Abstract:
A switching device facilitates access, repair, maintenance of the device during operation in a electrical substation, and minimizes real estate and equipment in the electrical substations. The device integrates air disconnect switches, preferably mounted atop each bushing. The device further comprises wheels, a removable rail system, and a staggered height arrangement of the switches on the bushing to allow translation of the device from a first position to an electrically isolated second position.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to electrical switching devices. More particularly, the present invention relates to electrical switching devices that have an architecture that facilitates access, maintenance, and repair to the device and reduces substation equipment and real estate. 
     BACKGROUND OF THE INVENTION 
     A high voltage circuit breaker is a device used in the transmission and distribution of three phase electrical energy. When a sensor or protective relay detects a fault or other system disturbance on the protected circuit, the circuit breaker operates to physically separate current-carrying contacts in each of the three phases by opening the circuit to prevent the continued flow of current. In addition to its primary function of fault current interruption, a circuit breaker is capable of load current switching. A circuit switcher and load break switch are other types of switching device. As used herein, the expression “switching device” encompasses circuit breakers, circuit switches, dead tank breakers, live tank breakers, load break switches, reclosers, and any other type of electrical switch. 
     The major components of a circuit breaker or recloser include the interrupters, which function to open and close one or more sets of current carrying contacts housed therein; the operating mechanism, which provides the energy necessary to open or close the contacts; the arcing control mechanism and interrupting media, which interrupt current and create an open condition in the protected circuit; one or more tanks for housing the interrupters; and the bushings, which carry the high voltage electrical energy from the protected circuit into and out of the tank(s) (in a dead tank breaker). In addition, a mechanical linkage connects the interrupters and the operating mechanism. 
     Circuit breakers can differ in the overall configuration of these components. However, the operation of most circuit breakers is substantially the same. For example, a circuit breaker may include a single tank assembly which houses all of the interrupters. U.S. Pat. No. 4,442,329, Apr. 10, 1984, “Dead Tank Housing for High Voltage Circuit Breaker Employing Puffer Interrupters,” discloses an example of the single tank configuration and is incorporated herein in its entirety by reference. Alternatively, a separate tank for each interrupter may be provided in a multiple tank configuration. An example of a prior art, multiple tank circuit breaker is depicted in FIGS. 1,  2 ,  3 , and  4 . Circuit breakers of this type can accommodate 72 kV, 145 kV, 242 kV, and 362 kV power sources. 
     The circuit breaker shown in FIG. 1 is commonly referred to as a “dead tank” because it is at ground potential. FIG. 1 provides a front view of a three phase or three-pole circuit breaker having three entrance bushing insulators,  10 ,  11 , and  12 , that correspond to each respective phase. The bushing insulators may be comprised of porcelain, composite, or a hardened synthetic rubber sufficient to withstand seismic stresses as well as stresses due to the opening and closing of the interrupter contacts within the device. In high voltage circuit breakers, the bushings for each phase are often mounted so that their ends have a greater spacing than their bases to avoid breakdown between the exposed conductive ends of the bushings. 
     The circuit breaker is comprised of three horizontal puffer interrupter assemblies enclosed in cylindrical tanks  15 ,  16 , and  17 . Current transformer assemblies  20  and  21  (referring to FIG.  2 ), which comprise one or more current transformers and their exterior housings, are located underneath the bushing insulators on the exterior of the breaker to facilitate their replacement in the field. Current transformers  20  and  21  measure the outgoing current. 
     FIG. 2 provides a side view of the three-pole circuit breaker of FIG. 1 that shows the corresponding exit bushing insulator,  13 , of the interrupter assembly housed in tank  15 . FIG. 2 illustrates how entrance bushing insulator  10  and exit bushing insulator  13  is associated with tank  15 . The entrance and exit bushing insulators for the interrupters in tanks  16  and  17  (not shown in FIG. 2) are arranged in a similar fashion. 
     Referring to FIG.  1  and FIG. 2, the three interrupter tank assemblies are mounted on a common support frame  19 . The operating mechanism that provides the necessary operating forces for opening and closing the interrupter contacts is contained within an operating mechanism housing or cabinet  18 . The operating mechanism is typically mechanically coupled to each of the interrupter assemblies through a common linkage such as a drive cam. The operating mechanisms can be, but are not limited to, compressible springs, solenoids, hydraulic, or pneumatic-based mechanisms. 
