Arc suppression gradient resistor switch

Abstract

When a switch is turned off, if there is an inductive load, an arc discharge occurs between the electrodes due to the induced electromotive force. This causes the electrodes to deteriorate. In particular, with electrodes using liquid metal, this can lead to the scattering and oxidation of the liquid metal. [Solution] The reason induced electromotive force is generated is that the switch rapidly disconnects the electrodes, following Lenz's law. In the case of an electrode pair with a structure in which a needle is inserted into an electrode made of liquid metal, there is vertical depth, so by changing the resistance value and length of the needle, the resistance change when the switch is turned on / off can be made to have an exponential slope. This prevents arc discharge.

Description

Technical Field

[0001] The present invention relates to a technology capable of reducing arc discharge when turning off a switch connected with an inductive load

Background Art

[0002] In recent years, solar power generation and wind power generation have become widespread, and along with this, power transmission technologies such as HVDC have also advanced. Furthermore, devices that operate with on-board batteries, such as EVs, drones, and robots, have become popular. All of these systems use switches and breakers, and service plugs may also be used. A problem here is that these contacts separate metal electrodes to perform on / off operations. From a microscopic perspective, the surfaces of the metal contacts have irregularities, and since they are connected at the actual contact area, the contact resistance stops decreasing. Nevertheless, the maximum current flows through these contacts, causing heat generation. Energy is wasted and consumed.

[0003] In order to reduce such heat generation at contacts, it has been successful to sandwich liquid metal between electrodes to reduce the resistance value to about 1 / 100. When handling large currents, the loss increases in proportion to the square of the current value, so significant effects can be expected in applications using large currents. In particular, in data centers, heat generation in UPS transfer switches and breakers arranged in multiple stages has become a problem. However, arc discharge occurs during on / off operations. Due to the arc discharge, the liquid metal scatters, and although part of it re-adheres, the liquid metal eventually decreases. Furthermore, the liquid metal oxidizes during scattering, leading to performance degradation.

[0004] Many technologies have been proposed as countermeasures against arc discharge, but most of them are countermeasures that use magnetic force to disperse plasma, which is a component of arcs, or countermeasures that utilize the fact that arc discharge does not occur in semiconductors, and none of them take countermeasures based on the root cause of arc discharge.

[0005] As a fundamental solution, he has proposed a method to eliminate arc discharge altogether. In this method, the switch itself has capacitance and stores charge, and when turned on, the capacitance increases until just before the contacts come into close proximity. However, when the contacts come into close proximity, the electric field strength between the contacts exceeds the dielectric strength of the air, and discharge begins. When turned off, capacitance is generated and charge is stored the moment the contacts separate, and discharge occurs when the charge exceeds the insulation pressure. To address this problem, he has proposed a method that combines a secondary electrode with surge protection elements such as a varistor, and has confirmed that it works experimentally. However, when a switch with an inductive load connected to it is turned off, Lenz's Law causes a large voltage to be generated in the inductance, resulting in an arc discharge in the switch. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent Application No. 2023-219624 [Patent Document 2] PCT / JP2023 / 014924 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The problem we aim to solve is to eliminate the arc discharge that occurs when a switch connected to an inductive load is turned off. [Means for solving the problem]

[0008] This invention involves changing the resistance value gradually, rather than abruptly, when switching the switch on and off. This reduces the induced electromotive force by decreasing the derivative shown in Equation 1. Specifically, when switching the switch from On to Off, the inter-electrode resistance is increased exponentially by changing the shape, material properties, and number of electrodes. Unlike conventional switches, the switch resistance is not changed instantaneously. [Effects of the Invention]

[0009] In the process of turning the switch of the present invention off, the resistance value gradually increases, the amount of change in current is small, and the derivative shown in Equation 1 becomes small, resulting in a small induced electromotive force, which prevents arc discharge between the electrodes of the switch. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is an explanatory diagram showing the voltage across a switch when the switch is rapidly switched on and off in a circuit connected to an inductive load. [Figure 2] Figure 2 is an explanatory diagram showing that no induced transient voltage is generated in the switch when the switch's resistance is tilted to switch it on and off in a circuit connected to an inductive load. [Figure 3] Figure 3 is an explanatory diagram showing a method for sloping the resistance value when switching the switch on and off. (Example 1) [Figure 4] Figure 4 is an explanatory diagram illustrating an example of when the resistance of a switch is sloped, showing the relationship between the distance between the electrodes of the switch and the resistance value using a linear graph and a semi-logarithmic graph. [Figure 5] Figure 5 is an explanatory diagram showing that an arc can occur when the switch is turned on or off, even in a circuit with a resistive load connected. [Figure 6] Figure 6 is an explanatory diagram illustrating the principle by which an arc is generated at the switch contacts even under a resistive load. [Figure 7] Figure 7 is an explanatory diagram showing how surge protection elements are combined to address different arc generation causes in a tilt switch for an inductive load where the switch resistance changes in a gradient. (Example 2) [Figure 8] Figure 8 shows a different configuration of the liquid retention method in the switch shown in Figure 3. (Example 3) [Figure 9] Figure 9 shows a different embodiment of the high-resistance needle shown in Figures 3 and 7. (Example 4) [Figure 10]FIG. 10 is a diagram showing an embodiment using knife-edge type electrodes as the intermediate resistance needle and high resistance needle shown in FIG. 3 and FIG. 7. (Example 5) Detailed Description of the Embodiments

