Patent Publication Number: US-10784064-B2

Title: Reduced size fault interrupter

Description:
BACKGROUND 
     Field 
     This disclosure relates generally to a pole unit for a switchgear and, more particularly, to a pole unit for a switchgear, where the pole unit includes a vacuum interrupter switch and an electromagnetic actuator electrically coupled together at a line potential and a pair of wireless power transfer coils for providing power to the actuator. 
     Discussion of the Related Art 
     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 turbine engines, nuclear reactors, coal-fired generators, hydro-electric dams, etc. The power plants provide a high voltage AC signal on 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. The substations provide the medium voltage power to a number of three-phase feeder lines. The feeder lines are coupled to a number of lateral lines that provide the medium voltage to various 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, interrupters, etc. that control the flow of power throughout the network. Some of these components are enclosed in a number of external housings that are mounted on, for example, a concrete pad, mounted underground or overhead, and are generally referred to herein as switchgear. The number and type of switchgear are application specific to the particular power network. 
     A typically switchgear includes a number of pole units, for example, three pole units for a three-phase network. Each pole unit is an assembly of components that include a fault interrupter switch including opposing contacts for disconnecting the power line, an electromagnetic actuator for actuating the switch, energy storage elements, control electronics, etc. Usually the fault interrupter switch is a vacuum interrupter switch that employs opposing contacts, one fixed and one movable, positioned within a vacuum enclosure. When the interrupter switch is opened by moving the movable contact away from the fixed contact the arc that is created between the contacts is quickly extinguished by the vacuum. A vapor shield is provided around the contacts to contain the arcing. For certain applications, the vacuum interrupter switch is encapsulated in a solid insulation housing that has a grounded external surface. 
     Workman are often restricted during the installation of switchgear by access, real estate, size and weight of the components. For example, space is a premium in underground vaults that have other equipment and small hatches. Pad-mounted switchgear use ground-level real estate that often requires lease payments based on area. Overhead installations often have limited truck/crane access, and thus the easier the switchgear is to maneuver the more pole-top sites become available. Thus, there is an effort in the industry to reduce the size of the switchgear. Further, by reducing the size and part count in a pole unit, mechanical performance may be more robust and handling becomes easier. 
     Modern fault interrupters employ solid state dielectrics where the interrupter is encapsulated in an epoxy. In known switchgear designs, especially for three-phase switchgear, the actuator that opens the switch is electrically isolated from the switch, where the interrupter switch is generally at the medium voltage line potential and the actuator is at ground potential so that it can interface with the electronics, which are also at ground potential. This electrical isolation requires a significant air gap between the switch and the actuator that can be on the order of 5-10 inches for medium voltage power levels. If this air gap can be eliminated, then the size and weight of the pole unit can be reduced. 
     SUMMARY 
     The following discussion discloses and describes a pole unit applicable to be part of a switchgear. The pole unit includes an outer housing and a first terminal and a second terminal extending into the housing. The pole unit also includes a vacuum interrupter switch having a vacuum chamber, a fixed contact extending into one end of the vacuum chamber and being electrically coupled to the first terminal, and a moving contact extending into an opposite end of the chamber. A sliding contact is rigidly coupled to the moving contact and slidably coupled to the second terminal, but could be rigidly coupled to the second terminal in a different design. The pole unit also includes an electromagnetic actuator having a coil wound on an annular or rectangular member, a rod extending into the member and being coupled to the sliding contact and a spring positioned against the rod and applying a spring bias, where actuation of the actuator forces the moving contact against the fixed contact to make an electrical connection therebetween, and where the annular member is electrically coupled to the second terminal. The pole unit further includes a power assembly having a transmitter coil and a receiver coil that are electromagnetically coupled, where the receiver coil is electrically isolated from the transmitter coil. In this configuration, the interrupter switch, the actuator and the receiver coil are at line potential and the transmitter coil is at ground potential. 
     Additional features of the disclosure will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional type view of an inside pole unit including a vacuum interrupter switch, an electromagnetic actuator and energy storage elements all at line potential; 
         FIG. 2  is an isometric view of an outside pole unit including a vacuum interrupter switch, an electromagnetic actuator and energy storage elements all at line potential; and 
         FIG. 3  is a cross-sectional type view of the pole unit shown in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The following discussion of the embodiments of the disclosure directed to a pole unit for a switchgear, where the pole unit includes a vacuum interrupter switch and an electromagnetic actuator electrically coupled together at line potential and a pair of wireless power transfer coils for providing power to the actuator, is merely exemplary in nature, and is in no way intended to limit the invention or its applications or uses. For example, as mentioned, the pole unit has particular application for use in medium voltage switchgear. However, as will be appreciated by those skilled in the art, the pole unit may have other applications. 
