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distribution substations. However, this reference didn%t take the operation modes of
several transformers in a substation into account.
!& a result, combining distribution network load distribution with the
transformer operation mode is of feasibility and necessary. 'istribution network
load distribution strategy considering the economy of parallel transformers is put
forward in this paper. $t is emphasi#ed that the ob(ect of study are all double
winding transformer.
! distribution network load distribution model is proposed which takes
distribution network reliability, transformer economic operation and load balancing
as the ob(ect function. E)pected energy not supplied *EE&+, comprehensive
power loss of transformer and the ma)imum difference among the load factor are
regarded as the evaluation indicators of distribution network reliability, transformer
economic operation and load balancing, respectively.
1.2 LITERATURE SURVEY
• Haibo iu, heng)iong Mao, iming u, 'an Wang in their paper
/0arallel operation of electronic power transformer based on distributed
logic control1 proposed that an ac2dc hybrid parallel operation control
scheme of E0T based on distributed logic control is proposed in order to
eliminate circulation current and further improve redundancy performance in
this paper. The proposed ac2dc hybrid parallel operation control scheme
consists of a dc side current-sharing control scheme and an ac side current-
sharing control scheme. The reali#ation of current-sharing no matter in theac side or in the dc side is based upon instantaneous average current method.
'etailed computer simulations based on M!T!32&$M4$5 for the two
E0Ts parallel operation is conducted, and this parallel system is also
implemented in laboratory based on '&0 TM&67897:;7. &imulation results
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and e)perimental results show that the proposed control scheme has good
current-sharing performance under both steady-state and dynamic operation.
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9ig ;.; oss profile of a =>5?! Transformer
1.3.2 LOAD LOSS
!ssociated with the full load current flow in the transformer windings and
varies with the s"uare of the load current *$7A+.!long with it there is linear loss
which is due to the temperature rise in the windings.
9ig ;.7 inear oss of a =>5?! Transformer
These losses are directly proportional to the rating of the transformers that is
when the transformer rating increases these losses value will also increase.
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1.4 PROPOSED SYSTEM
$n the proposed system we are splitting the transformer rating i.e. we are
using two small transformers instead of a single high rated transformer. Then we
are sensing the load current and switching the transformer according to the load
re"uirement. 'uring the lighter load conditions both the transformers are not
employed instead we are using anyone transformer that is most suitable for the
load. &o the losses are minimi#ed and the efficiency, reliability of the transformers
are improved and thus improving the whole systems efficiency.
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CHAPTER 2
BLOCK DIAGRAM
Fig 2.1 Block diagram of the Load optimization by implementing
embedded system in parallel operated transformers
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The block diagram consists of Transformers, Aelays, Microcontroller
*0$;B9::=+, ' 'isplay, urrent &ensor and oad.
When we switch C the power supply the Microcontroller starts it
functions. $nitially the Transformer *T;+ is connected to the bus and driving the
load the urrent &ensor senses the load current and produces proportional voltage
to the current in the circuit and gives it to the Microcontroller. 'epending upon the
load current the Microcontroller switches the Transformers i.e. connects or
disconnect the Transformers to the bus using Aelays.
$f the load current is minimum the Microcontroller connects Transformer
*T;+ alone to the bus so that it get energi#es and drive the load. &uppose if the load
increases then the Microcontroller connects Transformer *T7+ to the bus along with
Transformer *T;+ so that both the Transformers get energi#es and drives the load.
$n addition to that the Microcontroller disconnects both the transformers from the
bus and the load when over current occurs.
The Microcontroller shows the load current value and the status of the
Transformers in an ' 'isplay.
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CHAPTER 3
OVERALL CIRCUIT DIAGRAM
!
