JP3615170B2 - Method for determining the application of DC voltage in an AC cable line, a method for removing the DC voltage, and a device for preventing an increase in potential of the AC cable line during a ground fault - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
This invention grounds each phase on the secondary side of the transformer of the high-voltage three-phase AC distribution line via a capacitor, and in the distribution line using the DC device on the load side of the electric line, there is some electrical problem. The present invention relates to a method for discriminating the state of application of direct current voltage in a three-phase alternating current distribution line, a method for removing the direct current voltage, and a ground potential rise prevention device caused by a ground fault.
[0002]
[Prior art]
Conventionally, as shown in FIG. 5, in the factory, each phase on the secondary side of the transformer of the high-voltage three-phase AC distribution line is limited to the purpose of suppressing an abnormal voltage rise indoors during a ground fault and the ground fault current. There is a case where it is grounded via the capacitor 2 for the purpose. In particular, in electronic equipment and precision machinery factories, not only DC devices (not shown) such as electronic devices are connected to the load side of the electrical line 1, but also an ionizer is installed to remove the charge. doing. When any electrical failure occurs on the load side to which such a DC device is connected, no abnormality is found in the ionizer, the DC device, etc., but the DC device may not actually operate. The cause of the problem is an obstacle to the production equipment of the factory, so the cause is investigated, but the cause cannot be easily determined.
[0003]
Conventionally, in a building or the like, as shown in FIG. 7, among the secondary sides of the transformer of the high-voltage three-phase AC distribution line 1, for example, the S phase is grounded at the ground point 3, and this S phase grounding wire 7 is often connected to the N phase of the AC low-voltage distribution line 6 such as a single-phase three-wire type. In this case, the three-phase AC distribution line 1 and the AC low-voltage distribution line 6 are grounded in the same system. In this type of distribution line, if a ground fault occurs in the ungrounded R-phase or T-phase, the ground-to-ground voltage with the neutral point grounded is 100 V and the single-phase three-wire AC low-voltage distribution line 6 Voltage of 300V or more is applied. Normally, a varistor (not shown) provided so that an abnormal voltage is not applied acts on the load-side connected device, and a ground fault breaker (not shown) installed in the AC low-voltage distribution line 6 for the ground fault current flowing through the varistor. When the operation is detected, the power supply to the load side is cut off. However, since many varistors usually correspond to a voltage of 300 V or less, they cannot cope with a ground fault.
[0004]
In addition, when an earth leakage breaker is not installed, an overcurrent may flow through the varistor, the varistor may burn out, and the distribution breaker may operate. As a result, important production equipment such as factory production equipment and bank ATMs may be shut down, causing significant damage.
Therefore, as shown in FIG. 8, each phase on the secondary side of the transformer of the three-phase AC distribution line 1 is grounded at the grounding point 3 through the capacitor 2, and this grounding wire 7 is connected to a single-phase three-wire AC or the like. The low voltage distribution line 6 is connected to the N phase via a capacitor. As a result, ground faults in each phase as described above are all grounded, so that an abnormally high voltage is not applied to the AC low-voltage distribution line 6 such as a single-phase three-wire system even during a ground fault. Yes.
[0005]
[Problems to be solved by the invention]
When an abnormality was found in the DC device itself in a factory such as an electronic device or a precision machine, the cause was immediately pursued in the field, but no abnormality was found in the DC device as described above. If the DC device does not work, ask the electrical construction company in charge of laying the electrical wiring in the factory to investigate the cause of the wiring system and respond accordingly. I also left it to work. In addition, since such a situation rarely occurs, there is almost no pursuit of the cause inside the factory, and next time, even if the same thing happens, technology that can understand the reason and respond to it Because there were few people.
In order to cope with such a situation, a measuring instrument such as a clamp type milliampere meter is usually used, but it is difficult to find the cause.
[0006]
The present inventor also tried to find out the cause by using a normal measuring device, but since a rectification voltmeter was permanently installed in the field, this was used as a measuring device, and the ground voltage of the electric line 1 was I tried to measure.
