JPS5845124B2 - vacuum switchgear - Google Patents

Description

Detailed Description of the Invention This invention has a gas replenishment device in a vacuum container, and when opening and closing an electric circuit using vacuum discharge, the generation of abnormal voltage that may cause dielectric breakdown of the circuit is provided. The present invention relates to a vacuum switchgear designed to prevent this.

There are various types of vacuum switching devices, but a typical example is one that mechanically opens and closes electrodes in a vacuum.
There is a vacuum switch that opens and closes electrical circuits.

The present invention will be explained below using this vacuum switch.

FIG. 1 is an example of a conventional vacuum switchgear.

It is a sectional view showing a conventional vacuum switch.

The conventional vacuum switch will be explained below using FIG. 1.

In FIG. 1, reference numeral 1 denotes a vacuum container, which is made to have a completely airtight structure, and is degassed and exhausted under high-temperature heating to remove gases contained in the vacuum container 1 itself and the constituent members housed in the vacuum container 1. Since the vacuum container 1 is sealed after being completely discharged, the inside of the vacuum container 1 is maintained at a high vacuum.

Reference numerals 2 and 3 denote electrodes, both of which are supported within the vacuum container 1 and insulated from each other.

Electrode 2 is fixed to vacuum container 1, and electrode 3 facing this
are supported by the vacuum container 1 via an extensible part made of bellows of the vacuum container 1, so that the electrodes 2 and 3 can be connected to each other by being driven from outside the vacuum container 1 by a drive device (not shown). can be opened and closed.

The electrodes 2 and 3 are connected to an AC power source and a load, respectively, to form an electric circuit, and a drive device opens and closes the electrodes 2 and 3, thereby passing the current flowing through the electric circuit into the vacuum chamber 1. It was used as an AC breaker that opened and closed in high vacuum.

The conventional vacuum switch is constructed as described above and opens and closes an AC circuit, and its operation will be explained next.

When the power supply voltage is applied to the vacuum switch, electrode 2 and electrode 3
When the is open, power supply voltage is applied between the electrodes, or a high vacuum is maintained between the electrodes, so the vacuum withstand voltage between the electrodes is extremely high, and no current flows between the electrodes, so the load No voltage is applied to the load circuit, and the load circuit remains disconnected from the power supply.

When the drive device operates and the electrodes 2 and 3 are brought into close contact, current is supplied from the power source to the load through the electrodes 2 and 3.

In order to cut off this load current, the drive device
When the contact surface between electrode 2 and electrode 3 is about to separate, a spark is generated by the current passing through the contact surface, and an arc is created between electrode 2 and electrode 3. Unfortunately, the load current flows through this arc.

During the opening process in which the distance between electrodes 2 and 3 gradually widens, the arc is extended as the distance between the electrodes increases, and the load current passes only through this arc to the electrodes 2 and 3.
continues to flow.

There is a high vacuum between the electrodes 2 and 3, and there are no gas molecules to maintain the arc at all. 3
The metal material that makes up the arc is evaporated, and this metal vapor is ionized to maintain the arc and continue to flow the load current.

In order for the load current to flow stably in the arc, the metal vapor necessary for the current flow must be distributed between the electrodes 2 and 3 depending on the magnitude of the load current value.
must be evaporated from the cathode bright spot to continue supplying the arc.

When the load current value is large, the temperature of the electrodes near the cathode bright spot of electrodes 2 and 3 is high and a large amount of metal vapor evaporates, so the arc is supplied with a sufficient amount of ionized metal vapor molecules, so the arc is stable, and the load current continues to flow stably.

As the load current value decreases, the temperature of the electrodes near the cathode bright spot of electrodes 2 and 3 decreases, and the amount of evaporation of metal vapor decreases, resulting in a shortage of ionized metal vapor molecules in the arc, causing an arc. becomes unstable, so the flow of load current also becomes unstable.

