How to reduce transformer losses

Submitted to- Submitted by-
Dr. Sandeep Gupta Mr. kamal soni
Assistant Professor
B. Tech.- 6th Sem (EE)

TANSFORMER INTRODUCTION
 A transformer is an electrical device that
transfers electrical energy between two
or more circuits through electromagnetic
induction.
 A varying current in one coil of the
transformer produces a varying magnetic
field, which in turn induces a voltage in
a second coil.
 Faraday's law of induction discovered in
1831 described this effect.
 Transformers are used to increase or
decrease the alternating voltages in
electric power applications.

TANSFORMER INTRODUCTION
 Primary winding 1 - input (primary coil)
–AC Source is connected to it.
–Magnetizing current flows and establishes the flux in core .
 Primary winding 2 (secondary coil)
–Load
 Magnetic circuit (core)
 Problems ?
Stray flux, Transient, Heating, Vibrations, Noise, Losses, Regulation,
Saturation, Human errors, Dielectrics (high voltage insulation), Non-linear
magnetic, Fluid dynamics, Material defects, Contamination, etc.

Transformers Classifications
 By Field Usage:
 Power transformer for transmission network
 Distribution transformer for distribution networks
 Power supply
 Isolation
 Rectifier
 Arc furnace

 Number of phases:
 Single phase
 Three phase
 According to frequency:
 Low frequency (power and distribution transformer)
 Very high, high frequency transformers (communication and power
electronic devices)
 Intermitted frequency transformer (communication)

 Cooling :
 Self air cooled (dry type)
 Air blast cooled (dry type)
 Liquid immersed, dry cooled
 Oil immersed, combination self cooled and air blast
 Oil immersed, water cooled
 Oil immersed, forced air cooled
 Oil immersed, combination self cooled and water cooled

Shell Type Transformer
• high voltage bushing
• tank top section
• cooling equipment
• oil circulating pump
• tank bottom section
• pancake coil
• inter-phase block
• L.V. coil group
• H.V. coil group
• tank shielding

TANSFORMER LOSSES
 Real transformer energy losses are dominated by winding resistance joule,
eddy current and core losses. Transformers' efficiency tends to improve with
increasing transformer capacity.
 The efficiency of typical distribution transformers is between about 98 and
99 percent.

TANSFORMER LOSSES
 No-load losses (iron losses) :
 No-load losses occur in the core material due to hysteresis and
eddy currents, and are present almost continuously while the
transformer is connected to the electricity supply (i.e. 8,760 hours
per year).
 The hysteresis losses are proportional to the frequency and the
induction.
 Eddy current losses are also proportional to the frequency and the
amplitude of induction but mainly also to the thickness of the
magnetic steel.

TANSFORMER LOSSES
 Load losses (Copper losses) :
 Load losses occur in the windings, the connecting conductors and
the tank.
 They are caused by the effects of Joule’s law (Ohmic losses), eddy
currents and ux leakages.
 Ohmic losses are equal to the product of the square of the current
and the resistance of the conductor.
 The capitalization values for no-load losses are considerably higher
than those for load losses , which is logical because no-load losses
occur continuously.

Distribution Transformer Main Parts
 MAIN TANK
 RADIATORS
 BREATHER UNIT
 CONSERVATOR
 PRESSURE RELEIF
SYSTEM
 OIL LEVEL
INDICATOR
 TEMPERATUER DIAL
 TAP CHANGER
 HV/LV BUSHINGS
 OIL FILLING PLUG
 DRAIN PLUG
 CABLE BOX

Transformer Core
 This magnetic circuit, know more commonly as
the “transformer core” is designed to provide a
path for the magnetic field to flow around, which
is necessary for induction of the voltage between
the two windings.
 The two most common and basic designs of
transformer construction are the Closed-core
Transformer and the Shell-core Transformer.
 In the “closed-core” type (core form) transformer,
the primary and secondary windings are wound
outside and surround the core ring.
 In the “shell type” (shell form) transformer, the
primary and secondary windings pass inside the
steel magnetic circuit (core) which forms a shell
around the windings.

