Internship report

Report on internship at vignesh vidyuth control
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b m s institute of technology
AND MANAGEMENT
report on internship
at
vignesh vidyuth control
on MANUFACTURING OF DISTRIBUTION TRANSFORMERS
with the support of
mr A N madhusudhan
mr murali krishna b
UNDER THE GUIDANCE OF:
 MANJUNATH D P
 RAJASHEKAR C
SUBMITTED BY:
 MEGHANA N R [1BY13EE023]
 NAGASHREE B [1BY13EE024]
 SAHANA MUNEGOWDA[1BY13EE039]
 VIJAYALAKSHMI S[1BY13EE054]
 SUNNY JHA [1BY13EE058]

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introduction
I take pleasure in introducing “Vignesh Vidutyh Controls
(VVC)” as one of the leading manufacturer of TRANSFORMERS
for over 6 years with special experience in repairing and
manufacturing of Distribution Transformer.
VVC offers better latest computerized design, assured quality,
quicker delivery, economical price and total prompt service right
from initial stage to commissioning and thereafter to ensure
smooth and economical working.
To ensure reliability most of the vital components are
manufactured in our work-shop for which necessary manufacturing
infrastructure exists including an excellent testing room, dust free air
conditioned winding room, vacuum filtering, fabrication department,
painting, and assembly department etc. All the “VIGNESH VIDYUTH
CONTROLS (vvc)” products are manufactured to conform relevant
ISO 9001-2008 certified and our quality plan and are engineered to

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perfectly meet provided specifications and each product is backed by
a comprehensive service, which includes application, assistance,
layout plan and pre installation advice. VVC is well positioned to
provide its customers with technology-driven, value-added solutions,
leveraging a broad product portfolio on the one hand, and enhancing
the entire value-chain quality, delivery, and services on the other
hand.
Vignesh Vidyuth Controls is the pioneer manufacturer of
distribution transformers in Karnataka. The company has always
been contributing towards the advancement and development of
the engineering sector by introducing a range of quality electrical
equipments.
The internship basically revolved around the distribution
transformer manufacturing, and maintenance. This report stated
a very brief review of what we have seen and learnt during our
internship.
we have mentioned all these as we have made an internship as
according to the schedule. This report will give its reader
knowledge about the Vignesh Vidyuth Control and power division
especially about transformer unit.

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HISTRORY OF ORGANANIZATION
Established in 2000, Vignesh Vidyuth controls company is one
of the leading manufacturers of Distribution Transformers in
Bangalore. Vignesh Vidyuth controls company was established in
the year 2000 basically for the purpose of repairing of existing
transformers and later in the year 2008 started the process of
manufacturing the distribution transformers. And then till now
the company is producing the effective and quality distribution
transformers to contribute towards the society.
ORGANIZATION STRUCTURE
PRODUCTS MANUFACTURED
 Manufacturing of Distribution Transformer: A distribution
transformer or service transformer is a transformer that
provides the final voltage transformation in the electric
power distribution system, stepping down the voltage used
in the distribution lines to the level used by the customer.
 Distribution Transformers
 Pole Mounted Substation
Rated Output (KVA):25,63,100, 160, 200, 250.
 Indoor mounted transformer
Rated Output (KVA):25, 63, 100, 160,200,
250,315,400,500,630,750 ,1000,1250,1500 to 2000 KVA.

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SERVICES OFFERED BY COMPANY
 Repairing of existing Transformers: Vignesh Vidyuth
Controls will also undertake the repairing of existing
transformers from various customers for any different
types of faults that results in distribution transformers.
Table of Contents
1.About transformer
 Parts
 Classification
 Principle of operation
 Working and construction
 Types of transformer
o INDOOR [pad- mounted]
o OUTDOOR[pole- mounted]
 Different KVA rated transformers
 losses in transformer
2. About the department
 Distribution department
 Design department
 Purchase department
 Production department
 Quality control
 Testing of transformer
3. Task performance
 Manufacturing process:
o Core section

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o Winding section
o Assembly section
o Inspection on quality
o Testing of transformers
4. Reflection of notes
 Experience
 Technical and Non-Technical outcomes
5. Conclusion
6. Reference
7.Acknowlegement

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TRANSFORMERS
Definitionof Transformer-
A transformer is a static machine used for transforming power
from one circuit to another without changing frequency. This is a
very basic definition of transformer.

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History of Transformer:
The history of transformer was commenced in the year 1880.
In the year 1950, 400KV electrical power transformer was
introduced in high voltage electrical power system. In the early
1970s, unit rating as large as 1100MVA was produced and 800KV
and even higher KV class transformers were manufactured in
year of 1980.
Use of Power Transformer:
Generation of electrical power in low voltage level is very much
cost effective. Hence electrical power is generated in low voltage
level. Theoretically, this low voltage level power can be
transmitted to the receiving end. But if the voltage level of a
power is increased, the current of the power is reduced which
causes reduction in ohmic or I2R losses in the system, reduction in
cross sectional area of the conductor i.e. reduction in capital cost
of the system and it also improves the voltage regulation of the
system. Because of these, low level power must be stepped up for
efficient electrical power transmission. This is done by step up
transformer at the sending side of the power system network. As
this high voltage power may not be distributed to the consumers
directly, this must be stepped down to the desired level at the
receiving end with the help of step down transformer. These are
the uses of electrical power transformer in the electrical power
system. Two winding transformers are generally used where ratio
between high voltage and low voltage is greater than 2. It is cost
effective to use auto transformer where the ratio between high
voltage and low voltage is less than 2. Again three phase single
unit transformer is more cost effective than a bank of three single
phase transformer unit in a three phase system. But still it is
preferable to use than the later where power dealing is very large
since such large size of three phase single unit power transformer
may not be easily transported from manufacturer's place to work
site.

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PARTS OF TRANSFORMER
Basic Parts of a transformer:
The following are the basic components of a transformer.
1. Laminated core
2. Windings
3. Insulating Materials
4. Transformer oil
5. Tap changer
6. Conservator

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7. Breather
8. Cooling tubes
9. Buchholz Relay
10.Explosion vent
Of the above mentioned, first four can be seen in almost all the
transformers whereas the rest can be found only in transformers
more than 50KVA.
 CORE
Core is used to support the windings in the transformer. It
also provides a low reluctance path to the flow of magnetic flux. It
is made up of laminated soft iron core in order to reduce eddy
current loss and Hysteresis loss. The composition of a
transformer core depends on such factors as voltage, current, and
frequency. Diameter of the transformer core is directly
proportional to copper loss and is inversely proportion to the iron
loss. If diameter of the core is decreased, the weight of the steel in
the core is reduced which leads to less core loss of transformer
and the copper loss increase. The vice versa happen when the
diameter is increased.

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Windings
There are two windings wound over the transformer core
which are insulated from each other. Windings consists of several
turns of copper coils bundled together an each bundles are
connected in series to form a winding.
Windings can be classified in two different ways.
a) Based on the input and output supply
b) Based on the voltage range
Based on the supply the windings are classified into
a) Primary windings
It is the winding to which the input voltage is applied.

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b) And secondary windings.
It is the winding to which the output voltage is applied.
Based on the voltage the windings can be classified as follows
a) High voltage winding
High voltage windings are made up of copper coil. The
number of turns in it is the multiple of the number of turns in the
low voltage windings. It has copper coils thinner than that of the
low voltage windings.
b) Low voltage windings
Low voltage winding has lesser number of turns than that of the
high voltage windings. It is made up of the thick copper
conductors. This is because the current in the low voltage
windings is higher than that of high voltage windings.
Transformer can be supplied from either LV or HV windings
based on the requirement.

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Windings are made of copper due to the following reasons.
 High conductivity
1. minimizes amount of copper needed for winding (volume &
weight of winding)
2. minimizes losses
 High ductility
1. Easy to bend conductors into tight winding around core thus
minimizes amount of copper and volume of winding
 Insulating materials
Insulating papers and card boards are used in transformers of to
isolate primary and secondary winding from each other and from
transformer core. Transformer oil is also a insulating material.

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Transformer oil
Transformer oil performs two important functions of
insulation as well as cooling for the core and coil assembly. Core
and windings of the transformer must be completely immersed in
the oil. Normally hydrocarbon mineral oils are used as
transformer oil. Oil contamination is a serious problem because it
robs its dielectric properties and renders it useless as an
insulating medium.

