work and did not cause a failure. On the other hand, in order for the original switch and circuit breaker of the cable to detect the failure and operate, it is when the ground fault current continues for a certain period of time or when the short circuit failure occurs.

When such a single-shot ground fault occurs in a high-voltage power cable (6.6 kV or 3.3 kV class CV, CVT cable), the insulation is temporarily restored and it can be used, but after that, the ground fault location expands. , Causes a complete ground fault due to intrusion surge. In this case, power transmission may be stopped or a fire accident may occur. In addition, if a single ground fault continues, the voltage of the healthy phase jumps up due to the characteristics of the non-grounded system, which may lead to serious failures such as short-circuit failure and short-circuit failure of other lines.

The single-shot ground fault phenomenon is known in some cases because as a result of disassembling the cable that caused a serious failure, many traces of the single-shot ground fault remained on the cable insulator, and also from the cable before the failure. This is due to the observation results such as the fact that a small snapping sound was heard.

Patent Document 1 has invented a detection device before a cable failure based on the theoretical elucidation result of this single-shot ground fault phenomenon.

The invention of Patent Document 1 detects a pulsed current from a flowing current by using the output of a current transformer of the main line for each of the high-voltage power cable lines of a wide variety of high-voltage power cable lines. The polarity is compared with that of a multi-phase or other line, and based on the result, the cable with a single ground fault is cut off and switched to another line. Patent Document 1 describes such a method for predicting a ground fault in a high-voltage power cable.

In such a high-voltage power cable ground fault prediction method, a large-scale device that compares the output from the current transformer of the cable body and the pulse polarity of each line for each high-voltage power cable line is required everywhere. Not only that, it required a considerable cost for its installation and maintenance, and it did not reach general practical use.

As an alternative device, it was considered whether this pulsed current could be detected by the ground wire of the high-voltage power cable. However, since the ground wire of the high-voltage power cable is grounded at one end and has a large antenna state, it constantly picks up noise. Among the noise, the switching surge that occurs when opening and closing the power supply and the lightning surge from the outside are expected to be higher than the peak value of the single-shot ground fault, so the pulse-shaped single-shot ground fault current can be discriminated. It was considered difficult to put into practical use, and no further consideration was given.

On the other hand, it has been several decades since CVs and CVT cables made of cross-linked polyethylene as a cable material for high-voltage power cables have been widely used, and many failures due to deterioration have occurred. In the past, it was performed in the form of deterioration diagnosis of CV cables, but for that purpose it is necessary to stop the equipment, and in the operating state, deterioration detection such as partial discharge that is smaller than the noise of normal aerial radio waves is practical. However, the deterioration to the extent that the insulation resistance decreased did not make a decision to replace the cable. A device for predicting a full-scale failure, which is a device for determining that a cable as in the present invention is already in an unusable state, is desired.

FIG. 4 shows the measured waveforms of the single-shot ground fault waveform and the complete ground fault waveform referred to here.

Japanese Unexamined Patent Publication No. 5-343397

The problem to be solved by the present invention is not to detect a single ground fault from the current transformer of the main line of the high-voltage power cable line, but to detect the current transformer which is a single sensor in the ground wire of the sheath of each high-voltage power cable. If a single ground fault current can be detected, a device or method that can be predicted without a large-scale facility as in Patent Document 1 of the previous term is provided.

However, in the prior art, it is difficult to distinguish between the single-shot ground fault and the noise because the ground wire connected to the high-voltage power cable sheath has noise larger than the single-shot ground fault current. The noise is an opening / closing surge that accompanies the opening / closing of a circuit breaker, etc., and a lightning surge that flows through various routes. Since the peak value is higher than the peak value of the single-shot ground fault current, it is considered that discrimination is not possible. Was being done. Therefore, it was necessary to solve this problem.

Until now, it was thought that single-shot ground faults and noise detected by the ground wire could not be discriminated from noise at the peak value, and could only be discriminated by polarity as in Japanese Patent Application Laid-Open No. 5-343397. However, this problem is solved. As a means for this purpose, the present invention was completed by focusing on the amount of electric charge, which is the energy of the current, rather than the peak value of the current value of a single ground fault or noise.

From the observation results of the actual single-shot ground fault current, as shown in Fig. 5, the single-shot ground fault is unipolar, and a current with a waveform about one-fourth of the commercial frequency flows, so its duration is in milliseconds. On the other hand, the opening / closing surge and the lightning surge have a short duration of the microsecond unit, and since the opening / closing surge has a repetitive waveform, the amount of electric charge is offset and becomes small.

In addition, as a result of theoretical calculation of the single-shot ground fault current, not only the current due to the capacitance of the single-shot ground fault phase flows in, but also the current for the AC power supply passes through the capacitance of the other non-ground fault phase. As a result, it was found that the current flows in continuously, and as a result, the charge amount of the single ground fault current is much larger than the charge amount of the noise.

