Power actuator for vacuum interrupter

Abstract

An actuator for a circuit interrupter has a fixed magnetic boss, a movable magnetic armature, and a drive rod. The drive rod is aligned on an axis of the circuit interrupter. The drive rod has two stable positions, circuit interrupter closed and circuit interrupter open. The drive rod has a surface that the armature contacts to move the drive rod from the circuit interrupter closed position to the circuit interrupter open position. In the circuit interrupter closed position, the armature and the surface are separated by a pre-travel distance. The armature moves toward the fixed magnetic boss and contacts the surface to initiate circuit interrupter open movement of the drive rod, with momentum transferred to the drive rod.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. Provisional Application No. 62 / 858,904, filed June 7, 2019, entitled “Kinetic Actuator for Vacuum Interrupter,” which is incorporated herein by reference. Technical Field

[0003] The technical field of this disclosure relates to high-voltage switches with linear actuators. Background Technology

[0004] Injecting reactance into power transmission lines offers the opportunity to achieve significant improvements in overall system capacity and stability. However, there are situations where it becomes appropriate to completely and thoroughly eliminate reactance injection. These situations typically correspond to one type of fault or another. Grounding, short circuits, or open circuits are all types of faults that can destroy the system if not corrected or isolated. Injected reactance can obscure the location of such faults. Faults can become more localized, such as loss of power or function of the injected equipment. Since reactance-injected systems operate largely in connection with the energy flow through the lines, the most reliable way to eliminate their effects is to provide a switch that will manually or automatically bypass the reactance injection module when the system detects a fault.

[0005] One component that allows for the economical and efficient construction of bypass switches is the vacuum interrupter. This component is manufactured by many companies, including ABB, Eaton, GE, Siemens, etc. A representative pair of simplified cross-sections appears... Figure 1The vacuum interrupter components shown in the figure are sometimes referred to as "bottles", so called due to their hermetically sealed ceramic envelope 110. At the top of the vacuum interrupter, there is a fixed connector 120 that provides electrical contact to the upper portions of two contacts 130 (shown in the closed position) and 132 (shown in the open position). The lower portions of the two contacts are accessed via movable connectors 160 (closed), 162 (open). The separation of the contacts in their open position 132 is referred to as the throw of the switch, and it is clear that the greater the separation, the greater the voltage that the switch can withstand. In order to open the switch, the movable connector 162 must be pulled down by the distance that the contacts are open. This compresses the metal bellow 150 or 152, which forms part of the overall vacuum seal. (The shroud 140 prevents sputtered metal from the contacts from reaching the ceramic wall 110 of the vacuum interrupter and damaging the electrical insulation between the two ends of the interrupter.) The action of the actuator is to move the movable connector between its closed position 160 and open position 162 by providing a controlled linear displacement along the axis of the vacuum interrupter.

[0006] While a vacuum is a nearly ideal environment for high power electrical switches, there are residual risks. Under some conditions of transient voltage at the instant of switch closure and contact surface roughness, a tiny weld can form between the fixed and movable contacts (130 in the figure). These increase the energy required to open the switch contacts beyond the normal range of values. Figure 1

[0007] Within the switch, the size and surface of the contacts 130 determine the current handling characteristics of the switch. All other aspects of the switch or bypass switch performance are determined by the actuator, including the throw that defines the operating voltage, the rest condition of the interrupter (which is typically one of normally open, normally closed, or its most recent state.

[0008] To use a bypass switch in the context of a power line reactance injector, the requirements of the application must be met. The prescribed action of the interrupter is to trigger the injector by opening the switch and bypass the injector when the switch is closed. Therefore, the passive state is "switch closed", i.e., the application requires a normally closed switch. In addition, in the event of a power failure, the actuator should automatically place the interrupter in the passive "switch closed" state without any signal or power. Finally, the typical operating condition with respect to the reactance injector requires the switch to be open, and in this state the actuator must operate at low power levels to minimize heating. Therefore, there is a need in the art for a solution that overcomes the shortcomings described above. BRIEF DESCRIPTION OF DRAWINGS

[0009] ​The claims, which expressly point out those elements that are to be considered essential to the invention, are what is regarded as the proper subject matter of the present invention. The foregoing and other objects, features and advantages of the present invention will be apparent from the following detailed descriptions of the application, particularly when read in conjunction with the accompanying drawings.

