Patent Application
20130092658
Solid dielectric switchgear typically includes a source conductor and a vacuum interrupter with at least one stationary contact and at least one movable contact. Switchgear also includes a contact-moving mechanism for moving the movable contact included in the vacuum interrupter and an operating rod (e.g., a drive shaft) that connects the mechanism to the movable contact. In addition, switchgear can include one or more sensors, such as a current sensor, a current transformer, or voltage sensor. All of these components are commonly over-molded in a single epoxy form. Therefore, the vacuum interrupter, contact-moving mechanism, operating rod, and any sensors are molded within a single coating or layer of epoxy to form integrated switchgear.
The single epoxy form provides structural integrity and dielectric integrity. In particular, the components of the switchgear are over-molded with epoxy that has high dielectric strength. The molded epoxy also can be formed into skirts on the outside of the switchgear that increase the external creep distance. The single epoxy form also protects against environment elements.
There are many issues, however, related to integrated switchgear. First, over-molding the switchgear as one part poses manufacturing challenges. In particular, molding over multiple components increases the risk of forming voids. Voids reduce electrical integrity by creating air pockets that may become charged. Voids can lead to coronal discharge and voltage stress that shortens the life of the switchgear.
In addition, when all of the components are tied together in one integrated module, the complexity of the switchgear is increased. For example, if an area within the switchgear is not over-molded properly, the entire switchgear may be unusable. The over-molding also limits the flexibility of the switchgear design. For example, if switchgear is needed that has specific requirements (e.g., voltage rating, sensor requirements, etc.), a completely new design is needed for the integrated switchgear even if just one component is changed.
Also, integrated switchgear is typically grounded and connected to a metal tank or housing assembly that holds operating mechanisms for the switchgear. The creep distance of the switchgear, however, is measured from the high voltage areas of the switchgear to the metal housing assembly. Therefore, the size of the switchgear must be designed to allow for the proper creep distance between the metal housing assembly and the high voltage areas. In general, this requires that the switchgear be larger to provide a proper creep distance.
Similarly, integrated switchgear also provides an area for the operating rod to function while providing an internal creep distance to the contact-moving mechanism. Without space to place skirts, the creep distance needed increases the height requirements of the switchgear. The operating rod also defines a creep distance over its surface to the contact-moving mechanism. To increase this creep distance, horizontal ribs are sometimes placed along the operating rod. However, adding these ribs often increases the height of the switchgear.
As described above, the integrated switchgear includes a vacuum interrupter. A vacuum interrupter includes a ceramic bottle with two contacts vacuum-sealed inside the bottle. Fault interruption is performed in the vacuum. However, the contacts must have enough holding force so that the contacts do not weld together during a short circuit interruption. The need for a strong holding force creates challenges for the design of the contact-moving mechanism that operates the vacuum interrupter, which leads to complicated and expensive mechanism design. Additionally, to achieve a high mechanical life, a dampening system is used, which adds cost and complexity to the switchgear.
When a current transformer is included in the switchgear, it can be molded into the single-form epoxy of the integrated switchgear or can be externally mounted on the epoxy. Typically, wires are then attached between the current transformer and monitoring equipment. However, attaching external wires to the current transformer creates additional manufacturing challenges during final assembly of the switchgear.
Accordingly, embodiments of the invention provide non-integrated switchgear that is, in general, lower-cost and easier-to-manufacture and increases design flexibility, reduces production scrap, and improves serviceability. For example, a modular design can be used that reduces manufacturing challenges (e.g., risk of void formation) and increases design flexibility. In addition or alternatively, the housing assembly can be separately molded from the vacuum interrupter and source conductor. A plastic housing assembly can then be used that provides more external over surface distance from line to ground. The housing assembly can house the operating rod and provide the needed internal electrical creep distance. In some constructions, the housing assembly can include internal skirts to provide additional creep distance. Also, the operating rod can include vertical skirts to minimize the overall height of the switchgear while maximizing internal creep distance. Furthermore, a flexible conductor that connects in series with the vacuum interrupter can be used to provide more holding force for the vacuum interrupter during current interruptions. The flexible conductor, therefore, can allow for lighter and less expensive mechanisms and can provide dampening to increase the mechanical life of the switchgear. In addition, a current transformer can be molded into a portion of the switchgear and can include a molded connector to simplify wiring assembly.
