Patent Application
20230116363
This disclosure relates generally to a vacuum interrupter and, more particularly, to a vacuum interrupter including a flexible conductor and a vacuum insulated drive rod.
An electrical power distribution network, often referred to as an electrical grid, typically includes a number of power generation plants each having a number of power generators, such as gas turbines, nuclear reactors, coal-fired generators, hydro-electric dams, etc. The power plants provide power at a variety of medium voltages that are then stepped up by transformers to a high voltage AC signal to be connected to high voltage transmission lines that deliver electrical power to a number of substations typically located within a community, where the voltage is stepped down to a medium voltage for distribution. The substations provide the medium voltage power to a number of three-phase feeders including three single-phase feeders that carry the same current, but are 120° apart in phase. A number of three-phase and single phase lateral lines are tapped off of the feeder that provide the medium voltage to various distribution transformers, where the voltage is stepped down to a low voltage and is provided to a number of loads, such as homes, businesses, etc.
Power distribution networks of the type referred to above typically include a number of switching devices, breakers, reclosers, current interrupters, etc. that control the flow of power throughout the network. Vacuum interrupters are typically employed in many types of these switching devices to provide load and fault current interruption, where the vacuum interrupter is controlled by a magnetic actuator. A vacuum interrupter typically includes a cylindrical insulator, usually ceramic, and end caps sealed to the ends of the insulator to form a vacuum chamber or bottle. A fixed contact is electrically coupled to and extends through one of the end caps into the vacuum chamber and a movable contact is electrically coupled to and extends through the other end cap into vacuum chamber. When the contacts are in contact with each other current can flow through the vacuum interrupter. When the movable contact is moved away from the fixed contact, a plasma arc is created between the contacts that is quickly extinguished by the vacuum through a zero current crossing. The separated contacts in vacuum provides dielectric strength that exceeds power system voltage and prevents current flow, and the insulator prevents current flow between the end caps outside of the contacts.
The magnetic actuator used in these types of switching devices typically have an armature or plunger that is moved by an electrical winding wound on a stator to open and close the vacuum interrupter contacts, where the plunger and the stator provide a magnetic path for the magnetic flux produced by the winding, and where the plunger is rigidly fixed to the movable contact by a drive rod. In one design, when the actuator is controlled to close the vacuum interrupter, the winding is energized by current flow in one direction, which causes the plunger to move and seat against a latching plate. The current is then turned off to de-energize the coil and permanent magnets hold the plunger against the latching plate and against a compression force of an opening spring. When the actuator is controlled to open the vacuum interrupter, the winding is energized by current flow in the opposite direction, which breaks the latching force of the permanent magnets and allows the opening spring to open the vacuum interrupter. A compliance spring is provided in addition to the opening spring to provide an additional opening force at the beginning of the opening process so as to break the weld on the interrupter contacts.
The vacuum interrupter operates at system potential and the magnetic actuator usually operates at ground potential. The drive rod, typically a fiberglass rod, connecting the plunger to the movable contact extends through air and thus must be long enough to prevent arcing between the vacuum interrupter at relatively high voltage and the grounded actuator. However, the assemblies for these drive rods are heavy, expensive and add length to the switching device, all of which are generally undesirable. Further, the size of the drive rod significantly increases the mass that needs to be moved during the switching operation.
The following discussion discloses and describes a vacuum interrupter including an insulator having a first insulator portion and a second insulator portion, a first end cap sealed to one end of the first insulator portion, a second end cap sealed to one end of the second insulator portion, and a current ring sealed to an end of the first insulator portion opposite to the first end cap and sealed to an end of the second insulator portion opposite to the second end cap, where the first insulator portion, the second insulator portion, the first end cap, the second end cap and the current ring define a sealed vacuum chamber. The vacuum interrupter further includes a fixed contact extending through the first end cap and into the chamber and being sealed thereto, a movable contact positioned within the chamber relative to the fixed contact so that a gap is defined between the fixed contact and the movable contact when the vacuum interrupter is open and the fixed contact and the movable contact are in contact with each other when the vacuum interrupter is closed. The vacuum interrupter also includes a bellows sealed to the second end cap, an insulated drive rod rigidly coupled to the movable contact opposite to the fixed contact and the bellows, and a flexible conductor coupled to the movable contact and the current ring, where the flexible conductor flexes when the movable contact is moved by the drive rod so as to maintain an electrical connection between the movable contact and the current ring. In one embodiment, the flexible conductor includes a plurality of circular laminates stacked on top of each other and including a plurality of spirals defining gaps therebetween. In another embodiment, the flexible conductor is a linear spring trampoline conductor including an inner ring and an outer ring attached by springs.
Additional features of the disclosure will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.
The following discussion of the embodiments of the disclosure directed to a vacuum interrupter including a flexible conductor and a vacuum insulated drive rod is merely exemplary in nature, and is in no way intended to limit the disclosure or its applications or uses. For example, the discussion herein refers to the vacuum interrupter being used in a magnetically actuated fault interrupting device for use in medium voltage power distribution networks. However, as will be appreciated by those skilled in the art, the vacuum interrupter will have other applications.