       FIG. 1  is a cross-sectional view of a pole unit  10  that has application for use in, for example, pad-mounted switchgear, underground switchgear, metal-enclosed switchgear, metal-clad switchgear, air insulated ring main units, wind turbine switchgear, etc. The pole unit  10  generally includes from top to bottom a vacuum interrupter switch  12 , an electromagnetic actuator  14 , an electronics assembly  16  and a wireless power assembly  18  including a receiver coil  20  and a transmitter coil  22  all configured within an outer housing  24 . As will be discussed in detail below, the interrupter switch  12 , the actuator  14 , the electronics assembly  16  and the receiver coil  20  are all at line potential and the transmitter coil  22  is at ground potential. By configuring the pole unit  10  in the manner shown and described, the air gap normally necessary to electrically isolate the interrupter switch  12  from the actuator  14  in traditional pole units because the switch  12  is at line potential and the actuator is at ground potential can be eliminated, thus reducing the size of the unit  10 . 
     The vacuum interrupter switch  12  includes a cylindrical vacuum chamber  30  defined by an insulating enclosure  32 . The vacuum interrupter switch  12  further includes a fixed contact  34  extending through a top end of the chamber  30  and having an annular contact portion  36  positioned within the chamber  30  and a moving contact  40  extending through a bellows  42  into the chamber  30  and having an annular contact portion  44  positioned within the chamber  30 , where the bellows  42  maintains the vacuum within the chamber  30  when the contact  40  moves. The fixed contact  34  is electrically coupled to an upper unit terminal  50  and the moving contact  40  is electrically and rigidly coupled to a sliding contact  52  that is electrically and slidably coupled to a lower unit terminal  54 , where the terminals  50  and  54  extend out of the housing  24  to be connected to the power line (not shown). When the electromagnetic actuator  14  is actuated and the switch  12  is closed, the contact portions  36  and  44  are held in contact with each other, discussed in further detail below, and when the switch  12  is opened under spring bias, the contact portion  44  is moved away from the contact portion  36  to define a gap therebetween. A Rogowski coil  56  known to those skilled in the art encircles the lower terminal  54  and measures the current flow therethrough. 
     The actuator  14  includes a coil  60  wound on an annular or rectangular member  62  that is rigidly mounted to the terminal  54  by rods  64  and  66  and secured thereto by bolts (not shown). The actuator  14  further includes a slidable rod  68  slidably mounted within a sleeve  70  and being concentrically positioned within the member  62 , where the rod  68  extends through and is rigidly coupled to the sliding contact  52  and is mounted to the contact  40 . When the coil  60  is energized, the rod  68  moves upward against the bias of a spring  58  and with the assist of a spring  72  to move the contact portion  44  against the contact portion  36  to close the switch  12 . When the coil  60  is de-energized, the spring  58  assists to open the switch  12 , and permanent magnet forces hold the rod  68  in place. 
     Because the actuator  14  is at line potential it needs to be electrically isolated from ground potential, but still needs to be energized from a power source at ground potential. This electrical connection is provided through magnetic coupling between the coils  20  and  22  that are electrically separated, where the coil  20  is at line potential and the coil  22  is at ground potential. The coils  20  and  22  are potted within a potting material  46  to provide the electrical isolation therebetween and be rigidly held within the housing  24 . 
     The electronics assembly  16  is configured in a chamber  74  between the electromagnetic actuator  14  and the power assembly  18 , where the assembly  16  is separated from the actuator  14  by a plate  76 . The assembly  16  includes an energy storage unit  80 , such as a capacitor, super-capacitor, battery, etc., an actuator coil drive circuit  82 , a power receiver coil harvesting circuit  84 , a Rogowski coil measurement acquisition circuit  86  and a communications circuit  88 . The receiver coil  20  is connected to the power receiver coil harvesting circuit  84 , the harvesting circuit  84  is connected to the actuator drive circuit  82  and the drive circuit  82  is connected to the actuator coil  60  through a suitable switching network (not shown). The acquisition circuit  86  receives the current measurement signals from the Rogowski coil  56 . The communications circuit  88  provides signals to and receives signals from a main switchgear controller (not shown) such as through optical signaling, for example, infrared, across the potting material  46 . 
     The pole unit  10  has a particular shape and may have application to be used for enclosed switchgear for inside use. Other designs may be more applicable for outside uses.  FIG. 2  is an isometric view and  FIG. 3  is a cross-sectional view of a pole unit  90  that may have such a use. In this design, the pole unit  90  includes an outer housing  92  having current sheds  94 , where one terminal  96  extends into a side of the housing  92  and another terminal  98  extends through a top of the housing  92 .  FIG. 3  shows the vacuum interrupter switch  12 , the actuator  14 , the electronics assembly  16  and the wireless power assembly  18  positioned within the housing  92  and being configured in the same manner as described above as shown by the same reference numbers. 
     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.