Then, I noticed that the ground voltage, which was initially high, gradually decreases. In this decrease, the present inventor is that the capacitor connected to each phase blocks the DC current flowing from the DC device, and the DC voltage is still applied to the AC distribution line. He realized that he had completed this invention. That is, when DC leakage, DC charge discharge, or the like occurs, a small amount of DC current flows from the DC device to the AC distribution line 1, but a capacitor 2 is provided in each phase at the grounding point 3 of the AC distribution line 1. As a result of the connection, a direct current did not flow through each of these capacitors 2, and it was recalled that a direct current voltage was still applied to the alternating current distribution line 1. Since it is grounded through the capacitor 2, an alternating current flows in the case of a ground fault, but it is in an insulated state with respect to the direct current. Therefore, until now, it has been difficult to discover whether an abnormal DC voltage is applied to the load-side AC distribution line 1. Therefore, the load-side DC device could not be quickly returned.
[0007]
Further, in the wiring of FIG. 8, the AC is grounded, but since the capacitor 2 is provided, it is insulative with respect to the DC. The three-phase AC distribution line 1 is often loaded with noise voltage or other DC voltage due to high-frequency current from an inverter or the like. In such a situation, if a DC leakage current or a DC charge discharge of the ionizer occurs, the DC voltage is abnormal in the equipment on the load side of the single-phase AC low voltage distribution line 6 connected to the ground line 7. As a high voltage, troubles of these devices may occur.
[0008]
Therefore, according to the present invention, in the case where a DC device that does not operate although some electrical malfunction has occurred and no abnormality is found occurs, whether or not a DC voltage is applied to the AC distribution line in order to quickly recover it. In addition to providing a method that can be determined very easily, a method for removing a DC voltage in that case is provided. In addition, even when a ground fault occurs in the three-phase AC distribution line, the ground fault current flows without any problem, but by always grounding the DC voltage on the three-phase AC distribution line, An object of the present invention is to provide a potential rise prevention device that does not generate an abnormal high voltage even in an AC low-voltage distribution line, and solves the above problems.
[0009]
[Means for Solving the Problems]
According to the first aspect of the present invention, each phase on the secondary side of the transformer of the high-voltage three-phase AC distribution line is grounded via a capacitor, and a DC device is connected and used on the load side of the line. When the DC device stops operating even though there is no abnormality in the device, when a DC voltmeter or a half-wave rectification voltmeter is connected to this AC distribution line, a voltage exceeding the rated value is measured and time passes. Accordingly, a method for discriminating the applied voltage of the DC voltage is determined in which it is determined that a DC voltage is applied to the AC distribution line when the measured voltage is attenuated.
[0010]
Further, in the invention of claim 2, when it is determined in claim 1 that a DC voltage is applied, a resistor is connected in parallel to the capacitor of each phase of the grounding location, and the applied DC voltage The DC voltage removal method was used. Further, the invention of claim 3 is the case where each phase on the secondary side of the transformer of the high-voltage three-phase AC distribution line is grounded via a capacitor, and a DC device is connected and used on the load side of the line. By connecting each resistor in parallel to the capacitor of each phase at the grounding location in advance, when the DC device stops operating even though there is no abnormality in the DC device, A direct voltage removal method was adopted in which the applied direct voltage was removed.
[0011]
Further, the invention of claim 4 is the case where each phase on the secondary side of the transformer of the high-voltage three-phase AC distribution line is grounded via a capacitor, and a DC device is connected and used on the load side of the line. A device for preventing a potential increase in a high-voltage three-phase AC distribution line at the time of a ground fault, in which a resistor is connected in parallel to each phase capacitor at the grounding location. According to a fifth aspect of the present invention, the capacitor and the resistor of each phase in the fourth aspect of the present invention are such that the capacitor and the resistor connected in parallel are housed in a box for each of the transformers. It was set as the electric potential rise prevention apparatus of the high voltage | pressure three-phase alternating current distribution line at the time of a tangle.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
1 to 3 show an embodiment of the present invention. FIG. 1 shows a situation in which each phase of the secondary distribution line of the transformer in the AC distribution line 1 introduced indoors from the outside is grounded at the ground location 3 via the capacitor 2. On the load side of the electric line 1, a DC device (not shown) such as an ionizer or an electronic device is connected and used. In the load side distribution line, when a DC leakage current or a DC charge discharge phenomenon caused by an ionizer or the like occurs, when a half-wave rectification voltmeter 4 is connected to the AC distribution line 1 as shown in FIG. As shown by the solid line in FIG. 3, when the half-wave rectification type voltmeter 4 measures a voltage exceeding the rating (shown by the dotted line) and the measured voltage attenuates over time, It can be seen that a DC voltage is applied to the AC distribution line. This is because a resistor 4a is connected to the half-wave rectification type voltmeter 4, and when the voltmeter 4 is connected to the AC distribution line 1, a direct current is transmitted through the resistor 4a of the voltmeter 4. The direct current is consumed by the resistance of the resistor 4a, and the direct current voltage is attenuated.