     FIG. 3 is a partial, cross-sectional view of the interrupter assembly housed within cylindrical tank  15  and shown in FIG.  1  and FIG. 2. A typical circuit interrupter is comprised of stationary and movable contact assemblies  31  and  23 , respectively. Entrance insulator bushing  10  houses a central conductor  22  which supports movable contact assembly  23  within conductive tank  24 . Movable contact assembly  23  is affixed to an insulator tube  25  through which a linearly operating rod  26  extends. Rod  26  operates movable contact  27  between its open and closed position in a well-known fashion. 
     Exit insulator bushing  13  houses a central conductor  30  which is connected to the stationary contact assembly  31  and is also supported within conductive tank  24 . An insulator tube  32  extends between the stationary contact assembly  31  and the movable contact assembly  23 . 
     The interior volume of tank  24 , as well as the entrance and exit insulating bushings  10  and  13 , are preferably filled with an inert, electrically insulating gas such as SF 6 . The electrically insulating gas fulfills many purposes. The arcing contacts within both the stationary and movable contact assemblies are subject to arcing or corona discharge when they are opened or closed. Such arcing can cause the contacts to erode and disintegrate over time. Current interruption must occur at a zero current point of the current waveshape. This requires the interrupter medium to change from a good conducting medium to a good insulator or non-conducting medium to prevent current flow from continuing. Therefore, a known practice (used in a “puffer” interrupter) is to fill a cavity of the interrupter with an inert, electrically insulating gas that quenches the arc formed. During operation of the contacts in assemblies  23  and  31 , a piston, which moves with the movable contact in assembly  23 , compresses the gas and forces it the compressed gas between the separating contacts and toward the arc, thereby cooling and extinguishing it. The gas also acts as an insulator between conductive parts within housing  15  and the wall of tank  24 . 
     Circuit breakers can switch various devices in an electric utility system. Primarily, these devices include transmission lines, transformers, shunt capacitor banks, and shunt reactors within an electrical substation, power distribution substation, or power transformer and distribution substation. The electrical substation converts the high voltage power carried by long-distance transmission lines into lower distribution voltage that services homes and businesses. FIG. 4 provides a top view of the circuit breaker of FIG. 1 as it is commonly installed within an exterior electrical substation. These substations generally cover a large surface area and are not aesthetically pleasing. Given their design, these substations require a great deal of maintenance due to their continuous exposure to climatic and seismic events. 
     As FIG. 4 shows, the conductive ends of the bushings are connected to a series of individual air disconnect switches or blades  40  that relate and connect each phase of the circuit breaker to the overhead, electrical substation bus (not shown in FIG.  4 ). Air disconnect switches  40 , that relate to incoming and outgoing voltage, are each independently supported on electrically grounded frames. This arrangement requires electrical clearance on both sides of the circuit breaker to allow sufficient electrical isolation during maintenance and repair. In general, conventional disconnect switches are located on both sides of the breaker and are larger than the breaker. Thus, the disconnect switches occupy a larger surface area, or foot print, than the breaker itself. This arrangement may become impractical and unsafe if space in the electric utility system is limited. Moreover, more intensive maintenance and repair tasks, or a complete over-haul of the switching device, may be more difficult due to the limited real estate in the electric utility system. 
     SUMMARY OF THE INVENTION 
     The present invention fulfills these needs in the art by providing electrical switching devices that conserve real estate and reduce equipment within an electrical substation. In many instances, conventional breaker and disconnect switch assemblies occupy a surface area or footprint about three times greater than that of the present invention. The present invention also reduces maintenance and repair costs and time by facilitating access to the switching device and its sub-components. 
     According to the invention, the electrical switching device comprises a frame that supports a plurality of legs that terminate with wheels, one or more tanks that house the circuit interrupter assembly, and bushings. The bushings extend outwardly from the circuit interrupter tank and terminate with a conductive end. In preferred embodiments, the frame further comprises a locking device on the wheels and a winch. One or more disconnect switches connect the conductive ends of the bushings to incoming and outgoing power sources within the electrical system such as an overhead bus. In preferred embodiments, the disconnect switches are mounted onto the switching device rather than the substation power sources. The height of these disconnect switches, or the conductive ends of the bushing if the switches are mounted onto the bus, are staggered with respect to each other. 