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Insulating oil in an electrical power transformer is commonly
known as transformer oil. It is normally obtained by fractional
distillation and subsequent treatment of crude petroleum. That is
why this oil is also known as mineral insulating oil.
Transformer oil serves mainly two purposes one it is liquid
insulation in electrical power transformer and two it dissipates
heat of the transformer i.e. acts as coolant.

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In addition to these, this oil serves other two purposes, it helps to
preserve the core and winding as these are fully immersed inside
oil and another important purpose of this oil is, it prevents direct
contact of atmospheric oxygen with cellulose made paper
insulation of windings, which is susceptible to oxidation.
Types of Transformer Oil
Generally there are two types of transformer Oil used in
transformer,
1. Paraffin based transformer oil
2. Naphtha based transformer oil
Naphtha oil is more easily oxidized than Paraffin oil. But
oxidation product i.e. sludge in the naphtha oil is more soluble
than Paraffin oil. Thus sludge of naphtha based oil is not
precipitated in bottom of the transformer. Hence it does not
obstruct convection circulation of the oil, means it does not
disturb the transformer cooling system.

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But in the case of Paraffin oil although oxidation rate is lower
than that of Naphtha oil but the oxidation product or sludge is
insoluble and precipitated at bottom of the tank and obstruct the
transformer cooling system. Although Paraffin based oil has
above mentioned disadvantage but still in our country it is
generally used because of its easy availability. Another problem
with paraffin based oil is its high pour point due to the wax
content, but this does not affect its use due to warm climate
condition of India.
Properties of Transformer Insulating Oil
Some specific parameters of insulating oil should be considered to
determined the serviceability of that oil.
Parameters of Transformer Oil
The parameters of transformer oil are categorized as,
1. Electrical parameters :– Dielectric strength, specific
resistance, dielectric dissipation factor.
2. Chemical parameter :- Water content, acidity, sludge
content.
3. Physical parameters :- Inter facial tension, viscosity, flash
point, pour point.

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Cooling system
Conservator
Conservator conserves the transformer oil. It is an airtight
metallic cylindrical drum which is fitted above the transformer.
The conservator tank is vented to the atmosphere at the top and
the normal oil level is approximately in the middle of the
conservator to allow expansion and contraction of oil during the
temperature variations. It is connected to the main tank inside the
transformer which is completely filled with transformer oil
through a pipeline.

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Breather
The insulating oil of transformer is provided for cooling and
insulating purpose. Expansion and contraction of oil during the
temperature variations cause pressure change inside the
conservator. This change in pressure is balanced by the flow of
atmospheric air into and out of the conservator. Transformer
breather is a cylindrical container which is filled with silica gel.
Insulating oil reacts with moisture can affect the paper insulation
or may even lead to some internal faults. So it is necessary that
the air entering the tank is moisture free. For this purpose
breather is used. Breather consists of silica gel contained in a
chamber. When the atmospheric air passes through the silica gel
breather the moisture contents are absorbed by the silica crystals.
Silica gel breather is acts like an air filter for the transformer and
controls the moisture level inside a transformer. It is connected to
the end of breather pipe

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TAP CHANGER
The output voltage may vary according to the input voltage
and the load. During loaded conditions the voltage on the output
terminal fall and during off load conditions the output voltage
increases. In order to balance the voltage variations tap changers
are used. Tap changers can be either on load tap changer or off
load tap changer. In on load tap changers the tapping can be
changed without isolating the transformer from the supply and in
off load tap changers it is done after disconnecting the
transformer. Automatic tap changers are also available.

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 Cooling tubes
Cooling tubes are used to cool the transformer oil. The
transformer oil is circulated through the cooling tubes. The
circulation of the oil may either be natural or forced circulation. In
natural circulation, when the temperature of the oil raises the hot
oil naturally moves to the top and the cold oil moves downwards.
Thus the oil keeps on circulating through the tubes. In forced
circulation, an external pump is used for circulating the oil.

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cooling tubes:
When transformer supplies a load, two types of losses occur
inside the transformer. The iron losses occur in the core while
copper losses occur in the windings. The power lost due to these
losses appears in the form of heat. This heat increases the
temperature of the transformer.
Key Point : To keep the temperature rise of the transformer
within limits, it is necessary to dissipate the heat developed
to the surroundings.
A suitable coolant and cooling method is necessary for each
transformer to dissipate the heat, effectively to the surroundings.
Basically there are two types of transformers, dry type
transformers and oil immersed transformers. In dry type, the heat
is taken to the walls of tank and dissipate to the surrounding air
through convection. In oil immersed type, the oil is used as
coolant. The entire assembly including core and windings is kept
immersed in a suitable oil. The heat developed is transferred to
the walls of tank by convection through oil. And finally heat is
transferred to the surroundings from the tank walls by radiation.
The various cooling methods are designated using letter symbols
which depend upon :
i) Cooling medium used
ii) Type of circulation employed
The various coolants used along with their symbols are,
1. Air - A, 2. Gas - G, 3. Synthetic oil - L,

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4. Mineral oil - O, 5- Solid insulation - S and 6. Water - W
There are two types of circulations which are,
1. Natural - N and 2. Forced - F
In natural cooling, the coolant circulating inside the transformer
transfers entire heat to the tank walls from where it is dissipated
to the surroundings and transformers gets cooled by natural air
circulating surrounding the tank walls.
In forced cooling, the coolant circulating inside the transformer
gets heated as it comes in contact with windings and core. The
coolant partly transfers heat to the tank walls but mainly coolant
is taken to the external heat exchanger where air or water is used
in order to dissipate heat of the coolant.
Cooling Methods by Dry Type Transformers
The cooling methods of dry type transformers are classified as,
1. Air Natural (AN) :
This method uses atmospheric air as cooling medium. The natural
air surrounding the tank walls is used to carry away the heat
generated, by natural convection. It is used for small voltage
transformers. Due to the available insulating materials like glass
and silicon resins now a days, the method can be used for the
transformers up to ratings 1.5 MVA.
2. Air Blast (AB) :
In large transformers, cooling by natural air is inadequate. In such
cases, the transformer is located above the air chamber and a
blast of compressed air is forced on core and windings with the
help of blowers or fans. This improves the heat dissipation and
hence higher specific loadings are allowed in dry type
transformers. This reduced the size of transformers. The air
supply must be property filtered to prevent accumulation of dust
particles.

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Cooling Methods for Oil Immersed Transformers
The oil used as a coolant has following advantages,
1. It is good conductor of heat than air.
2. It has high coefficient of volume expansion. Due to this,
adequate circulation is easily obtained.
3. The oil acts as an insulating medium, which increases the
insulating strength.
The only limitation of oil immersed transformers is that these
transformers can not be used at places like mines where there are
chances of fire hazard.
The various cooling methods used for such oil immersed
transformers are classified as,
1. Oil natural (ON) :
The transformer is immersed in oil so heat generated in core and
windings is passed on to oil by conduction. The heated oil transfer
heat to the tank wall from where it is taken away to the
surrounding air. The assembly of oil immersed transformer is
shown .

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Oil immersed transformer
The tubes are provided on the sides of a transformer tank. The oil
in the tank is taken to the tubes. The circulation of oil through
tubes causes the cooling.
The temperature rise of a transformer can be reduced by,
1. Increasing the area of heat dissipation.
2. Decreasing the cooling coefficient.
As the rating of transformer increases the plain walled tank can
not be used. It is necessary to reduce the cooling coefficient. This
is achieved by use of some improved methods of cooling.
The transformers up to 30 KVA use plain walled tanks. But
transformer with ratings higher than 30 KVA use corrugations,
fins, tubes and radiator tanks.
Tanks with tubes and radiators
The heat developed inside the transformer is taken outside with
the help of oil. The oil is cooled with the help of fins, tubes or
external radiations by natural circulation of air.
Hence these methods are called Oil Natural and Air Natural
(ONAN) methods. The tubes are used for transformers up to
ratings 5 MVA.
2. Oil Natural Air Forced (ONAF) :
In this method, the tank is made hollow and compressed air is
blown into the hollow space to cool the transformer. The oil
circulating inside takes heat to the tank walls. The method is

