1. Field of the Invention
The subject matter of this invention relates generally to metal clad switchgear and more particularly to electrically insulating interphase barriers for multiphase drawout type switchgear.
2. Description of the Prior Art
Drawout metal-clad switchgear is well known in the art. In particular, a metal enclosure or cabinet has disposed in one portion thereof, usually the rear, high voltage terminations for an electrical system to be protected or served by the switchgear. In the front portion or low voltage portion of the switchgear cabinet, parallel tracks or rails are provided upon which a wheel mounted circuit breaker may be disposed so as to be moved into the cabinet to a disposition of electrical connection with the aforementioned high voltage terminations or out of the cabinet to a disposition of disconnection from the high voltage terminations. Generally, safety interlock means are provided for lowering shutters or the like to a disposition in front of the high voltage terminals when the circuit breaker has been withdrawn. Other interlocking means are provided to perform other safety functions. with the advent of the vacuum circuit interrupter the size of the drawout element became reducible because of the relatively small size of the vacuum circuit interrupter unit. The vacuum circuit interrupter has the property of being able to withstand relatively high voltages between the opened contacts thereof even though the distance between the open contacts is relatively small when compared with other types of circuit interrupters. This is because of the voltage withstand properties of a vacuum. As the size of the circuit interrupter equipment became progressively smaller with advancements in the art it was found that the open circuit voltage breakdown characteristic became more closely associated with the non-interrupter portions of the switchgear than with the interrupter. As a result attempts were made throughout the development of the art to prevent voltage flashover or breakdown in the non-interrupter area of interest. One such development included the use of an interphase insulating barrier system between each of the three phases and ground of a circuit interrupter system. An example is shown in U.S. Pat. No. 3,793,494, issued Feb. 19, 1974 to C. M. Cleveland, entitled "Drawout Type Vacuum Circuit Breaker Assembly With Hinged Barrier." Generally, the vertical and horizontal dimensions of the vertically oriented interphase barriers were adequate relative to the size of the drawout circuit breaker described therein. As the art continued to develop however it was found that the size of the drawout vacuum circuit interrupter could be reduced further by judiciously placing the operating mechanism on an appropriate part of the drawout cart for the vacuum interrupter. In particular, the height of the vacuum circuit interrupter system could be reduced over what was found in the prior art. This meant among other things that two vacuum circuit interrupters could be more easily disposed in tandem, one above the other vertically. In the past the previously described interphase barriers were disposed upon the movable cart and usually represented an extensive vertical expanse relative to the size of the cart. With a reduction in the size of the vacuum circuit interrupter drawout system in the tandem placement one above the other it was found that sufficient vertical clearance could not easily be obtained if the barriers remained upon the cart. Consequently the barriers were stored in the switchgear cabinet. Therefore the barriers became associated with the cabinet rather than the cart. In metal-clad switchgear it has been found that insulating spouts projecting frontwardly from the high voltage section and encircling the high voltage terminals was safe and useful. When the circuit interrupter is withdrawn, shutters deploy in front of the openings of the spouts to protect personnel in the forward portion of the metal-clad switchgear compartment from the high voltage terminals which would otherwise be exposed through the opening in the front of the bottles. If this shutter is to remain in one piece for a three phase circuit interrupter system, as is desired for efficiency and safety, and if the interphase barriers are to protrude sufficiently rearwardly, a problem develops. It has been found that the barriers interfered with the shutter movement and vice versa. It would be advantageous therefore if this interference between the barriers and the shutter could be overcome without otherwise negatively affecting the effectiveness of either or both. Another example of a barrier system may be found in U.S. Pat. No. 2,689,293, issued Sept. 14, 1954 to G. L. Claybourn and A. L. Fletcher in which a barrier is fixedly disposable between conductor members of an electrical system. An example of a vertically translating shutter system may be found in U.S. Pat. No. 4,216,521, filed Jan. 26, 1979 by C. R. Merola and entitled "Composite Groundable Barrier For Switchgear." Pivotal shutter systems may also be found as shown in portions of the drawings of this application. An example of a vacuum drawout circuit interrupter may be found in U.S. Pat. application Ser. No. 060,513, now abandoned, filed July 25, 1979, for F. Bould and entitled "Vacuum Circuit Interrupter With Improved Torque Loading on the Support Insulator." Another reference which may be relevant is U.S. Pat. No. 3,691,332, issued Sept. 12, 1972to W. T. Sharp, entitled "Vacuum-Type Electrical Switchgear." Another item of interest is a paper entitled "Vacuum Circuit Breaker Metal-Clad Switchgear," written by Stanton H. Telander, Senior Member IEEE, Allis-Chalmers Corporation, Milwaukee, WI, which is copyrighted material of the IEEE and designated Conference Record 75CHOD89-4-1A, Paper No. PCI-75-1.