Since the electrodes 2 and 3 first open, the waveform of the current flowing through the arc during the opening process is a half-wave AC sine wave current waveform because the power source is an AC power frequency voltage. , the instantaneous current value gradually decreases from the maximum value according to the sine waveform, and when the current value reaches 0, the cathode bright spots of electrodes 2 and 3 disappear, the arc is extinguished, and the load current decreases. Distribution will be stopped.

When the load current value becomes 0 and the arc is extinguished, the ions of the ionized metal vapor existing between the electrodes scatter in the surrounding vacuum space and adhere to the electrodes 2 and 3 and the vacuum vessel 1, so that the ions between the electrodes become 0. Deionization begins, in which ionized metal vapor ions rapidly decrease.

As the deionization effect progresses, the residual ions between the electrodes decrease and the withstand voltage between the electrodes increases, and when the circuit voltage applied between the electrodes no longer allows current to flow again, Load current interruption is completed.

When the electrode opening operation between electrodes 2 and 3 is completed, the distance between the electrodes is sufficiently widened, the ions remaining between the electrodes are completely annihilated, and the evaporated metal vapor is also scattered, the distance between the electrodes returns to its original state. The high vacuum state is restored, the extremely high vacuum withstand voltage between the electrodes is restored, and the load circuit is disconnected from the power supply.

Vacuum switches operate as described above to open and close AC circuits, but conventional vacuum switches have the following drawbacks.

The first drawback, the cutting of load current, will be explained.

Electrode 2 and electrode 3 start opening operation, and while a half-wave AC sine wave load current is flowing through the arc, the temperature of the cathode bright spot decreases as the current value decreases from the maximum value. do,
As mentioned above, the amount of evaporation of metal vapor from the electrodes 2 and 3 decreases and the arc becomes unstable.

When the current further decreases and the amount of evaporated metal vapor decreases, the ionized metal vapor required to flow the load current becomes insufficient and it becomes impossible to maintain the arc.
A phenomenon occurs in which the arc is suddenly extinguished and the current flow is cut off, even though the current is still flowing, without waiting for the current value to become zero.

This phenomenon is called load current cutting, and the current value at this time is called cutting current.

When the load current is cut off, the actance of the load circuit through which the load current flows induces a voltage, and when the cutoff current is large, a high and steep induced voltage is generated.

When this induced voltage is excessive and exceeds the dielectric strength of the electrical equipment connected to the load circuit, it damages the insulator, causing burnout or dielectric breakdown of the electrical equipment.

Therefore, it is necessary to keep the cutting current as low as possible so that the induced voltage generated in the load does not exceed an allowable voltage that will not damage the load.

However, in conventional vacuum switches, large current interruptions often occurred, posing the risk of accidents such as insulation breakdown.

The second drawback, the occurrence of high frequency intermittent oscillating discharge, will be explained.

As mentioned above, when the electrodes 2 and 3 are opened, the arc is extinguished, and the load current is stopped, the deionization action begins.

However, immediately after the load current is cut off, when the deionization effect has not yet progressed sufficiently and the withstand voltage between the electrodes is low, a discharge occurs between the electrodes due to the high electric current L in the f1 charge circuit induced by the cutting current. Sometimes.

At this time, charges accumulated in a floating container such as the inter-wiring capacitance C of the load circuit flow as a discharge current between the electrodes through the reactance 7 of the wiring.

The waveform of this discharge current is a current with a frequency determined by the inter-wiring capacitance C and the wiring reactance (■), but since both C and L are extremely small values, this discharge current is, for example, l0KI (z This becomes an extremely high high frequency current of ~1 Iz, and generates a high frequency current discharge between the electrodes.

The high-frequency current generated in this manner has a small inter-wiring capacitance C, is accumulated, and has a small amount of ≠2 charges, so the discharge current value is also small.