[0010] Figure 1 is a simplified section of a vacuum interrupter member.

[0011] Figure 2 is a block diagram of the elements of the entire bypass switch including the actuator.

[0012] Figure 3 is a schematic section of the described actuator in its switch closed condition.

[0013] Figure 4 is a schematic section of the described actuator in its switch open condition.

[0014] Figure 5 is a schematic section of the actuator in its switch open condition showing the magnetic holding circuit.

[0015] Figure 6 is a schematic section of the actuator in its switch closed condition showing the distance associated with the pre-travel of the armature.

[0016] Figure 7 is a schematic section of the actuator realized in a straight or magnetic piece configuration.

[0017] Figure 8 is a schematic section of a position monitoring method based on micro switches.

[0018] It will be appreciated that the schematic drawings show the principle of the invention without showing all structural elements, connectors or protection elements. DETAILED DESCRIPTION

[0019] The described trigger enables the bypass switch to meet these operational requirements and adds a level of reliability to the transition from contact closed to contact open.

[0020] As Figure 2 shown in the figure, for the bypass switch there are several sections. The vacuum interrupter 225 with contacts sealed in vacuum is housed, protected and insulated in the area marked 220. Above that is the contact 210 between the top fixed contact of the vacuum interrupter 225 and the line to be switched. Area 230 provides contact between the movable end of the vacuum interrupter 225 and the line to be switched. Area 240 provides isolation between the high voltage contacts in area 230 and the rest of the bypass switch. This isolation can allow separation of different atmospheres or different voltages.

[0021] The focus of the present disclosure is the area 250, the trigger. Its role is to move the drive rod 55 up or down in a controlled manner depending on the electrical signal applied or not applied to the trigger. This movement is applied to the movable end of the vacuum interrupter 225, causing the switch contacts (130 or 132 in Figure 1 ) to open, close or remain in the desired position. The drive rod 55 is shown as a single uniform structure in order to clarify its role in transferring movement from the trigger up or down in the area 250. In practice, the drive rod 55 will be composed of different pieces including different materials and different sections in order to meet the need for adjustability and isolation along its length, and the drive rod 55 can include mechanical damping. It remains aligned along the axis of the vacuum interrupter 225.

[0022] Figure 2 The last area is the monitor in area 260. In some embodiments, this area 260 is optional, but it can be desirable to electrically verify the position of the drive rod 55 which can extend into the monitoring area 260. Within this area 260, one can employ monitoring as simple as a micro switch operated by a cam on the drive rod, or the monitoring can be as complex as a laser interferometer measuring the position of the drive rod.

[0023] The essence of the trigger is shown in Figure 3 and Figure 4 ; both are partial and schematic sections of the trigger structure. Figure 3 The trigger is depicted in the closed or activated position. In this case, the drive rod 55 is in its uppermost position and the contacts are in the vacuum envelope, the vacuum interrupter is forced together so they can carry current between the two circuits mentioned in Figure 2 . The lateral movement of the drive rod 55 is constrained by the guide plates 10 carried on the rails 15. The non-magnetic metal support members 17, 18 and 19, which can be support plates, provide mechanical support for the magnetic structure that dominates the trigger.

[0024] The first magnetic, i.e. magnetizable, structure is the armature, here shown in two armature pieces 20 and 25. While Figure 3 they are shown in cross section, as viewed along the axis of the drive rod 55, they are circular armature pieces 20 or cylindrical armature pieces 25. The armature 20, 25 can also be composed of a single piece of ferromagnetic material, eliminating the joint between the armature piece 20 and the armature piece 25. The ferromagnetic material forming the armature 20, 25 should be a metal such as permalloy, mild steel or electrical steel, which has a low level of coercivity (less than 160 A / m) to ensure the responsiveness of the magnetic circuit.

