JP2003070158A - Method for discriminating dc voltage applied to ac electric line, method for eliminating the dc voltage, and apparatus for preventing potential rise on ac electric line during line-to-ground fault - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow easily determine whether a DC voltage is applied onto an AC distribution line so as to quickly restore a DC device which does not operate although not abnormal after a line-to-ground fault. SOLUTION: Each phase on the secondary side of a transformer of the high voltage three-phase AC distribution line 1 is grounded through a capacitor 2. When the DC device is used on the load side of the line 1 and electrical problems occur on the load side and the DC device is not abnormal but does not operate, a DC voltage meter or a half-wave rectifying voltage meter 4 is connected to the AC distribution line 1. When a rated voltage or more is measured and the measured voltage is attenuated with time, it is determined that the DC voltage is applied to the AC distribution line 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distribution line in which each phase on the secondary side of a transformer of a high-voltage three-phase AC distribution line is grounded via a capacitor, and a DC device is used on the load side of the distribution line. In the above, the present invention relates to a method for determining the state of DC voltage application in a three-phase AC distribution line caused by some electrical failure, a method for removing the DC voltage, and a ground potential rise prevention device caused by a ground fault. .

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 5, in a factory, each phase on the secondary side of a transformer of a high-voltage three-phase AC distribution line has the purpose of suppressing an abnormal voltage rise when a ground fault occurs indoors. It may be grounded via the capacitor 2 for the purpose of limiting the accident current. Especially in electronic equipment and precision machinery factories,
Not only is a DC device (not shown) such as an electronic device connected to the load side of the device, but an ionizer or the like is installed to remove the charge. When some electrical trouble occurs on the load side connected to such DC equipment,
Although no abnormality is found in the ionizer or DC equipment, the DC equipment may not actually operate. Since this would impede the production facilities of the factory, the cause was investigated, but the cause could not be easily identified.

Further, conventionally, indoors such as in a building, for example, as shown in FIG. 7, of the secondary side of the transformer of the high-voltage three-phase AC distribution line 1, for example, the S phase is grounded at the grounding point 3, and this S phase is grounded. In many cases, the grounding wire 7 is connected to the N-phase of the AC low-voltage power distribution line 6 such as a single-phase three-wire system. In this case, the three-phase AC distribution line 1 and the AC low-voltage distribution line 6 are grounded in the same system. When a ground fault occurs in the R and T phases that are not grounded in the distribution line of this system, the AC low-voltage distribution line 6 of the single-phase three-wire system whose ground point is 100V and whose ground point is grounded is 100V. Is applied with a voltage of 300 V or more. Normally, a varistor (not shown) provided so that an abnormal voltage is not applied acts on the connected device on the load side, and a ground fault current flowing through the varistor is connected to an earth leakage breaker (not shown) installed in the AC low-voltage distribution line 6. When it detects and operates, the power supply to the load side is cut off.
Since many of them support voltages below 00V, they cannot handle ground faults.

If no earth leakage breaker is installed, an overcurrent may flow through the varistor, causing the varistor to burn out and the distribution breaker to operate. As a result, the production equipment of the factory and important equipment such as the ATM of the bank may be stopped, resulting in great damage. Therefore, as shown in FIG. 8, the three-phase AC distribution line 1
Each phase on the secondary side of the transformer is grounded at the grounding point 3 via the capacitor 2, and this grounding wire 7 is connected to the N phase of the AC low voltage power distribution line 6 such as a single-phase three-wire system via the capacitor. There is. As a result, all of the ground faults in each phase as described above are grounded, so that an abnormally high voltage should not be applied to the AC low-voltage power distribution line 6 such as the single-phase three-wire system even during a ground fault. There is.

[0005]

When an abnormality is found in a DC device itself in a factory for electronic equipment or precision machinery, the cause was immediately sought in the field. If no abnormality is found in the equipment, but if the DC equipment does not work, it is suspected that there is a problem in the distribution system, and the cause of the wiring system was determined by the electrician who was in charge of laying the electric wiring at the factory. I was asked to investigate, and I was also entrusted with countermeasures. In addition, such a situation,
Since it rarely happens, we rarely pursue the cause inside the factory, and even if something similar happens next time,
This is because there were few engineers on site who could understand the reason and deal with it. Further, in order to deal with such a situation, a measuring device such as a clamp type milliampere meter is usually used, but it is difficult to find out the cause.

