Current switchgear

Abstract

To suppress arc discharge that occurs every time the switch is turned on and off.SOLUTION: In a switch in which a first electrode and a second electrode are separated, a surge protection element and an auxiliary electrode are attached to the first electrode. During the On operation, the auxiliary electrode is brought into contact with the second electrode just before the first electrode comes into contact with the second electrode, and the current that flows as an arc discharge is passed through the surge protection element. During the Off operation, the auxiliary electrode and second electrode remain connected even immediately after the first electrode and second electrode are separated, and the current caused by the charge generated when the electrodes are separated is passed through the surge protection element. Therefore, by not passing the arc discharge in the space between the electrodes but instead passing it through the surge protection element, wear on the electrodes can be prevented.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a mechanical switch with arc discharge mitigation measures. [Background technology]

[0002] We proposed a relay switch using liquid metal, and successfully tested it by turning a current of 60 A on and off 100,000 times at 5 V. The resistance value at that time was 0.1 mΩ or less, and it is possible to further reduce the resistance. This resistance value is sufficiently smaller than that of existing switches using metal contacts or semiconductor switches, making it possible to pass a large current.

[0003] We are now moving towards a decarbonized society, and for EVs, rapid-chargeable batteries have appeared, bringing about major advances in terms of charging time and safety. However, rapid charging of these batteries requires not only a high voltage but also a large current. Furthermore, hydrogen generation devices also require electrolysis at a current of 1000A or more. The lines (HVDC) that transmit energy from wind and solar power generation require not only high voltage but also high current transmission. Thus, the number of situations where large currents are handled is increasing.

[0004] The liquid metal switch we developed is indeed suitable for passing large currents and is in demand in society, but there are problems with its use at high voltages. As the voltage increases, the arc current becomes larger, causing problems such as liquid metal scattering and electrode deterioration.

[0005] As one of the improvement measures, there is the auxiliary electrode method. This involves preparing an auxiliary electrode in parallel with the main electrode. The auxiliary electrode makes contact just before the main electrode connects, and when the main electrode separates, the auxiliary electrode remains connected and the electrode separates with a delay. As a result, arc discharge always occurs at the auxiliary electrode, and the main electrode is protected from arc discharge. It functioned as intended, and arcs were observed at the auxiliary electrode. However, there remains the problem that the auxiliary electrode melts and deteriorates due to the occurrence of arcs. To solve this problem, a method has been proposed in which when the auxiliary electrode operates, the arc generation site moves and does not stop the arc at a specific location, but instead runs the heating site. It has been filed as a patent application.

[0006] As a different approach, Mr. Shimada of the Tokyo Institute of Technology has proposed a method of inducing an arc current into a semiconductor without causing arc discharge. In this method, a semiconductor switch is installed in parallel with a mechanical switch. It is a method of turning on just before the mechanical switch connects and flowing the arc current through the semiconductor. Even when the mechanical switch is turned off, the semiconductor remains connected for a while and induces the arc current into the semiconductor. With this method, arc discharge itself does not occur. It utilizes the fact that arcs do not occur in switching by MOSFETs. However, it is necessary to synchronize and move the mechanical switch and the semiconductor switch. If the lead time is too long, the time during which a large current flows through the semiconductor becomes long. Since the on-resistance of the semiconductor element itself is not low, it generates heat. Therefore, it is necessary to attach a heat sink or the like, and the housing becomes large.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] The problem to be solved is that the size of the element and the housing does not increase, the arc current is induced to an external element, arc discharge is not generated in the space, and the electrode contact is protected.

Means for Solving the Problem

[0009] The present invention proposes a structure in which a surge suppression element is incorporated into an auxiliary electrode.

Effect of the Invention

[0010] In the current liquid metal switch, one electrode is a micro needle, the surface thereof is coated with liquid metal, and the other electrode is impregnated with liquid metal in sintered metal. By inserting the micro needle into the sintered metal, the liquid metals are mixed with each other to enable a low-resistance connection. Due to the low resistance, it has the ability to conduct a large current. Even if the liquid metal at the tip of the micro needle is scattered due to arc discharge, it only reattaches to the surroundings and the liquid metal does not disappear. However, since it oxidizes and the conductivity decreases, nitrogen gas is filled. Although such measures are taken, it is limited to use at low voltages. When the voltage is increased and the arc current is increased, deterioration of the micro needle electrode is observed. However, by adding the content of this patent, it becomes possible to use at high voltages. Originally, since the liquid metal switch has a small contact resistance value, it can be used for large current applications, and once it is in contact, there is no problem even if the voltage is high. The arc current generated when the switch is turned on or off increases as the voltage increases, so it is not possible to increase the voltage. If this is solved, it can be used for high-power applications. The content of this patent is not limited to liquid metal switches, but can also be used for general switches and can exhibit a life-prolonging effect.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Modes for Carrying Out the Invention