The present invention distinguishes between single-shot ground faults and noise, detects only single-shot ground fault currents, finds deterioration points and surge intrusion points at the stage of single-shot ground fault occurrence, and determines locations with a high probability of causing cable failure. It is an object of the present invention to provide a single-shot ground fault detection device that predicts, displays and warns.

The single-engine ground fault detector of the present invention made to achieve the above object is a current converter that measures the current flowing through the ground wire of the sheath for each high-voltage power cable line, and integrates the current and converts it into a charge amount. A single-engine ground fault detection device having an integrating circuit for discriminating only a predetermined amount or more of the charge amount, and a display and / or alarm for the result, in the high-voltage power cable. By discriminating between a single ground fault having a pulsed discharge and other noises such as open / close surge or lightning surge, and detecting and displaying / or alarming only the single ground fault, a cable failure due to a complete ground fault current is reached. It is characterized in that it predicts the cable failure in advance.

This single-engine ground fault detector can be discriminated from other noises by attaching a current transformer to the ground wire of the sheath of each power cable line and converting it into an electric charge through an integrating circuit that integrates the currents. , Only a single ground fault is detected, and a display or alarm that displays the discriminated result is used to predict and display a cable failure due to the ground fault.

In this single-shot ground fault detection device, the integrating circuit may, numerically speaking, integrate the single-shot ground fault having a waveform (about 5 milliseconds) of about one-fourth of the commercial frequency. As a result, the single-shot ground fault current can be completely distinguished from the noise current, which can be detected by a current transformer attached to the ground wire, an integrating circuit, and a discrimination circuit, and a display circuit or alarm that displays the result. It can be displayed on a circuit.

This single-engine ground fault detector is a current transformer with low frequency characteristics for measuring the current flowing through the ground wire that grounds the sheath of each high-voltage power cable line (only high-frequency components can be measured with a normal ferrite core). It consists of an integrator for integrating the measured current waveform and converting it into an electric charge, a circuit for comparing and discriminating the magnitude of the electric charge, and an indicator for displaying or alarming when the level exceeds a certain level.

This single-shot ground fault detector digitally converts all the current waveforms from the current transformer, discriminates the single-shot ground fault waveform from the characteristics of each waveform, and generates the above display and / or alarm. It may be characterized by detecting the current of the waveform.

The single-shot ground fault detection device may have a surge counter and / or an indicator thereof for counting the number of times the single-shot ground fault is identified.

The single-shot ground fault detection device may be connected to an alarm device that warns of the identification result of the single-shot ground fault.

The single-shot ground fault detection method of the present invention made to achieve the above object measures the single-shot ground fault current and noise having a pulsed discharge while measuring the current flowing through the ground line connected from the sheath of each high-voltage power cable line. The process of capturing the open / close surge current or lightning surge current, which is the current, the process of integrating those currents with an integrating circuit and converting them into a charge amount, and distinguishing between noise and a single ground fault according to the integrated charge amount. By having the step of displaying the result on the display and / or driving the alarm when the single ground fault is identified, the cable is before the cable failure due to the complete ground fault current. It is characterized by predicting a failure.

Specifically, this single-shot ground fault detection method is a process of measuring the current flowing through the ground wire connected to the sheath of each power cable line, capturing the current flowing into the cable sheath, and integrating those currents and capturing them as the amount of charge. Also, the step of comparing the magnitudes of this level and identifying only the pulsed single-shot ground fault waveform, thereby displaying the result on the display and / or the alarm when the single-shot ground fault is identified and discriminated. By having a step of driving the cable, a cable failure due to the complete ground fault current is predicted, displayed and / or warned.

According to the single-shot ground fault detection device of the present invention, the phenomenon can be detected at the stage of single-shot ground fault, which can be said to be the initial dielectric breakdown of the high-voltage power cable, and if measures such as cable replacement are taken at that stage. , It is possible to prevent the development of a major failure accompanied by a fire or the like.

As described above, 6.6 kV and 3.3 kV class CV and CVT high voltage power cables are generally used in ungrounded systems. In the non-grounded system, when one of the three phases has a ground fault, the voltage of the healthy phase jumps up, and this single-shot ground fault causes a short-circuit failure or a short-circuit failure with another line that straddles the line. May cause. According to the present invention, it is possible to predict in advance and take countermeasures before these major electrical failures occur.

As a method of predicting deterioration leading to dielectric breakdown of high-voltage power cables, deterioration diagnosis methods such as detecting partial discharge of high-voltage power cables and measuring insulation resistance have been performed, but all of them use high-voltage power cables. It was necessary to carry out with a power outage, and it was difficult to judge the progress of deterioration.