[0025] Figure 3The other elements of the magnetic circuit in FIG. 1 are the magnetic shell 30 and the magnetic boss 35. These elements are also preferably formed of a ferromagnetic metal with low coercivity. Permalloy, soft carbon steel, and electrical steel are all materials with coercivity less than 160 A / m. A single cylindrical permanent magnet 45 or smaller magnet ring 45 is positioned between the magnetic shell 30 and the magnetic boss 35. The magnetism of the permanent magnet 45 must be oriented so that the force magnetic lines point radially normal to the drive rod 55. It is contemplated Figure 5 The magnetization of these permanent magnets 45 will be oriented so that the outer surfaces are both north poles (as a specific example). The various embodiments are agnostic as to having a north or south pole on the outer surface.

[0026] The other key element in the magnetic construction is the solenoid 40. This coil is used to open the interrupter and to hold it in the open position. In each case, the solenoid 40 is energized so its induced magnetic field is in the same direction as the field induced by the permanent magnets 45 (e.g., permanent magnet rings). The fields of the permanent magnets 45 and the solenoid 40 are additive. The solenoid 40 typically has several components, the most important of which is the wire winding, but there are connections, bobbin, and insulation. These are common and are incidental to the described operation of the trigger.

[0027] The drive rod 55 is axially movable relative to the structural support members 17, 18, and 19 and is movable relative to the magnetic shell 30 (e.g., housing), the magnetic boss 35, and the solenoid 40. With the trigger in the closed condition, with the drive rod 55 in its up position, the force on the vacuum interrupter is established by the main spring 60, which is carried on the collar 56 of the drive rod 55. There is a second spring 70 that holds the armatures 20, 25 in their up reset position. The upper portion of the armature (armature member 20) is free to move along the drive rod 55, but its motion is limited at one extreme by contact with the collar 56 and at the other extreme it is limited by a stop 58 that is attached to or integral with the drive rod 55.

[0028] When no power is applied to the trigger, Figure 3 The condition shown in FIG. 1 is appropriate. The drive rod 55, in its highest position, holds the contacts 130 in the vacuum interrupter together as shown in the closed position in Figure 1 The circuit between the two external line contacts is on. To open the switch, DC power must be applied to the solenoid 40 in the sense of augmenting the magnetic field applied by the permanent magnets 45 (e.g., permanent magnet rings). For a solenoid 40 of 360 turns, a current of 30 to 40 amperes provides sufficient attraction to overcome the upward pressure of the armature reset spring 70 and then the main spring 60, pulling the armatures 20, 25 down, finally reaching Figure 4The exemplary force overcome by solenoid 40 is about 150 N from the armature return spring 70 plus about 3000 N from the main spring 60.

[0029] Figure 4 The trigger is shown in the condition where the contacts 132 in the vacuum interrupter are held open (as in Figure 1 Figure 4 Figure 3 In this open position, the upper part of the ferromagnetic armature (armature piece 20) is in contact with the magnetic shell 30 and the inner part of the armature (armature piece 25) is in contact with the magnetic boss 35. In this position, the armature piece 20 is carried on the collar 56 of the drive rod 55, keeping it down. This corresponds to the open condition of the switch in Figure 1

[0030] Figure 5 In the open condition again shown in

[0031] There are two extreme approaches to maintain the switch open condition shown in Figure 5 The first would be to have the current through the solenoid at a level sufficient to withstand the total upward force exerted by the main spring 60 and the armature return spring 70. The other extreme would be to have the permanent magnet 45 designed with a magnetic flux sufficient to maintain the armature 20, 25 in contact with the magnetic shell 30 and the magnetic boss 35. This option is not acceptable because of the operational requirements including having the actuator in its closed condition without the application of power.

[0032] The numerical examples contained in the following paragraphs are illustrative for a 15 KV, 2000 Amp vacuum switch with a peak transient current rating of 65000 Amp. Higher ratings will generally require larger forces, stronger magnetism and larger operating currents.