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Fig 3.1 "irc#it diagram of the Load optimization by implementing
embedded system in parallel operated transformers
3.1 CIRCUIT DIAGRAM DESCRIPTION.
3.1.1 POWER SUPPLY
$he main f#nction of a po%er so#rce is to con&ert the '"
&oltage to (" &oltage at the re)#ired le&el. *ince all electronic
circ#its %orks only %ith lo% (" &oltage %e need a po%er so#rce
#nit to pro&ide the appropriate &oltage s#pply.' +5, (" s#pply is
re)#ired for microcontroller- L"( /(0L- L(s #sed in thisproect and +12, (" &oltage is re)#ired for the 12, L'*.
3.1.2 TRANSFORMER
!n isolation transformer is employed to step down the voltage from !
mains re"uired level of smaller ! voltage. The transformer rating used here is
768? D*;7-8-;7+? and operates at the fre"uency of >8H#. The secondary of the
transformer is connected to the rectifier block.
3.1.3 RECTIFIER
$t is a circuit which converts ! voltage into the pulsating ' voltage. Here
bridge rectifier is used which consists of diodes, that converts ;7? ! voltage
from the output of transformer is converted to ;7? ' voltage.
3.1.4 FILTER
$he rectied (" &oltage consists of ripple and 7#ct#ations. '
capacitor lter of 1888#F is employed to remo&e the ripple from
the (" o#tp#t of the bridge rectier. $he property of a capacitor is
allo%(" component and the blocks the '" component.
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3.1.5 REGULATOR
$he reg#lator is a de&ice %hich maintains the terminal
&oltage constant e&en if the inp#t &oltage or load c#rrent &aries.
'n :"!85- :"!12 ;ed &oltage reg#lators are #sed in this circ#it.
$he f#nction of thesereg#lator is to pro&ide a +5, -+12, constant
(" s#pply- e&en there are 7#ct#ation in the reg#lator inp#t. $his
reg#lator helps to maintain a constant &oltage thro#gho#t the
circ#it operation.
3.1.6 DARLINGTON DRIVER
The output of the microcontroller is F>?.3ut there will be a situation where
we need to drive ;7v relays. These 'arlington drivers are open collector they
can sink current, but they cannot sourcecurrent. They are used as a ground-side
switch for all kinds of things very popular with hobbyists to control stepper motors
and relays basically, higher current loads than standard TT levels support. Here
we have used 47:86 which consists of : channel darlington array
Fig 3.2
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3.1.7CURRENT SENSOR
This is a device that detects electric ! or ' current flowing in a
conductor and gives out a corresponding signal *analogue voltage2current2digital
pulse+. The detected signal can be used for various purposes like measuring the
amount of current in the conductor, controlling of another device etc.
The !llegro !&=;7ETA-68!-T has a low-offset linear Hall sensor
circuit that has a conduction path made of copper located ne)t to the die. !
magnetic field is caused by the current flowing through the copper conductor. This
magnetic field is detected by the integrated Hall $ which converts it into a voltage
proportional to the magnetic flu). ! current of ;! flowing in a conductor produces
BBm?. The close pro)imity of the magnetic signal to the Hall transducer optimi#es
the device accuracy. To attain precision, in terms of voltage produced, a low-offset,
chopper-stabili#ed 3i-MC& Hall $ is used.
Fig 3.3
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elay is a component- %hich allo%s a lo% po%er circ#it to
s%itch a relati&ely high c#rrent on and o>- or to control signals
that m#st be electrically isolated from the controlling circ#it itself.
elays are composed of a coil of %ire aro#nd a steel core- a s%itch
and a spring that holds one or more contacts.
?hen an electrical c#rrent 7o%s thro#gh the coil it gets
energized- acting like an electromagnet. $he ref#se eld opens
the contacts and also closes the circ#it. ?hen the electrical
c#rrent stops 7o%ing- the opposite occ#rs.
Fig 3.4 *chematic of elay
3.1.10 LCD MODULE
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Fig 3.5 L"( mod#le %ith
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CHAPTER 4
MICROCONTROLLER
4.1 INTRODUCTION
! microcontroller *sometimes abbreviated J, u or M4+ is a small computer on
a single integrated circuit containing a processor core, memory, and programmable
input2output peripherals. 0rogram memory in the form of CA flash or CT0ACM
is also often included on chip, as well as a typically small amount of A!M.
