FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
AND
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2005
COMPLETE SPECIFICATION (See section 10 and rule 13)
TITLE OF THE INVENTION
A multi-phase support insulator element for Gas Insulated Switchgear (GIS) equipment
APPLICANTS (S)
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTOR (S)
Bhangaonkar Avinash Sudhakar and Rajan Aravind; both of Crompton Greaves Ltd, Analytics Centre, CG Global R&D Centre, Kanjurmarg (East), Mumbai 400042, Maharashtra, India; Both Indian Nationals.
PREAMBLE TO THE DESCRIPTION:
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

FIELD OF THE INVENTION:
This invention relates to the field of mechanical assemblies and switchgear equipment.
Particularly, this invention relates to a multi-phase support insulator element for Gas Insulated Switchgear (GIS) equipment.
BACKGROUND OF THE INVENTION:
The term 'switchgear', used in association with the electric power system, or grid, refers to the combination of electrical disconnects, earthing-switches and/or circuit breakers used to isolate electrical equipment and networks. Switchgear is used both to de-energize equipment to allow maintenance work to be done and to clear faults.
An effective form of switchgear is gas insulated switchgear (GIS). In a GIS, there is a plurality of electrical components where the conductors and contacts are electrically insulated by pressurized sulfur hexafluoride gas (SF6).
A Gas Insulated Switchgear (GIS) comprises of a plurality of electrical components and includes gas as primary insulating medium typically at high voltages. For a 3-phase GIS switchgear equipment, three conductors are utilised. Typically, these three conductors run parallel to each other and for supporting them, a disc shaped supporting element is provided, such that the conductors pass through slots in the disc and gain support. This supporting disc is a support insulator element.

The support insulator element, used for multi-phase systems (typically three-phase), is a complete disc.
1. Direct electrical surface creepage path exists between the high voltage conductor and earthed enclosure.
2. Weight of insulator is relatively higher.
Creepage distance is defined as the minimum path length available along the surface of a solid insulator between live and earth conductors, and between two phases. The longer the path, lesser are the chances of surface breakdown. Also, the surface breakdown of a solid insulator takes place at a much lower electrical stress than breakdown across the gas filled in the enclosure. Consequently, higher reliability can be expected.
OBJECTS OF THE INVENTION:
An object of the invention is to provide a support insulating element with optimum creepage distance between conductors.
Another object of the invention is to provide a support insulating element with relatively lower electrical breakdown probability.
Yet another object of the invention is to provide a support insulating element with relatively lesser direct creepage problems.
Still another object of the invention is to provide a support insulating element with relatively lower weight.

An additional object of the invention is to provide a support insulating element with relatively lesser electrical stress.
SUMMARY OF THE INVENTION:
According to this invention, there is provided a multi-phase support insulator element for Gas Insulated Switchgear (GIS) equipment, said element being a disc element including three hollow projections equi-angularly distributed about a radial axis of said disc element, said hollow projections being spaced apart from each other and spaced apart from the circumferential edge of said disc element, characterized in that, said disc element includes at least an elongate peripheral slot located between each of said hollow projections and its nearest sector on the circumferential edge of said disc.
According to this invention, there is also provided a Gas Insulated Switchgear (GIS) equipment with a multi-phase support insulator element for, said element being a disc element including three hollow projections equi-angularly distributed about a radial axis of said disc element, said hollow projections being spaced apart from each other and spaced apart from the circumferential edge of said disc element, characterized in that, said disc element includes at least an elongate peripheral slot located between each of said hollow projections and its nearest sector on the circumferential edge of said disc.
Typically, one edge of said peripheral slot is in curvilinear synchronism with said circumferential edge.