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effective and can be used for large rating transformers. Another
way to force air blast is to use elliptical tubes separated from tank
walls through which air is forced by fans.
3. Oil Natural Water Forced (ONWF) :
In this method, the copper cooling coils or pipes are fitted above
the core but below the oil surface. The cool water is forced
through these coils or pipes which provides the additional cooling
where natural water head is available, this method is very cheap.
The pipes are provided with fans to increase conduction of heat
from oil to pipes. The major disadvantage of this method is, in
case of leakage of water. the water can contaminate the oil
reducing the dielectric strength of oil.
Oil Forced Methods With Heat Exchangers
In these method, forced circulation oil (OF) is the main feature.
The motor driven pump is used to force the oil from top of
transformer to the external heat exchanger. In the heat exchanger,
the oil is cooled with some methods like use of air blast, water
blast etc. The cold oil is circulated back to the transformer from
the bottom.
The oil forced methods are classified depending on how the oil is
cooled in the heat exchangers. These methods are,
1. Oil Forced Air Natural (OFAN) :
The oil is circulated with the help of pump and in the heat
exchanger it is cooled with the help of natural air. This method is
rarely used in practice.
2. Oil Forced Air Forced (OFAF) :
In the external heat exchanger the compressed air is blasted with
the help of fans to cool is the oil. The advantage of this method is
at low loads when losses are less there is no need to use the fans
to cool the oil. The natural air is sufficient. At higher loads, both

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fans and pump are switched on by sensing the temperature which
improves the cooling. Hence efficiency of this system is higher.
The scheme is shown in the Fig. 4.
Oil forced air forced cooling method
3. Oil Forced Water Forced (OFWF) :
In this method, in the heat exchanger instead of air blast, water
blast is used to cool the oil. The pressure oil is kept higher than
water so oil mixes with water in case of leakage but water dose
not mix with oil. Due to this method, smaller transformer size is
sufficient as it is not necessary to employ water tubes inside the
transformer tank. The method is suitable for transformers having
ratings more than 30 MVA. The method is used for the
transformers at hydroelectric stations as large water supply with
appropriate water head is easily available.

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Oil forced Water forced method
 Buchholz Relay
It is a protective device container housed over the connecting
pipe from main tank to conservator tank. It is used to sense the
faults occurring inside the transformer. It is a simple relay which
is operated by the gases emitted due to the decomposition of
transformer oil during internal faults. It helps in sensing and
protecting the transformer from internal faults.
 How does a Buchholz relay work?
Buchholz relay is a type of protection relay universally used
on all oil immersed transformers having rating more than
500 KVA. From this article its principle and working can be
understood.
Explosion vent
Explosion vent is used to expel the boiling oil in the transformer
during heavy internal faults in order to avoid the explosion of the
transformer. During heavy faults the oil rushes out of the vent.
The level of the explosion vent is normally maintained above the
level of the conservatory ta

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nk
PRINCIPLE
A Transformer is basically is very simple static(or stationary)
electromagnetic passive electrical device that works on a
principle of faraday's electromagnetic induction by converting
electrical energy from one value to another
The transformer does this by linking together two or more
electrical circuits using common oscillating magnetic circuit
which is produced by the transformer itself . A transformer
operates on the principle of electromagnetic induction

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Mutual induction is the process by which a coil of wire
magnetically induces a voltage into another coil located in close
proximity to it. Then we say that transformers work in the
"magnetic domain" and transformers get their name from the
fact that they transform one voltage or one current level to
another
WORKING
Basic working of transformers:
The basic transformer consists of two types of coils, namely:
1. Primary coil
2. Secondary coil
Primary coil
The coil to which the supply is given is called as the primary coil.
Secondary coil
The coil from which the supply is taken is called as the secondary

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coil.
Based on the required output voltage the number if turns in the
primary coil and the secondary coil are varied.
The processes occurring inside the transformer can be grouped
into two:
1. Magnetic flux is produced in a coil whenever there is a
change in current flowing through the coil.
2. Similarly change in magnetic flux linked with the coil
induces EMF in the coil.
The first process occurs in the windings of the transformer. When
the ac supply is given to the primary winding alternating flux is
produced in the coil
The second process occurs in the secondary winding of the
transformer. The flux alternating flux produced in the
transformer links the coils in the secondary winding and hence

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emf is induced in the secondary winding.15.
CLASSIFICTION OF TRANSFORMERS

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BASED ON OUTPUT VOLTAGE

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BASED ON CORE CONSTRUCTION
• According to SIZE
1. DISTRIBUTION TRANSFORMER – Used from transferring
power from a primary distribution circuit to a secondary
distribution circuit
2. POWER TRANSFORMER – Are used for transferring power
from any part of the system between the generator down to the
primary distribution system
Those transformers installed at the sending or receiving end of
long high voltage transmission lines are the power transformers.

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The distribution transformers (generally pole mounted) are those
installed in the location of the city to provide utilization voltage at
the consumer terminals.
• Power transformers are used in transmission network of
higher voltages for step-up and step down application (400
kV, 200 kV, 110 kV, 66 kV, 33kV) and are generally rated
above 200MVA.
• Distribution transformers are used for lower voltage
distribution networks as a means to end user connectivity.
(11kV, 6.6 kV, 3.3 kV, 440V, 230V) and are generally rated
less than 200 MVA.
• A power transformer usually has one primary and one
secondary, and one input and output. A distribution
transformer may have one primary and one divided or
“Tapped” secondary, or two or more secondary's.
• Power transformers generally operate at nearly full – load.
However, a distribution transformer operates at light loads
during major parts of the day.
• The performance of the power transformers is generally
judged from commercial efficiency whereas the performance
of a distribution transformer is judged from all – day –
efficiency.
• The rating of a high transformer is many times greater than
that of distribution transformer.
• In Power Transformer the flux density is higher than the
distribution transformer.
• Power transformer’s primary winding always connected in
star and secondary winding in delta while in distribution
transformer primary winding connected in delta and
secondary in star.
• In The Sub station end of the transmission line, The Power
Transformer Connection is Star-Delta.( For the purpose of
Step down the Voltage Level)

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• In the star up of the Transmission line (H-T), The Connection
of the power Transformer is Delta – Star (For the purpose of
Step Up the Voltage Level) But in case of Distribution
Transformer, But Generally it is used in there-phase Step
down distribution transformer( Delta – Star).
• According to INSULATION
1. LIQUID- IMMERSED TRANSFORMERS – Are those whose core
and coils are immersed in an insulating liquid.
– Liquid can either be mineral or synthetic.
– Liquid should be non-flammable
2. DRY TYPE TRANSFORMERS – Whose core and coils are
gaseous or dry compound insulating medium.
– Usually LV and MV systems
• According to LOCATION
1. INDOOR TRANSFORMERS – Is one which because of
construction much be protected from weather.
– Usually dry type or non flammable oil immersed type.
PAD MOUNTED TRANSFORMER – Is used as part of an
underground distribution system.
– They are mounted on a foundation pad.
2. OUTDOOR TRANSFORMERS – Is of weather resistant
construction suitable for service without the additional protection
from weather.
– Usually of the mineral oil immersed
POLE-TYPE TRANSFORMER – Is one which is suitable for
mounting on a pole or similar structure.
4.VAULT TYPE TRANSFORMER – Is constructed so as suitable
for occasional submerged operation in water under specified

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conditions of time and external pressure.
Potential Transformer
Potential transformer or voltage transformer gets used in
electrical power system for stepping down the system voltage to a
safe value which can be fed to low ratings meters and relays.
Commercially available relays and meters used for protection and
metering, are designed for low voltage. This is a simplest form of
potential transformer.
Voltage Transformer or Potential Transformer
A voltage transformer theory or potential transformer theory
is just like a theory of general purpose step down transformer.
Primary of this transformer is connected across the phase and
ground. Just like the transformer used for stepping down purpose,
potential transformer i.e. PT has lower turns winding at its
secondary. The system voltage is applied across the terminals of
primary winding of that transformer, and then proportionate
secondary voltage appears across the secondary terminals of the
PT. The secondary voltage of the PT is generally 110 V.
In an ideal potential transformer or voltage transformer, when
rated burden gets connected across the secondary; the ratio of
primary and secondary voltages of transformer is equal to the

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turns ratio and furthermore, the two terminal voltages are in
precise phase opposite to each other. But in actual transformer,
there must be an error in the voltage ratio as well as in the phase
angle between primary and secondary voltages. transformer
theory.
Current Transformer
Generally current transformers and ammeters are used together
as a matched pair in which the design of the current transformer
is such as to provide a maximum secondary current
corresponding to a full-scale deflection on the ammeter. In most
current transformers an approximate inverse turns ratio exists
between the two currents in the primary and secondary windings.
This is why calibration of the CT is generally for a specific type of
ammeter.
Most current transformers have a the standard secondary rating
of 5 amps with the primary and secondary currents being
expressed as a ratio such as 100/5. This means that the primary
current is 100 times greater than the secondary current so when
100 amps is flowing in the primary conductor it will result in 5
amps flowing in the secondary winding, or one of 500/5 will
produce 5 amps in the secondary for 500 amps in the primary
conductor, etc.