4.2 PIC16F887 INTRODUCTION
Microcontroller PIC16F887 is one of the 0$Micro 9amily microcontroller
which is popular at this moment, start from beginner until all professionals.
3ecause very easy using PIC16F887 and use 9!&H memory technology so that
can be write-erase until thousand times.
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The superiority this A$& Microcontroller compared to with other
microcontroller :-bit especially at a speed of and his code compression.
PIC16F887 have 8 pin by 66 path of $2C.
PIC16F887 perfectly fits many uses, from automotive industries and
controlling home appliances to industrial instruments, remote sensors, electrical
door locks and safety devices. $t is also ideal for smart cards as well as for battery
supplied devices because of its low consumption.
EE0ACM memory makes it easier to apply microcontrollers to devices
where permanent storage of various parameters is needed *codes for transmitters,
motor speed, receiver fre"uencies, etc.+.
ow cost, low consumption, easy handling and fle)ibility make PIC16F887
applicable even in areas where microcontrollers had not previously been
considered *e)ampleG timer functions, interface replacement in larger systems,
coprocessor applications, etc.+.
$n &ystem 0rogrammability of this chip *along with using only two pins in
data transfer+ makes possible the fle)ibility of a product, after assembling and
testing have been completed.
This capability can be used to create assembly-line production, to store
calibration data available only after final testing, or it can be used to improve
programs on finished products.
04 is not different from other microcontrollers 04. 0$ microcontroller
04 consists of !rithmetic logic unit *!4+, memory unit *M4+, control unit
*4+, !ccumulator etc. we know that !4 mainly used for arithmetic operations
and taking the logical decisions, memory used for storing the instruction which is
to processed and also storing the instructions after processing, ontrol unit is used
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for controlling the all the peripherals which are connected to the 04 both internal
peripherals and e)ternal peripherals. !ccumulator is used for storing the results
and used for further processing. !s $ said earlier 0$ micro controller supports the
A$& architecture that is reduced instruction set computer
!4.3 ARCHITECTURE OF PIC16F887
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9ig .; !rchitecture of 0$;B9::=
4.3.1 M"#$%&
1
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This microcontroller has three types of memory- ACM, A!M and
EE0ACM. !ll of them will be separately discussed since each has specific
functions, features and organi#ation.
4.3.1.1 ROM M"#$%&
ACM memory is used to permanently save the program being e)ecuted. This
is why it is often called /program memory1. The 0$;B9::= has :5b of ACM *in
total of :;K7 locations+. &ince this ACM is made with 9!&H technology, its
contents can be changed by providing a special programming voltage *;6?+.
!nyway, there is no need to e)plain it in detail because it is automatically
performed by means of a special program on the 0 and a simple electronic device
called the 0rogrammer.
4.3.1.2 EEPROM M"#$%&
&imilar to program memory, the contents of EE0ACM is permanently saved,
even the power goes off. However, unlike ACM, the contents of the EE0ACM can
be changed during operation of the microcontroller. That is why this memory *7>B
locations+ is a perfect one for permanently saving results created and used during
the operation.
4.3.1.3 RAM M"#$%&
This is the third and the most comple) part of microcontroller memory. $n
this case, it consists of two partsG general-purpose registers and special-function
registers *&9A+.Even though both groups of registers are cleared when power goes
off and even though they are manufactured in the same way and act in the similar
way, their functions do not have many things in common.
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4.3.2 G"'"%()P*%+$," R"-,/"%,
Leneral-0urpose registers are used for storing temporary data and results
created during operation. 9or e)ample, if the program performs a counting *for
e)ample, counting products on the assembly line+, it is necessary to have a register
which stands for what we in everyday life call /sum1.
&ince the microcontroller is not creative at all, it is necessary to specify the
address of some general purpose register and assign it a new function. ! simple
program to increment the value of this register by ;, after each product passes
through a sensor, should be created.
Therefore, the microcontroller can e)ecute that program because it now
knows what and where the sum which must be incremented is. &imilarly to this
simple e)ample, each program variable must be pre assigned some of general-
purpose register.
