The invention relates to medium voltage air insulated switchgears and, more particularly, to a method and structure for fastening and electrically isolating busbars that are insulated with heat-shrink material.
It is known from the art that air-insulated high and medium-voltage electric stations use a system of busbars. Each busbar is preferably covered in heat-shrink material and appropriately connected to a main electric power supply line and to a power transformer.
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Thus, there is a need to provide proper electrical insulation of a busbar without damaging the heat-shrink material.
An objective of the invention is to fulfill the need referred to above. In accordance with the principles of the present invention, this objective is obtained by providing isolation structure for electrically isolating a busbar mounted to a post insulator by a fastener via a busbar mounting hole. The busbar has insulating material covering the busbar except for surfaces defining the mounting hole. The isolation structure includes an electrically insulating sleeve constructed and arranged to be disposed around a portion of a periphery of the fastener and to be received in the busbar mounting hole. At least first and second electrically insulating washers are provided, each having a bore that receives the insulating sleeve. The insulating washers are constructed and arranged to engage with the surfaces defining the mounting hole on opposing sides of the busbar so as to sandwich the busbar between the first and second insulating washers.
In accordance with another aspect of the disclosed embodiment, a method is provided for electrically isolating a busbar when fastened to a post insulator. The busbar has a mounting hole and insulating material covering the busbar except for surfaces defining the mounting hole. The method provides a fastener having a head at one end thereof. An insulating sleeve is placed around a portion of a periphery of the fastener. The sleeve is provided through the mounting hole of the busbar and through a bore in at least a first and a second insulating washer so that the insulating washers engage the surfaces defining the mounting hole on opposing sides of the busbar, thereby sandwiching the busbar between the first and second insulating washers. The fastener is secured to the post insulator.
Other objects, features and characteristics of the present invention, as well as the methods of operation and the functions of the related elements of the structure, the combination of parts and economics of manufacture will become more apparent upon consideration of the following detailed description and appended claims with reference to the accompanying drawings, all of which form a part of this specification.
The invention will be better understood from the following detailed description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like parts, in which:
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A flat washer 27 is preferably provided between the proximal insulating washer 22 and a spring washer 28. A mounting fastener such as a screw 30 couples the busbars 12′ to a post insulator 32 since the mounting screw 30 is in threaded engagement with the post insulator 32. A head 34 of the screw 30 thus clamps on the spring washer 28, with the spring washer 28 maintaining sufficient clamping force on the flat washer 28, insulating washers 22 and 23 and busbars 12′ during thermal expansion thereof.
Each washer 22, 23, 26, 28 is of disk shape have a central bore 36 therethrough, receiving the screw 30 and an electrically insulating sleeve 38 disposed over a portion of the periphery of the screw 30. The sleeve 38 is received in busbar mounting holes 20 and electrically isolates the mounting screw 30 from the busbars 12′. The sleeve 38 is preferably of a heat-shrink material such as any conventional insulating material.
The use of flanged washers 22 and 23 provides proper electrical isolation of busbars 12′ without damaging the heat-shrink insulating material 14′. With the isolation structure 16 of the embodiment, a shorter post insulator 32 can be used, as compared to the conventional one, because this mounting method provides adequate sealing to meet operational creepage and clearance requirements, saving space and busbar material. In addition, with reference to
The foregoing preferred embodiments have been shown and described for the purposes of illustrating the structural and functional principles of the present invention, as well as illustrating the methods of employing the preferred embodiments and are subject to change without departing from such principles. Therefore, this invention includes all modifications encompassed within the spirit of the following claims.