The present inventor has also used the usual measuring equipment to
Although I tried to find out the cause, since a rectification type voltmeter was permanently installed at the site, I tried to measure the ground voltage of the electric line 1 by using this as a measuring instrument. Then, I noticed that the ground voltage, which initially showed a high value, gradually decreased. In this reduction, the inventor
I realized that the capacitors connected to each phase blocked the direct current flowing from the direct current equipment, and the direct current voltage remained on the alternating current distribution line, and I completed this invention. Of. That is, when a DC leak, a 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 at the grounding point 3 of the AC distribution line 1 there is a capacitor 2 for each phase. Since they are connected, no DC current flows through each of these capacitors 2, and I remembered the state in which a DC voltage was still applied to the AC distribution line 1. Since it is grounded via the capacitor 2, an AC current flows in the case of a ground fault, but is insulated from DC. Therefore, it has been difficult to find out whether or not an abnormal DC voltage is applied to the AC distribution line 1 on the load side. Therefore, the DC device on the load side cannot be quickly restored.

In the wiring shown in FIG. 8, the AC is grounded, but since the capacitor 2 is provided, it is insulated from the DC. The three-phase AC distribution line 1 is often loaded with noise voltage due to high-frequency current from an inverter or the like and other DC voltage. In such a situation, when a DC leakage current or a DC charge discharge of the ionizer occurs, the DC voltage becomes abnormal in the load side device of the single-phase AC low-voltage distribution line 6 connected to the ground line 7. As a high voltage is applied, troubles with these devices may occur.

Therefore, according to the present invention, in the case where some kind of electrical failure occurs and a DC device which is not found to be operating abnormally but does not work is generated, is there a DC voltage on the AC distribution line in order to quickly restore it? The present invention provides a method for determining whether or not it is extremely easy, and a method for removing a DC voltage in that case. In addition, even if a ground fault occurs in the three-phase AC distribution line, the ground fault current will flow 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 abnormally high voltage in an AC low-voltage power distribution line and solve the above-mentioned problems.

[0009]

According to a first aspect of the present invention, each phase on the secondary side of a transformer of a high-voltage three-phase AC distribution line is grounded via a capacitor, and a DC device is connected on the load side of the line. When a DC voltmeter or a half-wave rectifier voltmeter is connected to this AC distribution line when it is in use and some electrical trouble occurs on this load side, and the DC equipment is not abnormal but stops working. , The voltage above the rated value is measured,
Moreover, when the measured voltage is attenuated with time, it is determined that the DC voltage is applied to the AC distribution line, and the method for determining the DC voltage application state is used.

Further, according to the invention of claim 2, when it is determined that a DC voltage is applied in claim 1, a resistor is connected in parallel to the capacitor of each phase at the grounding point, and a voltage is applied. The DC voltage is removed by removing the DC voltage. In the invention of claim 3, when 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 used on the load side of the electric line, the above-mentioned condition is set in advance. By connecting a resistor in parallel with each phase capacitor at the grounding point, remove the DC voltage applied to the AC distribution line in the event of any electrical failure. Was removed.

According to the invention of claim 4, when 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 used on the load side of the electric line. A potential rise prevention device for a high-voltage three-phase AC distribution line at the time of a ground fault, in which resistors are connected in parallel to the capacitors of the respective phases at the grounding point. In addition, claim 5
According to the invention of claim 4, in the capacitor and the resistor of each phase in claim 4, the transformer and the capacitor connected in parallel are housed in a box for each of the transformers. It was used as a potential rise prevention device for the three-phase AC distribution line.

[0012]

BEST MODE FOR CARRYING OUT 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 a secondary side distribution line of a transformer of an AC distribution line 1 introduced from outdoors to indoors is grounded at a grounding point 3 via a 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. When a DC leakage current or a DC charge discharge phenomenon due to an ionizer or the like occurs in the load side distribution line, if a half-wave rectification type voltmeter 4 is connected to the AC distribution line 1 as shown in FIG. As shown by the solid line in FIG.
If a voltage higher than the rated value (shown by the dotted line) is measured by the half-wave rectification type voltmeter 4 and this measured voltage is attenuated over time, a DC voltage is applied to the AC distribution line. You can see that 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 DC current is transmitted through the resistor 4a of the voltmeter 4. As a result, the direct current is consumed by the resistance of the resistor 4a, and the direct current voltage is attenuated. In this way, when some electrical trouble occurs on the load side and a DC voltmeter or a half-wave rectifier voltmeter is connected to the AC distribution line 1, initially, a voltage above the rated value is attenuated over time. In that case, it is determined that a DC voltage is applied to the AC distribution line 1. The resistance of the half-wave rectifier type voltmeter 4 is 10K.
In the case of Ω, the voltage decreased to the rated voltage in about 10 seconds.