[0012] Fig. 1(a) shows a circuit in which a single-break switch is inserted between a power supply and a load. Electrodes 1 and 2 of the switch are separated by a distance d1 and are capacitors with a capacitance C1. A voltage V is applied between both electrodes, and charges Q1 are accumulated on both electrodes. Fig. 1(b) shows the state when the On operation is started and the electrode distance is reduced to d2. The capacitance becomes C2, the stored charges increase to Q2 respectively, and an arc discharge (Is) 5 flows as the electric field strength between the electrodes exceeds the breakdown voltage (capacitive discharge). Since there is no prominent resistance component, discharge occurs in an extremely short time, the current value increases, and the electrode surface is microscopically melted to form unevenness. Fig. 1(c) shows the state when the electrodes are completely closed, and a current determined by the power supply voltage V and the load resistance R flows. The potential between the electrodes is the same, and there is no capacitance. If the contact part is in contact with a convex part, current may concentrate here, heat up, melt, and join. Figure (d) shows the start of the Off operation with the electrode spacing increased. At the moment the electrodes separate, a large capacitance is generated, and at the same time, arc discharge occurs. Furthermore, plasma is generated around the area where the arc discharge occurred, creating an environment conducive to the continuation of the discharge. For this reason, the discharge continues until the electrode spacing has opened to a certain extent. Due to this discharge, the electrodes are further partially melted, increasing the degree of unevenness. The switch cycles through such a process until the electrodes deteriorate and reach the end of their lifespan. The greater the voltage, the greater the charge stored between the electrodes, resulting in a discharge in a short time and a large current flowing as an arc discharge between the electrodes, causing the electrodes to locally melt and deteriorate.

Embodiment

[0013] An embodiment of the device of the present invention with a surge protection element is described with reference to FIG. 2. FIG. (a) shows the Off state, where electrode 1 and electrode 2 are separated by a distance d3. A surge protection element 6 and a spring electrode 7 are attached to electrode 1 via an insulating layer 8. The surge protection element is a two-terminal component, with one terminal attached to electrode 1 and the other to spring electrode 7. The spring electrode is fully extended, but its end does not reach electrode 2. Although not shown in FIG. 2, it depicts only the electrode part of FIG. 1, assuming that the power supply and the load are connected. A voltage is applied to the surge protection element 6. However, from the I-V characteristics of the surge protection element (see Table 1), when no voltage is directly applied, it is almost an insulator, so no large electric field is generated between the spring electrodes and electrode 2, and no arc emerges from the tip of the spring electrode. FIG. (b) shows the situation immediately before the electrodes come into contact, at a distance d4 just before arc discharge occurs between the electrodes. Since the spring electrode is in contact with electrode 2, the voltage of the power supply is applied to the surge protection element. Since the breakdown voltage 11 of the surge protection element is set lower than the power supply voltage, the charge accumulated between the electrodes flows beyond the breakdown voltage 11. As a result, no arc discharge flows between the electrodes. Figure (c) shows the situation when the electrodes are in complete contact. Even with spring electrodes, when the electrodes are pressed together, the spring compresses, so it does not prevent the electrodes from contacting each other. Since the electrodes are in contact, even if a voltage is applied from the outside, the voltage applied to the surge protection element is almost 0. Therefore, even if an arrester is used as the surge protection element, continuous current can be prevented. If Figure (b) is regarded as the figure immediately after the electrodes are separated, capacitance accumulates at the moment the electrodes separate. However, since the spring electrodes remain in contact, a voltage is applied to the surge protection element and exceeds the breakdown voltage 11, so current flows through the surge protection element and arc discharge can be suppressed. In this way, it is possible to mechanically move the spring electrodes to make contact earlier than the electrodes themselves when turned on and keep them in contact even after the electrodes are separated when turned off. By combining this spring electrode with a surge protection element, although no electric field is applied when not in contact, current flows after contact, preventing arc discharge from flowing in space and preventing electrode deterioration.

[0014]

Table 1

[0015] Table 1 shows the items that can be used as surge protection elements (there is also IsoMOV). The voltage values at the breakdown points for each element are called Zener voltage, varistor voltage, and arrester voltage, but these are collectively referred to as breakdown voltage 11. The breakdown voltage 11 of each element is set to a value smaller than the power supply voltage when only one is used, but to a value smaller than half of the power supply voltage when two elements are used in series. Also, when used for alternating current, those with symmetric I-V characteristics can be used. Regarding arresters, as can be seen from the circuit symbol, there is no polarity in general, but some products have polarity. In this case, those with different polarities are used in parallel with the positive and negative poles.