     In preferred embodiments, a rail system or a pair of removable beams is used to translate the device from a first position to a second position for maintenance. The locking devices on the wheels of the switching device, such as foundation clamps in preferred embodiments, are disengaged to allow translation of the device from its fixed or first position. The wheels on the switching device engage the rails and the switching device is translated across the rails by a winch or other means to a second position. The distance between the first position and the second position is sufficient to provide adequate electrical clearance. In preferred embodiments, this distance is at least about 30 inches multiplied by a factor of 1, 2, 4, or 8 for 72 kV, 145 kV, 242 kV, or 362 kV devices, respectively. The staggered height of the disconnect switches or conductive ends of the bushings allow the device to translate from the first position and the second position without interference. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and are intended to provide further explanation of the invention as claimed. The accompanying drawings are included to provide a further understanding of the invention. In the drawings, like reference characters denote similar elements throughout several views. It is to be understood that various elements of the drawings are not intended to be drawn to scale. 
     A more complete understanding of the present invention, as well as further features and advantages of the invention such as its application to other electrical devices within a substation or system, will be apparent from the following Detailed Description and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a typical three-pole circuit breaker of the prior art. 
     FIG. 2 provides a side view of the three-pole circuit breaker of FIG.  1 . 
     FIG. 3 is a partial, cross-sectional view of the circuit interrupter assembly housed of FIG. 1 with its contacts open. 
     FIG. 4 provides a top view of a typical installation of the circuit breaker of FIG. 1 in an electrical substation. 
     FIG. 5 provides a front view of an electrical switching device of the present invention. 
     FIG. 6 provides a side view of the electrical switching device of the present invention. 
     FIG. 7 shows the translation of an embodiment of the present invention from first position to second position. 
     FIG. 8 a top view of a rail system of the circuit breaker of the present invention in an electrical substation. 
     FIG. 9 provides a detailed side view of a wheel of one embodiment of the present invention. 
    
    
     Reference will now be made in detail to a presently preferred embodiment of the invention, an example of which is illustrated in the accompanying drawing. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention is directed to electrical switching devices. More particularly, the present invention provides electrical switching devices that minimize the real estate and equipment in an electrical substation. Moreover, electrical switching devices of the present invention reduce labor costs and equipment down-time and increase safety due to accessibility of these devices for maintenance and repair. 
     FIG. 5 provides a front view of an electrical switching device of the present invention. The electrical switching device shown is a three pole or three phrase circuit breaker. It is anticipated, however, other device configurations may be made in accordance with the present invention. The device in FIG. 5 is comprised of a support frame  50  that contains one or more legs  51  and an operating mechanism  52 . The support frame further supports one or more tanks  53 ,  54 , and  55 . Tanks  53  through  55  contain the circuit interrupter assemblies (not shown). One or more insulating bushings  56 ,  57 , and  58 , preferably two bushings that correspond to each phase or pole of the device, extend upwardly from the tanks. FIG. 6 provides a side view of the electrical switching device of FIG.  5 . FIG. 6 shows how the entrance insulating bushing  56  and exit insulating bushing  59  relate to tank  53 . 
     Referring to FIG. 5, the insulating bushings have a conductive tip or end  60 . Air disconnect switches or switch assemblies  61  are attached directly atop the conductive ends on each bushing. Air disconnect switch  61  is further comprised of a conductive blade  61   a  and a contact  61   b . The height of air disconnect switches  61 , or length of their conductive blade  61   b , are of variable or staggered height with respect to each pole or phase. The variable height of each switch assembly  61  allows the insulating bushings of each phase to have sufficient clearance as the device is moved from its fixed position or first position to a maintenance or second position. Switches  61  are connected to a rigid, installed overhead or substation bus  62 . 