Therefore, in the wiring in the above situation, as shown in FIG. 2, the resistor 5 is provided in parallel with the capacitor 2 of each phase of the grounding point 3 of the AC distribution line 1 in advance. If connected, the DC current flowing through the AC distribution line 1 will flow into the ground through the resistor 5 at the grounding point 3 and the DC voltage will not remain applied to the AC distribution line 1. Further, even if a ground fault occurs, the resistor 5 does not interfere with the ground fault current. That is, in order to remove the DC voltage to be applied, as described above, it suffices to connect the resistors in advance in parallel with the capacitors of the respective phases at the grounding point. The specific value of the resistor connected in advance may be about 1 to 20 KΩ.

Next, FIG. 6 shows the ground wire 7 as shown in FIG.
The description has been given for the case where the AC line is connected to the single-phase three-wire AC low-voltage power distribution line 6, and each phase on the secondary side of the transformer of the three-phase AC power distribution line 1 introduced indoors from the outdoors is connected to the capacitor 2
It is grounded at a grounding point 3 via an AC line, and a single-phase three-wire AC low-voltage distribution line 6 is connected to the grounding line 7 without a capacitor or a resistor.

In the wiring in the above situation, since the resistors 5 are connected in parallel to the capacitors 2 of each phase of the three-phase AC distribution line 1, the three-phase AC distribution line 1 is connected. The DC current flowing through the resistor 3 flows through the resistor 5 into the ground at the grounding point 3, and the DC voltage does not remain applied to the three-phase AC distribution line 1. Therefore, even if there is a leakage current from a DC device or a DC charge discharge such as an ionizer in the three-phase AC distribution line 1, an abnormally high voltage is not generated in the AC low-voltage distribution line 6. 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 abnormally high voltage is generated in the AC low-voltage distribution line 6,
No trouble occurs in the equipment connected to the load side of the AC low-voltage distribution line 6. Also in this case, the specific value of the resistor 5 connected in parallel to the capacitor 2 is 1 to 2
It may be about 0 KΩ.

The capacitor 2 and the resistor 5 may be connected in parallel by any method, but as shown by the dotted line 8 in FIG. 6, the capacitors are connected in parallel in advance. By storing 2 and the resistor 5 in an iron box or the like, the troublesomeness of connecting them one by one on the site is released and the installation time is shortened. Further, when the capacitors 2 and the resistors 5 connected in parallel are housed in a box body or the like, space is not taken by designing the box body to have a small shape. Therefore, the present invention can be easily applied not only to a new factory, but also to the laying of the capacitor 2 and the resistor 5 when the factory is renewed.

In the above embodiment, whether the DC voltage is present on the AC distribution line 1 is determined by connecting the half-wave rectification type voltmeter 4. However, the present invention is not limited to this. Similar results are obtained when used. Further, in the above-described embodiments, the present invention has been described with respect to the secondary side AC distribution line of the delta connection type transformer, but the present invention is not limited to these, and the secondary side AC distribution line of the star connection type transformer is not limited thereto. The same applies to railroad tracks.

[0018]

According to the first aspect of the present invention, when a DC device which is not abnormal but does not operate due to some electrical defect, it can be very easily determined whether or not a DC voltage is present on the AC distribution line. . According to the invention of claim 2, when it is determined that a DC voltage is applied, the DC voltage applied can be easily reduced by connecting the resistors in parallel to the capacitors of each phase at the grounding point as described above. Can be removed. Therefore, the operation of the DC device can be quickly restored. In the invention of claim 3, since the resistor is connected in parallel to the capacitor of each phase at the grounding point in advance,
The DC voltage on the AC distribution line is always removed, and it does not hinder the operation of DC equipment. Especially recently
Many companies are installing not only semiconductor factories, but also hospitals, banks, offices, etc., measuring instruments, and DC electronic devices such as computers, but it is not possible to take countermeasures when some kind of electrical failure occurs. The present invention has the above-described effects in a place where many such DC electronic devices are installed.

