FIELD OF INVENTION:
This invention relates to development of auto transformer with voltage variation
on 132 kV (IV) side, with ±10% tapping range and with special impedances
followed for 100 MVA, 400 kV class, 3-phase, Auto Transformer.
Tapping winding is provided on 132 kV IV terminal of the auto transformer in a
fork type arrangement to achieve the required unique impedance pattern. The
variation in tapping winding voltage is done with the help of on load tap changers.
BACKGROUND OF THE INVENTION:
The majority of auto transformers of 400/132 kV class have variation on HV side.
The impedance pattern is also generally constant ohmic type for HV voltage
variation. In the transformer under consideration the requirement is of constant
ohmic type impedance but with IV voltage variation. When voltage variation
terminal is shifted from HV to IV side, the same design, with same winding
placement, changes from constant ohmic to constant percentage and vice versa.
Due to this it was thought off to provide tapping windings on 132 kV, IV terminal
of the auto transformer in a fork type arrangement.
One or more drawbacks of conventional systems and process for a method for
improving yield strength of a workpiece and an apparatus are overcome, and
additional advantages are provided through the apparatus and a method as
claimed in the present disclosure. Additional features and advantages are realized
through the technicalities of the present disclosure. Other embodiments and
aspects of the disclosure are described in detail herein and are part of the claimed
disclosure.
The foregoing summary is illustrative only and is not intended to be in any way
limiting. In addition to the illustrative aspects, embodiments, and features
described above, further aspects embodiments, and features will become
apparent by reference to the drawings and the following detailed description.

OBJECTS OF THE INVENTION:
Considering the above criteria, following analysis have been envisaged to
determine the objective of invention:
It is an object of the invention to achieve desired constant ohmic type impedance
with IV voltage variation.
Another object of the invention is to provide optimum size and weight of HV, IV
and Tap windings.
Further object of the invention is to ensure lower short circuit fault currents.
Another object of the invention is to provide better ampere turns balance.
SUMMARY OF THE INVENTION:
Various objects, features, aspects, and advantages of the inventive subject matter
will become more apparent from the following detailed description of preferred
embodiments, along with the accompanying drawing figures in which like
numerals represent like components.
It is to be understood that the aspects and embodiments of the disclosure
described above may be used in any combination with each other. Several of the
aspects and 10 embodiments may be combined to form a further embodiment of
the disclosure.
The foregoing summary is illustrative only and is not intended to be in any way
limiting. In addition to the illustrative aspects, embodiments, and features
described above, further aspects, embodiments, and features will become
apparent by reference to the drawings and the following detailed description.
Development of auto transformer with voltage variation on 132 kV (IV) side, with
±10% tapping range and with special impedances followed for 100MVA, 400kV
class, 3-phase, Auto Transformer with constant ohmic type impedance pattern is
desired.

To achieve this, tapping winding is provided on 132 kV, IV terminal of the auto
transformer in a fork type. The variation in tapping winding voltage is done with
the help of on load tap changers.
Developed 100 MVA, 400/132/33 kV auto transformer, successfully tested and
achieved the required impedance values as under:

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
It is to be noted, however, that the appended drawings illustrate only typical
embodiments of the present subject matter and are therefore not to be considered
for limiting of its scope, for the invention may admit to other equally effective
embodiments. The detailed description is described with reference to the
accompanying figures. In the figures, the left-most digit(s) of a reference number
identifies the figure in which the reference number first appears. The same
numbers are used throughout the figures to reference like features and
components. Some embodiments of system or methods in accordance with

embodiments of the present subject matter are now described, by way of example,
and with reference to the accompanying figures.
Figure 1. shows the schematic diagram indicating the 400 kV HV Terminals
(1U,1V,1W), 132 kV IV Terminals (2U,2V,2W), 33 kV LV Terminals (3U,3V,3W) and
Neutral terminal (N).
Figure 2. shows the connection diagram indicating various windings placement.
Figure 3. shows the top view of tap winding terminal gear and interconnection to
OLTC. Terminal markings at lead take out are marked on the drawing.
Figure 4. shows the side view of terminal gear indicating tap changer and routing
of leads to OLTC and individual LV bushing for each phase.
Figure 5. shows the front view of tap winding terminal gear indicating top and
bottom lead take out positions for HV, LV, IV and tap windings.
The figures depict embodiments of the present subject matter for the purposes of
illustration only. A person skilled in the art will easily recognize from the following
description that alternative embodiments of the structures and methods
illustrated herein may be employed without departing from the principles of the
disclosure described herein.
DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS:
It should be noted that the description and figures merely illustrate the principles
of the present subject matter. It should be appreciated by those skilled in the art
that conception and specific embodiment disclosed may be readily utilized as a
basis for modifying or designing other structures for carrying out the same
purposes of the present subject matter. It should also be appreciated by those
skilled in the art that by devising various arrangements that, although not
explicitly described or shown herein, embody the principles of the present subject
matter and are included within its spirit and scope. Furthermore, all examples
recited herein are principally intended expressly to be for pedagogical purposes
to aid the reader in understanding the principles of the present subject matter

