FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION (See section 10 and rule 13)
TITLE OF INVENTION
Improved Insulation arrangement for sandwiched type windings
APPLICANTS:
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India; an Indian Company
INVENTOR (S):
Patil Shubhangi of Crompton Greaves Ltd, High Voltage Product Technology Centre, CG Global R&D Centre, Kanjurmarg (E), Mumbai 400042, 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 windings and shunt reactors.
Particularly, this invention relates to the insulation arrangements in shunt reactors.
Yet more particularly, this invention relates to the insulation arrangement in sandwiched type windings of a shunt reactor.
BACKGROUND OF THE INVENTION:
A transformer is a device which transfers energy from one circuit to another. The transformer has a set of coils which perform this function. It is static equipment. The set of coils are conductors which are inductively coupled. The coils are a set of primary winding coils which are typically connected to a first energy source and a set of secondary winding coils to which the transfer of energy takes place. The windings are wound around a central core limb.
Like transformers, shunt reactors are vital part of the efficient operation of long transmission or AC cable high voltage power lines. The shunt reactor compensates the capacitive generation on power lines to avoid non-controlled voltage rise especially on lightly loaded lines. In remote areas, the power supply requirement necessitates the use of a three phase transformer. The transformer supplies power to a substation. But considering the limitation of remote areas and applications, it becomes essential to make a shunt reactor which can work as a transformer without disturbing its application of reactive power compensation.

Thus the shunt reactors need to have two windings same as transformer. Shunt reactors contain the same components as power transformers, like windings, core, tank, bushings and insulating oil and are suitable for manufacturing in transformer factories. The main difference is the reactor core limbs, which have non-magnetic gaps inserted between packets of core steel.
These shunt reactors use a laminated steel core with copper or aluminum windings. Core is GRGO laminated core made up of radially laminated packets. These packets are arranged one above the other by keeping air gap in between them as per the designed estimated air gap required for shunt reactor. Windings form an important part of shunt reactors. In a two winding shunt reactor two windings would be present. The one which is connected to a voltage source and creates the flux is called as a primary winding. The second winding where the voltage is induced by induction is called a secondary. Windings can be appropriately designated as High Voltage (HV) and Low Voltage (LV) windings. The winding with more number of turns will be a HV winding. The current on the HV side will be lower as V-I product is a constant and given as the VA rating of the machines. Also the HV winding needs to be insulated more to withstand the higher voltage across it, HV also needs more clearance to the core, yoke or the body. These aspects influence the type of the winding used for the HV or LV windings. Windings are of enamel coated copper conductors and wound in disc type arrangement.
The windings have a solid insulation of refined paper, and highly refined mineral oil is the insulating and cooling medium for the entire reactor. The insulation used in the case of electrical conductors in a transformer is varnish or enamel in dry type of transformers. To improve the heat transfer characteristics the conductors are

insulated using un-impregnated paper or cloth and the whole core-winding assembly is immersed in a tank containing oil. The oil thus has dual role. It is an insulator and also a coolant. The porous insulation around the conductor helps the oil to reach the conductor surface and extract the heat. The conductor insulation may be called the minor insulation as the voltage required to be withstood is not high. The major insulation is between the windings. Oil ducts are also used as part of insulation between windings. The oil used in the tank should be free from moisture or other contamination to be of any use as an insulator.
The core, windings, and insulation all have specific thermal capabilities. Losses in the winding and core cause temperature rises in the shunt reactor, which are transferred to the insulating oil. Failure to limit these temperature rises to the thermal capability of the insulation and core materials can cause premature failure of the reactor. Thus, to avoid failures, better insulation materials, different alternative options for insulation material are become important. This developed shunt reactor has improved insulation arrangement in terms of lower Hi-Lo gaps and improved insulating materials like FRP or nomex sheet.
EP 1041587 discloses a transformer, or reactor includes several sandwich- or pancake-windings connected electrically in parallel and/or in series, of which each has one or more turns arranged in a common plane.
JP 10256057 discloses an insulation arrangement having a reduced insulation dimension between a high-voltage coil winding and a low-voltage coil winding by extending first and second insulation cylinders so that they project in upper and lower directions from the edge part of low- voltage and high-voltage coil windings,

fixing the first and second insulation cylinders at the upper and lower edge parts, and preventing a solid insulator from being arranged at an insulation gap.
JP 2263412 discloses Hi-Lo winding sustained firmly with the help of a solid insulator.
However, none of the above inventions discloses an insulation arrangement in sandwich type windings of a shunt reactor that would reduce the Hi-Lo gaps thus providing higher impedance. Thus, a need remains to reducing the Hi-Lo gap between the windings to provide an insulation arrangement which would be compact. Such winding arrangement would provide higher impedance and insulation arrangement in sandwiched windings pattern improve the breakdown strength of the reactor.
OBJECTS OF THE INVENTION:
An object of the invention is to provide an extra/secondary winding as an auxiliary winding to the shunt reactor.
Another object of the invention is to provide an auxiliary winding to the shunt reactor in a sandwiched type fashion.
Yet another object of the invention is to provide an auxiliary winding to the shunt reactor to act as a transformer without disturbing the reactive power control function of shunt reactor.