A coupling rod 72 extends from the vacuum interrupter 42 through the end cap 54 and is sealed to the bellows 60, where the bellows 60 maintains the vacuum within the chamber 58 when the rod 72 moves. A ceramic drive rod 76 is fixed to the coupling rod 72 in the chamber 58 at one end and to a movable contact stem 78 at an opposite end in the chamber 58, where the stem 78 includes a shaft portion 80 and a cup portion 82 defining a shoulder 84 therebetween. An arcing contact 86 is electrically secured to the cup portion 66 and an arcing contact 88 is electrically secured to the cup portion 82 so that a gap is defined therebetween when the vacuum interrupter 42 is open. Vapor shields 90 and 92 are secured to the shoulders 68 and 84, respectively, and are provided around the cup portions 66 and 82, respectively, that help prevent metal vapor emitted from the contacts 86 and 88 when the plasma arc occurs when the contacts 86 and 88 are separated from condensing on an inside surface of the insulator 44, which would otherwise create a conductive metal coating on the inside surface of the insulator 44, and thus provide a conduction path in parallel with the contacts 86 and 88. A cup-shaped vapor shield 94 protects the drive rod 76 from the vapor and a cup-shaped vapor shield 96 protects the bellows 60 from the vapor.
The conductive path between the current ring 50 at system voltage and the end cap 54 at ground potential outside of the insulator 44 is still through air. Therefore, an outer insulating housing 100, such as an epoxy enclosure, encloses the insulator 44 for this purpose. Shielding conductors 102 and 104 are provided within the housing 100 to reduce electric field stress points at various locations in the vacuum interrupter 42. When in use, a power line (not shown) will be connected to the stem 62 opposite to the arcing contact 86 and a power line (not shown) will be connected to the current transfer ring 50.
A flexible conductor 110 including a series of spiral laminates 112 stacked on top of each other is electrically coupled to the stem 78 opposite to the arcing contact 86 and the current transfer ring 50, thus making an electrical connection between the power lines when the vacuum interrupter 42 is closed.
The switch assembly 40 also includes an actuator 130 that controls the drive rod 76 to open and close the vacuum interrupter 42. The actuator 130 includes an annular latching plate 132 having a central opening 134 through which the coupling rod 72 extends. The actuator 130 also includes a stator 136 defining a central opening 138, where a magnetic plunger 140 having a top shoulder 142 defining an opening 144 is slidably positioned within the opening 138. A coil 146 is positioned against the stator 136 in the opening 138 and a series of permanent magnets 148 are positioned between the plate 132 and the stator 136. A cup member 152 is rigidly secured to the plunger 140 and an opening spring 154 is provided within the cup member 152 and is positioned against the stator 136. A stop member 156 including an annular flange 158 is provided within the plunger 140 and is rigidly attached to the coupling rod 72 through the opening 144 in the plunger 140. A compliance spring 160 is provided within the cup member 152 and is positioned against the flange 158, which pushes the flange 158 against the shoulder 142.
The vacuum interrupter 42 is shown in the open position in
The flexible conductor 110 provides one suitable embodiment for transferring current in the vacuum interrupter 42, as described. However, other designs may also be applicable and may have better results in reducing high stress points in the conductor, which could reduce ripping and tearing in the conductor.
A series of spaced apart coiled springs 176, here eight, are electrically coupled to the rings 172 and 174 to provide the necessary electrical connection between the rings 172 and 174 and provide the necessary flexibility of the conductor 170. In one embodiment, tabs 178 are provided where the springs 176 are connected to the rings 172 and 174 to reduce mechanical stresses at the connection point. In one non-limiting embodiment, the rings 172 and 174 and the springs 176 are oxygen free copper and ends of the springs 176 are laser welded to the rings 172 and 174 at the tabs 178. The number of the springs 176 is dependent on the current magnitude and the cross-sectional area of the wires that the springs 176 are made of. Minimizing mechanical stress in the copper of the springs 176 may also include maximizing the length of the springs 176 by reducing the width of the rings 172 and 174. By using a copper coil spring, the length of the copper wire can more easily be increased by increasing the number of the coils or the diameter of coils. Specific embodiments include six 11-AWG wire springs, five 10-AWG wire springs or four 9-AWG wire springs based on the material of oxygen free copper and its resistance.
The conductive material used for the conductor 170 is limited because of outgassing in the vacuum environment and other limitations. Oxygen free copper has been suggested above as one suitable material, however, that material is soft and deforms easily. Other materials may also be applicable, such as copper chromium zirconium (CCZ).
The foregoing discussion discloses and describes merely exemplary embodiments of the present disclosure. One skilled in the art will readily recognize from such discussion and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the spirit and scope of the disclosure as defined in the following claims.
This application claims the benefit of priority from the U.S. Provisional Application No. 63/253,353, filed on Oct. 7, 2021, the disclosure of which is hereby expressly incorporated herein by reference for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 63253353 | Oct 2021 | US |