In this way, when an electrical failure occurs on the load side and a DC voltmeter or a half-wave rectification voltmeter is connected to the AC distribution line 1, the voltage that is initially measured is attenuated over time. In this case, it is determined that a DC voltage is applied to the AC distribution line 1.
When the resistance of the half-wave rectification voltmeter 4 was 10 KΩ, it attenuated to the rated voltage in about 10 seconds.
[0013]
Therefore, in the wiring in the above situation, as shown in FIG. 2, the resistor 5 is connected in parallel to the capacitor 2 of each phase of the grounding point 3 of the AC distribution line 1 in advance. If this is the case, the direct current flowing through the AC distribution line 1 will flow into the ground through the resistor 5 at the ground point 3, and a DC voltage will not remain on the AC line 1. Further, even if a ground fault occurs, the resistor 5 does not interfere with the ground fault current. In other words, in order to remove the applied DC voltage, it is only necessary to connect resistors in advance in parallel with the capacitors of each phase at the ground as described above. The specific value of the resistor connected in advance may be about 1 to 20 KΩ.
[0014]
Next, FIG. 6 explains the case where the ground wire 7 is connected to the single-phase three-wire AC low voltage distribution line 6 as shown in FIG. Each phase on the secondary side of the transformer of the line 1 is grounded at a grounding point 3 via a capacitor 2, and a single-phase three-wire AC low-voltage distribution line 6 is connected to the ground line 7 via a capacitor and a resistor. It is a connected thing.
[0015]
In the wiring in the above situation, since the resistors 5 are connected in parallel to the capacitors 2 of the respective phases of the three-phase AC distribution line 1, the direct current flowing through the three-phase AC distribution line 1 is connected. The current flows through the resistor 5 into the ground at the grounding point 3, and a DC voltage does not remain on the three-phase AC distribution line 1. Therefore, no abnormal high voltage is generated in the AC low voltage distribution line 6 even if the three-phase AC distribution line 1 has a leakage current from a DC device or a DC charge discharge such as an ionizer. In addition, even if a ground fault occurs in the three-phase AC distribution line 1, the ground fault current flows from the grounding point 3 into the ground, so that no abnormal high voltage is generated in the AC low-voltage distribution line 6, and this AC low voltage Troubles of devices connected to the load side of the distribution line 6 do not occur.
Also in this case, the specific value of the resistor 5 connected in parallel to the capacitor 2 may be about 1 to 20 KΩ.
[0016]
The capacitor 2 and the resistor 5 may be connected in parallel by any method. However, as indicated by the dotted line 8 in FIG. If the container 5 is stored in an iron box or the like, it is freed from the hassle of connecting each time in the field, and the laying time is shortened.
Further, when the capacitor 2 and the resistor 5 in parallel connection are housed in a box or the like, a space is not taken up by designing the box to have a small shape. For this reason, the present invention can be easily applied not only to a new factory but also to the installation of the capacitor 2 and the resistor 5 when the factory is renewed.
[0017]
In the embodiment described above, whether or not a DC voltage is on the AC distribution line 1 is determined by connecting the half-wave rectification voltmeter 4, but the present invention is not limited to this, and a DC voltmeter may be used. Similar results are obtained. In the above embodiment, the present invention has been described with the secondary AC distribution line of the delta connection type transformer. However, the present invention is not limited thereto, and the secondary side AC distribution of the star connection type transformer. The same applies to the track.
[0018]
【The invention's effect】
According to the first aspect of the present invention, when a DC device that does not operate abnormally occurs due to some electrical failure, it can be very easily determined whether or not a DC voltage is applied to the AC distribution line. In the invention of claim 2, when it is determined that a DC voltage is applied, the applied DC voltage can be easily reduced by connecting a resistor in parallel to each phase capacitor at the ground as described above. Can be removed. For this reason, the operation of the DC device can be quickly returned.