Yet another object of the invention is to provide an improved insulation arrangement for sandwiched type winding of the shunt reactor.
Yet another object of the invention is to provide an improved insulation arrangement for sandwiched type winding of the shunt reactor with reduced Hi-Lo gap and winding arrangement with higher impedance.
Still yet another object of the invention is to provide a shunt reactor which can act as a transformer.
Still yet another object of the invention is to reduce the stress level in the insulation thus improving the breakdown strength.
SUMMARY OF THE INVENTION:
According to the invention, there is provided an improved insulation arrangement for sandwiched type windings in a shunt reactor comprising:
a) a main winding wound concentrically over a central portion of the central limb;
b) a pair of auxiliary windings connected in series and wound concentrically over the respective end portions of the central limb and electrically insulated therefrom such that the main winding remains disposed between the auxiliary windings along the length of the central limb;
c) layers of washers/ wraps dividing the total oil gap equally; and
d) at least one thin layer of washer of higher permittivity material which helps
to improve the breakdown strength for first oil gap and lowers the stress level at
larger oil gap area.

Typically, said winding has center lead arrangement with equal distribution of ampere turns in two equal halves.
Typically, said corners of the windings are covered with angle caps.
Typically, the angle caps can be made of pressboard and the like.
Typically, the thickness of the washer / wraps ranges between 1.5 - 2.0 mm
Typically, the washers / wraps are extended in left and right side of the main winding.
Typically, the layers of washers / wraps are at least three in number and placed equidistantly.
Typically, the thin layer of washer is placed near the top or bottom surface of the main winding.
Typically, the thickness of thin layer of washer ranges between 0.5 - 1.0mm.
Typically, the thin layer of washer (immediate to top of winding ranges) can be made of pressboard, Nomex sheet or the like.
Typically, the stress level is lowered to 4 - 4.5kV/mm.

Typically, due to thin improved material insulating washers, angle caps extended towards the center of radial thickness of winding, stress level for creepage distances(>20mm) is lowered to 7 kV/mm for each layer.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 illustrates insulation arrangement for windings in a shunt according to the prior art.
The invention will now be described in relation to the accompanying drawings, in which:
Figure 2 illustrates a complete view of the shunt reactor.
Figure 3 illustrates a cross sectional view of shunt reactor with auxiliary winding placed at top and bottom.
Figure 4 illustrates the insulation arrangement between the main and auxiliary windings
Figure 5 illustrates the line diagram view of the winding arrangement (sandwiched type) of the reactor.
Figure 6 illustrates the sectional view of line diagram view of the winding arrangement (sandwiched type) of the reactor.

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 illustrates an insulation arrangement (10) for windings of a shunt reactor (100) with a core wound with concentric winding (13) and with an SER (Static End Ring) (12), according to the prior art.
The invention will now be described in relation to the accompanying drawings, in which:
Figure 2 illustrates a complete view of the shunt reactor.
According to the invention, there is provided a gapped iron core shunt reactor (100) where the core is made up of thin laminations of electrical steel to achieve the required reluctance of magnetic circuit. Shunt reactor comprising a core and coil assembly disposed in a protective tank (not shown) , the core comprising at least one air-gapped central limb (1) placed between two lateral limbs (2) in a spaced apart relationship therewith, the limbs held vertically between a bottom yoke (3) and a top yoke (4), all made of magnetic material laminations, and the coil comprising a main winding (5) wound concentrically over a central portion of the central limb (1) and electrically insulated therefrom; and a pair of auxiliary windings (6) and (7) connected in series and wound concentrically over the respective end portions of the central limb (1) and electrically insulated therefrom such that the main winding remains disposed between the auxiliary windings along the length of the central limb. Both the windings are continuous disc windings.
A single phase shunt reactor comprises one central limb and a three phase shunt reactor comprises three central limbs. Preferably, the main winding is wound over

a majority area of the central limb and the auxiliary windings are wound over an equal area on the end portions of the central limb. The free winding lead of the auxiliary winding in top portion of the central limb is connected to a load and the free winding lead of the auxiliary winding in bottom portion of the central limb is connected to earthing.
Figure 3 illustrates the line diagram view of the winding arrangement of the reactor (sandwiched type) of the reactor.
In accordance with an embodiment of the invention, windings are arrangement is such that the gap between the main winding which is a High Voltage winding (5) and auxiliary winding which is a Low Voltage winding (6) and (7) is reduced which makes the reactor compact. Also sandwiched type windings (layered windings) provide higher impedance.
Figure 4 illustrates the insulation arrangement (200) between the main and auxiliary windings.
In accordance with an embodiment of the invention, the winding has center lead arrangement (20) with equal distribution of ampere turns in two equal halves allowing the forces generated by the reactor to be controllable. In order to minimize the stress at the corner of the windings, angle caps (28) are provided. The length of the angle cap (28) is equal to l/4th of radial thickness of the winding. The thickness of the angle cap is about 1.5mm. The material of angle caps includes of pressboard or the like.