[0033] ​​​​The actuator uses permanent magnet 45 that is only strong enough to provide 45% to 55% of the total force (e.g., 3400 N) exerted by springs 60 and 70. In addition to the force of permanent magnet 45, holding the trigger in the open position requires a magnetic flux of between 1 and 3 amperes of current through solenoid 40. Note that this current represents solenoid power, which is roughly 25% of the power required without permanent magnet 45. More impressively, it is a very small fraction, about 0.3% of the power required during the transition from closed to open. These particular numbers are examples; a smaller or larger switch vacuum interrupter will require less or more energy for the transition and holding, but the use of a permanent magnet significantly reduces the power required to hold the actuator in the contact open condition, and additionally reduces the energy required to drive the contacts from closed to open (albeit to a lesser extent). The particular values of current are affected by the choice of ferromagnetic material, the number of turns in the solenoid, and the strength of the permanent magnet. Still fundamental in some embodiments is that the restraining force of permanent magnet 45 is not enough to hold armatures 20, 25 in their switch open condition. There must be additional magnetic force from the holding current in solenoid 40 to maintain the bypass switch in its open condition.

[0034] The transition from contact closed to contact open is addressed by Figure 6 Figure 6 The actuator is shown in the contact closed condition. Armatures 20, 25 are stopped by stop 58, which is fixed relative to drive rod 55, leaving a gap Yl between the mating face of the magnetic housing 30 and the upper armature (i.e., armature piece 20). There is this same gap Yl between the inside 25 of the armature and the magnetic boss 35. In the contact closed condition, there is a gap Y2 between the surface of the upper armature piece 20 and the collar 56 of drive rod 55. In the transition from closed to open, as soon as solenoid 40 is triggered, armatures 20, 25 will be opposed by the relatively weak armature return spring 70, and will begin to move downward through a distance Y2 (a pre-travel before the movement of drive rod 55 and its collar 56 begins). During this travel, the mass of armatures 20, 25 accumulates velocity, so that the movement of drive rod 55 and its collar 56 begins with the transfer of momentum from moving armatures 20, 25. In the contact Figure 1 The jerk provides additional kinetic energy during the contact (130 in FIG. 1) opening, and this additional kinetic energy breaks any micro-welds on the contact faces.

[0035] ​The net stroke applied to the vacuum interrupter is the total stroke Yl of the armatures 20, 25 minus the pre-stroke Y2. An example value for Yl is 17 mm, and a representative value for Y2 (pre-stroke) is 10 mm. In this example, the net stroke applied to the vacuum switch is 7 mm. The net stroke is a design parameter of the system, with longer strokes accommodating higher operating voltages for the switch, and shorter strokes minimizing metal fatigue and extending the operating life of the vacuum switch.

[0036] The above Figures 3 to 6 The magnetic elements, armatures 20, 25, magnetic shells 30 and magnetic bosses 35 are all depicted as circular or cylindrical as viewed on the axis of the drive rod 55 and constructed of solid ferromagnetic alloy. The circular configuration has the advantage that it is insensitive to accidental rotation about the axis of the drive rod 55. The principles listed above apply equally to magnetic elements that are rectangular or square when viewed along the axis of the drive rod 55. Figure 7 A schematic cross-section of a trigger is shown in which the magnetic element armature 21, the magnetic shell 31 and the magnetic boss 36 all have a straight profile. While it is possible for the armature 21, the magnetic shell 31 and the magnetic boss 36 to be formed of solid ferromagnetic material, it is also possible for them to be formed of thin slices of ferromagnetic metal, as is common for transformers. Thus, some or all of the armature 21, the magnetic shell 31 and the magnetic boss 36 can be implemented as a stack of thin ferromagnetic sheets, with the slices being oriented in the direction of the magnetic field as seen in the cross-section of Figure 7

[0037] If sheet material is used, additional bushings 23 can be used to protect the sheet edges from movement relative to the drive rod 55 and impact with the collar 56. In addition, the rectangular geometry requires additional guidance, so any accidental rotation of the armature 21 about the axis of the drive rod 55 is too small to affect the integrity of the magnetic circuit formed when the actuator is in its switch open condition. The accidental rotation must also be limited to avoid bringing the armature 21 into contact with the solenoid 40 or any of its protective elements. The drive rod 55 and the collar 56 must be centered in the armature 21 to avoid twisting during the open and close operations.