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By increasing the number of secondary windings, N2, the
secondary current can be made much smaller than the current in
the primary circuit being measured because as N2 increases, I2
goes down by a proportional amount. In other words, the number
of turns and the current in the primary and secondary windings
are related by an inverse proportion.
We know from our tutorial on double wound voltage
transformers that its turns ratio is equal to:
from which we get:
As the primary usually consists of one or two turns whilst the
secondary can have several hundred turns, the ratio between the
primary and secondary can be quite large. For example, assume
that the current rating of the primary winding is 100A. The
secondary winding has the standard rating of 5A. Then the ratio
between the primary and the secondary currents is 100A-to-5A,
or 20:1. In other words, the primary current is 20 times greater
than the secondary current.
It should be noted however, that a current transformer rated as
100/5 is not the same as one rated as 20/1 or subdivisions of
100/5. This is because the ratio of 100/5 expresses the
“input/output current rating” and not the actual ratio of the
primary to the secondary currents. Also note that the number of
turns and the current in the primary and secondary windings are
related by an inverse proportion.
But relatively large changes in a current transformers turns ratio
can be achieved by modifying the primary turns through the CT’s
window where one primary turn is equal to one pass and more

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than one pass through the window results in the electrical ratio
being modified.
So for example, a current transformer with a relationship of say,
300/5A can be converted to another of 150/5A or even 100/5A
by passing the main primary conductor through its interior
window two or three times as shown. This allows a higher value
current transformer to provide the maximum output current for
the ammeter when used on smaller primary current lines.
Current Transformer Primary Turns Ratio
Types of transformers in "VIGNESH VIDYUT
CONTROLS"-

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1. According to location:
INDOOR: Is one in which because of construction much be
protected from weather.
– Usually dry type or non flammable oil immersed type
OUTDOOR: – Is of weather resistant construction suitable for
service without the additional protection from weather.
– Usually of the mineral oil immersed

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2. According to different KVA rating:

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Losses in Transformers
Transformer is the most efficient electrical machine. Since the
transformer has no moving parts, its efficiency is much higher
Rating
(KVA)
No load loss
watts
(Max.)
Full load loss
(watts) (Max.)
Total loss
(watts)
Impedance % (subject
to tolerance as per
IS:2026)
15/16 80 475 555 4.5
25 100 685 785 4.5
63 180 1235 1415 4.5
100 260 1760 2020 4.5
200 400 3000 3400 5.0
250 500 3000 3500 5.0
300 580 3630 4210 5.0
500 850 5800 6650 5.0
750 1200 6640 7840 5.0
1000 1500 8000 9500 5.0

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than that of rotating machines. The various losses in a
transformer are enumerated as follows:
1. Core loss
core losses comprises of two components:
 Hysteresis loss
 Eddy current loss
When the magnetic core flux varies in a magnetic core with
respect to time, voltage is induced in all possible paths enclosing
the flux. This will result in the production of circulating currents
in the transformer core. These currents are known as eddy
currents. These eddy currents leads to power loss called Eddy
current loss. Copper loss occurs in the winding of the transformer
due to the resistance of the coil
About the department

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Distribution Transformers
USUAGE:
Distribution transformers are used for distribution networks in
urban cities, high rise buildings, rural electrification and
industrial units. Vignesh Vidyut Controls supplied the equipments
to various applications. Vignesh Vidyut Controls manufacture 3
phase oil cooled transformers and are available from 25KVA to
2000KVA.
DESIGN:
The windings form the vital part of the transformer. Highly
sophisticated design techniques are applied for electrical,
mechanical and thermal stability.
Helical and continuous disc type windows are made as they
provide maximum strength and short circuit withstand
capabilities. The coils are pressed before core-coil assembly to
ensure proper trouble free service. Clamping rings are placed on
top and bottom of the winding to ensure high short circuit
withstand capability to the transformer.
PROCESS:
The core-coil assembly is gently finished and cleaned tanks and
locked into position. The assemble then goes for a controlled
heating and vacuum drying process to ensure complete removal
of moisture from the assembly. At the end of the drying process
oil is filled under high level of vacuum in the transformer and
then fixing of external components and top cover assembly is
done. Soon after the vacuum filing , the transformer will be
offered for expiry of a specified standing time.

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DESIGN DEPARTMENT:
The design and drawings division is computerized and the
company is adopting the latest technology in designing the
transformers as per the BI standards and customers
specifications.
Every transformer is individually designed to its specific
requirements and applications. The following specially-developed
computer programs are used to further ensure the reliability of
the product.
1. Optimization of design in relation to labour and material costs,
loss evaluation and sound level.
2. distribution of voltage stresses during lightning impulse and
switching surge conditions
3. behaviour during short-circuit conditions
4. analysis of those areas where high electrical stresses can occur
and
5. calculations of stray losses and thermal effects
Design Team:
Before being issued to the plant, new designs are reviewed by a
team consisting of representatives from Engineering, Quality
Assurance, Manufacturing, Testing and Research and
development. Each design remains the responsibility of the
individual project engineer, who carefully follows and checks
progress throughout the manufacturing process.

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PURCHASE DEPARTMENT
The main functions of the purchase department are defined as
follows
1. Procurement of stores through indigenous and foreign sources
as required in accordance with the rules in force
2. Checking of requisitions/purchase indents.
3. Selection of suppliers for issue of enquiries.
4. issuing enquiries/tenders and obtaining quotations.
5. Analysing quotations and bids etc., and preparation of
comparative statement (quotation charts).
6. Consultation with the Indenter for selection and approval of
quotations and with accounts officer for pre-audit.
7. Negotiating contracts.
8. Checking legal conditions of contracts . Consulting
Administrative Officer or Secretary.
9. Issue of purchase orders.
10.Follow-up of purchase orders for delivery in due time.
11. Verification and passing of suppliers' bills to see that
payments are made promptly.
12. Correspondence and dealing with suppliers, carriers etc.
regarding shortages, rejections etc. reported by the Stores
Department.
13. Maintenance of purchase records.
14. Maintenance of progressive expenditure statement, sub-head
wise.

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15. Maintenance of vendor performance records/data.
16. Arrangement for Insurance Surveys as and when necessary.
17. Clearance of foreign consignments.
18. Keeping various Departments/Divisions informed of the
progress of their indents in case of delay in obtaining supplies.
19. Servicing as an information centre on the materials
knowledge i.e. their prices, source of supply, specifications and
other allied matters.
20. Development of reliable and alternate sources of supply.
The purchasing team handles all purchase requirements for the
following areas:
1. Production materials
2. Non-production materials
3. Capital equipment
4. Engineering prototypes
5. First article samples
6. Services
7. Contracts/Agreements
8. Returns
9. Invoice discrepancies
10. Vendor-managed inventory

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The major raw-materials required for manufacture of good
quality of transformers are as follows:-
1. Silicon steel Laminations- Cold Rolled Grain Oriented Steel.
2. Electrical Grade Double Paper Covered Copper/Aluminium
Conductors.
3. Transformer Oil.
4. Insulating Materials like Insulating paper, Press boards,
Porcelain insulators, Varnish, Paper tubes, Varnish and Paints etc.
5. Bushing Metal parts and various other MS items
6. Various other fittings like OIL GUAGES.
7. Silica gel Breathers etc.
8. Mild steel tanks

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materials and suppliers

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PRODUCTION DEPARTMENT
It is the responsibility of the manufacturing department to
manufacture different components of transformer and then
assemble them to make a transformer. Production department
has following sections:
1.Winding section
2. Core section
3. Tank section
4. Assembly section