The shunt reactor comprising a core and coil assembly disposed in a protective tank (not shown) contains highly refined mineral oil. The total oil gaps of the insulation arrangement between the main and each of the auxiliary winding are equally divided into smaller gaps by washers or wraps. This gives an appearance of an alternate layer of washers or wraps (22 and 24), and highly refined mineral oil.
Three layers of washers are provided which are equidistantly placed. The thickness of the washers is in the range of 1.5mm to 2.0mm. Further, the edges of the washers are extended on the right and left side of the winding thereby reducing the creepage stress.
Also, there is provided a thin washer (26) which is placed near the top and bottom surface of the main winding. The thickness of the washer is about 0.5 - l.Omm.The thinner layer helps in reducing stress level, thus improving the breakdown strength. The material of thin washer includes to a thin pressboard or Nomex sheet or the like.
According to one of the embodiment of the invention, the design of shunt reactors with auxiliary windings have a main winding on a central limb and auxiliary windings on the top and bottom portion of the same limb or even on the side limbs based on the impedance and the regulation targeted.
The table 1 illustrates the insulation arrangement of the invention and the acceptable stress levels.

Table 1. Analytical data for HiLo gap insulation gap of 60mm for 550kV.

Sr. No Insulation arrangement Acceptable stress level
1 Top-bottom winding arrangement Applied 550kV as BIL for testing
2 Insulation total gap 60 mm 5 kV/mm with corner stress level 7kV/mm
3 With 4 different angle rings 2.5kV/mm stress level for nearest angle ring surface
4 Thin Nomex/FRP/Pressboard sheet (0.5-1 mm) 4.5 kV/mm for nearest insulation layer
5 Equal distribution of oil gaps 4.5 kV/mm equal stress distribution due to equal oil gaps
Compared to concentric coils arrangement with insulation of 110 mm gap, this has given stress level lower to 4.5kV/mm instead 5.5 kV/mm in other arrangements. Also due to thin insulating washers, angle caps extended towards the center of radial thickness of winding, stress level for creepage distances(>20mm) has been lowered to 7 kV/mm for each layer.
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. An improved insulation arrangement for sandwiched type windings in a shunt reactor comprising:
a) a main winding wound concentrically over a central portion of the central limb;
b) a pair of auxiliary windings connected in series and wound concentrically over the respective end portions of said central limb and electrically insulated therefrom such that said main winding remains disposed between said pair of auxiliary windings along the length of said central limb;
c) layers of washers/ wraps dividing equally the total oil gap in said shunt reactor; and
d) at least one thin layer of washer of higher permittivity material which helps to improve the breakdown strength and lowers the stress level at larger oil gap area.

2. An improved insulation arrangement for sandwiched type windings in a shunt reactor as claimed in claim 1 wherein, the winding has center lead arrangement with equal distribution of ampere turns in two equal halves.
3. An improved insulation arrangement for sandwiched type windings in a shunt reactor as claimed in claim 1 wherein, the corners of the windings are provided with angle caps.
4. An improved insulation arrangement for sandwiched type windings in a shunt reactor as claimed in claim 1 wherein, the corners of the windings are provided with angle caps, said angle caps being made of pressboard and the like.

5. An improved insulation arrangement for sandwiched type windings in a shunt reactor as claimed in claim 1 wherein, the thickness of the washer / wraps ranges between 1.5 - 2.0 mm
6. An improved insulation arrangement for sandwiched type windings in a shunt reactor as claimed in claim 1 wherein, the washers / wraps are extended in left and right side of the main winding.
7. An improved insulation arrangement for sandwiched type windings in a shunt reactor as claimed in claim 1 wherein, the layers of washers / wraps are at least three in number and placed equidistantly.
8. An improved insulation arrangement for sandwiched type windings in a shunt reactor as claimed in claim 1 wherein, said thin layer of washer is placed near the top or bottom surface of the main winding.
9. An improved insulation arrangement for sandwiched type windings in a shunt reactor as claimed in claim 1 wherein, the thickness of thin layer of washer ranges between 0.5 - 1.0mm
10.An improved insulation arrangement for sandwiched type windings in a shunt reactor as claimed in claim 1 wherein, thin layer of washer ranges can be made of pressboard, Nomex sheet or the like.
11.An improved insulation arrangement for sandwiched type windings in a shunt reactor as claimed in claim 1 wherein the stress level lowered to 4.5kV/mm.

12.An improved insulation arrangement for sandwiched type windings in a shunt reactor as claimed in claim 1 wherein due to thin insulating washers, angle caps extended towards the center of radial thickness of winding, stress level for creepage distances(>20mm) has been lowered to 7 kV/mm for each layer.