Reduction of High-Frequency
Conduction Losses Using a Planar Litz
Structure(Shen Wang)IEEE 2005
 Definitions for a Planar Litz Conductor
 Strand/s: Narrow conductors used to make up a planar litz
conductor.
 Planar Litz Conductor: A planar conductor comprised of
many isolated strands that are weaved together to form a
single high-frequency, higher-current-carrying-capacity
conductor.
 Strand Angle: The angle the strand makes with the direction
of the planar litz conductor.
 Planar Litz Lines: The lines parallel to the direction of the
conductor, which are spaced equidistant across the width of
the planar litz conductor.
 Advantages
 Round litz wire is comprised of several insulated strands that
are transposed along the conductor length so that they
ideally occupy all the possible positions in the conductor
cross section equally.
 Therefore, litz wire results in a more uniform current
distribution across the conductor cross section so that losses
due to the skin and proximity effects are effectively reduced,
although usually over just a certain frequency range.

Core Losses
 Hysteresis Losses
 Transformer Hysteresis Losses are caused because of the friction of
the molecules against the flow of the magnetic lines of force
required to magnetize the core, which are constantly changing in
value and direction first in one direction and then the other due to
the influence of the sinusoidal supply voltage.
 This molecular friction causes heat to be developed which
represents an energy loss to the transformer.
 Lowering the frequency of the supply will result in increased
hysteresis and higher temperature in the iron core.
 So reducing the supply frequency from 60 Hertz to 50 Hertz will
raise the amount of hysteresis present, decreased the VA capacity
of the transformer.

Core Losses
Eddy Current Losses
 The magnetic field surrounding a coil which
is carrying AC current varies with time.
 This varying magnetic field induces voltages
in nearby conductive material like metal
equipment cabinets, transformer cores and
so on. The resulting current is known as
Eddy current.
 The currents flow in a circular manner like
eddies in the brook, so they are called as
eddy current.
 They create unwanted power loss which is
known as eddy current loss

Method to decrease Core losses
 Eddy current losses within a transformer
core can not be eliminated completely,
but they can be greatly reduced and
controlled by reducing the thickness of
the steel core.
 Instead of having one big solid iron core
as the magnetic core material of the
transformer or coil, the magnetic path is
split up into many thin pressed steel
shapes called “laminations”.
 The losses of energy, which appears as
heat due both to hysteresis and to eddy
currents in the magnetic path, is known
commonly as “transformer core losses”.

Influence of Transformer Core Design
on Power Losses (Zvonimir valkovic )
IEEE MARCH 1982
 The magnetic properties of a transformer
core are influenced by three basic factors:
 quality (grade) of material
 processing of steel sheet during core
manufacture
 core design
 Corner and T-Joint Design
 The influence of corner form on the
building factor was investigated on the
single-phase models.
 Besides the models with a 45" mitered
overlap joint, similar models were made
with a 90" butt and lap joint.

Stray Losses in Transformer Tank
(Vogel and Adolphson )IEEE 2005
 In 1954, Vogel and Adolphson proposed a model
to determine stray losses and heating of tanks
for a core-type transformer.
 An oval-shaped tank is considered in this article,
and the losses in the tank wall versus the
distance for the top of the high-voltage coils are
determined.
 ADVANTAGES:-
 The steel achieves the best performance among
the three materials, which means that the
shielding effect of the material with both high
conductivity and high permeability is better
than the one only with high conductivity and
the one only with high permeability.
 The transformer enclosed by such material
tanks can maintain the leakage magnetic field
in a very small magnitude .

Transformer Core Grounds
 Power transformers are
usually supplied with a
ground from the core of the
transformer to the tank.
 The core ground diverts this
voltage safely to ground.

Copper Losses
 Transformer Copper Losses are mainly due to the electrical resistance
of the primary and secondary windings.
 Most transformer coils are made from copper wire which has resistance
in Ohms, ( Ω ).
 This resistance opposes the magnetizing currents flowing through
them.
 When a load is connected to the transformers secondary winding, large
electrical currents flow in both the primary and the secondary
windings, electrical energy and power ( or the I2 R ) losses occur as
heat.
 Generally copper losses vary with the load current, being almost zero at
no-load, and at a maximum at full-load when current flow is at
maximum.

Methods to reduce Copper Losses
 Transformers with high voltage and current ratings require conductors
of large cross-section to help minimize their copper losses.
 Increasing the rate of heat dissipation (better cooling) by forced air or
oil, or by improving the transformers insulation so that it will
withstand higher temperatures can also increase a transformers VA
rating.

TRANSFORMER OIL
 In 1887, the year after Stanley designed
and built the first transformers in the
U.S., Elihu Thompson patented the idea
of using mineral oil as a transformer
cooling and insulating medium (Myers et
al.,1981).
 As per I.A.S. breakdown strength of oil
used must be 50kv RMS
 One of the e.g. is chlorinated dephenyl is
a synthetic oil its permittivity is 4.5

The function of the oil in the Transformer
 Cooling
 Internal temperature rise in transformer if left could cause serious
damage on transformer.
 Oil easily penetrates between windings and heat is transferred to
oil.
 Heat is them being rejected out of the oil either through fans or
radiators or through the contact between the transformer body and
the oil itself.
 Insulation
 Insulation between windings themselves and between the windings
and the core.