Example

[0016] Figure 3 is the same as Figure 2, but shows the case where the spring electrode is attached to the electrode 2 side. In this case, a contact electrode 9 is attached to the spring electrode side of the surge protection element, and the spring electrode attached to the electrode 2 side is separated from the contact electrode, which is basically the same as Figure 2.

[0017] Figures 4 to 7 show four examples as other methods instead of the spring electrode. These are attached to the electrode 1 side, but can also be attached to the electrode 2 side in the same way as Figure 3.

Example

[0018] Figure 4 shows an example where a slide electrode 12 is attached instead of the spring electrode, showing the on state and the off state. By sliding a plate-shaped and elastic metal flat plate on the electrode 2, it contacts earlier than the electrodes 1 and 2 come into contact with each other without preventing the contact between the electrodes 1 and 2, and maintains the contact even immediately after the electrodes 1 and 2 are separated.

Example

[0019] In Figure 5, since it is expected that the contact pressure will be small if only the slide electrode 12 is attached, a ferromagnetic flat plate electrode 13 is used for the slide electrode, and a permanent magnet 14 is embedded on the electrode 2 side to magnetically adsorb and reduce the contact resistance. Copper is used as the material of the electrode, and since it is a non-magnetic material, the magnetic force can be exerted even if a permanent magnet is embedded. In this method as well, it contacts earlier than the electrodes 1 and 2 come into contact with each other without preventing the contact between the electrodes 1 and 2, and maintains the contact even immediately after the electrodes 1 and 2 are separated.

Example

[0020] Figure 6 shows a method in which the needle 15 is used instead of the spring electrode, a hole 16 sealed with liquid metal is provided on the electrode 2 side, and the needle is inserted into the liquid metal. Since the liquid metal has wettability if the electrode 2 is made of copper, it can be sealed while maintaining the liquid state. However, since it solidifies when the environmental temperature is below the melting point of the liquid metal, it is necessary to attach a heater in cold regions. When using a eutectic alloy of gallium, indium, and tin instead of mercury, the boiling point is 2000 °C or higher, so it does not vaporize during normal use.

Example

[0021] Figure 7 shows a case where a connector pin 17 is used instead of the spring electrode and a connector socket 18 is attached to the electrode 2 side. Also in this method, without interfering with the contact between the electrode 1 and the electrode 2, it contacts earlier than the electrode 1 and the electrode 2 come into contact, and maintains the contact even immediately after the electrode 1 and the electrode 2 separate.

Example

[0022] Figure 8 shows a double-break switch in which a short bar 19 is simultaneously contacted and separated from the electrode 1 and the electrode 2 by a rotary solenoid to perform an On / Off operation. For the electrode 1 and the electrode 2 in Figure 5, a varistor is selected as a surge protection element and attached via an insulating layer. One terminal of the surge protection element is attached to the electrode 1 or the electrode 2, and the other terminal is attached to the spring electrode 7. Figure (a1) in the same figure is a plan view when it is On, and Figure (a2) is a cross-sectional view taken along the line A-A' of Figure (a1). From this, the spring electrode 7 and the electrode 1 in the shape of a folded flat plate electrode, the short electrode 19, and the electrode 2 and the short electrode 19 are in contact with each other to be in the On state. Figures (b1) and (b2) show the Off state. Figure (b2) shows the B-B' cross-section of Figure (b1). From this, the spring electrode 7 extends beyond the contact surfaces of electrodes 1 and 2, and the spring electrode contacts the short electrode immediately before the electrode contacts the short electrode. In this case, since two varistors are connected in series, the breakdown voltage 11 of the varistor is set to a value less than half of the power supply voltage.

Embodiment

[0023] Figure 9 shows a double-break switch that operates in an On / Off manner by simultaneously contacting and separating a short bar 19 with respect to electrodes 1 and 2 using a rotary solenoid, which is the same as Figure 5. However, the method of installing the varistor is different. Between electrode 2 and the short bar 19, it is connected by a varistor and a spring electrode 7, but between electrode 1 and the short bar 19, a conducting wire 21 is used and the varistor 6 is not used. As a result, since there is only one varistor 6 used in this switch, the breakdown voltage 11 is set to be less than the power supply voltage.

Industrial Applicability

[0024] By attaching a surge protection element with a sub-electrode structure to the switch, it is possible to suppress arc discharge during On / Off, and the arc current generated in the space between the switch electrodes can be made to flow through the surge protection element, so that the generation of unevenness due to melting of the electrodes can be suppressed, and the life of the switch can be extended.