In the invention of claim 3, since the resistor is connected in parallel to the capacitor of each phase at the grounding location, the DC voltage of the AC distribution line is always removed, which hinders the operation of the DC device. Never do. Recently, in addition to semiconductor factories, many companies have installed DC electronic devices such as hospitals, banks, offices, measuring instruments, computers, etc., but measures should be taken in the event of any electrical failure. Is not perfect. The present invention achieves the effects as described above at a place where many such DC electronic devices are installed.
[0019]
Further, in the invention of claim 4, the direct current flowing through the three-phase AC distribution line flows into the ground through the resistor at the grounding point, and a DC voltage is applied to the AC line and the single-phase AC low-voltage distribution line. It will not be. Therefore, even if a ground fault occurs in the three-phase AC distribution line, the ground fault current flows from the ground to the ground, and no abnormal high voltage is generated in the single-phase AC low-voltage distribution line. Trouble of the equipment connected to the load side of the AC low-voltage distribution line of the phase does not occur. Therefore, even if the current building has the same system for grounding the three-phase AC distribution line and the AC low-voltage distribution line, simply connecting a resistor to each capacitor at the grounding point makes it easy to This is extremely convenient because it is possible to prevent an increase in potential.
Further, in the invention of claim 5, the parallel connection of the capacitor and the resistor is not performed in the field, but at the factory or the like, by storing the capacitor and the resistor connected in parallel in the box beforehand, Since it is only necessary to connect the box at the site, construction time can be greatly reduced.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an embodiment of a method for determining the application of a DC voltage in an AC electric line according to the present invention.
FIG. 2 is a schematic configuration diagram showing an embodiment of a method for removing a DC voltage in an AC line according to the present invention.
FIG. 3 is a graph showing a voltage waveform at the time of power application determination in the embodiment of the method for determining the application of direct current voltage in the AC power line according to the present invention.
FIG. 4 is a schematic configuration diagram showing another embodiment of the method for determining the DC voltage application in the AC electric line according to the present invention.
FIG. 5 is a schematic configuration diagram of a place where the method for determining the application of direct current voltage in an alternating current electric line according to the present invention is used.
FIG. 6 is a schematic configuration diagram of an embodiment of an apparatus for preventing an abnormal potential increase during a ground fault according to the present invention.
FIG. 7 is a schematic configuration diagram of a conventional abnormal potential rise prevention device during a ground fault.
FIG. 8 is a schematic configuration diagram of a conventional improved abnormal potential rise prevention device during a ground fault.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 AC distribution line 2 Capacitor 3 Ground location 4 Half wave rectification type voltmeter 5 Resistor 6 AC low voltage distribution line 7 Ground line EB Earth leakage breaker 8 Box

Claims (5)

Although each phase on the secondary side of the transformer of the high-voltage three-phase AC distribution line is grounded via a capacitor and a DC device is connected on the load side of the wire line, there is no abnormality in the DC device. When the DC device stops operating, when a DC voltmeter or half-wave rectification voltmeter is connected to this AC distribution line, a voltage exceeding the rated voltage is measured, and the measured voltage decays over time. And determining whether a DC voltage is applied to the AC distribution line. When it is determined in claim 1 that a DC voltage is applied, a resistor is connected in parallel to the capacitor of each phase of the grounding location to remove the applied DC voltage, DC voltage removal method. When grounding each phase on the secondary side of the transformer of the high-voltage three-phase AC distribution line via a capacitor and connecting and using a DC device on the load side of the line, the capacitor for each phase at the grounding location in advance By connecting the resistors in parallel to each other, the DC voltage applied to the AC distribution line is removed when the DC device stops operating even though there is no abnormality in the DC device. A method of removing a DC voltage, characterized in that When grounding each phase on the secondary side of the transformer of the high-voltage three-phase AC distribution line via a capacitor and connecting and using DC equipment on the load side of the line, A device for preventing a potential increase in a high-voltage three-phase AC distribution line at the time of a ground fault, wherein resistors are connected in parallel. The capacitor and resistor of each phase in claim 4 are characterized in that the capacitor and resistor connected in parallel are housed in a box for each of the transformers. A device for preventing a potential increase in a high-voltage three-phase AC distribution line during a ground fault.

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