Therefore, when this high-frequency current flows between the electrodes, the above-mentioned new phenomenon occurs, and when the discharge current value reaches the severing current, the current is cut off, and if the maximum value of the high-frequency current is smaller than the severing current. Since the current is cut off immediately after the discharge starts, the high-frequency current cannot continue to flow stably, and the discharge start and current cut are repeated, causing intermittent high-frequency vibration between the electrodes. Electric discharge occurs.

Once such a high frequency intermittent oscillating discharge occurs,
When the discharge starts, the current is immediately cut off and the current does not continue to flow, so the wiring capacitance C
Since the charges accumulated in the electrodes are not dissipated, the high-frequency intermittent oscillating discharge continues without interruption between the electrodes.

If such high-frequency intermittent oscillating discharge continues between electrodes 2 and 3, where the deionization effect has not yet fully developed after the current is cut off, this will cause the power applied between the electrodes to If discharge is induced by the voltage, the load current will flow between the electrodes again, making it impossible to cut off the load current, and there is a risk of burnout of the load.

As described above, in the conventional vacuum switch, high-frequency intermittent oscillating discharge occurs between the electrodes, which poses a risk of inducing an accident.

The third drawback, the excessive rise in discharge starting voltage, will be explained.

As described above, electrodes 2 and 3 are opened, the arc is extinguished, the load current is stopped, deionization progresses, and the withstand voltage between the electrodes increases.

However, the withstand voltage between the electrodes in vacuum, that is, the discharge starting voltage at which the electrodes 2 and 3 start discharging, is greatly influenced by the minute local conditions of the surfaces of the electrodes 2 and 3, and the dispersion of the discharge starting voltage each time a discharge occurs. big.

Especially after cutting off a large load current, the discharge starting voltage may drop significantly because the surface of the electrode 2.3 is often rough.

In such a case, if you repeatedly apply an electric voltage between the electrodes,
First, four times, vacuum discharge is started between the weakest points (for example, minute needle-like protrusions) on the electrode surface with the lowest voltage resistance.

When a discharge occurs between the weakest point of the electrodes 2 and 3 (for example, a minute needle-like protrusion), a cathode bright spot is generated at the weakest point (for example, the tip of the minute needle-like protrusion). The weakest point local area (for example, the tip of a minute needle-like projection) melts and evaporates, changing its local shape, so that the weakest point local area (for example, the minute needle-like projection) disappears.

Furthermore, when a voltage is applied between the electrodes at the mouthpiece, the weakest point of electrodes 2 and 3 has disappeared, so the discharge does not start at the previous voltage, and the voltage between the next weak point of electrodes 2 and 3 is higher than the previous one. Since the discharge is started with a voltage, the discharge starting voltage is higher than the previous time.

In this way, when a heavy application is repeatedly applied to the electrodes 2 and 3, the discharge starting voltage between the electrodes is characterized in that it increases with variations each time a discharge occurs.

Furthermore, when the gap between electrodes 2 and 3 is sufficiently opened, residual ions and evaporated metal vapor between the electrodes are completely eliminated, and the space between the electrodes returns to a high vacuum state, the discharge between the electrodes starts. The voltage recovers to a very high vacuum withstand voltage, and the load circuit is completely disconnected from the power supply, completing the opening of the load circuit.

If the above-mentioned high-frequency intermittent oscillating discharge continues to occur between electrodes 2 and 3 after the load current is disconnected, the high-frequency discharge and stop E will be repeated, and as explained above, the The discharge starting voltage increases.

Since the voltage of the inter-wiring capacitance C repeats intermittent charging and discharging due to high-frequency intermittent oscillating discharge between the electrodes while receiving the power supply voltage, it increases from the charging voltage immediately after the current stops.

The increased charge in the inter-wiring capacitance C is an intermittent oscillating discharge between the electrodes, and the current is cut off as described above and cannot flow stably. As the discharge starting voltage increases, the high-frequency oscillating voltage increases more and more.

When the discharge starting voltage between the electrodes rises to a very high vacuum withstand voltage and the high-frequency intermittent oscillating discharge stops, the inter-wiring capacitance C has a voltage close to the very high vacuum withstand voltage when the discharge stops. It will accumulate and the load circuit will be opened.