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QUALITY CONTROL AND TESTING DEPARTMENT
The division will monitor the various manufacturing activities, up
to final testing of transformers to ensure that the transformers
coming out will confirm to the Indian Standards and costumers
requirement. The various inspection procedures adopted are as
under:
1. Inspection of raw materials received from various vendors.
2. Stage inspection at various levels in manufacturing shops.
3. Final testing of the transformers as per Indian Standards
4. Inspection at the dispatch area before dispatch to ensure that
the transformers are fitted with all accessories etc.
The various procedures and tests conducted as per the Indian
Standards which are quite elaborative. This department is headed
by qualified and experienced engineers and is having a team of
qualified personnel at various stages and they will be
independent from production department to ensure that the
quality parameters are compiled with , at various stages of
manufacture.
The raw materials are tested to ensure that the quality is up to the
recommended standards, these tests are done to check the
durability, strength of the material.
The raw materials that are being tested are oil, Aluminium
conductors, bushings, press boards ,Kraft paper and cork sheet.
OIL:
Three tests are carried out for oil by using BDV test set and
resistivity/tan delta test set.
1. Breakdown voltage test(BDV) 2. Resistivity test
3. tan delta test

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DPC ALUMINIUM CONDUCTOR:
 Lapping test
 Tensile strength test
BUSHINGS:
 BDV test
 Porosity test
PRESS BOARDS:
 BDV test
KRAFT PAPER:
CORK SHEET:

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TRANSFORMERTESTING:
Testing is an important activity in the manufacture of a
transformer. The basic testing requirements and testing codes are
set according to the IS (Indian Standard) standards 1180.
There are seven vital tests that are performed on a transformer
before it is being dispatched.
The various tests performed are
 High Voltage (HV) test
 Double the voltage-double the frequency(DVDF) test
 Short Circuit (SC)test
 Open Circuit(OC) test
 Turns ratio test
 Resistance test
 Megger test.

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LIST OF EQUIPMENTS REQUIRED FOR TESTING

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TASK PERFORMANCE
Manufacturing process:

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Core section
The magnetic core of the transformer is built up of cold rolled
grain oriented(CRGO) magnetic steel laminations. Hi-B grade and
laser scribed lamination is used to reduce the no load losses and
noise. Laminations are cut at an angle of 45° . Core leg and yoke
laminations are interleaved in mitred joints in order to facilitate
the passage of the magnetic flux, to avoid hot spots and to reduce
no load losses and sound level.
By using gauges and jigs, the laminations are assembled into a
core, taking much care to reduce the air gaps between the
laminations to the minimum. The lamination of the upper yoke
are interleaved after fitting the windings.

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Winding section
The windings are designed to optimize dynamic, thermal,
mechanical & electrical stresses depending upon the current &
voltage requirements.
Depending on the specific design criteria, spiral, cross over
Helical, continuous disc, partly interleaved or fully interleaved
windings are used.
Steel winding mandrels are used to ensure tight tolerances. The
winding machines are equipped with hydraulic braking devices
which ensure that the proper tension is maintained on the
winding.

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Dovetailed Key spaces are employed to give the winding extra
strength. Axial and radial cooling ducts in and between sections of
the windings allow the free flow of oil around the conductor.
Individual coils are dried and hydraulically pressed to size in
accordance with the calculated short circuit forces to obtain the
design height and to guarantee full short circuit resistance.

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Assembly section
The magnetic core with the windings and some accessories are
the active part of the transformer. The windings are slipped over
the legs of the core and the lamination of the upper yoke are
interleaved. All connections between windings and bushings and
the connections between the high voltage lapping and the tap
changer are made. The Tap changer allows the increase or
decrease of a certain number of turns in the high voltage winding
in order to compensate for a voltage drop or to adapt the
transformer to an unstable supply, so that the rated low voltage

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can be maintained. Subsequently, the top cover on which the
bushings for high voltage and low voltage are already fixed is
fitted.
1. Core-coil assembly:
The "active" part of the Transformer consists of the magnetic
core with windings and accessories. The windings are placed over
the core limbs and necessary connections are made as per the
tapings and vector group. Sufficient ducts are provided between
the coils to ensure heat dissipation through circulation of oil. Best
quality insulation is provided at all joints and gaps. The optimum
design of Core-Coil Assembly is achieved by considering the
required technical particulars including cooling, size compactness
and tapping arrangement. All leads and conductors are rigidly
supported by special clamping arrangement.
2. Before connection test:

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The ratio of the turns are checked using the transformer turns
ratio meter to verify the standard ratio i.e. 44 and a tolerance of
0.05% is allowable.
If the turns ratio less than 44 then turns are added and if it is
more than it is removed.
3. HT and LT connections
The high voltage side is connected as delta and low voltage side is
connected as star. The connections are done by a process called
BRAZING using ALOTETIC [brazing powder].

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4. After connection test:
It is usually done for tapped transformers and tapping connect
ratio is +2.5% to -10%. This ratio is kept to avoid the short circuit
of the tappings.
The turns ratio for different tappings are:
1st tap= 45.1
2nd tap=44
3rd tap=43.9
4th tap=41.8
5th tap=40.7
6th tap=39.6
5. Furnace:

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In order to remove the moisture content in the ACTIVE PART of
the transformer and to increase the insulation resistance the
transformer is kept in the furnace and is heated for 48 to 72 hours
at the temp. of 120˚celcius.
Furnace contains HEATERS, FAN FOR COOLING, THERMOCOUPLE
which is heat sensitive device.

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6.Cover plate assembly:
After the transformer is furnaced ,it should be placed in the tank
within 5-6 hours. Bushings are used in order to indicate the
contact between earth and phase.
7. Pre tanking section
8. Oil filling section:
Oil should be free of moisture and its BDV should be 30KV to
60KV. Transformer oil serves mainly two purposes one it is
liquid insulation in electrical power transformer and two it
dissipates heat of the transformer i.e. acts as coolant.

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9. Varnish and painting:
The tank is first varnished and then painted for good look and to
prevent RUST.
10. Finishing:
Many tests are conducted finally to set it ready for dispatch.

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Inspection and Test Plan for Transformer
The inspection and test plan for power transformer article
provides you information about power transformer test and
power transformer inspection in manufacturing shop. The draft
Inspection and test plan provided as well.
The IEC, NEC, NEMA, FDF, ISO ANSI, CI, IPCEA standard
requirements normally are applied for inspection and test plan in
manufacturing shop.
The witness of some inspection and test by third party inspector
is mandatory and cannot be waived.
Some others must only monitored and fully witnessing are not
necessary, for these thing, the inspection man-days etc. depends
to the purchaser decision, some prefer stringent monitoring and
even assign resident inspector in manufacturing shop and some
others relay to quality control system of the manufacture and
assign only few days for monitoring points.
These are some of inspection points which need to be witnessed,
checked, monitored and reviewed by third party inspector in
Power Transformer manufacture shop.
Inspection and Test Plan for Power Transformer - Important
Points
 Witness of out of tank inspection, consisting of check of
wiring for adequacy of insulation, cleaning and termination,
if tap changer switch fitted, check for all electrical
connections and switch mechanism and check for
identification of winding ends (primary, secondary and
phase)
Final inspection after tanking, consisting of witness full tests,

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including heat run or standard abbreviated tests as may be
specified, check tank seams for signs of oil leakage, check of
handling for cable boxes, size and quantity of cable glands and
position of entries, functionally test alarm relays, if fitted, for
position of contacts, check of all ancillary equipment fitted as
requisitioned, dimensional check to GA Drawing and check for
rating plate and general paint etc.
For confirming the specifications and performances of an
electrical power transformer it has to go through numbers of
testing procedures. Some tests are done at manufacturer
premises before delivering the transformer. Mainly two types of
transformer testing are done at manufacturer premises- type
test of transformer and routine test of transformer. In
addition to that some transformer tests are also carried out at
the consumer site before commissioning and also periodically in
regular & emergency basis throughout its service life.

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TESTING IN TRANSFORMER
Type of Transformer Testing
Tests done at factory
1. Type tests
2. Routine tests
3. Special tests
Tests done at site
1. Pre-commissioning tests
2. Periodic/condition monitoring tests
3. Emergency tests
Type Test of Transformer
To prove that the transformer meets customer’s specifications
and design expectations, the transformer has to go through
different testing procedures in manufacturer premises. Some
transformer tests are carried out for confirming the basic design
expectation of that transformer. These tests are done mainly in a
prototype unit not in all manufactured units in a lot. Type test of
transformer confirms main and basic design criteria of a
production lot.
Routine Tests of Transformer
Routine tests of transformer is mainly for confirming
operational performance of individual unit in a production lot.
Routine tests are carried out on every unit manufactured.