[0011] FIG. 1(a) shows a circuit in which a battery, a switch, and an inductive load are directly connected as a circuit having an inductive load. The change in switch resistance when the switch is turned on / off is shown in FIG. 1(b). At this time, the voltage induced in the switch is shown in FIG. 1(c), which indicates that an inductive transient voltage (induced electromotive force) is generated only when the switch is off. This voltage follows Lenz's law, and as shown in Equation 1, the voltage is generated by the product of the time rate of change of current and inductance. As is clear from the equation, this is because the switch is turned off abruptly, resulting in a large differential coefficient.

[0012] [Equation] [Examples]

[0013] FIG. 2 shows the same circuit as FIG. 1, in which the resistance change of the switch is not changed abruptly but is changed with a slope characteristic. As shown in FIG. 2(b), the resistance change of the switch has an exponential slope characteristic. As shown in FIG. 2(c), the induced electromotive voltage is greatly suppressed, and arc discharge is suppressed.

[0014] FIG. 3 shows a measure for providing a slope characteristic to the resistance change of the switch. FIG. 3(a) shows the electrode structure described in the previously filed patent, in which a liquid metal (gallium-based liquid metal) is fixed to electrode B using a copper sintered metal. Furthermore, it shows a structure in which microneedles (low-resistance needles) are pierced into the liquid metal-impregnated sintered metal. Although it depends on the area, low-resistance contact of about 10 μΩ can be realized, achieving a resistance value of about 1 / 100 of that of a conventional contact (about 1 mΩ). In panel (b) of the same figure, in order to impart gradient properties to the contact resistance, needles of different lengths are prepared as high-resistance needles and intermediate-resistance needles (multiple stages can be set). The high-resistance needle is the longest, and a high-resistance material such as stainless steel or titanium is used as the material. For this reason, it makes contact the earliest when switched on, but has a high resistance value. Furthermore, since the needle has a sharpened tip, the contact resistance is large when it is pierced, and the resistance gradually decreases as the needle penetrates into the liquid metal-impregnated sintered metal. The next longest is the intermediate-resistance needle. Although only one set of intermediate-resistance needles is depicted in this figure, multiple stages may be provided. The intermediate-resistance needle is shorter than the high-resistance needle and longer than the low-resistance needle. Within this length range, multiple sets of different lengths between the high-resistance needle and the low-resistance needle may be prepared. For this intermediate-resistance needle, iron, nickel, brass and the like can be used. Aluminum cannot be used because it becomes brittle when exposed to gallium-based liquid metals. As shown in Table 1, the material can be appropriately selected and used from a plurality of types. Furthermore, the resistance value can also be varied by changing the thickness and number of the needles. In this way, the shape (length, thickness, number) of the needles and the materials (materials with different resistance values shown in Table 1) can be selected.

[0015] Panels (c), (d), and (e) of the same figure show the state in which the group of needles attached to electrode A pierces into the liquid metal-impregnated sintered metal attached to electrode B. In panel (c) of the same figure, only the long high-resistance needle reaches the liquid metal. In panel (d) of the same figure, in addition to the high-resistance needle, the intermediate-resistance needle also reaches the liquid metal, and the resistance value of the entire electrode is lowered. In panel (e) of the same figure, a large number of low-resistance needles are also pierced. The low-resistance needles are large in number and short in length, and since copper or a copper alloy is used, low contact resistance can be achieved.

[0016] Panels (f) and (g) of the same figure show the arrangement of the intermediate-resistance needles and the high-resistance needles in the depth direction. By slightly varying the lengths in this manner, an even more pronounced gradient in resistance is intended to be achieved.

