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 corona ring assembly for a Surge arrester
APPLICANTS (S)
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company.
INVENTOR (S)
Devraj John Yesuraj, of Crompton Greaves Limited, Switchgear (SI & S4) R&D Division, Switchgear Complex, Crompton Greaves Limited, A3, Ambad, Nashik, Maharashtra, India; Awkale Ramesh Ramkrishna, of Crompton Greaves Limited, SI-R&D Division, Switchgear Complex, Crompton Greaves Limited, A3, Ambad, Nashik, Maharashtra, India; Jha Nitin, of Crompton Greaves Limited, S4 R&D Division, Switchgear Complex, Crompton Greaves Limited, A3, Ambad, Nashik, Maharashtra, India; and Selvraj Saravanan - of Crompton Greaves Limited, Analytics Centre, Global R&D Centre, Crompton Greaves Ltd, Bhaskara Building, Kanjurmarg (East), Mumbai - 400042, India; all Indian National.
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 switchgear equipment.
Particularly, this invention relates to Surge Arrester equipment.
More particularly, this invention relates to a corona ring assembly for a Surge arrester.
BACKGROUND OF THE INVENTION:
A Surge arrester is a device used on electrical power systems to protect the insulation on the system from the damaging effect of Surge. Surge arrestors or surge protectors are designed to be reliable with extreme thresholds of working. They are designed to work efficiently or maintain their life over a specified time period or over the number of time surges are handled.
Environmental conditions and proper maintenance essay an important role in governing their life and health status. If a Surge arrestor malfunctions, its repercussions may be felt on all the associated equipment which needs to be protected from the surge, thus causing irreparable damage.
For use in a High Voltage line, a Surge arrestor or a plurality of Surge arrestors are placed at pre-defined locations through the line. Surge arrester is designed to dissipate or divert surges within itself in the form of energy.
A plurality of adjacently placed Surge arrester columns is common practice in the art to earth a large surge. Typically, a 1200 kV Surge arrester has 4 parallel columns which are interconnected by inter column connectors. The Surge arrestor

includes a plurality of stacks of conductor (ZnO) blocks with the stacks laid out end to end vertically. There are end connectors (Al) between two stacks. These end connectors (pressure relied plates) are end annular plates where axial and radial dissipation of heats occurs. These end connectors are subject to corona discharge and electric field stress due to their sharp edges / corners.
In electricity, a corona discharge is an electrical discharge brought on by the ionization of a fluid surrounding a conductor, which occurs when the potential gradient (the change in the strength of the electric field) exceeds a certain value, but conditions are insufficient to cause complete electrical breakdown or arcing.
In case of Surge / surge arresters, the heart of such components is metal oxide varistors. Their behaviour is highly non-linear and when used in Surge / surge arresters, it forms an ungraded system because of its capacitance which is nearly the same as the stray capacitance. As a result of which, the voltage distribution is not uniform along the axial length. With increase in the height of the Surge / surge arresters, this non-linear distribution of voltage also increases. Top units (stacks) will share more voltage as compared to the bottom unit (stacks). This equalization of voltage is done with the help of grading ring which makes the voltage distribution uniform up to certain extent, but the floating electrode i.e. the interconnecting electrodes due to high voltage and geometry of electrode. As a result, these electric field stresses create corona and RIV.
In a 1200 kV Surge / surge arrester, there are four parallel columns capable of dissipating 55MJ of energy. The axial voltage distribution along the arrester is highly non-linear due to which top portion shares more voltage as compared to the

bottom portion. The interconnecting plates and flanges acts as a floating electrode and having electrical field stress which is sufficient to cause corona.
There is a need to reduce the possibility of corona by reducing the electrical field stress by masking the floating electrode.
PRIOR ART:
JP20011679 discloses a series resistor to prevent breakdown along an inside layer of a cylindrical insulator. Here, single ringed corona ring is disclosed. Its relatively reduces performance is illustrates in Figure 6b of the accompanying drawings.
WO2010120643 discloses a folding high voltage insulating column. Here, substantially circular corona rings are discloses. Although, it is a two-ringed assembly, the ring is not entirely circular. There is an opening provided, which leads to undesirable field configuration changes.
US5218508 discloses an electrical surge arrester / diverter which is a plate-like or a plate-shaped assembly. Here, undesirable water retention can be seen, leading to ingress in dry zones.
OBJECTS OF THE INVENTION:
An object of the invention is to reduce electric field stress locally to obtain good corona and RTV performance.
Another object of the invention is to provide electrically stable Surge arrestors.