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Special Tests of Transformer
Special tests of transformer is done as per customer
requirement to obtain information useful to the user during
operation or maintenance of the transformer.
Pre Commissioning Test of Transformer
In addition to these, the transformer also goes through some
other tests, performed on it, before actual commissioning of the
transformer at site. The transformer testing performed before
commissioning the transformer at site is called
pre-commissioning test of transformer. These tests are done to
assess the condition of transformer after installation and compare
the test results of all the low voltage tests with the factory test
reports.
Routine tests of transformer include
1. Transformer winding resistance measurement.
2. Transformer ratio test.
3. Transformer vector group test.
4. Measurement of impedance voltage/short circuit impedance
(principal tap) and load loss (Short circuit test).
5. Measurement of no load loss and current (Open circuit test)
6. Measurement of insulation resistance.
7. Dielectric tests of transformer.
8. Tests on on-load tap-changer.
9. Oil pressure test on transformer to check against leakages
past joints and gaskets.
That means Routine tests of transformer include all the type tests
except temperature rise and vacuum tests. The oil pressure test
on transformer to check against leakages past joints and gaskets
is included.

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Special Tests of transformer include
1. Dielectric tests.
2. Measurement of zero-sequence impedance of three-phase
transformers
3. Short-circuit test.
4. Measurement of acoustic noise level.
5. Measurement of the harmonics of the no-load current.
6. Measurement of the power taken by the fans and oil pumps.
7. Tests on bought out components / accessories such as
buchhloz relay, temperature indicators, pressure relief
devices, oil preservation system etc.

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Types of tests conducted at "VIGNESH
VIDYUT CONTROL"
Routine test:
1.Parametric test
a. No load test
b. Load loss test
c. Winding resistance test
d. Turns ratio test
2.Dielectric test
a. Separate source power frequency test[HV test]
b. Induced over voltage test[DVDF test]
c. Insulation resistance test
d. Dielectric value test[BDV test]
Special test:
1. Magnetic balance test
2. Vector group test
We conducted test on 25KVA transformer the tests and the readings
are as follows-

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1.Open circuit or No load test on
Transformer
AIM:TO DETERMINE THE CORE LOSSES OF THE TRANSFORMER
AND HENCE PREDETERMINE THE EFFICIENCY AND
REGULATION
Open circuit test or no load test on a transformer is performed to
determine 'no load loss (core loss)' and 'no load current I0'. The
circuit diagram for open circuit test is shown in figure
usually high voltage (HV) winding is kept open and the low
voltage (LV) winding is connected to its normal supply. A
wattmeter (W), ammeter (A) and voltmeter (V) are connected to
the LV winding as shown in the figure.

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procedure
 Applied voltage of 433V is slowly increased from zero to
normal rated value of the LV side with the help of a variac.
 When the applied voltage reaches to the rated value of the
LV winding, readings from all the three instruments are
taken.
 The ammeter reading gives the no load current I0. As I0
itself is very small, the voltage drops due to this current can
be neglected.
 The input power is indicated by the wattmeter (W). But, as
the other side of transformer is open circuited, there is no
output power. Hence, this input power only consists of core
losses and copper losses.
 But as described above, short circuit current is so small
that these copper losses can be neglected. Hence, now the
input power is almost equal to the core losses. Thus, the
wattmeter reading gives the core losses of the transformer.
Sometimes, a high resistance voltmeter is connected across the
HV winding. Though, a voltmeter is connected, HV winding can be
treated as open circuit as the current through the voltmeter is
negligibly small. This helps in to find voltage transformation
ration (K).

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CALCULATIONS:
The two components of no load current can be given as,
Iμ = I0sinΦ0 and Iw = I0cosΦ0.
cosΦ0 (no load power factor) = W / (V1I0). ... (W = wattmeter
reading)
From this, shunt parameters of equivalent circuit parameters of
equivalent circuit of transformer (X0 and R0) can be calculated as
X0 = V1/Iμ and R0 = V1/Iw.
(These values are referring to LV side of the transformer.)
Hence, it is seen that open circuit test gives core losses of
transformer and shunt parameters of the equivalent circuit.
TABULAR COLUMN:
I IN AMPERES V IN VOLTS POWER IN WATTS
0.666 434.00 83.49
CONCLUSION:THE READING OF THE WATTMETER GIVES THE
CORE LOSS OF THE TRANSFORMER

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2.Short circuit or Impedance test on
Transformer
AIM : TO FIND THE COPPER LOSSES OF THE TRANSFORMER AND HENCE
PREDETERMINE THE EFFIENCY AND REGULATION OF THE TRANSFORMER
PROCEDURE
 The connection diagram for short circuit test on
transformer is shown in the figure. A voltmeter, wattmeter,
and an ammeter are connected in HV side of the transformer
as shown.
 The voltage at rated frequency is applied to that HV side
with the help of a variac of variable ratio auto transformer
 The LV side of the transformer is short circuited. Now with
the help of variac applied voltage is slowly increased until
the ammeter gives reading equal to the rated current of the
HV side.

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 After reaching at rated current of HV side, all three
instruments reading (Voltmeter, Ammeter and Watt-meter
readings) are recorded.
 The ammeter reading gives the primary equivalent of full
load current IL. As the voltage applied for full load current in
short circuit test on transformer is quite small compared to
the rated primary voltage of the transformer, the core losses
in transformer can be taken as negligible here.
Let’s say, voltmeter reading is Vsc. The input power during test is
indicated by watt-meter reading. As the transformer is short
circuited, there is no output; hence the input power here consists
of copper losses in transformer. Since, the applied voltage Vsc is
short circuit voltage in the transformer and hence it is quite small
compared to rated voltage, so core loss due to the small applied
voltage can be neglected. Hence the wattmeter reading can be
taken as equal to copper losses in transformer.
CALCULATION
The ammeter reading gives primary equivalent of full load
current (Isc).
The voltage applied for full load current is very small as compared
to rated voltage. Hence, core loss due to small applied voltage can
be neglected. Thus, the wattmeter reading can be taken as copper
loss in the transformer.
Therefore, W = Isc2Req....... (where Req is the equivalent resistance
of transformer)

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Zeq = Vsc/Isc.
Therefore, equivalent reactance of transformer can be calculated
from the formula Zeq2 = Req2 + Xeq2.
These, values are referred to the HV side of the transformer.
Hence, it is seen that the short circuit test gives copper losses of
transformer and approximate equivalent resistance and reactance
of the transformer.
TABULAR COLUMN:
V IN VOLTS I IN AMPERES P IN WATTS
50%
LOADING
253.43 0.659 88.77
100%
LOADING
506.32 1.315 353.97
CONCLUSION :THE READING OF THE WATTMETER GIVES THE
COPPER LOSS OF THE TRANSFORMER

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3.WINDING RESISTANCE TEST
Transformer Winding Resistance Measurement
Transformer winding resistance measurement is carried out to
calculate the I2R losses and to calculate winding temperature at
the end of a temperature rise test. It is carried out as a type test as
well as routine test. It is also done at site to ensure healthiness of
a transformer that is to check loose connections, broken strands
of conductor, high contact resistance in tap changers, high voltage
leads and bushings etc.
There are different methods for measuring of transformer
winding, likewise
Current voltage method of measurement of winding resistance.
Bridge method of measurement of winding resistance.
Kelvin bridge method of Measuring Winding Resistance.
Measuring winding resistance by Automatic Winding
Resistance Measurement Kit.
NB:- Transformer winding resistance measurement shall be
carried out at each tap

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DELTA CONNECTION
R RESISTANCE PER PHASE AT 25˚CELCIUS=115.14Ω
76.8Ω 76.9Ω
B Y
76.6Ω
STAR CONNECTION
R
RESISTANCE PER PHASE
86.5Ω 85.6Ω AT25˚CELCIUS=42.98Ω
B Y
86.4Ω

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CALCULATION:
R R(RY)=Ra||2Ra Ω/ph
Ra= 𝟑
𝟐
R(RY)
Ra Ra
B Y
Ra
R R(RY)=Ra+Ra
Ra Ra=
𝑹(𝑹𝒀)
𝟐
Ra
Ra
B Y
R
R

