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 transformer with improved key spacer element arrangement
APPLICANT(S):
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company.
INVENTOR (S):
Paramane Sachin and Joshi Kishor; both of Crompton Greaves Ltd, Analytics Centre, CG Global R&D Centre, Kanjurmarg (E), 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 electrical and electronics engineering.
Particularly, this invention relates to the field of transformers.
More particularly, this invention relates to transformer windings.
Specifically, this invention relates to a transformer with improved key spacer element arrangement.
BACKGROUND OF THE INVENTION:
A transformer is an electrical device that transfers energy from one circuit to another by magnetic coupling without any moving parts. It works on the Principle of Faradays Law of Electromagnetic Induction together with other laws of electricity. When a magnetic flux linked with an electric circuit varies, an electro motive force (voltage) is generated in the electric circuit, proportional to the rate of variation of flux with time.
The basic functional components of the transformer are a core made of magnetic material, a primary winding, and a secondary winding. The primary winding is connected to a source of an alternating current and the secondary winding is connected to the output. As the alternating current flows through the primary winding, the change in current in the primary windings creates a time-varying magnetic flux in the core, which induces a voltage in the secondary windings.

There is insulation medium between the windings and the windings and core of the transformer which forms the core coil assembly of the transformer. This insulation may be gas insulation, the gas being sulfur hexafluoride gas (SF6).
Power transformers rated up to a few KVA can be adequately cooled by natural convective air-cooling, sometimes assisted by fans. Some power transformers are immersed in specialized transformer oil that acts both as a cooling and insulating medium, thereby extending the lifetime of the insulation transformer. The transformers get heated due to iron and copper losses occurring in them. It is necessary to dissipate this heat so that the temperature of the winding is kept below the value at which the insulation begins to deteriorate. For efficient working of the transformer, it is required to maintain the temperature of the oil, which in turn maintains the temperature of the components of the transformer.
The windings of the transformer are made up of stacked discs. Key spacer elements are used to space apart adjacent discs in the stacked lot of discs.
According to the prior art, key spacer elements are placed in-line between the windings (i.e. one above the other in a collinear manner). Inflow of oil is from the operative bottom of the stack of windings towards the operative top of the stack of windings. The oil is a cooling and insulating medium. This collinear arrangement causes lower oil velocities in horizontal ducts and also causes non-uniform oil flow distribution. As the oil gains height i.e. as it passes over more and more windings, it gains heat and relative transfer of heat from the relatively upper stack of windings is lesser than optimum or desired. This results in higher winding temperature and higher hot spot temperature

(especially in the operative upper zone) and impedes heat transfer resulting in lower thermal performance. This results in the lower life of insulation and thus that of the transformer.
Hence, there is a need for a key spacer arrangement which obviates the limitations of the prior art.
OBJECTS OF THE INVENTION:
An object of the invention is to reduce hot spot temperature m transformer windings.
Another object of the invention is to reduce hot spot temperature in transformer windings using improved key spacers arrangement between windings of the transformer.
Yet another object of the invention is to achieve better oil flow distribution characteristics through the disc windings of a transformer.
SUMMARY OF THE INVENTION:
According to this invention, there is provided a transformer with improved key spacer element arrangement, each key spacer element being disposed between two adjacent discs, said arrangement comprises: a. first stack of key spacer elements adapted to be collinear with respect to each other in a stacked form; and

b. second stack of key spacer elements adapted to be collinear with respect
to each other in a stacked form, characterised in that, said first stack being linearly axially or angularly displaced with respect to said second stack, thereby providing corresponding axially displaced paths for cooling by oil.
According to this invention, there is also provided a transformer with improved key spacer element arrangement, each key spacer element being disposed between two adjacent discs, said arrangement comprises:
each operative upper key spacer element being angularly displaced in its axial placement with respect to each immediate lower adjacent key spacer element, thereby providing corresponding angularly displaced paths for cooling by oil.
Typically, each operative upper key spacer element being angularly displaced with respect to each immediate lower adjacent key spacer element, said angular displacement being in reference to placement axis of said key spacer elements.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 illustrates an angular section of the geometry (isometric view) of an in-line arrangement of key spacer elements in the disc winding stack of the prior art; and
Figure 2 illustrates a front view of an in-line arrangement of key spacer elements in the disc winding stack of the prior art.