     The air disconnect switches  61  employed in the present invention are comprised of materials that are durable enough to survive extreme environmental as well as operational conditions. The switches are also resistant to high magnetic and high electrical current forces. Typical materials that may be used include high conductivity, high strength aluminum alloys that are combined with stainless steel bolts, nuts, and pins along the current path to minimize corrosion. In preferred embodiments, the air disconnect switch  61  is connected to the conductive ends of the bushing  60  or, alternatively the substation bus, by jaw contacts  61   b . Jaw contacts  61   b  may be comprised of tinned, hard drawn reverse loop copper jaw fingers backed by stainless steel springs to improve current-carrying capability and resistance to corrosion. An example of a preferred jaw contact is the TTR8 manufactured by ABB Power T &amp; D Company Inc. However, other disconnect switches, switch assemblies, and contacts may be used without departing from the spirit of the present invention. In preferred embodiments, the jaw contacts are mounted onto the overhead bus  62  as shown in FIG.  5  and FIG.  6 . Alternatively, the contacts may be mounted onto the conductive end of the bushings. The device is disengaged from the overhead bus by opening the air disconnect switch assemblies  61  on each bushing. 
     FIG. 7 depicts the translation of the device from its fixed or first position to a maintenance or second position. The distance between the first position and the second position must provide sufficient electrical isolation to allow a person to safely work on the device. In preferred embodiments, this distance is at least about 30 inches multiplied by a factor, R, wherein the factor R is equal to 1, 2, 4, or 8 for 72 kV, 145 kV, 242 kV, or 362 kV devices, respectively. The translation of the device is preferably horizontal and in one direction to prevent interference of the disconnect switches  61  with the rigid overhead bus  62 . 
     Referring to FIG.  5  through FIG. 7, the electrical switching device further comprises wheels  63  attached to the base of the legs  51  on frame  50 . In exterior substations, the equipment is typically placed on a gravel yard. To facilitate translation, the wheels  63  engage a rail system  64  or similar means. FIG. 8 provides a top view of a rail system that may be used with the present invention. In preferred embodiments, a pair of I-beams, which can be removed from the substation yard when not in use, can be used. Additional beams may be used to support the I-beams. The size of the I-beam must be suitable to provide rigid support of the device. The length of the I-beams must be at least 2 times the length of the device plus the distance between the first position and second position to provide sufficient electrical isolation for maintenance or repair. The distance between first position and second position is at least 30 inches multiplied by a factor, R, wherein the factor R is equal to 1, 2, 4, or 8 for 72 kV, 145 kV, 242 kV, or 362 kV devices, respectively. 
     The device can be translated through manual or automated means. Some means for translation of the device may include, but is not limited to a pulley, winch, motor, or a system incorporating some or all of these components. FIG. 7 shows a winch  65  that is used to translate the device from first position to second position. Winch  65  may be mounted on the rail system  64  as shown or on frame  50 . The winch can be manually or automatically operated. 
     FIG. 9 provides a side view of one embodiment of the present invention. In preferred embodiments, wheels  63  have V-grooves. These V-grooves on the wheel engage a metal dowel  66  that is disposed atop the I-beam. Other wheel configurations though may be selected without departing from the spirit of the present invention. Dowel  66  allows for the smooth translation and guidance of the device as it moves across rail  64 . FIG. 9 further shows a foundation clamp  67  that locks or holds the device in the first position. The clamp  67  is shown as locking onto the rail  64 . Other embodiments, however, may comprise a brake system that is mounted onto frame  50 , or one or more wheels  63 , to prevent movement of the device during operation. 
     The present invention is directed to parts and apparatuses, that include, but are not limited to, electrical switching devices, regardless of any specific description in the drawing or examples set forth herein. It will be understood that the present invention is not limited to use of any of the particular parts or assemblies discussed herein. Indeed, this invention can be used in any switching device. Further, the apparatus disclosed in the present invention can be used with the method of the present invention or a variety of other applications. 
     While the present invention has been particularly shown and described with reference to the presently preferred embodiments thereof, it will be understood by those skilled in the art that the invention is not limited to the embodiments specifically disclosed herein. Those skilled in the art will appreciate that various changes and adaptations of the present invention may be made in the form and details of these embodiments without departing from the true spirit and scope of the invention as defined by the following claims.