When the discharge starting voltage between the electrodes rises to the vacuum withstand voltage in this way, there is a risk of inducing an overvoltage that is higher than the allowable voltage of the insulation of the load circuit and causing a dielectric breakdown accident.

In order to solve the drawbacks of the vacuum switch shown in FIG. 1, a predetermined pressure necessary to prevent IE from generating an abnormal voltage that would cause an insulation breakdown accident in the vacuum container 1 shown in FIG. It is conceivable to fill it with gas.

However, when the load current is interrupted by electrodes 2 and 3 in this gas, the gas molecules existing in the arc path are ionized and heated to a high temperature, so when the arc is extinguished, they are ionized together with the metal vapor by the ionization action. It is adsorbed to the other high potential parts of the electrodes 2 and 3, and diffuses to the low temperature and low pressure part due to the high pressure increased by the arc heat, and hits the other low temperature parts of the vacuum vessel 4, causing it to enter the constituent parts. Since some gas molecules are adsorbed and do not return, a depletion effect of the enclosed gas occurs.

Therefore, as the load current is repeatedly cut off, the vacuum vessel 4
The pressure of the gas sealed inside decreases, the cutting current increases as shown in Figure 1 above, high-frequency intermittent vibration occurs, and the discharge starting voltage increases, resulting in abnormal voltage. It was confirmed that the risk of inducing dielectric breakdown accidents increases.

For this reason, even if gas is sealed to prevent abnormal voltage from occurring,
In order to withstand long-term use, preventing a drop in gas pressure has become an important issue.

Q) The drawbacks of the conventional vacuum switch mentioned above are also common to various devices that switch on and off current in a ground-type vacuum. The defect was that it generated abnormal voltage and caused accidents such as insulation breakdown.

An object of the present invention is to provide a vacuum switching device that can suppress abnormal voltages that occur when switching current in a vacuum for a long period of time, thereby preventing accidents such as dielectric breakdown.

This explanation will be explained in detail below, taking a vacuum switch as an example.

FIG. 2 is a diagram showing a vacuum switch which is an embodiment of the present invention.

In FIG. 2, 2 and 3 are exactly the same as those in FIG. 1, indicated by the same reference numerals.

Reference numeral 4 denotes a vacuum container, which is made to have the same structure as the conventional vacuum container shown in step 1 in Figure 1. Cheeky science fiction
A small amount of gas of 6 is sealed as a gas that stabilizes the vacuum discharge to maintain a predetermined low pressure of 10-r or less, and the chamber is completely hermetically sealed.

Reference numeral 5 denotes a gas replenishment device, which is made of porous activated carbon and is heated and evacuated in a vacuum in advance to discharge all the gases contained in the material. The activated carbon is placed under a specified pressure of the same hexafluoric yellow SF6, so that the gas at the specified pressure is sufficiently absorbed into the porous structure, and the gas molecules are adsorbed onto the activated carbon, which is attached to the vacuum container 4.

Therefore, this gas replenishment device has a specified pressure of hexagonal yellow S.
A large amount of F6 molecules are adsorbed and stored in vacuum container 4.
When the gas sealed inside is depleted, the adsorbed gas is released to replenish the gas.

Reference numeral 6 denotes a heating device, which is a heater through which electric current is passed from outside the vacuum container 4', and heats the gas supply device to raise the temperature of the activated carbon and release the gas adsorbed on the activated carbon. promote

The vacuum switch shown in Fig. 2 is constructed as described above, and as in the conventional case, electrodes 2 and 3 are connected to an AC power source and a load circuit, respectively, and a driving device opens and closes electrodes 2 and 3 to generate an AC current. Used as an AC breaker that opens and closes.

The operation will be sequentially explained below based on FIG. 2.

The first effect, the effect of preventing load current from cutting, will be explained.