Explanation of Reference Numerals

[0025] 1 Electrode 1 2 Electrode 2 3 Power supply 4 Load 5 Arc current (Is) 6 Surge protection element 7 Spring electrode 8 Insulating layer 9 Contact electrode 10 Arc current (Is’) 11 Yield voltage 12 Flat spring electrode 13 Ferromagnetic flat spring electrode 14 Permanent magnet 15 Insertion pin 16 Liquid metal filling hole 17 Connector pin 18 Connector socket 19 Short bar 20 Rotary solenoid shaft 21 Conductive wire

Claims

1. In a single-break switch having a first electrode and a second electrode that turn on or off by coming into contact with or separating from each other, a two-terminal surge protection element and a slip electrode are attached to the first electrode with an insulating layer interposed therebetween. One terminal of the surge protection element is connected to the first electrode, and the other terminal is connected to the spring electrode. The spring electrode protrudes beyond the first electrode and contacts the second electrode ahead of the first electrode when turned on, but does not prevent the first electrode and the second electrode from contacting each other. When the first electrode and the second electrode separate when turned off, the spring electrode contacts the second electrode for a while and separates with a delay, a single-break switch.

2. In the single-break switch according to Claim 1, a two-terminal surge protection element and a contact electrode are attached to the first electrode with an insulating layer interposed therebetween. One terminal of the surge protection element is connected to the first electrode, and the other terminal is connected to the contact electrode. A spring electrode is fixed to the second electrode, and the contact electrode and the spring electrode are made to contact each other when turned on. The spring electrode protrudes beyond the second electrode and contacts the contact electrode fixed to the first electrode ahead of the first electrode and the second electrode contacting each other when turned on, but does not prevent the first electrode from contacting the second electrode. When the first electrode and the second electrode separate when turned off, the spring electrode contacts the contact electrode for a while and separates with a delay, a single-break switch.

3. In the single-break switch according to Claims 1 and 2, the first electrode and the second electrode are incorporated into a circuit connecting the power supply and the load in series, and when the distance between the first electrode and the second electrode is reduced, the spring electrode and the second electrode, or the contact electrode and the spring electrode, contact at a position farther than the distance at which an arc is generated by the charge accumulated between the first electrode and the second electrode, a single-break switch

4. In the single-break switch according to Claims 1 to 3, any one of a Zener diode, varistor, arrester, ESD suppressor, IsoMOV, and combinations thereof is used as the surge protection element, a single-break switch

5. In the single-break switch according to claims 1 to 4, in the surge protection element, the yield voltage of these elements is smaller than the power supply voltage in a DC power supply and smaller than the effective value voltage in an AC power supply. Single-break switch

6. In the single-break switch according to claims 1 to 5, the spring electrode is a flat spring material fixed to electrode 1, protruding in front of the contact surface of electrode 1, and sliding on the upper end surface of electrode 2. Single-break switch

7. In the single-break switch according to claims 1 to 5, the spring electrode is a ferromagnetic flat spring material fixed to electrode 1, protruding in front of the contact surface of electrode 1, and when electrode 1 and electrode 2 are close, by a magnet embedded in electrode 2, the ferromagnetic flat spring material slides while being adsorbed on the surface of electrode 2. Single-break switch

8. In the single-break switch according to claims 1 to 5, the spring electrode is an insertion pin fixed to electrode 1, protruding in front of the contact surface of electrode 1, and piercing into a liquid metal encapsulation hole formed in electrode 2. Single-break switch

9. In the single-break switch according to claims 1 to 5, the spring electrode is a connector pin fixed to electrode 1, protruding in front of the contact surface of electrode 1, and inserted into a connector socket formed in electrode 2. Single-break switch

10. A double-break switch having a first electrode and a second electrode, with a short electrode that contacts by translation or rotation between them, the short electrode being in simultaneous contact with the first electrode and the second electrode to turn on, and the short electrode being separated from at least one or both of the first electrode and the second electrode simultaneously to turn off. A double-break switch provided with the surge protection element, the spring electrode, and the contact electrode that satisfy claims 1 to 4 at each contact point between the first electrode and the short electrode or between the second electrode and the short electrode.

11. In the double-break switch according to claim 10, only one contact point uses the surge protection element having the functions of claims 1 to 5, while the other contact point replaces the surge protection element of claims 1 and 2 with a conducting wire. Double-break switch

12. In the double-break switch according to claim 10 and claim 11, in the double-break switch having a mechanism in which the contact timing of the first electrode and the short bar is delayed in contact and separated earlier than the contact timing of the second electrode and the short bar, The double-break switch according to claim 1 to claim 5, wherein a surge protection element, a spring electrode, and a contact electrode are installed between the first electrode and the short bar

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