and the concepts contributed by the inventor(s) to furthering the art and are to
be construed as being without limitation to such specifically recited examples and
conditions. The novel features which are believed to be characteristic of the
present subject matter, both as to its organization and method of operation,
together with further objects and advantages will be better understood from the
following description when considered in connection with the accompanying
figures.
As used in the description herein and throughout the claims that follow, the
meaning of “a”, “an” and “the” includes plural reference unless and context clearly
dictates otherwise. Also, as used in the description herein, the meaning of “in”'
includes “in” and “on” unless the context clearly dictates otherwise.
The terms "comprises", “comprising”, or any other variations thereof used in the
disclosure, are intended to cover a non-exclusive inclusion, such that a device,
system, assembly that comprises a list of components does not include only those
components but may include other components not expressly listed or inherent
to such system, or assembly, or device. In other words, one or more elements in
a system or device proceeded by “comprises... a” does not, without more
constraints, preclude the existence of other elements or additional elements in
the system, apparatus or device.
These and other advantages of the present subject matter would be described in
greater detail with reference to the following figures. It should be noted that the
description merely illustrates the principles of the present subject matter. It will
thus be appreciated that those skilled in the art will be able to devise various
arrangements that, although not explicitly described herein, embody the
principles of the present subject matter and are included within its scope.
This invention details developing a 100 MVA, 400/132/33 kV Auto transformer
with ±10 % tapping on IV side for IV voltage variation having the following unique
impedance pattern requirement.



Table-2. Required Impedance pattern with IV variation
The above requirement of HV-IV impedances pertains to constant ohmic type
design, wherein the ohmic value of transformer impedance remains within a
narrow range, while the % impedances vary at various tap positions.
During detail design of these transformers it has been felt that using the
conventional design philosophies, it is not feasible to meet all the impedance
requirements as specified above, even with various winding placement
combinations and other design variables.
Even as per latest Indian CBIP manual publication no. 317 dated April 2013,
page 110, the impedances for a 100 MVA Auto transformer has been specified as:

However, the above impedances are for an Auto transformer with HV variation,
while in the present development, IV variation has been envisaged. When voltage
variation terminal is shifted from HV to IV side, the same design, with same
winding placement, changes from constant ohmic to constant percentage and vice

versa. This is due to change in Ampere turn of the tapping winding (current vector
in tap winding follows IV (common) winding current instead of HV (series).
Hence, for IV variation, possible impedance pattern using conventional design
philosophies is as follows:

Hence, to achieve the required Impedance pattern with IV variation as in Table 2,
tapping winding is provided on 132 kV, IV terminal of the auto transformer in a
fork type arrangement. Also the HV winding is split in 78.5:21.5 ratio and placed
physically apart to achieve the desired impedance pattern.
Figure 1. shows the schematic diagram indicating the 400 kV HV Terminals
(1U,1V,1W), 132 kV IV Terminals (2U,2V,2W), 33 kV LV Terminals (3U,3V,3W) and
Neutral terminal (N).
Figure 2. shows the Connection diagram indicating various windings placement.
HV winding is split and placed physically apart as indicated. The winding
arrangement around the core is as follows:

Core - LV - HV-I – IV –TAP - HV-II.
To achieve the desired voltage variation in 132 kV IV voltage as well as specific
impedances, it is an aim to put the TAP winding in fork type arrangement as
indicated in Figure 1. This modification alone does not produce the required
constant ohmic impedance pattern.
To achieve this, it was required to split the HV winding into two separate windings
in the ratio 78.5: 21.5 and place them physically apart as shown in Figure 2. The
winding arrangement is Core - LV - HV-I – IV –TAP - HV-II. The specific ratio and
placement of the HV-I winding between LV and common (IV) winding is really
unique and was finalized after detailed analysis keeping in view of balancing the
ampere turns and minimizing the short circuit fault currents.
Figure 3. shows the top view of tap winding terminal gear and interconnection to
OLTC. Terminal markings at lead take out are marked on the drawing. The figure
also shows how meticulously the interconnection has been done maintaining the
required clearances from earth parts.
Figure 4. shows the side view of terminal gear indicating tap changer and routing
of leads to OLTC and individual LV bushing for each phase.
Figure 5. shows the front view of tap winding terminal gear indicating top and
bottom lead take out positions for HV, LV, IV and tap windings. Routing of leads
for Neutral terminal is also indicated.
Each of the appended claims defines a separate invention, which for infringement
purposes is “reorganized as including equivalents to the various elements or
limitations specified in the claims. Depending on the context, all references below
to the “invention” may in some cases refer to certain specific embodiments only.
In other cases, it will be recognized that references to the “invention” will refer to
subject matter recited in one or more, but not necessarily all, of the claims.
Groupings of alterative elements or embodiments of the invention disclosed
herein are not to be construed as limitations. Each group member can be referred
to and claimed individually or in any combination with other members of the
group or other elements found herein. One or more members of a group can be
included in, or deleted form, a group for reasons of convenience and/or