Typically, the other edge of said peripheral slot is in curvilinear synchronism with said circumferential edge but indents at the point where it runs beside the hollow projection.
Typically, each of said peripheral slots is spaced apart from the neighbouring peripheral slot.
Typically, the outer edge of said hollow projection is spaced apart from the perimeter of the neighbouring elongate peripheral slot.
Typically, said disc element includes a central slot located in the region defined by the hollow projections as the edges.
Typically, said disc element includes a central slot located in the region defined by the hollow projections as the edges, said central slot being a substantially triangular slot and including smooth indentations to accommodate for said hollow projections such that the inner edge of the hollow projection is spaced apart from the perimeter of the central slot.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 illustrates an isometric front view of the multi-phase support insulator element;
Figure 2 illustrates an isometric through view of the multi-phase support insulator element; and

Figure 3 illustrates another isometric through view of the multi-phase support insulator element.
The invention will now be described in relation to the accompanying drawings, in which:
Figure 4 illustrates an isometric front view of the multi-phase support insulator element;
Figure 5 illustrates an isometric through view of the multi-phase support insulator element; and
Figure 6 illustrates another isometric through view of the multi-phase support insulator element;
Figures 7 and 9 illustrate a FEM analysis of the multi-phase support insulator element of the prior art; and
Figures 8 and 10 illustrate a FEM analysis of the multi-phase support insulator element of the invention.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 illustrates an isometric front view of the multi-phase support insulator element.

Figure 2 illustrates an isometric through view of the multi-phase support insulator element.
Figure 3 illustrates another isometric through view of the multi-phase support insulator element.
There is provided a disc element (100) which includes three hollow projections (12) which are equi-angularly distributed about a radial axis of the disc element. These hollow projections are spaced apart from each other and spaced apart from the circumferential edge (14) of the disc element. These hollow projections allow for conductors to pass through. The provisioning of three hollow projections is for three corresponding conductors. The limitations of this design are mentioned above.
According to this invention, there is provided a multi-phase support insulator element for Gas Insulated Switchgear (GIS) equipment.
Figure 4 illustrates an isometric front view of the multi-phase support insulator element (200).
Figure 5 illustrates an isometric through view of the multi-phase support insulator element (200).
Figure 6 illustrates another isometric through view of the multi-phase support insulator element (200).

In accordance with another embodiment of this invention, there is provided at least an elongated peripheral slot (22) located between each of the hollow projections (12) and its nearest sector (14) on the circumferential edge of the disc. The slots are provided to disallow creepage between the conductor and the relatively nearer circumferential sector edge of the disc. One edge of the peripheral slot is in curvilinear synchronism with the circumferential edge, while the other edge of the peripheral slot is also in curvilinear synchronism with the circumferential edge but indents, but not necessarily, at the point where it runs beside the hollow projection. Each of the peripheral slots is spaced apart from the neighbouring peripheral slot. The outer edge of the hollow projection is spaced apart from the perimeter of the neighbouring elongated peripheral slot.
In accordance with yet another embodiment of this invention, there is provided a central slot (24) located in the region defined by the hollow projections as the edges. The central slot is a substantially triangular slot but includes smooth indentations to accommodate for the hollow projections. The inner edge of the hollow projection is spaced apart from the perimeter of the central slot.
Although, electrical advantages in relation to creepage are achieved due to the reduction of metal conduction possibility, mechanical strength needs to be sustained in order to support the conductor passage through the hollow projection. Hence, care needs to be taken in order to design the dimensions of each of the elongate peripheral slots and also the central slot.
In terms of electrical parameter enhancements provided by this invention, all the direct (shortest-distance) paths between the high-voltage conductors and earthed enclosure, and between two high-voltage conductors are broken (hence, isolation

provided) by ensuring that slots are present. Thus, there is lower electrical breakdown probability and lesser direct creepage problems. Also, there is lower weight of insulator.
Creepage distance is defined as the minimum path length available along the surface of a solid insulator between live and earth conductors, and between two phases. The longer the path, lesser are the chances of surface breakdown and consequently higher reliability can be expected. The table illustrates the increase in increase in creepage distance over two areas (1 - phase-to-earth; and 2 - phase-to-phase), thereby justifying the technical advancement of the invention.