[0017] [Table 1]

[0018] Figure 4 shows, as an example, the change in resistance with respect to electrode position when intermediate resistance needle groups and high resistance needle groups are added to the low resistance needle group. Figure (a) is shown as a linear graph. Figure (b) is shown as a semi-logarithmic graph. As can be seen, an exponential gradient resistance characteristic is obtained. Looking at the semi-logarithmic graph, the low resistance value contributed by the low resistance needle group is approximately 4 μΩ, achieving an extremely low resistance value and realizing a switch that does not generate heat even with high currents. Although a step is visible in the characteristics on a semi-logarithmic graph, the intermediate resistance needle group and the high resistance needle group enable the realization of an exponentially graded resistance characteristic. Since this is the part that suppresses arc discharge, the step between it and the low resistance needle group is not a problem. This graph shows the needle from the deep contact state in Figure 3(e) to the state where the tip of the high-resistance needle is touching the surface in Figure 3(c). The drive distance is 3 mm. Since the solenoid can move 1 cm, sufficient voltage resistance can be ensured when it is in the OFF position as a switch. [Examples]

[0019] Figure 5 shows the case where a resistor is attached as a load. Figure (b) shows that the resistance change of the switch is steep. Even without an inductive load, arc discharge occurs when the switch is turned on and off, as shown in Figure (c).

[0020] The principle is shown in Figure 6. Figure (a) shows the circuit when the switch is Off. The electrodes of the switch are separated, but a voltage V is applied by an external power supply. In this case, if the capacitance between the electrodes is C1, a charge Q1 is accumulated between the electrodes. The distance between the electrodes is d1. If d1 is reduced, the capacitance increases, and the electric field strength between the electrodes also increases. Next, Figure (b) shows the case when the electrode spacing is narrowed to d2, the capacitance increases to C2, and the charge also increases to Q2. At this point, the electric field strength exceeds the dielectric strength, an arc is generated, and the charge of Q2 is released. In Figure (c), the electrodes are connected and current is flowing. Figure (d) shows the Off state. A junction capacitance C3 is formed the moment the electrodes separate, and a charge Q3 attempts to accumulate. At that moment, the electric field strength should exceed the dielectric strength, causing an arc discharge. Unlike the case of an inductive load, arc discharge is observed even when the system is ON. The arc discharge when the system is OFF is indistinguishable from the arc caused by induced electromotive force, but it should be a larger arc discharge due to a synergistic effect. In such cases, inserting a surge protection element between the switch electrodes will not be effective. A previously filed patent (Japanese Patent Application No. 2023-219624) proposes this countermeasure. Experimental testing has also confirmed arc discharge suppression (when the device is ON). The method involves using a secondary electrode, which is attached before the main electrode. However, a surge protection element such as a varistor is placed between the main electrode and the secondary electrode. Therefore, the secondary electrode is recognized as an insulator, and no arc discharge occurs until the secondary electrode touches the opposing electrode. However, after contact, if the varistor voltage is set to a value lower than the power supply voltage, the accumulated charge is released instantaneously. As a result, no arc discharge occurs when the connection is made. Even when the device is OFF, the varistor voltage should be exceeded the moment the electrodes separate, causing the stored charge to discharge.

[0021] Figure 7 proposes a configuration in which the aforementioned electrode structure with gradient resistors is fitted with a surge protection element that prevents arc discharge caused by charge accumulation on the switch electrodes. This should suppress arc discharge during On / Off operation. The high-resistance needle is positioned in a way that allows it to function as a secondary electrode. However, it is necessary to insulate the high-resistance needle from electrode A and to attach a surge protection element such as a varistor between the high-resistance needle and electrode A. Such a structure is shown in Figure 7. This is the final form. [Examples]

[0022] Figure 8 shows another example of a structure that can hold liquid metal while inserting needles. In Figure 8 (a), the holes in the punch-through metal are aligned with the needles and welded to electrode B to fix the liquid metal-impregnated sintered metal. In Figure 8 (b), needles are also placed on electrode B, alternating with the needles attached to electrode A, and liquid metal is filled between the needles. [Examples]

[0023] Figure 9 proposes a curved trapezoidal electrode as an alternative to a high-resistance needle. Since this electrode slides along a surface rather than being inserted like a needle, a flat plate electrode can be used as the counter electrode. For use as a high-resistance electrode, stainless steel spring material is suitable. Initially, it is a point contact, but as it is pressed, it becomes a surface contact, reducing the contact resistance. Because the spring properties of stainless steel alone may change over time, it is backed with an elastic foam material. Using a closed-cell foam material provides durability. [Examples]