In one construction, the invention provides modular switchgear. The modular switchgear includes a vacuum interrupter assembly, a source conductor assembly, and a housing assembly. The vacuum interrupter assembly has a first end and a second end and includes a bushing, a vacuum interrupter including a movable contact and a stationary contact and at least partially molded within the bushing, and a fitting positioned adjacent to the second end. The source conductor assembly has a first end and a second end and includes a bushing, a source conductor molded within the bushing, and a fitting positioned adjacent the second end. The housing assembly includes a housing defining a chamber, a drive shaft positioned within the chamber and configured to interact with the movable contact included in the vacuum interrupter, a conductor positioned within the chamber and configured to electrically couple the vacuum interrupter and the source conductor, a first receptacle for receiving the fitting of the vacuum interrupter assembly, and a second receptacle for receiving the fitting of the source conductor assembly. The vacuum interrupter assembly, the source conductor assembly, and the housing assembly are coupled without molding the assemblies within a common housing.
In another construction, the invention provides a method of manufacturing switchgear. The method includes providing a vacuum interrupter assembly including a vacuum interrupter molded within a bushing and including a fitting, the vacuum interrupter including a movable contact and a stationary contact; providing a source conductor assembly including a source conductor molded within a bushing and including a fitting; and providing a housing assembly including a drive shaft configured to couple to the movable contact, a conductor configured to electrically couple the vacuum interrupter and the source conductor, a first receptacle for receiving the fitting of the vacuum interrupter assembly, and a second receptacle for receiving the fitting of the source conductor assembly. The method also includes coupling the vacuum interrupter assembly to the housing assembly using the fitting of the vacuum interrupter assembly and the first receptacle without molding the vacuum interrupter assembly and the housing assembly within a common housing and coupling the source conductor assembly to the housing assembly using the fitting of the source conductor assembly and the second receptacle without molding the source conductor assembly and the housing assembly within a common housing.
In still another construction, the invention provides a vacuum interrupter assembly for modular switchgear. The vacuum interrupter assembly has a first end and second end and includes a bushing, a vacuum interrupter having a movable contact and a stationary contact and molded within the bushing, and a fitting positioned adjacent to the second end configured to couple the vacuum interrupter assembly to a receptacle on a housing assembly. The housing assembly includes a drive shaft configured to interact with the movable contact and a conductor configured to electrically couple the vacuum interrupter and a source conductor. The vacuum interrupter assembly is coupled to the housing assembly without molding the vacuum interrupter assembly and the housing assembly in a common housing.
In yet another construction, the invention provides a source conductor assembly for modular switchgear. The source conductor assembly has a first end and second end and includes a bushing, a source conductor molded within the bushing, and a fitting positioned adjacent the second end configured to couple the source conductor assembly to a receptacle on a housing assembly, the housing assembly including a drive shaft configured to interact with a vacuum interrupter and a conductor configured to electrically couple the source conductor and the vacuum interrupter. The source conductor assembly is coupled to the operating housing without molding the source conductor assembly and the housing assembly in a common housing.
Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.
Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.
The VI assembly 34 also includes a VI 50 at least partially molded within the bushing 46. The VI 50 includes a movable contact and a stationary contact. The movable contact is movable to establish or break contact with the stationary contact. Therefore, the movable contact can be moved to establish or break a current path through the switchgear 30.