As a method of detecting deterioration of a high-voltage power cable during use of the cable, attempts have been made to detect partial discharge, etc. with the ground wire of the cable sheath, but the sheath of the power cable is grounded at one end and has an antenna of several hundred meters. It is almost impossible to detect a much minute partial discharge current in a large noise. Even if a partial discharge is detected, it cannot be used as a guide for how long the high-voltage power cable can be used.

However, this single-shot ground fault detector and the failure prediction method using it do not require troublesome operations or circuits to compare the polarity and magnitude of the current with other high-voltage power cable lines, and detect it. It can be dealt with only by detecting the cable line.

Moreover, according to this single-engine ground fault detection device and the failure prediction method using the device, it is only necessary to attach it to the ground wire from the sheath of the cable for each high-voltage power cable line, and it is possible to predict a full-scale failure of the power cable. .. It is also possible to notify by an alarm instead of the display. Therefore, it is not necessary to drastically change the existing equipment, and there is no need for a power outage for installation.

It is a schematic diagram which shows one aspect of the ungrounded high voltage system to which the single-shot ground fault detection device to which this invention is applied is attached. It is a figure which shows the example of the integration circuit of the single-shot ground fault detection apparatus to which this invention is applied. It is the schematic diagram which shows one aspect of the non-grounded system high voltage system which attached the single-shot ground fault detection device which is the Example of this invention, and the schematic perspective view which shows one aspect of the single-shot ground fault detection device. It is a schematic diagram which shows the difference of the measured waveform between a single-shot ground fault and a complete ground fault. It is a schematic diagram which shows the difference between a single-shot ground fault and an opening / closing surge.

Hereinafter, embodiments for carrying out the present invention will be described in detail, but the scope of the present invention is not limited to these embodiments.

An embodiment of the single-shot ground fault detection device of the present invention and the implementation of the single-shot ground fault detection method using the same will be described with reference to the drawings.

As shown in FIG. 1 as a schematic diagram, the single-shot ground fault detection device 1 is installed on the ground wire 24 of the sheath 23 of the power cable 21 connected to the high-voltage power cable line 20. The ground wire 24 is connected and grounded.

As shown in FIG. 1, the single-shot ground fault detection device 1 has a current transformer (CT) 11, an integrator circuit 12, a discrimination circuit 13, and a display 14 as a basic configuration.

The present invention includes a current transformer (CT) 11 that captures the current waveform that flows into the ground wire attached to the ground wire, an integrating circuit 12 that integrates the current waveform and converts it into a charge amount, and other noise after conversion. A single-occurrence ground fault is detected by having a discrimination circuit 13 for identifying and discriminating a single-occurrence ground fault current having a large level difference and a display unit 21 for displaying the result.

The integrator circuit 12 may be in the form of using an integrator circuit of a type that does not require a separate power supply (see FIG. 2A), and if a separate power supply is obtained, for example, another type of integrator circuit (FIG. 2B). (See) may be used.

The core of the current transformer (CT) 11 may be a ring type, although the core of the clamp type that can be retrofitted is shown in FIG. 3 (b) in the present invention. However, a core dedicated to high frequencies such as a normal ferrite core cannot be used. In the present invention, a core capable of detecting even a low frequency region is used.

CV cables used in non-grounded systems where the distribution voltage class of the high-voltage power cable line 20 is 6.6 kV, 3.3 kV, 2.2 kV, etc. in factories, etc., suffers from dielectric breakdown due to cable insulation deterioration. It is known by some engineers that most of them initially become a single-shot ground fault as shown in FIG. 4, and then shift to a complete ground fault waveform as the single-shot ground fault is repeated.

On the other hand, even if an attempt is made to detect this pulsed single-shot ground fault current with the ground wire 24, noise such as an opening / closing surge and other lightning surges in FIG. Since it flows into the sheath 23 and its peak value may be larger than the single-shot ground fault current, it was considered difficult to detect only the single-shot ground fault current in FIG. 5 (a).

The noise current such as switching surge that occurs when the power is turned on and off is a value that exceeds the single ground fault current at the peak value, but when this is integrated and converted into the amount of charge, it is as shown in Fig. 5 (b-2). Because of the vibration waveform and the high frequency, it becomes an extremely small value when integrated and converted into an electric charge amount.

On the other hand, the characteristic of the single-shot ground fault waveform includes the commercial frequency component seen in FIG. 5A as the measured waveform. In the theoretical calculation, after the peak waveform that discharges the capacitance of the geological phase, the commercial frequency component flows with the capacitance of the AC power supply and other healthy phases as a series circuit. If this current is integrated and replaced with an electric charge, a large difference can be made with the integrated waveform charge amount such as an opening / closing surge.