Calculated creepage distance
Phase-to-earth Phase-to-phase
Prior Art 120 mm 264 mm
Invention 163 mm 470 mm
% Increase 35.83% 78.03%
Figures 7 and 9 illustrate a FEM analysis of the multi-phase support insulator element of the prior art.
Figures 8 and 10 illustrate a FEM analysis of the multi-phase support insulator element of the invention.
It can be seen through Figures 7 and 8 which depict the X - component of the tangential surface field on the spacer that peak stress reduced from 11.7 kV/mm to 9.49 kV/mm (18.9%).

It can be seen through Figures 9 and 10 which depict the Y - component of the tangential surface field on the spacer that Peak stress reduced from 14.6 kV/mm to 8.29 kV/mm (43.2%) and Peak stress reduced from -9.83 kV/mm to -5.81 kV/mm (40.9%).
While this detailed description has disclosed certain specific embodiments of the present invention for illustrative purposes, various modifications will be apparent to those skilled in the art which do not constitute departures from the spirit and scope of the invention as defined in the following claims, and it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

We claim,
1. A multi-phase support insulator element for Gas Insulated Switchgear (GIS) equipment, said element being a disc element including three hollow projections equi-angularly distributed about a radial axis of said disc element, said hollow projections being spaced apart from each other and spaced apart from the circumferential edge of said disc element, characterized in that, said disc element includes at least an elongated peripheral slot located between each of said hollow projections and its nearest sector on the circumferential edge of said disc.
2. An equipment as claimed in claim 1 wherein, one edge of said peripheral slot is in curvilinear synchronism with said circumferential edge.
3. An equipment as claimed in claim 1 wherein, the other edge of said peripheral slot is in curvilinear synchronism with said circumferential edge and indents, but not necessarily, at the point where it runs beside the hollow projection.
4. An equipment as claimed in claim 1 wherein, each of said peripheral slots is spaced apart from the neighbouring peripheral slot.
5. An equipment as claimed in claim 1 wherein, the outer edge of said hollow projection is spaced apart from the perimeter of the neighbouring elongated peripheral slot.
6. An equipment as claimed in claim 1 wherein, said disc element includes a central slot located in the region defined by the hollow projections as the edges.

7. An equipment as claimed in claim 1 wherein, said disc element includes a central slot located in the region defined by the hollow projections as the edges, said central slot being a substantially triangular slot and including smooth indentations to accommodate for said hollow projections such that the inner edge of the hollow projection is spaced apart from the perimeter of the central slot.
8. A Gas Insulated Switchgear (GIS) equipment with a multi-phase support insulator element for, said element being a disc element including three hollow projections equi-angularly distributed about a radial axis of said disc element, said hollow projections being spaced apart from each other and spaced apart from the circumferential edge of said disc element, characterized in that, said disc element includes at least an elongated peripheral slot located between each of said hollow projections and its nearest sector on the circumferential edge of said disc.
9. An equipment as claimed in claim 8 wherein, one edge of said peripheral slot is in curvilinear synchronism with said circumferential edge.
10. An equipment as claimed in claim 8 wherein, the other edge of said peripheral slot is in curvilinear synchronism with said circumferential edge and indents, but not necessarily, at the point where it runs beside the hollow projection.
11 .An equipment as claimed in claim 8 wherein, each of said peripheral slots is spaced apart from the neighbouring peripheral slot.

12.An equipment as claimed in claim 8 wherein, the outer edge of said hollow projection is spaced apart from the perimeter of the neighbouring elongate peripheral slot.
13.An equipment as claimed in claim 8 wherein, said disc element includes a central slot located in the region defined by the hollow projections as the edges.
14.An equipment as claimed in claim 8 wherein, said disc element includes a central slot located in the region defined by the hollow projections as the edges, said central slot being a substantially triangular slot and including smooth indentations to accommodate for said hollow projections such that the inner edge of the hollow projection is spaced apart from the perimeter of the central slot.