4.3.3 SFR R"-,/"%,
&pecial-9unction registers are also A!M memory locations, but unlike
general-purpose registers, their purpose is predetermined during manufacturing
process and cannot be changed. &ince their bits are physically connected to
particular circuits on the chip *!2' converter, serial communication module, etc.+,
any change of their contents directly affects the operation of the microcontroller or
some of its circuits.
9or e)ample, by changing the TA$&! register, the function of each port !
pin can be changed in a way it acts as input or output. !nother feature of these
memory locations is that they have their names *registers and their bits+, which
considerably facilitates program writing. &ince high-level programming language
can use the list of all registers with their e)act addresses, it is enough to specify the
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register@s name in order to read or change its contents.
4.3.4 RAM M"#$%& B('0,
The data memory is partitioned into four banks. 0rior to accessing some
register during program writing *in order to read or change its contents+, it is
necessary to select the bank which contains that register. Two bits of the &T!T4&
register are used for bank selecting, which will be discussed later. $n order to
facilitate operation, the most commonly used &9As have the same address in all
banks which enables them to be easily accessed.
4.3. STACK
! part of the A!M used for the stack consists of eight ;6-bit registers.
3efore the microcontroller starts to e)ecute a subroutine *! instruction+ or
when an interrupt occurs, the address of first ne)t instruction being currently
e)ecuted is pushed onto the stack, i.e. onto one of its registers.
$n that way, upon subroutine or interrupt e)ecution, the microcontroller
knows from where to continue regular program e)ecution. This address is cleared
upon return to the main program because there is no need to save it any longer, and
one location of the stack is automatically available for further use.
$t is important to understand that data is always circularly pushed onto the
stack. $t means that after the stack has been pushed eight times, the ninth push
overwrites the value that was stored with the first push. The tenth push overwrites
the second push and so on. 'ata overwritten in this way is not recoverable. $n
addition, the programmer cannot access these registers for write or read and there
is no &tatus bit to indicate stack overflow or stack underflow conditions. 9or that
reason, one should take special care of it during program writing.
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4.3.6 I'/"%%*+/ S&,/"#
The first thing that the microcontroller does when an interrupt re"uest
arrives is to e)ecute the current instruction and then stop regular program
e)ecution. $mmediately after that, the current program memory address is
automatically pushed onto the stack and the default address *predefined by the
manufacturer+ is written to the program counter.That location from where the
program continues e)ecution is called the interrupt vector. 9or the 0$;B9::=
microcontroller, this address is 888h. !s seen in 9ig. ;-= below, the location
containing interrupt vector is passed over during regular program e)ecution. 0art
of the program being activated when an interrupt re"uest arrives is called the
interrupt routine. $ts first instruction is located at the interrupt vector.
How long this subroutine will be and what it will be like depends on the
skills of the programmer as well as the interrupt source itself. &ome
microcontrollers have more interrupt vectors *every interrupt re"uest has its
vector+, but in this case there is only one. onse"uently, the first part of the
interrupt routine consists in interrupt source recognition. 9inally, when theinterrupt source is recogni#ed and interrupt routine is e)ecuted, the microcontroller
reaches the AET9$E instruction, pops the address from the stack and continues
program e)ecution from where it left off.
4.4 PIN DIAGRAM
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9ig .7 0in diagram of 0$;B9::=
4. FEATURES OF PIC16F887
The 0$;B9::=! is one of the latest products from Microchip. $t features all
the components which modern microcontrollers normally have. 9or its low price,
wide range of application, high "uality and easy availability, it is an ideal solution
in applications such asG the control of different processes in industry, machine
control devices, measurement of different values etc. &ome of its main features are
listed below.
• A$& architecture
Cnly 6> instructions to learn
!ll single-cycle instructions e)cept branches
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• Cperating fre"uency ;;.8>K7 MH#
• 0recision internal oscillator
9actory calibrated
&oftware selectable fre"uency range of :MH# to 6;5H#
• 0ower supply voltage 7.8->.>?
onsumptionG 778u! *7.8?, MH#+, ;;u! *7.8 ?, 67 5H#+ >8n!