The function of the oil in the Transformer
 Protection
 Covers all metallic parts and prevents oxidation process which
affects conductivity and prevents any other chemical reactions that
causes corrosion.
 Fault diagnosis
 Used to detect many internal faults in the transformer. Fault cause
changes in the chemistry of the oil due to the large energy
accompanied by faults.
 Oil is analyses and results are used to determine the type of
internal fault inside of the transformer

Radiator of Transformer
 Due to this flowing of electric current, heat is
produced in the windings, this heat ultimately rises
the temperature of transformer oil.
 Under loaded condition, warm oil increases in
volume and comes to the upper portion of the main
tank.
 Then this oil enters in the radiator through top
valve and cools down by dissipating heat through
the thin radiator wall.
 This cold oil comes back to the main tank through
the bottom radiator valve.
 This cycle is repeated continuously till the load is
connected to the transformer.
 These fans are fitted either on the radiator bank
itself or fitted nearby the bank but all the fans must
be faced towards the radiator.
 Sometime, the cooling rate of convectional
circulation of oil is not sufficient. That time an oil
pump may be used for speeding up oil circulation.

Fan Specifications
 All fans are very similar with only a few
variations depending on the transformer
requirements:
 Fan ratings(HP,CFM, dBA)
 Electrical ratings(V, Phases ,FLA, etc.)
 One or two blades per fan
 Rotation of blades
 Mounting Adapter

Different Transformer Cooling Methods
ONAN Cooling of Transformer
 This is the simplest transformer cooling
system. The full form of ONAN is "Oil
Natural Air Natural". Here natural
convectional flow of hot oil is utilized for
cooling.
 In convectional circulation of oil, the hot oil
flows to the upper portion of the transformer
tank and the vacant place is occupied by cold
oil.
 This hot oil which comes to upper side, will
dissipate heat in the atmosphere by natural
conduction, convection & radiation in air and
will become cold.
 In this way the oil in the transformer tank
continually circulate when the transformer
put into load.

ONAF Cooling of Transformer
 The full form of ONAF is "Oil Natural Air
Forced".
 As the heat dissipation rate is faster and
more in ONAF transformer cooling method
than ONAN cooling system, electrical
power transformer can be put into more
load without crossing the permissible
temperature limits.
 Heat dissipation can obviously be increased,
if dissipating surface is increased but it can
be make further faster by applying forced air
flow on that dissipating surface.
 Fans blowing air on cooling surface is
employed. Forced air takes away the heat
from the surface of radiator and provides
better cooling than natural air.

OFAF Cooling of Transformer
 OFAF means "Oil Forced Air Forced"
cooling methods of transformer.
 In OFAF cooling system the oil is forced
to circulate within the closed loop of
transformer tank by means of oil
pumps.
 The heat dissipation rate can be still
increased further if this oil circulation
is accelerated by applying some force.
 The main advantage of this system is
that it is compact system and for same
cooling capacity OFAF occupies much
less space than farmer two systems of
transformer cooling.

OFWF Cooling of Transformer
 We know that ambient temperature of water is much less than the
atmospheric air in same weather condition. So water may be used as better
heat exchanger media than air.
 In OFWF cooling system of transformer, the hot oil is sent to a oil to water
heat exchanger by means of oil pump and there the oil is cooled by applying
sowers of cold water on the heat exchanger's oil pipes.
ODAF Cooling of Transformer
 ODAF or oil directed air forced cooling of transformer can be considered as
the improved version of OFAF. Here forced circulation of oil directed to flow
through predetermined paths in transformer winding.
 ODAF or oil directed air forced cooling of transformer is generally used in very
high rating transforme

Tank Losses Due to High-current
Bushings (Juan C.)IEEE 2008
 There are few studies related to a single
current-carrying conductor in the presence
of conducting permeable surfaces.
 The means of preventing local overheating
in the windings and other elements of
transformers have been studied, but the
means to prevent overheating on the
structure surrounding the distribution
transformer bushings are very scarce.
 Advantages:-
 Reduces eddy current losses.
 Its to use and easy to change the tapings to
get desired voltages.
 Help transformer on low supply voltage to
feed constant output voltage