The VI assembly 34 also includes a fitting 52 positioned adjacent to the second end 38. The first receptacle 38 of the housing assembly 32 receives the fitting 52. For example, as shown in
The source conductor assembly 36 is also coupled to the housing assembly 32. As shown in
In addition, the source conductor assembly 36 includes a sensor assembly 70. The sensor assembly 70 can include a current transformer, a voltage sensor, or both. As described in further detail below with respect to
The source conductor assembly 36 also includes a fitting 74 positioned adjacent to the second end 62. The second receptacle 40 of the housing assembly 32 receives the fitting 74. For example, as shown in
As shown in
The housing assembly 32 includes a drive shaft 84, such as a rod, which is positioned within the chamber 82. The drive shaft 84 interacts with the VI 50 included in the VI assembly 34. In particular, the fitting 52 included in the VI assembly 34 is positioned adjacent an opening in the bushing 46 that allows the drive shaft 84 to access and interact with the movable contact of the VI 50. Similarly, the first receptacle 38 is positioned adjacent an opening in the housing assembly 32 that allows the drive shaft 84 to be coupled to the VI 50.
The housing assembly 32 also houses a flexible conductor 86, which is also positioned within the chamber 82 defined by the housing 80. The flexible conductor 86 electrically couples the VI 50 and the source conductor 68. As described in more detail with respect to
Therefore, as described above, the VI 50 and the source conductor 68 are each molded in separate bushings and are not over-molded within a common housing. Rather, the separately molded VI 50 and source conductor 68 are coupled to the housing assembly 32, which houses the drive shaft 84 and the flexible conductor 86, using the fittings 52, 74 and receptacles 38, 40. This modularity provides manufacturing and design flexibility. For example, using the modular VI assembly 34 and source conductor assembly 36 allows a similar housing assembly 32 to be used for switchgear with different voltage ratings, VI ratings, current transformer requirements, etc. In particular, modular VI assemblies 34 can be created with different VI ratings but with a similar fitting 52 that mates with the first receptacle 38 on the housing assembly 32. This allows the same housing assembly 32 to be used with different VI assemblies 34 (e.g., with different VIs 50). Similarly, modular source conductor assemblies 36 can be created with different source conductors 68, sensor assemblies 70, or both but with a similar fitting 74 that mates with the second receptacle 40 on the housing assembly 32. Also, because the VI 50, source conductor 68, and drive shaft 84 and flexible conductor 86 are not over-molded in a common housing, such as a single epoxy form, any voids forming on individual components does not make the entire switchgear unusable or unsafe. Rather, because the components are separately molded, a component with a void can be replaced and the remaining components can be reused. Furthermore, in some embodiments, the modular VI assembly 34 and/or source conductor assembly 36 are removably coupled to the housing assembly 32, which allows them to be removed and replaced for maintenance purposes or design changes. Similarly, the modular assemblies 34 and 36 can be removed from one housing assembly 32 and installed on a new housing assembly 32 for maintenance or design purposes.
Accordingly, to manufacture the switchgear 30, the VI assembly 34 and the source conductor assembly 36 are created by separately molding the components. For example, to create the VI assembly 34, the VI 50 is placed within a mold and the mold is at least partially filled with an insulating material, such as one of an epoxy or molding compound, which forms the bushing 46 with the skirts 48 and the fitting 52. Similarly, to create the source conductor assembly 36, the source conductor 68 and sensor assembly 70 (and, optionally, the connector 72) are placed within a mold and the mold is at least partially filled with an insulating material, which forms the bushing 64 with the skirts 66 and the fitting 74.
Once the assemblies 34 and 36 are provided, the housing assembly 32 is also provided. Initially, the housing 80 of the housing assembly 32 can be formed using injection molding or other plastic-forming techniques. The housing 80 defines the chamber 82, where the drive shaft 84 and the flexible conductor 86 are positioned. The housing 80 also defines the first receptacle 38 and the second receptacle 40.
After the housing assembly 32 is provided, the VI assembly 34 is coupled to the housing assembly 32 using the fitting 52 of the VI assembly 34 and the first receptacle 38 of the housing assembly 32. As described above, coupling the VI assembly 34 to the housing assembly 32 can include screwing the fitting 52 into the first receptacle 38. As also described above, the gasket 54 can be placed between the fitting 52 and the first receptacle 38 to provide a secure coupling.