The invention will now be described in relation to the accompanying drawings, in which:
Figure 3 illustrates a front view of an angularly displaced arrangement of key spacer elements in the disc winding stack;
Figure 4 illustrates an isometric view of a first embodiment of arrangement of key spacer elements in the disc winding stack; and
Figure 5 illustrates an isometric view of a second embodiment of arrangement of key spacer elements in the disc winding stack.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 illustrates an angular section of the geometry (isometric view) of an in-line arrangement of key spacer elements in the disc winding stack of the prior art.
Figure 2 illustrates a front view of an in-line arrangement of key spacer elements in the disc winding stack of the prior art.
Reference numeral 10 refers to discs, which discs are stacked to form stacked disc windings. Reference numeral 12 refers to key spacer elements collinearly stacked in an intermittent fashion; each key spacer element being disposed between two adjacent discs.

According to the prior art, key spacer elements (12) were placed in-line between the windings (i.e. one above the other in a collinear manner) (10). Inflow of oil is from the operative bottom of the stack of windings towards the operative top of the stack of windings (as depicted by arrow in Figure 2 of the accompanying drawings). The oil is a cooling and insulating medium. This collinear arrangement causes lower oil velocities in horizontal ducts and also causes non-uniform oil flow distribution. As the oil gains height i.e. as it passes over more and more windings, it gains heat and relative transfer of heat from the relatively upper stack of windings is lesser than optimum or desired. This results in higher winding temperature and higher hot spot temperature (especially in the operative upper zone) and impedes heat transfer resulting in lower thermal performance. This results in the lower life of insulation and thus that of the transformer.
According to this invention, there is provided a transformer with improved key spacer arrangement.
Figure 3 illustrates a front view of an angularly displaced arrangement of key spacer elements in the disc winding (10) stack.
Figure 4 illustrates an isometric view of a first embodiment of arrangement of key spacer elements in the disc winding (10) stack.
In accordance with the first embodiment of this invention, there is a first stack of key spacer elements (20) adapted to be collinear with respect to each other in a stacked form. Further, there is a second stack of key spacer elements adapted to be collinear with respect to each other in a stacked form. However,

the first stack is linearly axially or angularly displaced with respect to the second stack. This provides axial displaced paths for cooling by oil.
The first stack of key spacer elements is depicted by reference numeral 22 in Figure 3 of the accompanying drawings. The second stack of key spacer elements is depicted by reference numeral 24 in Figure 3 of the accompanying drawings.
The oil is distributed in an angularly or axially displaced format. The arrows in Figure 4 of the accompanying drawings depict the dispersion of oil. Hence, residence time of oil with winding is lesser. This aids in reduction of hotspots. Typically, this arrangement results in better oil flow distribution at the upper part of winding and result in lower hot spot temperature.
Figure 5 illustrates an isometric view of a second embodiment of arrangement of key spacer elements in the disc winding stack.
In accordance with the second embodiment of this invention, the key spacer elements (20) are interspersed in between disc windings such that a key spacer element spaces apart two adjacently located disc windings, characterised in that, an operative upper key spacer element is angularly displaced in its axial placement with respect to an immediate lower adjacent key spacer element. Therefore, each operative upper key spacer element is angularly displaced with respect to an immediate lower adjacent key spacer element, said angular displacement being reference to placement axis of said key spacer elements. Hence, a radial dispersion of key spacer elements occur.

The system and arrangement of this invention is useful in reduce average temperature of transformer and in improving internal cooling of transformers. This also results in lower insulation temperature and increases life of the transformers. Also, for same temperature, lesser number of radiator fins can be used which aids in reduction of weight of transformer. It is noted that without affecting electrostatic performance of the transformer, the displaced arrangement of key spacer elements are able to improve heat transfer. This arrangement results in improved oil flow distribution in the transfer winding. This reduces the average winding temperature, hot spot temperature and thermal performance.
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 transformer with improved key spacer element arrangement, each key
spacer element being disposed between two adjacent discs, said
arrangement comprising:
a. first stack of key spacer elements adapted to be collinear with
respect to each other in a stacked form; and
b. second stack of key spacer elements adapted to be collinear with
respect to each other in a stacked form,
characterised in that, said first stack being linearly axially or angularly displaced with respect to said second stack, thereby providing corresponding axially displaced paths for cooling by oil.
2. A transformer with improved key spacer element arrangement, each
key spacer element being disposed between two adjacent discs, said
arrangement comprising:
each operative upper key spacer element being angularly displaced in its axial placement with respect to each immediate lower adjacent key spacer element, thereby providing corresponding angularly displaced paths for cooling by oil.
3. A transformer as claimed in claim 2, wherein each operative upper key
spacer element being angularly displaced with respect to each
immediate lower adjacent key spacer element, said angular

displacement being in reference to placement axis of said key spacer elements.