Distribution Transformer Losses Harmonic
Loads (Sara Tancradi)IEEE DEC. 2008
 Harmonic currents and voltages are created by
nonlinear loads connected on the power system.
 Harmonic distortion is a form of pollution in the
electric plant that can cause problems if the sum of
the harmonic currents increases above certain limits.
 A non-linear load is created when the load current is
not proportional to the instantaneous voltage. Non-
linear currents can be no sinusoidal, even when the
source voltage is a clean sine wave.
 ADVANTAGES:-
 The harmonic losses factor for eddy current winding
and other stray losses has been computed in order to
evaluate the equivalent KVA of the transformer for
supplying nonlinear loads.
 it is better to carry out monitoring on voltage and
current, to reach to useful capacity of transformer
based on available standards and the proposed
model, if harmonic components exist.

Partial Interleaving
(Michael Scofield)IEEE 2004
A Method to Reduce High Frequency Losses
and to Tune the Leakage Inductance in High
Current, High Frequency Transformer Foil
Windings .
 A conventional foil winding uses thickness
optimized foils to reduce the skin effect losses
and interleaving of the windings to reduce the
proximity effect losses. we introduce a new way
of interleaving called “Partial interleaving” .
 The main advantage of the partial interleaving
is that it fulfills the requirements in the same
time.
 would reduce the field strength in
comparison with the conventional winding
hence reduce the power losses
 keep the field strong enough to be able to
achieve the
 required value of the leakage inductance
 keep the winding simple without using
taps

Sudden pressure relay SPR
 The Sudden Pressure Relay is a device designed
to respond to the sudden increase in gas pressure
in a power transformer which would be caused
by an internal arc.
 A pressure sensing bellows , a micro switch and
a pressure equalizing orifice. All parts are
enclosed in a sealed case and mounted on the
outside of the transformer at the gas space.

BUCHHOLZ RELAY
 Placed when a conservator tank is
used, as it indicated faults and
errors such as oil loss when oil level
goes low, improper oil flow between
the oil tank and the transformer.
 Moreover, it shows gas emission
inside transformer due to any
unusual operation ( excessive
loading or short circuit) and can
issue a control signal which can be
used to disconnect the transformer.
 It is equipped with a release valve in
case oil exceeded its level.

PUMPS
 Transformer pumps allow
for maximum cooling which
allows for peak load
operation of oil cooled
transformers.
 There are two types of
pumps generally used, axial
and centrifugal, with
centrifugal pumps being the
most common.

Silica gel breather
 When the temperature changes occur in
Transformer insulating oil, the oil
expands or contracts and there an
exchange of air also occurs when
transformer is fully loaded.
 When transformer gets cooled, the oil
level goes down and air gets absorbed
within.
 This process is called breathing and the
apparatus that pass through the air is
called breather.
 Actually, Silica gel breathers controls the
level of moisture, entering electrical
equipment during the change in volume
of the cooling medium and/or airspace
caused by temperature increasing.

Pressure relieve device
 Mechanical device for relief of excessive
pressure accumulation of large volumes of
gas or fluid in transformer.
 Gasket system provides quick response
time and automatically reseals after
pressure has subsided.
 Options include local operation indication,
contacts (switches) for operation alarming,
and directional shield for hot oil and gas
exhaust control

Conclusion
 In above presentation we discuss about Transformer types ,
their losses and methods to reduce them.
 The typical transformer has the efficiency of 80-90%.
 We conclude that Transformer can achieve the efficiency of
about 98-99% if the following things are applied
successfully:
 Cooling the transformer properly.
 Shredding of core must be greater.
 Permeability of core material would be higher.
 Resistance of windings must be lesser.
 Proper structure of transformer core.
 Primary and secondary windings must be interleaving.

References
 M. Pavlovsky, S.W.H. de Haan, J.A. Ferreira Delft University of
Technology Department of Electrical Power Processing
Mekelweg4, 2628CD Delft, The Netherlands
 http://www.edisontechcenter.org/Transformers.html
 http://www.electronics-tutorials.ws/transformer/transformer-
construction.html
 http://www.aast.edu/pheed/staffadminview/pdf_retreive.php?u
rl=45_16255_EE543_2015_1__1_1_week_10_11.pdf&stafftype=staffc
ourses
 https://www.electrical4u.com/silica-gel-breather/
 https://www.electrical4u.com/transformer-cooling-system-and-
methods/
 https://www.electrical4u.com/radiator-of-transformer-function-
of-radiator/

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