When the load current is cut off, electrodes 2 and 3 begin an opening operation, and when the load current is flowing through the arc, in a conventional vacuum switch, the load current decreases from the maximum value toward O. During this process, as the current value decreases, the temperature of the cathode bright spots of electrodes 2 and 3 decreases, and the amount of evaporation of metal vapor decreases.
The disadvantage was that the load current was cut off due to the lack of ionized metal vapor needed to maintain the arc.

However, in the vacuum switchgear of this embodiment, gas at a predetermined pressure is sealed in the vacuum container 4, and between the electrodes 2 and 3, the gas molecules of hexagonal yellow SF6 are ionized by the arc. Therefore, even if there is a shortage of metal vapor evaporated from the electrode 2.3, the ions necessary to maintain the arc will be supplemented by ionized gas molecules, so the arc will not be extinguished due to the lack of ions. does not occur, and no load current disconnection occurs.

Therefore, the generation of induced voltage in the load circuit due to the cutting current is suppressed, thereby preventing the occurrence of dielectric breakdown accidents in the load circuit.

The second effect, the effect of preventing high-frequency intermittent oscillating discharge, will be explained.

After the load current is cut off, when a high-frequency discharge occurs between electrodes 2 and 3 due to the voltage accumulated in the inter-wiring capacitance C, in conventional vacuum switches, the current is cut off and does not flow stably, resulting in high-frequency discharge. There was a drawback that intermittent oscillating discharge occurred.

However, in the vacuum switch of this embodiment, no cutting current is generated as described above, so even a high frequency current with a small current value can continue to flow stably between the electrodes. The high frequency current flows through the load circuit between the electrodes, and the energy stored in the wiring is released and dissipated in a short period of time, thereby suppressing the occurrence of high frequency intermittent oscillating discharge.

Therefore, even if a high voltage is induced and accumulated in the load circuit,
Since it is released and disappears in a short period of time, it acts to prevent insulation breakdown accidents in the load circuit.

The third effect, which is the effect of preventing generation of excessive voltage O exceeding the allowable voltage of the load circuit, will be explained.

After the load current is cut off, when the accumulated voltage in the load circuit increases due to high-frequency intermittent oscillating discharge, etc., in a conventional vacuum switch, the discharge starting voltage between electrodes 2 and 3 increases each time the discharge is repeated, and eventually When the vacuum withstand voltage rises to an extremely high level, the high frequency oscillating voltage of the load circuit rises to the vacuum withstand voltage, inducing and accumulating an overvoltage that exceeds the allowable voltage for safely maintaining the insulation of the load circuit. there were.

However, in the vacuum switch of this embodiment, gas at a predetermined pressure exists between the electrodes, so even if the residual ions between the electrodes are completely extinguished and the evaporated metal vapor is dissipated, a complete vacuum cannot be reached. Therefore, it is impossible for the discharge starting voltage between the electrodes to rise to a high discharge starting voltage such as the vacuum withstand voltage.

When low-pressure gas exists between electrodes 2 and 3, the discharge starting voltage is determined by the gas pressure if the distance between the electrodes is constant.

Therefore, the gas pressure required to start discharge between the electrodes when the allowable voltage of the load circuit is reached can be determined in advance.

This vacuum switch is set at a predetermined pressure and is filled with gas at this predetermined pressure, so that the discharge start voltage is prevented from rising higher than the allowable voltage of the load circuit.

For this reason, if a voltage higher than the allowable voltage is induced and accumulated in the load circuit, discharge will start between the electrodes, current will flow through the load circuit, and the voltage will disappear. The fourth function, the gas pressure maintenance function, will be explained.

The activated carbon in the gas supply device 5 installed in the vacuum container 4 absorbs a large amount of gas at a specified pressure and stores it by adsorption on the activated carbon, so the surrounding gas surrounding the activated carbon absorbs a large amount of gas at a specified pressure. It has the effect of releasing more gas as the pressure decreases below the specified pressure to recover the drop in gas pressure, and the larger the amount of depleted gas, the more gas is released and replenished into the vacuum container 4 to meet the predetermined level. The action of adjusting the pressure inside the vacuum container 4 continues so that the pressure is restored to normal.

