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 collapsible high voltage corona shield for current transformer
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTOR
Awkale Ramesh Ramakrishna of Crompton Greaves Limited, S1-R&D Division, Switchgear Complex, A3, Ambad, Nashik, Maharashtra, India; an 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 current transformer equipment.
More particularly, this invention relates to a high voltage corona shield for current transformer.
Background of the Invention:
A current transformer (CT) is used for measurement of electric currents. Current transformer is an instrument transformer. When current in a circuit is too high to directly apply to measuring instruments, a current transformer produces a reduced current accurately proportional to the current in the circuit, which can be conveniently connected to measuring and recording instruments. A current transformer also isolates the measuring instruments from what may be very high voltage in the monitored circuit. Current transformers are commonly used in metering and protective relays in the electrical power industry.
High voltage stress may result in a corona. Corona is low current level conduction in the insulating media. 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.
A corona shield is placed about a point of high potential to redistribute electrostatic lines of force.

The placement of corona shields is important during high voltage testing of current transformers.
In the prior art, fixed ring type corona shields were used (refer to Figure 1 of the accompanying drawings). The disadvantages of the prior art include it being relatively bigger in size, relatively more in weight, and with relatively uneven field distribution.
There is a need to provide an installable corona shield for high voltage testing application which corona shield can be installed with appropriate ease of hoisting.
Prior Art:
US2434572 discloses a two-part hollow metallic corona shield for two high potential conductors together.
US3239600 discloses a shield with pair of hemispherical members for electrical assembly fitted by using bolt and nuts through the openings.
RU2266584 discloses a cylindrical casing comprising threaded metal stud and a supporting board for tight fitting with cylindrical shell.
None of the prior art document disclose an openable or a collapsible corona discharge shield for resting on a current transformer for even distribution of arc field during high voltage testing or even which has an easy to install hoist-based mechanism.

Objects of the Invention:
An object of the invention is to provide a corona shield.
Another object of the invention is to provide a corona shield for current transformers.
Yet another object of the invention is to provide a collapsible corona shield for current transformers.
Still another object of the invention is to provide a collapsible corona shield for current transformer during high voltage testing.
An additional object of the invention is to provide a collapsible corona shield for current transformers which can be installed with appropriate ease of hoisting.
Yet an additional object of the invention is to provide a collapsible corona shield, for current transformers, which is compact in size.
Another additional object of the invention is to provide a relatively light weight collapsible corona shield for current transformers.
Yet another additional object of the invention is to provide a relatively light weight collapsible corona shield, for current transformers, which provides even field distribution.

Summary of the Invention:
According to this invention, there is provided a collapsible high voltage corona shield for current transformer, said shield comprises:
a) dual hemi-barrel shaped elements adapted to form a barrel shaped complete structure with a relatively narrower top, a relatively broad middle segment and a relatively narrow base, said barrel shaped structure being a substantially hollow structure;
b) bellow guide chamber adapted to provide dead weight in line with the centre of gravity of said barrel shaped complete structure, said bellow guide chamber being a cylinder with a protruding shaft on its operative top side which co-operates with a guide rod extending in an operative downward manner in the interior of and from the top of said barrel shaped complete structure, in that, said co-operation of the protruding shaft with the guide rod being the aiding of up and down movement of said bellow guide chamber in a vertical plane in respect of a piston arrangement at said guide rod, said bellow chamber being further adapted to rest on current transformer;
c) hinge adapted to suspend said guide rod, said hinge spanning across said operative top opening of said barrel shaped complete structure; and
d) at least two levers, one for each hemi-barrel shaped element, each of said levers adapted to facilitate opening of each of said hemi-barrel shaped elements in an outwardly angular manner when said bellow guide chamber moves in an operative downward direction due to piston operation, to facilitate an open or closed position depending upon piston movement and subsequent lever action.

Typically, each of said hemi-barrel shaped elements is a shield structure which shields a current transformer from high voltage arcing during high voltage testing.
Typically, each of said hemi-barrel shaped elements is a 3mm Aluminum fabricated shield element.
Typically, said operative top of said barrel shaped structures is open.
Typically, said operative bottom of said barrel shaped structures is open, in that, said bottom end curls inwards to form a pipe interior the barrel structure.
Typically, said shield includes a lever pin adapted to connect said lever to said hemi-barrel shaped element.
Typically, said lever is an arcuate shaft member.
Brief Description of the Accompanying Drawings:
Figure 1 illustrates an existing current transformer with the fixed ring type corona shield of the prior art.
The invention will now be described in relation to the accompanying drawings, in which:
Figure 2a illustrates a top view of the corona shield;
Figure 2b illustrates a front sectional view of the corona shield;
Figure 2c illustrates a side view of the corona shield;

Figure 2d illustrates an auxiliary view of the corona shield;
Figure 3 illustrates a front sectional view of the corona shield;
Figure 4 illustrates a front full view which shows internal assembly of the corona shield;
Figure 5 illustrates a bellow guide chamber of the corona shield;
Figure 6 illustrates a bellow guide pin of the corona shield;
Figure 7 illustrates a guide rod of the corona shield;
Figure 8 illustrates a hinge rod of the corona shield;
Figure 9 illustrates a lever of the corona shield;
Figure 10 illustrates a lever pin of the corona shield;
Figure 1 la illustrates a first half portion of the corona shield; and
Figure 1 lb illustrates a second half portion of the corona shield.
Detailed Description of the Accompanying Drawings:
Figure 1 illustrates an existing current transformer (10) with the fixed ring type corona shield (12) of the prior art.
According to this invention, there is provided n collapsible high voltage corona shield for current transformer (100).
Figure 2a illustrates a top view of the corona shield.
Figure 2b illustrates a front sectional view of the corona shield.