Yet another object of the invention is to maintain the performance of a Surge arrester.
Still another object of the invention is to provide a Surge arrester with better reliability.
An additional object of the invention is to provide a corona ring assembly for Surge arrester which is easily assembled on to the Surge arrester.
Yet an additional object of the invention is to provide a corona ring assembly which masks high voltage electrode.
SUMMARY OF THE INVENTION:
According to this invention, there is provided a corona ring assembly for a Surge arrester, said corona ring assembly being a coaxial pair of rings, with their diameter relatively greater than the diameter of a column of Surge arrester upon which it is to be installed, said rings being interconnected at intermittent radial locations by means of plates, and further being provided with a protruding flange at each of said plates for abetting connecting with an end connector flange of said Surge arrester.
According to another embodiment of this invention, there is provided a Surge arrester having stacks of conductor blocks to form columns, said stacks being connected end to end, vertically with end connectors between the stacks with an end connector flange at the lower portion of a stack which connects with another

end connector flange at the upper portion of the next stack by means of an end connector plate, said Surge arrester having a corona ring assembly, said corona ring assembly being a coaxial pair of rings, with their diameter relatively greater than the diameter of a column of Surge arrester upon which it is to be installed, said rings being interconnected at intermittent radial locations by means of plates, and further being provided with a protruding flange at each of said plates for abetting connecting with an end connector flange of said Surge arrester.
Typically, said pair of rings are hollow rings.
Typically, said protruding flanges include holes for the purposes of connecting the ring.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
The invention will now be described in relation to the accompanying drawings, in which:
Figure 1 illustrates a schematic front view of the Surge arrester columns with corona ring assembly;
Figure 2 illustrates a schematic isometric view of the Surge arrester columns with corona ring assembly;
Figure 3 illustrates an isometric view of the corona ring assembly;
Figure 4 illustrates a top view of the corona ring assembly;

Figure 5 illustrates a side view of the corona ring assembly;
Figure 6a illustrates an Electricity Field Distribution Intensity plot of a Surge arrester without a corona ring assembly;
Figure 6b illustrates an Electricity Field Distribution Intensity plot of a Surge arrester without a single corona ring assembly; and
Figure 6c illustrates an Electricity Field Distribution Intensity plot of a Surge arrester without a dual-assembly corona ring assembly.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
According to this invention, there is provided a corona ring assembly (100) for a Surge arrester (12) having stacks of conductor (ZnO) blocks to form columns. The stacks are connected end to end, vertically with end connector between the stacks. There is an end connector flange (14) at the lower portion of a stack (12a) which connects with another end connector flange (16) at the upper portion of the next stack (12b) by means of an end connector plate (18). Since, the end connector flanges have sharp edges and corners, there is a greater chance of corona and radio interference (RIV). The corona ring assembly is therefore provided at such locations to provide corona discharge.
Figure 1 illustrates a schematic front view of the Surge arrester columns with corona ring assembly.

Figure 2 illustrates a schematic isometric view of the Surge arrester columns with corona ring assembly.
Figure 3 illustrates an isometric view of the corona ring assembly. Figure 4 illustrates a top view of the corona ring assembly. Figure 5 illustrates a side view of the corona ring assembly.
In accordance with an embodiment of this invention, there is a coaxial pair of rings (100a, 100b), with their diameter relatively greater than the diameter of the column of Surge arrester. The rings are interconnected at intermittent radial locations by means of plates (22). There is further provided a protruding flange (24) at each of said plates (22) for abetting connecting with end connector flange (16). The rings are hollow rings. There are holes provided at the protruding flanges (24) for the purposes of connecting the ring.
Figure 6a illustrates an Electricity Field Distribution Intensity plot of a Surge arrester without a corona ring assembly. Figure 6b illustrates an Electricity Field Distribution Intensity plot of a Surge arrester without a single corona ring assembly. Figure 6c illustrates an Electricity Field Distribution Intensity plot of a Surge arrester without a dual assembly corona ring assembly. It shows CFD Analysis of two ring used for excellent corona & Radio Interference (RIV) Voltage Performance.
With this art, the stress is reduced to a great extent as mention in the above models. For excellent corona and RIV performance electrical stress on the surface of the flange should be less, which is validated with two ring model. With the

implementation of this individual corona ring assembly in each column mask and the electrodes, it reduces the possibility of corona by reducing the electrical field stress by masking the floating electrode.
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 corona ring assembly for a Surge arrester, said corona ring assembly being a coaxial pair of rings, with their diameter relatively greater than the diameter of a column of Surge arrester upon which it is to be installed, said rings being interconnected at intermittent radial locations by means of plates, and further being provided with a protruding flange at each of said plates for abetting connecting with an end connector flange of said Surge arrester.
2. A corona ring assembly as claimed in claim 1 wherein, said pair of rings are hollow rings.
3. A corona ring assembly as claimed in claim 1 wherein, said protruding flanges include holes for the purposes of connecting the ring.
4. A Surge arrester having stacks of conductor blocks to form columns, said stacks being connected end to end, vertically with end connectors between the stacks with an end connector flange at the lower portion of a stack which connects with another end connector flange at the upper portion of the next stack by means of an end connector plate, said Surge arrester having a corona ring assembly, said corona ring assembly being a coaxial pair of rings, with their diameter relatively greater than the diameter of a column of Surge arrester upon which it is to be installed, said rings being interconnected at intermittent radial locations by means of plates, and further being provided with a protruding flange at each of said plates for abetting connecting with an end connector flange of said Surge arrester.

5. A Surge arrester as claimed in claim 1 wherein, said pair of rings are hollow rings.
6. A Surge arrester as claimed in claim 1 wherein, said protruding flanges include holes for the purposes of connecting the ring.