Due to the gas release action of the activated carbon, the gas replenishment device 5 releases gas according to the depleted amount each time the load current is cut off, so even if the cutoff operation is repeated, the gas pressure in the vacuum container 4 remains constant. The gas pressure between the electrodes 2 and 3 is maintained at a predetermined pressure without decreasing.

Note that the gas pressure after being refilled from the gas replenishing device 5 is
Although it is desirable to maintain the gas pressure initially sealed in the vacuum container, the gas pressure may be maintained at a level that overcomes the drawbacks of the prior art.

After using this vacuum switch for a long period of time and cutting off the current many times, a large amount of gas is released from the activated carbon.As a result, the amount of gas released is small, and the pressure recovery is slow. In this case, if the heating device 6 attached to the gas supply device 5 is energized to heat the activated carbon and raise the temperature of the activated carbon, the release of gas from the activated carbon will be promoted. ,
Since the amount of gas released increases, the pressure in the vacuum container 4 is reduced to -L.
It is possible to increase the pressure and hasten the recovery to the predetermined pressure.

The amount of gas adsorbed by activated carbon can store an extremely large amount of gas compared to the internal volume of the vacuum container 4, so the heating device normally maintains the gas pressure sufficiently without the need for a stage. The installation of the heating device 6 can be omitted except for vacuum switches which are opened and closed very frequently.

By installing this gas replenishment device 5, the vacuum switch maintains the gas in the vacuum container 4 at a predetermined pressure for a long period of time, so that insulation breakdown accidents due to abnormal voltage generation can be prevented over many years after installation. This makes it possible to manufacture a vacuum switch that is safe and highly reliable.

As the gas sealed in the vacuum container to stabilize the vacuum discharge and prevent the generation of abnormal voltage, we have explained the use of hexagonal yellow SF6, but there are also other gases such as helium (He) that can be used to stabilize the vacuum discharge and prevent the generation of abnormal voltages. Similar effects can be achieved by using an inert gas that does not chemically change other constituent materials and which can provide the desired discharge starting voltage, or a mixture thereof.

Although the description has been made using a vacuum switch that mechanically opens and closes electrodes as a typical example of the vacuum switch device according to the present invention, this invention is applicable not only to a mechanical vacuum switch but also to a vacuum switch that mechanically opens and closes electrodes in a vacuum. A constant voltage vacuum discharger that applies a constant voltage to start a discharge to switch on and off the current, a vacuum arrester that connects between distribution lines and short-circuits the electrodes in a vacuum when abnormal voltage occurs, Used in various types of vacuum switchgear, such as vacuum fuses that connect electrodes with a fuse and blow out the fuse when excessive current flows to quickly extinguish the arc, to stabilize vacuum discharge and prevent abnormal voltage from occurring. Similar effects can be achieved, such as prevention.

In this invention, as explained below, a gas replenishment device is provided in the vacuum container so that gas can be refilled, thereby preventing the occurrence of abnormal voltage over a long period of time.1. ) It is possible to prevent accidents such as IL and insulation breakdown.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a conventional vacuum switch, and FIG. 2 is a sectional view showing an embodiment of the present invention. In the figure, 2 and 3 are electrodes, 4 is a vacuum container, 5 is a gas supply device, and 6 is a heating device. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. A vacuum container sealed with a predetermined amount of gas, at least a pair of electrodes supported within the vacuum container, and provided within the vacuum container to store supplementary gas and operate the vacuum container within the vacuum container. A vacuum switchgear including a gas replenishment device that releases the gas when the gas pressure falls below a predetermined pressure. 2. The vacuum switchgear according to claim 1, wherein the gas is hexafluoride yellow SF6 or helium He. 3. The vacuum switchgear according to claim 1, wherein the gas replenishment device is activated carbon that stores replenishment gas.