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TO CALCULATE RESISTANCE AT T2 TEMPERATURE
R2=R ref
225+𝑡2
225+𝑡1
for aluminium
For delta connection
R at 75˚=137.07Ω
For star connection
R at 75˚=51.6Ω
CONCLUSION: From this test the resistance of the windings is found
ensure healthiness of a transformer that is to check loose
connections, broken strands of conductor, high contact resistance
in tap changers, high voltage leads and bushings

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4.TRANSFORMER TURNS RATIO TEST
aim: To check the specific turns ratio of the transformer.
The performance of a transformer largely depends upon
perfection of specific turns or voltage ratio of transformer. So
transformer ratio test is an essential type test of transformer.
This test also performed as routine test of transformer. So for
ensuring proper performance of electrical power transformer,
voltage and turn ratio test of transformer one of the vital tests.
procedure

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 .We just apply three phase 433 V supply to HV winding, with
keeping LV winding open.
 Then we measure the induced voltages at HV and LV
terminals of transformer to find out actual voltage ratio of
transformer.
 We repeat the test for all tap position separately.
readinds of 25KVA TRANFORMER
R 44.291
Y 44.265
B 44.255
READINDS OF TURNS ON THE TAPPED TRANSFORMER
TAPPING R Y B
1 45.17 45,190 45.15
2 42.885 43.055 42.970
3 41.755 41.905 41.83
4 40.690 40.640 40.73
5 39.560 39.510 39.420
CONCLUSION: The turns are checked and if the turns ratio is less
the turns are added and if turns ratio is more the turns are

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remove to get the proper ratio.
5.INSULATION RESISTANCE TEST
AIM: To ensure proper insulation system in the transformer

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Insulation resistance test of transformer is essential type
test. This test is carried out to ensure the healthiness of overall
insulation system of an electrical power transformer.
Procedure
 First disconnect all the line and neutral terminals of the
transformer.
 Megger leads to be connected to LV and HV bushing

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studs to measure insulation resistance IR value in
between the LV and HV windings.
 Megger leads to be connected to HV bushing studs and
transformer tank earth point to measure insulation
resistance IR value in between the HV windings and
earth.
 Megger leads to be connected to LV bushing studs and
transformer tank earth point to measure insulation
resistance IR value in between the LV windings and
earth.
NB : It is unnecessary to perform insulation
resistance test of transformer per phase wise in
three phase transformer. IR values are taken between
the windings collectively as because all the windings on
HV side are internally connected together to form
either star or delta and also all the windings on LV side
are internally connected together to form either star or
delta.
Measurements are to be taken as follows:
 For auto transformer: HV-IV to LV, HV-IV to E, LV to E.
 For two winding transformer: HV to LV, HV to E, LV to
E.
 Three winding transformer: HV to IV, HV to LV, IV to
LV, HV to E, IV to E, LV to E.
Oil temperature should be noted at the time of insulation
resistance test of transformer. Since the IR value of transformer
insulating oil may vary with temperature. IR values to be

BMSIT&M Page 89
recorded at intervals of 15 seconds, 1 minute and 10 minutes.
With the duration of application of voltage, IR value increases.
The increase in IR is an indication of dryness of insulation.
Absorption coefficient = 1 minute value/ 15 secs. value.
Polarization index = 10 minutes value / 1 minute value.
CONCLUSION: Form IR Test the insulation is checked the
resistance is around 5000MΩ .A PROPER INSULATION IS MUST
FOR AT TRANSFORMER
6.Separate Source Voltage Withstand Test
of Transformer
AIM: This dielectric test is intended to check the ability of main
insulation to earth and between winding.

BMSIT&M Page 90
Procedure
1. All three line terminals of the winding to be tested are
connected together.
2. Other winding terminals which are not under test and also
tank of the transformer should be connected to earth.
3. Then a single-phase power frequency voltage of shape
approximately sinusoidal is applied for 60 seconds to the
terminals of the winding under test.
4. The test shall be performed on all the windings one by one.
5. The test is successful if no breakdown in the dielectric of the
insulation occurs during test.
In this transformer testing, the peak value of voltage is measured,
that is why the capacitor voltage divider with digital peak
voltmeter is employed as shown in the diagram above. The peal
value multiplied by 0.707 (1/√2) is the test voltage.
The values of test voltage for different fully insulated winding are
furnished below in the table.

BMSIT&M Page 91
Nominal system
voltage rating
for equipment
Highest system
voltage rating
for equipment
Rated short duration
power frequency
withstand
voltage
415V 1.1 KV 3 KV
11 KV 12 KV 28 KV
33 KV 36 KV 70 KV
132 KV 145 KV 230 / 275 KV
220 KV 245 KV 360 / 395 KV
400 KV 420 KV 570 / 630 KV
CONCLUSION: The test is successful if no breakdown in the
dielectric of the insulation occurs during test.
7.Induced Voltage Test of
Transformer(DVDF)
AIM: The induced voltage test of transformer is intended to
check the inter turn and line end insulation as well as main
insulation to earth and between windings-

BMSIT&M Page 92
Double voltage double frequency test panel Double voltage
Double Frequency test panel is used to perform DVDF Test for
Power and distribution transformers. This test set provides a
continuously variable output voltage at double frequency to test
the insulation between turns of coils, layer to layer, terminals of
windings with either uniform or graded insulation and also
between the windings and earth, with graded insulation of both
Distribution and Power transformers. An alternating voltage of
sine wave form (as much as possible) at double frequency (100
Hz.) and double in amplitude can be applied at one side of the
transformer under test while the windings, which are not
connected to the source of excitation, are left on open circuit. This
higher frequency is considered to avoid excessive excitation
current during the testing.

BMSIT&M Page 93
PROCEDURE:
1. Keep the primary winding of transformer open circuited.
2. Apply three phase voltage to the secondary winding. The
applied voltage should be twice of rated voltage of
secondary winding in magnitude and frequency.
3. The duration of the test shall be 60 second.
4. The test shall start with a voltage lower than 1/3 the full test
voltage, and it shall be quickly increased up to desired value.
CONCLUSION: The test is successful if no break down occurs at
full test voltage during test.

BMSIT&M Page 94
8.Magnetic Balance Test of Transformer
AIM: Magnetic balance test of transformer is conducted only on
three phase transformers to check the imbalance in the magnetic
circuit.
Procedure of Magnetic Balance Test of Transformer
1. First keep the tap changer of transformer in normal
position.
2. Now disconnect the transformer neutral from ground.
3. Then apply single phase 230 V AC supply across one of
the HV winding terminal.
4. Measure the voltage between the terminals.
5. Compare the measured values with the standard values
The voltage induced in different phases of transformer in
respect to neutral terminals given in the table below.

BMSIT&M Page 95
SHORT COIL 1U-1V
VOLTAGE
1V-1W
VOLTAGE
1U-1W
VOLTAGE
1U-1V 186 148 34
1V-1W 93 186 93
1W-1U 34 148 186
Measured values
SHORT COIL 1U-1V
VOLTAGE
1V-1W
VOLTAGE
1U-1W
VOLTAGE
1U-1V 187 164 18
1V-1W 82 187 81
1W-1U 21 158 186
CONCLUSION: The measured voltage values of the terminals gives
the distribution of the flux in the terminals

BMSIT&M Page 96
9.VECTOR GROUP TEST
AIM: To check the Proper vector grouping which is an essential
criteria for parallel operation of transformers

BMSIT&M Page 97
In three phase transformer, it is essential to carry out a
vector group test of transformer. Proper vector grouping in
a transformer is an essential criteria for parallel operation of
transformers.
There are several internal connection of three phase
transformer are available in market. These several connections
gives various magnitudes and phase of the secondary voltage; the
magnitude can be adjusted for parallel operation by suitable
choice of turn ratio, but the phase divergence cannot be
compensated. So we have to choose those transformer for parallel
operation whose phase sequence and phase divergence are same.
All the transformers with same vector ground have same phase
sequence and phase divergence between primary and secondary.
So before procuring one electrical power transformer, one should
ensure the vector group of the transformer, whether it will be
matched with his or her existing system or not. The vector group
test of transformer confirms his or her requirements
PROCEDURE
1. Connect neutral point of star connected winding with earth.
2. Join 1U of HV and 2W of LV together.
3. Apply 415 V, three phase supply to HV terminals.
4. Measure voltages between terminals 2U-1N, 2V-1N, 2W-1N,
that means voltages between each LV terminal and HV
neutral.
5. Also measure voltages between terminals 2V-1V, 2W-1W and
2V-1W.