Other lightning surge waveforms and the like are not only high-frequency components originally, but also flow into the sheath side through the capacitance between the main line 22 and the cable sheath 23, so that they are more likely to become high-frequency components.

The present invention uses this feature to integrate the current flowing through the sheath and convert it into an amount of electric charge, making it possible to detect a single-shot ground fault current in a sheath with a large amount of noise, which was previously unthinkable. is there.

The failure prediction display 14 of the embodiment shown in FIG. 1 (or FIG. 3) is a device for finding a failure at the time of inspection that can be used even if it is left uninterruptible for a long time.

However, the sheath attachment port of the high-voltage power cable is usually located near the distribution board (cubicle), and the current transformer 11 and the integrator circuit 12 discrimination circuit 13 and the display unit 21 may be separated from each other.

The sheath attachment port of the high-voltage power cable is usually near the distribution board (cubicle), and if the power supply is near, the device can be made reasonably, and the whole is alerted at once, and a single-shot ground fault occurs here. It may be different from the display of the cable.

When the single-occurrence ground fault is identified, the single-engine ground fault detection device 1 displays the identification result and the number of identifications on the display 14 or gives an alarm by the alarm device 15, so that the high-voltage power cable line of the non-grounded voltage system The manager of 20 can recognize it as a warning and / or an alarm that predicts and displays a location that is likely to cause a cable failure. Therefore, by identifying the CV cable of the high-voltage power cable line 20 that will cause a failure accompanied by a power outage in the near future and replacing or repairing it as soon as possible, such as a complete ground fault or short-circuit failure. It is possible to avoid a full-scale cable failure.

As described above, the single-engine ground fault detection device 1 and the single-engine ground fault detection method using the single-engine ground fault detection device 1 include noise currents such as open / close surges and minute ground faults such as single-engine ground fault currents in the high-voltage power cable line 20. , The intrusion surge current can be identified only by the amount of charge and the integrated current, and no troublesome operation such as comparison with the polarity of other cables is required.

In this way, according to the single-engine ground fault detection device 1 and the single-engine ground fault detection method using the single-engine ground fault detection device 1, it is a dangerous place with a high probability of causing a cable failure, leading to a complete ground fault failure or a short-circuit failure. Can be displayed to make the administrator aware of these serious cable failures before they occur, which can be useful for maintenance and management of a non-grounded high-voltage system having a high-voltage power cable line 20.

This single-engine ground fault detection device and the single-engine ground fault detection method using it are applied to 6kV and 3kV class non-grounded high-voltage cables and high-voltage equipment used for power transmission and distribution to factories, etc. By detecting the occurrence of a small ground fault (single ground fault), it is possible to predict and display a serious cable failure such as a complete ground fault or short circuit failure in advance, ensuring the safety of ungrounded high-voltage systems. Can be used for.

1 is a single-engine ground fault detector, 11 is a current transformer, 12 is an integrator circuit, 13 is a discrimination circuit, 14 is an indicator, 15 is an alarm, 20 is a high-voltage power cable line of a non-grounded high-voltage system, and 21 is. The high-voltage power cable (CV cable), 22 is the main line, 23 is the sheath, and 24 is the ground line.

Claims (3)

A current transformer that measures the current flowing through the ground wire of the sheath for each high-voltage power cable line, an integrator circuit that integrates the current and converts it into an electric charge amount, and a discrimination circuit that discriminates only a predetermined amount or more of the electric charge amount. A single-shot ground fault detector having a display and / or an alarm for the result.
A complete ground fault is detected by discriminating between a single-shot ground fault having a pulsed discharge in the high-voltage power cable and another noise such as an open / close surge or a lightning surge, and detecting and displaying / or alarming only the single-shot ground fault. A single-engine ground fault detection device characterized in that the cable failure is predicted before the cable failure due to an electric current occurs. All the current waveforms from the current transformer are digitally converted, and the single-shot ground fault waveform is discriminated from the characteristics of each waveform, and the current of the single-shot ground fault that generates the above display and / or alarm is detected. The single-shot ground fault detection device according to claim 1, characterized by this. A process of capturing the single-shot ground fault current with pulsed discharge and the switching surge current or lightning surge current, which are noise currents, while measuring the current flowing through the ground wire connected from the sheath of each high-voltage power cable line.
The process of integrating those currents with an integrator circuit and converting them into electric charges,
A step of distinguishing between noise and a single-shot ground fault according to the integrated charge amount,
A step of displaying the result on the display and / or driving the alarm when the single-shot ground fault is identified.
By having
A single-shot ground fault detection method characterized in that the cable failure is predicted before the cable failure due to a complete ground fault current occurs.

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