Figure 2c illustrates a side view of the corona shield. Figure 2d illustrates an auxiliary view of the corona shield.
Figure 3 illustrates a front sectional view of the corona shield.
Figure 4 illustrates a front full view which shows internal assembly of the
corona shield.
In accordance with an embodiment of this invention, there are provided dual hemi-barrel shaped elements (2, 3) (refer Figure 11a and Figure 11b of the accompanying drawings for isolated views) adapted to form a barrel shaped complete structure with a relatively narrower top, a relatively broad middle segment and a relatively narrow base. The barrel shaped structure is a hollow structure. Typically, each hemi-barrel shaped element is a shield structure which shields a corona (11) (as shown in Figure 4 of the accompanying drawings) from high voltage arcing during high voltage testing. Typically, each hemi-barrel shaped element is a 3mm Aluminum fabricated shield element. The operative top of the barrel shaped complete structure is open. The operative bottom of the barrel shaped complete structure is open, in that, the bottom end curls inwards to form a pipe (13) interior the barrel structure.
In accordance with another embodiment of this invention, there is provided a bellow guide chamber (1) (refer Figure 5 of the accompanying drawings for isolated views) adapted to provide dead weight in line with the centre of gravity for the barrel shaped complete structure (9). The bellow guide chamber is a cylinder (13a) with a protruding shaft (13b) on its operative top

side which co-operates with a guide rod (5) extending in an operative downward manner in the interior of and from the top of the barrel shaped complete structure (9) (refer Figure 7 of the accompanying drawings for isolated views). The co-operation of the protruding shaft (13b) with the guide rod (5) is that the bellow guide moves up and down in a vertical plane in respect of a piston arrangement at the guide rod (5). The guide rod is suspended by means of a hinge (4) which spans across the operative top opening of the barrel shaped complete structure (9) (refer Figure 2a of the accompanying drawings and refer Figure 8 of the accompanying drawing for isolated views). The bellow chamber is adapted to rest on current transformer.
In accordance with yet another embodiment of this invention, there is provided at least two levers (6) (refer Figure 9 of the accompanying drawings for isolated views), one for each hemi-barrel shaped element (2, 3), said lever (6) is adapted to facilitate opening of each of said hemi-barrel shaped element (2, 3) in an outwardly angular manner when the bellow guide chamber (8) moves in an operative downward direction due to piston operation. Thus, the two hemi-barrel shaped elements can achieve an open position or a closed position depending upon piston movement and subsequent lever action. The lever (6) is connected to the hemi-barrel shaped element by means of a lever pin (7) (refer Figure 10 of the accompanying drawings for isolated views). The lever (6) is an arcuate shaft member.
When shield is lifted by crane it gets opened from the lower side because of dead weight applied by bellow chamber. Shield gets closed when bellow

chamber rests on current transformer. The shield according to this invention forms a spherical envelope around the current transformer which helps to reduce external partial discharge / corona discharges by evenly distributing field lines which are prominent during high voltage testing.
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 collapsible high voltage corona shield for current transformer, said shield comprising:
a) dual hemi-barrel shaped elements adapted to form a barrel shaped complete structure with a relatively narrower top, a relatively broad middle segment and a relatively narrow base, said barrel shaped structure being a substantially hollow structure;
b) bellow guide chamber adapted to provide dead weight in line with the centre of gravity of said barrel shaped complete structure, said bellow guide chamber being a cylinder with a protruding shaft on its operative top side which co-operates with a guide rod extending in an operative downward manner in the interior of and from the top of said barrel shaped complete structure, in that, said co-operation of the protruding shaft with the guide rod being the aiding of up and down movement of said bellow guide chamber in a vertical plane in respect of a piston arrangement at said guide rod, said bellow chamber being further adapted to rest on current transformer;
c) hinge adapted to suspend said guide rod, said hinge spanning across said operative top opening of said barrel shaped complete structure; and
d) at least two levers, one for each hemi-barrel shaped element, each of said levers adapted to facilitate opening of each of said hemi-barrel shaped elements in an outwardly angular manner when said bellow guide chamber moves in an operative downward direction due to piston operation, to facilitate an open or closed position depending upon piston movement and subsequent lever action.

2. A shield as claimed in claim 1 wherein, each of said hemi-barrel shaped elements is a shield structure which shields a current transformer from high voltage arcing during high voltage testing.
3. A shield as claimed in claim 1 wherein, each of said hemi-barrel shaped elements is a 3mm Aluminum fabricated shield element.
4. A shield as claimed in claim 1 wherein, said operative top of said barrel shaped structures is open.
5. A shield as claimed in claim 1 wherein, said operative bottom of said barrel shaped structures is open, in that, said bottom end curls inwards to form a pipe interior the barrel structure.
6. A shield as claimed in claim 1 wherein, said shield includes a lever pin adapted to connect said lever to said hemi-barrel shaped element.
7. A shield as claimed in claim 1 wherein, said lever is an arcuate shaft member.