BMSIT&M Page 98
short 1U-2U
Applied voltage
1U1V 400
1V1W 398
1U1W 401
Measured values
1u2w 15.5
1u2v 15.4
1w2w 392
1w2v 400
1u2n 391
1v2n 9.2
1v2w 392
1v2v 392
Results
1U2W=1U2V
1V2W=1V2V
1V2N=1U2N=1U1V
CONCLUSION: The vector group test of transformer confirms for
parallel operation whose phase sequence and phase divergence
are same.

BMSIT&M Page 99
10.Dielectric Strength of Transformer Oil
AIM: To check the dielectric strength of the transformer oil and to
measure the break down voltage
Dielectric strength of transformer oil is also known as
breakdown voltage of transformer oil or BDV of transformer
oil. Break down voltage is measured by observing at what voltage,
sparking strands between two electrodes immerged in the oil,
separated by specific gap. low value of BDV indicates presence of
moisture content and conducting substances in the oil.
PROCEDURE :
For measuring BDV of transformer oil, portable BDV
measuring kit is generally available at site.
 In this kit, oil is kept in a pot in which one pair of electrodes
are fixed with a gap of 2.5 mm (in some kit it 4mm) between
them.
 Now slowly rising voltage is applied between the electrodes.
 Rate of rise of voltage is generally controlled at 2 KV/s and
observe the voltage at which sparking starts between the
electrodes.
 That means at which voltage dielectric strength of
transformer oil between the electrodes has been broken
down.
 Generally this measurement is taken 3 to 6 times in same
sample of oil and the average value of these reading is taken.
BDV is important and popular test of transformer oil, as it is
primary indication of health of oil and it can be easily carried
out at site.
Dry and clean oil gives BDV results, better than the oil with
moisture content and other conducting impurities. Minimum
breakdown voltage of transformer oil or dielectric strength
of transformer oil at which this oil can safely be used in
transformer, is considered as 30 KV.

BMSIT&M Page 100
Specific Resistance of Transformer Oil
This is another important property of transformer oil. This is
measure of DC resistance between two opposite sides of one cm3
block of oil. Its unit is taken as ohm-cm at specific temperature.
With increase in temperature the resistivity of oil decreases
rapidly. Just after charging a transformer after long shut down,
the temperature of the oil will be at ambient temperature and
during full load the temperature will be very high and may go up
to 90°C at over load condition. So resistivity of the insulating oil
must be high at room temperature and also it should have good
value at high temperature as well. That is why specific resistance
or resistivity of transformer oil should be measured at 27°C as
well as 90°C. Minimum standard specific resistance of
transformer oil at 90°C is 35 × 1012 ohm–cm and at 27°C it is 1500
× 1012 ohm–cm.
CONCLUSION: By conducting the BDV test the dielectric strength
and breakdown voltage is found and if less the oil is further
filtered to improve the dielectric strength.

BMSIT&M Page 101
testing of 25KVA transformer
RATING 25KVA
CURRENT VOLTAGE
HV=1.3A
LV=33.3A
HV=11000V
LV=433V

BMSIT&M Page 102
TEST MEASUREMENT
 OC TEST NO LOAD LOSS
 LOAD LOSS IN WATT AT
75deg Celsius
 IMPEDANCE
PERCENTAGE
 WINDIND RESISTANCE
PER PHASE AT 27deg
Celsius
 WINDING RESISTANCE
PER PHASE AT 75 75deg
Celsius
EARTHING AIR
CLEARANCE PHASE TO
PHASE
 EARTHING AIR
CLEARANCE PHASE TO
EARTH

 INSULATION
RESISTANCE
 VOLTAGE RATIO TEST
83.49W
421.39W
4.6%
HV= 115.14Ω
LV=42.98Ω
HV=137.07Ω
LV=51.16Ω
HV=255V
LV=75V
HV=140V
LV=40V
HV TO LV=5000MΩ
HV TO EARTH=5000MΩ
LV TO EARTH=5000MΩ
R B
44.29 Y 44.265
44.255

BMSIT&M Page 103
 TOTAL LOAD LOSS 50%
AT 25 deg Celsius
 TOTAL LOSS AT 50% AT
75deg Celsius
 TOTAL LOSS AT 100%
LOAD AT 25deg Celsius
 TOTAL LOSS AT 100%
LOAD AT 75deg Celsius
 EFFICIENCY AT UPF
 EFFICIENCY AT 0.8PF
 STRAY LOSS AT 25deg
Celsius
 STRAY LOSs AT 75deg
Celsius
Load loss =88.17w
No load loss=83.49w
Total loss=171.66w
204.35w
Load loss=421.39w
No load loss=83.49w
Total loss=504.88w
601.04W
97.95%
97.46%
16.51w
13.868w

BMSIT&M Page 104
Experience
We the students of BMSIT&M are thankful to Madhusudhan Sir
who insisted us your company "VIGNESH VIDYUT CONTROLS".
We started our intern from Jan 5th ,firstly at "HORSE POWER
SERVICE STATION" where we had an opportunity to get to know
the error in transformers and methods of eliminating it. Secondly
at Vignesh Vidyuth Controls with full technical knowledge
Mr.Manjunath Sir and Mr.Rajashekar Sir guided us really well
towards gaining the knowledge of manufacturing and designing of
transformers. We were made two groups. There was a systematic
approach in explaining each and every process with a detailed
explanation with a perfect practical analysation.
Our theoretical ideas and thoughts were implemented practically.
Our knowledge was only to the creamy layer of the subject but
they made us to know the depth of it.

BMSIT&M Page 105
Technical outcomes:
The knowledge we received here has made us more confident
technically.
Knowledge we gained related to testing, winding, heating and
designing was truely helpful.
Non-Technical outcomes:
 Your patience, determination, interest towards subject and
building interest in all of us is just thanks giving.
 We are very much gratified for the acceptance and glad that
the atmosphere and the working skills made us learn things
stage by stage and level by level.
 The Communication and interaction of the respectful
mentors made us feel comfortable to ask questions and
clarify our doubts
 The over all experience has made us learn many professional
ethics such as
 Time management
 Regularity in work
 Consistency in performance
 Improvisation in our problem analysis and solving
ability
Ultimately your patience in making us aware of our
mistakes and correcting it and moulding us in
all aspects is just incredible

BMSIT&M Page 106
Conclusion
Our overall experience at "Vignesh Vidyut Controls" was just
phenomenal and with guides like you both made it more
knowledgeable and useful.
The experience and the knowledge we have gained here has made
us more confident to take up the concepts of transformers as our
PROJECT interest.
Thereby we are enough confident technically
We learnt to emerge as one of the finest technical and electrical
engineer of higher learning to develop engineering professional
who are technically competent, ethical and environmental
friendly for betterment of society and to accomplish stimulating
learning environment through high quality internship ,innovation
and industry institute interface.

BMSIT&M Page 107
Reference
Design of transformers - Author: INDRAJITH DAS GUPTHA
External links
1.
http://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&frm=1&sou
rce=web&cd=1&cad=rja&uact=8&ved=0ahUKEwj-3q_p1rrKAhXT
C44KHU2hDaoQFggdMAA&url=http%3A%2F%2Fwww.electrical
4u.com%2F&usg=AFQjCNEbrVX4cYLB62XgFVGMbIOaOqEpFg
2.
http://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&frm=1&sou
rce=web&cd=1&cad=rja&uact=8&ved=0ahUKEwjAybz81rrKAhX
OkY4KHS_CAf8QFggdMAA&url=http%3A%2F%2Fhubpages.com
%2F&usg=AFQjCNHYGuxOZz20dY_IshPuNiDmcLGQ7g

BMSIT&M Page 108
Acknowledgement
We hereby thank A.S .Madhusudhan Sir and Murali Krishna sir a
for giving us an opportunity to have an experience in his company
" VIGNESH VIDYUT CONTROL".
We also thank Manjunath Sir and Rajashekar Sir for spending
their working hours with us and guiding us to improve our
knowledge about transformers.
It was an exposure to our future industrial life. Our learning
experience here for 2 weeks will remain as a very good memory
in our electrical life.
We have gained a overall practical view of what transformer is!!!!
We had a brief knowledge about software atmosphere but this 2
week experience have inspired us to get into core industries. It
has held our ideas towards hardware. Overall was an awesome
experience and would surely insist our juniors and friends to visit
VIGNESH VIDYUT CONTROL.

BMSIT&M Page 109

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