Further, in the invention of claim 4, the DC current flowing through the three-phase AC distribution line flows into the ground through the resistor at the grounding point, and the DC voltage is applied to the AC line or the single-phase AC low-voltage distribution line. It does not stay on. Therefore, even if a ground fault occurs in the above three-phase AC distribution line, the ground fault current will flow from the grounding point to the ground, and no abnormally high voltage will be generated in the single-phase AC low-voltage distribution line. There is no trouble with the equipment connected to the load side of the AC low-voltage power distribution line. 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, it is easy to connect the resistor to each capacitor at the grounding point to easily establish the potential at ground fault. It is very convenient because it can be prevented from rising. Further, in the invention of claim 5, the parallel connection of the capacitor and the resistor is not performed in the field, but by storing the parallel-connected capacitor and the resistor in a box in advance in a factory or the like, Since it is sufficient to connect the boxes at the site, the construction time can be greatly reduced.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an embodiment of a method for discriminating charging of a DC voltage in an AC power line of the present invention.

FIG. 2 is a schematic configuration diagram showing an example of an embodiment of a DC current removing method in an AC electric line according to the present invention.

FIG. 3 is a graph diagram showing a voltage waveform at the time of the voltage application determination of the embodiment of the method for determining the voltage application of the DC voltage in the AC power line of the present invention.

FIG. 4 is a schematic configuration diagram showing another embodiment of the method for discriminating charging of a DC voltage in an AC power line of the present invention.

FIG. 5 is a schematic configuration diagram of a portion in which the method for discriminating charging of a DC voltage in an AC power line of the present invention is used.

FIG. 6 is a schematic configuration diagram of an embodiment of an abnormal potential rise prevention device 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 abnormal potential rise prevention device during a ground fault.

[Explanation of symbols]

1 AC distribution line 2 Capacitor 3 Grounding point 4 Half-wave rectification type voltmeter 5 Resistor 6 AC low-voltage distribution line 7 Grounding wire EB Leakage breaker
Mosquito box

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shigeyoshi Sakai             4-833 Shibaura, Minato-ku, Tokyo Co., Ltd.             KANDENKO (72) Inventor Hisao Noguchi             7-4-14 Ginza, Chuo-ku, Tokyo             Within the corporation (72) Inventor Hironobu Nakano             1-4-19 Moto-Okubo, Narashino City, Chiba Prefecture F term (reference) 2G035 AA15 AB01 AB08 AC01 AC13

Claims (5)

[Claims] 1. A high-voltage three-phase AC distribution line, wherein each phase on the secondary side of a transformer is grounded via a capacitor, and a DC device is used on the load side of the power line, and some electrical power is applied to this load side. In the event that a malfunction occurs and the DC equipment does not malfunction but ceases to operate, when a DC voltmeter or a half-wave rectifier voltmeter is connected to this AC distribution line, a voltage above the rated value is measured and time is exceeded. A DC voltage charging determination method, which is characterized in that when the measured voltage is gradually attenuated, it is determined that a DC voltage is applied to the AC distribution line. 2. When it is determined that a direct current voltage is applied in claim 1, a resistor is connected in parallel to each phase capacitor at the grounding point to remove the applied direct current voltage. A method of removing a DC voltage, characterized by: 3. When 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 used on the load side of the line, each phase at the grounding point is preset. DC voltage applied to the AC distribution line in the event of any electrical failure is eliminated by connecting a resistor in parallel with the capacitor of the DC voltage. Removal method. 4. When each phase on the secondary side of the transformer of the high-voltage three-phase AC distribution line is grounded via a capacitor and DC equipment is used on the load side of the power line, each phase at the grounding point A potential rise prevention device for a high-voltage three-phase AC distribution line at the time of a ground fault, characterized in that resistors are connected in parallel to the capacitor. 5. The capacitor and resistor of each phase according to claim 4, characterized in that, for each of the transformers, the capacitor and the resistor connected in parallel are housed in a box. Item 4. A potential rise prevention device for a high-voltage three-phase AC distribution line in the event of a ground fault.