[0024] Figure 10 proposes knife-edge electrodes with angled teeth as alternatives to intermediate and high-resistance needles. Two types of knife-edge electrodes made of different materials are prepared. When the end of the high-resistance knife-edge electrode is brought into contact with the liquid metal and gradually cut into it, the entire high-resistance knife-edge electrode sinks in and the resistance decreases. As the cut is made further, the end of the intermediate-resistance knife-edge electrode comes into contact with the liquid metal, and as the cut is made further, the entire intermediate-resistance knife-edge electrode also sinks into the liquid metal. If stainless steel is selected for the high-resistance knife-edge electrode and iron for the intermediate-resistance knife-edge electrode, an exponential gradient resistance can be created. Figures (a), (b), and (c) illustrate this. As shown in Figures (d) and (e), the sintered metal is separated, and liquid metal channels are formed in the gaps between them. This structure makes it easy to insert the material deeply. [Industrial applicability]

[0025] It is expected that many forms of autonomous mobility powered by AI, such as EVs, drones, and robots, will emerge. Battery technology to support these is currently developing. However, to make full use of these batteries, charging stations capable of rapid charging with standardized power supply ports will be necessary. In addition, contactors, circuit breakers, etc., will be required inside the mobility devices. Maximum current will always flow through these circuit elements, but with current switches, the resistance will plateau and generate heat. Therefore, liquid metal switches have been developed that require 1 / 100th the resistance of existing contacts. This reduces heat generation and increases energy efficiency. However, if there is arc discharge, oxidation and scattering of the liquid metal will increase, so it is desirable to suppress arc discharge. By using this technology, the aforementioned mobility society will be realized. [Explanation of symbols]

[0026] 1 Electrode A 2 Low-resistance needles 3 Intermediate Resistance Needle 4 High-resistance needle 5 Electrode B 6. Liquid metal impregnation sintered metal 7. Inclined needle length 8. Arc discharge 9 Switch electrodes 10 Insulator 11 Surge protection element 12 Punch-through metal or metal mesh 13 liquid metal 14 Needle electrodes 15. Curved trapezoidal electrode 16 Foam material 17 points contact 18 surface contact 19 Intermediate resistance knife edge electrode 20 High-resistance knife-edge electrodes 21 Knife-edge electrodes 22 Liquid metal channels

Claims

1. In a switch in which electrodes A and B function by contacting or separating, a flat plate-shaped sintered metal impregnated with liquid metal is welded to electrode B, and a group of low-resistance needles are attached to electrode A in a two-dimensional arrangement, the low-resistance needles penetrate the liquid metal-impregnated sintered metal when ON, and the low-resistance needles disengage from the liquid metal-impregnated sintered metal when OFF, a gradient resistance switch in which the switch resistance changes in steps when ON / OFF by replacing a portion of the low-resistance needle group with a group of intermediate resistance needles that are longer than the low-resistance needles, contact the liquid metal-impregnated electrode before the low-resistance needle electrode when ON, and disengage from the liquid metal-impregnated electrode later when OFF, and by setting the conductivity of the intermediate resistance needles to be lower than that of the low-resistance needles.

2. A gradient resistance switch according to claim 1, wherein the switch resistance in the On / Off state changes in three stages by replacing a portion of the low-resistance needle group and the early intermediate-resistance needle group with a high-resistance needle group that is even longer than the intermediate-resistance needle and has even lower conductivity.

3. In the gradient resistance switch according to claims 1 and 2, the intermediate resistance needles vary in length within the range of the difference in length between the low-resistance needle and the intermediate-resistance needle, and the high-resistance needles vary in length within the range of the difference in length between the intermediate-resistance needle and the high-resistance needle, thereby creating a gradient resistance switch in which the switch resistance changes in multiple stages when switched on / off.

4. A gradient resistance switch according to claim 3, wherein the longest high-resistance needle is insulated from electrode A, and the longest high-resistance needle and electrode A are connected by a surge protection element such as a varistor, thereby preventing arcing caused by charge accumulated on the electrode.

5. A gradient resistance switch according to claims 1 to 4, wherein, in order to reinforce the sintered metal attached to electrode B, a punch-through metal or metal mesh having a hole through which a needle attached to electrode A passes is welded to electrode B.

6. A gradient resistance switch according to claims 1 to 4, wherein instead of sintered metal attached to electrode B, a group of needles that pass each other, attached to electrode A, is welded to electrode B, and liquid metal is filled between the needles.

7. A gradient resistance switch in which the high-resistance needle described in the above claim is replaced with a curved trapezoidal electrode.

8. A gradient resistance switch in which the intermediate resistance needle group and high resistance needle group described in the above claim are replaced with an intermediate resistance knife-edge electrode and a high resistance knife-edge electrode, respectively, and sintered metal is separated to open a liquid metal channel through which these knife-edge electrodes can pass.

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