[0038] In the embodiment shown in Figure 3 and Figure 4 In the embodiment shown in Figure 8 ​A simple position indicator is shown schematically in Fig. 6. The simplest position indicator can be formed by a shaped cap 59 on the drive rod 55. This cap can act as a cam to press one or more micro switches 80 when the drive rod 55 is in its lower contact break position. Correspondingly, the micro switches are released when the drive rod 55 is in its upper contact make position. Other methods of indication can be employed. Examples include optical sensing of a light or dark pattern on the drive rod 55, or laser sensing of one or more gratings on the drive rod 55.

Claims

1. An actuator for a circuit interrupter comprising: a fixed magnetic boss; a movable magnetic armature; and a drive rod aligned on an axis of the circuit interrupter, the drive rod having two stable positions, circuit interrupter closed and circuit interrupter open, and a surface on the drive rod between the movable magnetic armature and the fixed magnetic boss such that the armature contacts the surface to move the drive rod from the circuit interrupter closed position to the circuit interrupter open position; wherein in the circuit interrupter closed position, the armature and the surface are separated by a pre-travel distance, such that the armature moves toward the fixed magnetic boss and contacts the surface to initiate circuit interrupter open movement of the drive rod, with momentum transferred to the drive rod. The range of travel for the drive rod and the switching contacts of the circuit interrupter is less than the range of travel for the armature.

2. The actuator of claim 1, wherein The actuator is arranged for a hermetically sealed circuit interrupter that includes a permanent magnet between a magnetic housing and the magnetic boss.

3. The actuator of claim 1, wherein The actuator is arranged for a hermetically sealed circuit interrupter that includes a DC solenoid within a magnetic housing, the DC solenoid sized to allow the magnetic armature to move within the solenoid in response to current through the solenoid.

4. The actuator of claim 1, wherein The actuator is arranged for a hermetically sealed circuit interrupter that holds the drive rod in the circuit interrupter closed position without applied power.

5. The actuator of claim 1, wherein The actuator is arranged for a hermetically sealed circuit interrupter that holds the drive rod in the circuit interrupter closed position using one or more springs without applied power.

6. The actuator of claim 1, wherein The actuator is arranged for a hermetically sealed circuit interrupter that changes the drive rod from the circuit interrupter open position to the circuit interrupter closed position using one or more springs without applied power.

7. The actuator of claim 1, wherein The actuator has a combination of permanent magnet force and magnetic force of a DC solenoid to effect the transition from the contacts of the circuit interrupter closed to the contacts of the circuit interrupter open.

8. The actuator of claim 1, wherein The actuator has a combination of permanent magnet, DC solenoid, and magnetic circuit to hold the contacts of the circuit interrupter open.

9. The actuator of claim 1, wherein The actuator has a combination of permanent magnet, DC solenoid, and magnetic circuit to hold the contacts of the circuit interrupter open using a specified low power level in the solenoid.

10. The actuator of claim 1, wherein The actuator has a magnetic circuit that includes a fixed magnetic housing with a pole, the fixed magnetic boss with an opposite pole, and the movable magnetic armature with an outer pole and an inner pole that mate with the corresponding poles on the magnetic housing and the magnetic boss to close the magnetic circuit when the drive rod is in the circuit interrupter open position.

11. The actuator of claim 1, wherein The solenoid magnetic field and the permanent magnetic field have the same orientation, avoiding the tendency of the triggering field to demagnetize the permanent magnet of the actuator.

12. The actuator of claim 1, wherein, ​ 13. The actuator of claim 1, wherein In the circuit interrupter open position, the combination of the permanent magnetic force and the magnetic force of the solenoid operating at a specified low power level exceeds the sum of the restoring forces of the spring pressing on the armature and the further spring pressing on the drive rod.

14. The actuator of claim 1, wherein In the circuit interrupter open condition, the permanent magnetic force is less than the sum of the restoring forces of the spring pressing on the armature and the further spring pressing on the drive rod.

15. The actuator of claim 1, wherein, The fixed magnetic housing, the magnetic boss and the movable magnetic armature each have a cylindrical shape.

16. The actuator of claim 1, wherein The fixed magnetic housing, the magnetic boss and the movable magnetic armature each have a rectangular shape.

17. The actuator of claim 1, wherein The fixed magnetic housing, the magnetic boss and the movable magnetic armature have a rectangular shape made of sheet-like magnetic material.

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