patentability. When any such inclusion or deletion occurs, the specification is
herein deemed to contain the group as modified thus fulfilling the written
description of all groups used in the appended claims.
With respect to the use of substantially plural and/or singular terms herein,
those having skill in the art can translate form the plural to the singular and/or
from the singular to the plural as is appropriate to the context and/or application.
The various singular/plural permutations may be expressly set forth herein for
sake of clarity.
It still be understood by takes within the art that in general, terms used herein,
and especially in the appended claims (e.g, bodies of the appended claims) are
generally intended as “open” terms (eg, the term “including” should be interpreted
as “including but not limited to,” the term “having” should be interpreted as
“having at least”, the term “includes” should be interpreted as “includes but is
not limited to” etc.)- It will be further understood by those within the art that if a
specific number of an introduced claim recitation is intended, such an intent will
be explicitly recited in the claim, and in the absence of such recitation no such
intent is present. For example, as an aid to understanding, the following
appended claim may contain usage of the introductory phrases “at least one” and
“one or more” to introduce claims recitations. However, the use of such phrases
should not be construed to imply that the introduction of a claim recitation by
the indefinite articles “a” or “an” limits any particular claim containing such
introduced claim recitation to inventions containing only one such recitation,
even when the same claims includes the introductory phrases “one or more” or
“at least one” and indefinite articles such a “a” or “an” (e.g, “a” and/or “an” should
typically be interpreted to mean “at least one” or “one or more”); the same holds
true for the use of definite article used to introduce claim recitations. In addition,
even if a specific number of an introduced claim recitation is explicitly recited,
those skilled in the art will recognize that such recitation should typically be
interpreted to mean at least the recited number (e.g the bare recitation of “two
recitation,” without other modifiers, typically mean at least two recitations, or two
or more recitations). Furthermore, in those instances where a convention
analogous to “at least one of the A, B and C, etc.” is used, in general such a
construction is intended in the sense one having skill in the art would understand

the convention (eg. “a system having at least one A, B and C etc. would include
but not be limited to systems that have A alone, B alone, C alone, A and B
together, A and C together, B and C together, and/or A, B and C together etc.).
In those instances , where a convention analogous to “at least one of A, B, or C,
etc.” is used, in general such a construction is intended in the sense one having
skill in the art would understand the convention (e.g., “a system having at least
one of A, B or C” would include but not be limited to systems that have A alone,
B alone, C alone, A and B together, A and C together, B and C together and/or A,
B and C together etc.). It will be further understood by those within the art that
virtually any disjunctive word and/or phrase presenting two or more alternative
terms, whether in the description, claims, or drawings, should be understood to
contemplate the possibilities of including one of the terms, either of the terms or
both terms. For example, the phrase “A or B” will be understood to include the
possibilities of “A” or “B” or “A and B”.
The above description does not provide specific details of manufacture or design
of the various components. Those of skill in the art are familiar with such details,
and unless departures from those techniques are set out, techniques, known
related art or later developed deigns and materials should be employed. Those in
the art are capable of choosing suitable manufacturing and design details.
The technology used herein is for the expose of describing particular
embodiments only and is not intended to be limiting of the present disclosure. It
will be appreciated that several of the above-disclosed and other features and
functions, or alternative thereof, may be combined into other systems or
application. Various presently unforeseen or unanticipated alternatives,
modification, variation, or improvements therein.
ADVANTAGES:
The advantages of the invention are as follows:
1. To achieve desired constant ohmic type impedance with IV variation.
2. It results in optimum size & weight of HV, IV and Tap windings.
3. Lower short circuit fault currents.
4. It results in better ampere turns balance.

WE CLAIM:-
1. Arrangement of windings in a 100 MVA 400/132/33 kV three-phase auto
-transformer in which the tapping winding is provided on IV terminal in a
fork type assembly and the high voltage winding is split into separate
windings in a predetermined ratio.
2. Arrangement of windings in a 100 MVA 400/132/33 kV three-phase auto
-transformer as claimed in claim 1, wherein the ratio of the two high voltage
windings is 78.5:21.5.
3. Arrangement of windings in a 100 MVA 400/132/33 kV three-phase auto
-transformer as claimed in claim 1, wherein the winding arrangement is
core – LV – HV-I – IV – TAP – HV-II.
4. Arrangement of windings in a 100 MVA 400/132/33 kV three-phase auto
-transformer as claimed in claim 1, as disclosed in enclosed diagrams.