The source conductor assembly 36 is also coupled to the housing assembly 32 using the fitting 74 of the source conductor assembly 36 and the second receptacle 40 of the housing assembly 32. Again, as described above, coupling the source conductor assembly 36 to the housing assembly 32 can include screwing the fitting 74 into the second receptacle 40. A gasket 76 can be placed between the fitting 74 and the second receptacle 40 to provide a secure coupling. The housing assembly 32 is also mounted on the base 88, which houses additional components for the switchgear 30. With the VI assembly 34 and the source conductor assembly 36 coupled to the housing assembly 32 and the housing assembly 32 mounted on the base 88, the switchgear 30 can be installed in a high-power distribution system.
As also shown in
Under normal operations, the flexible conductor 86 is connected in series with the circuit of the switchgear 30. Once the circuit is closed, current flows in and out of the bus bar 110 and the source conductor 68 and also through the flexible conductor 86. The flexible conductor 86 and the bus bar 110 form two reverse loops or paths. A full loop or path is between the bus bar 110 and the entire loop portion 102 of the flexible conductor 86. A half loop or path is between the loop portion 102 of the flexible conductor 86 and the remainder of the assembly 86. The two reverse loops generate repulsion forces due to the electromagnetic field effects generated by the current flowing through the loops, as shown in
In particular, the loop portion 102 causes repelling magnetic forces. The closer the faces of the loop portion 102 are to each other, the greater the forces. For example, the repulsion forces from the full loop acts on a washer (e.g., a Belleville washer) 122 and a jam nut 120 because the bus bar 110 is fixed. This force is symmetric around the movable contact 96 of the VI 50. The repulsion force from the half loop acts directly on the movable contact 96. The repulsion force from a current reverse loop is inversely proportional to the separation distance between the two currents running in opposite directions. The smaller the distance is, the higher the repulsion force. The flexible conductor 86 provides a minimum distance to the half loop using the thin jam nut 120. For the full loop, the separation distance is designed to be the stroke of the VI 50. This design ensures not only a minimal distance for the full loop, but also makes a laminated flexible loop 102 act as a damper during an open circuit.
In particular, a laminated flexible loop 102 is typically thicker in a free state than in a compressed state (when the thickness is squeezed to its minimum). During opening of the VI 50, the movable contact 96 is pulled by opening springs to separate the contacts. In this situation, as shown in
As noted above, the source conductor assembly 36 can include a sensor assembly 70 (e.g., including a current transformer). The sensor assembly 70 can be molded into the source conductor assembly 36 and can be grounded via an internal ground wire. To connect the sensor assembly 70 to external equipment, a connector 72 can be coupled to the sensor assembly 70.
Accordingly, the modular switchgear 30 allows for smaller, more flexible, and more cost-effective switchgear. Also, is should be understood that individual features of the design may be used separately and in various combinations. For example, the connector 72 with the exposed receptacle 130 can be used with switchgear of another design where a sensor is included in the switchgear, such as integrated switchgear described in the background section above. Also, in some embodiments, a modular VI assembly 34 can be used without a modular source conductor assembly 36 or vice versa to provide various levels of flexibility and modularity. For example, if a modular VI assembly 34 is not used, the components included in the VI assembly 34 can be housed within the housing assembly 32 or integrated with other switchgear components. Similarly, if a modular source conductor assembly 36 is not used, the components included in the source conductor assembly 36 can be housed within the housing assembly 32 or integrated with other switchgear components. Also, the modular bushings 34 and 36 can be used without using a housing assembly 32 made of plastic and/or used without a creep extender 90. Similarly, the plastic housing assembly 32 and/or the creep extender 90 can be used without one or both of the modular assemblies 34, 36. Furthermore, the flexible conductor 86 described above can be used in any type of switchgear and is not limited to being used in the switchgear 30 described and illustrated above. Also, a non-flexible conductor 86 can be used with the modular assemblies 34, 36.
Various features and advantages of the invention are set forth in the following claims.