*stand-by mode+
• 0ower-&aving &leep Mode
• 3rown-out Aeset *3CA+ with software control option
• 6> input2output pins
High current source2sink for direct E' drive
software and individually programmable pull-up resistor
$nterrupt-on-hange pin
• :5 ACM memory in 9!&H technology
hip can be reprogrammed up to ;88,888 times
• $n-ircuit &erial 0rogramming Cption
hip can be programmed even embedded in the target device
• 7>B bytes EE0ACM memory
'ata can be written more than ;,888,888 times
• 6B: bytes A!M memory
• !2' converter
;-channels
;8-bit resolution
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• 6 independent timers2counters
• Watch-dog timer
• !nalogue comparator module with
Two analogue comparators
9i)ed voltage reference *8.B?+
0rogrammable on-chip voltage reference
• 0WM output steering control
• Enhanced 4&!AT module
&upports A&-:>, A&-767 and $7.8
!uto-3aud 'etect
• Master &ynchronous &erial 0ort *M&&0+
supports &0$ and $7 mode
4.6 LIST OF PORTS
T!3E .; 0$;B9::= 0CAT&
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4.7 PIN DESCRIPTION
T!3E .7*a+ 0$;B9::= 0$ 'E&A$0T$C
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T!3E .7*b+ 0$;B9::=0$ 'E&A$0T$C
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4.8 I'/"%'() P"%+"%(),
9ig .6 $nternal 0eripherals
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4. MEMORY ORGANIATION OF PIC16F887
9ig .
Memory
organi#ation of 0$;B9::=
2!
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CHAPTER
TRANSFORMER
.1 TRANSFORMER
! /%(',5$%#"% is an electrical device that transfers energy between two or
more circuits through electromagnetic induction. ! varying current in the
transformer%s primary winding creates a varying magnetic flu) in the core and a
varying magnetic field impinging on the secondary winding. This varying magnetic
field at the secondary induces a varying electromotive force *EM9+ or voltage in the
secondary winding. Making use of 9araday%s aw in con(unction with high magnetic
permeability core properties, transformers can thus be designed to efficiently
change ! voltages from one voltage level to another within power networks.
Transformers range in si#e from A9 transformers less than a cubic centimetre in
volume to units interconnecting the power grid weighing hundreds of tons and is
shown in 9ig.>.;
9ig.>.;. Transformer
.2.1 IDEAL TRANSFORMER
29
http://en.wikipedia.org/wiki/Electromagnetic_inductionhttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Electromotive_forcehttp://en.wikipedia.org/wiki/Faraday's_law_of_inductionhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/wiki/RFhttp://en.wikipedia.org/wiki/Power_gridhttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Electromotive_forcehttp://en.wikipedia.org/wiki/Faraday's_law_of_inductionhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/wiki/RFhttp://en.wikipedia.org/wiki/Power_gridhttp://en.wikipedia.org/wiki/Electromagnetic_induction
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$t is very common, for simplification or appro)imation purposes, to analy#e
the transformer as an ideal transformer model as represented in the two images. !n
ideal transformer is a theoretical, linear transformer that is lossless and perfectly
coupled that is, there are no energy losses and flu) is completely confined within
the magnetic core. 0erfect coupling implies infinitely high core magnetic
permeability and winding inductances and #ero net magneto motive force. ! varying
current in the transformer%s primary winding creates a varying magnetic flu) in the
core and a varying magnetic field impinging on the secondary winding. This varying
magnetic field at the secondary induces a varying electromotive force *EM9+ or
voltage in the secondary winding. The primary and secondary windings are wrapped
around a core of infinitely high magnetic permeability so that all of the magnetic flu)
passes through both the primary and secondary windings.
.2.2 REAL TRANSFORMER
The ideal transformer model neglects the following basic linear aspects in real
transformers.
• Hysteresis losses due to nonlinear application of the voltage applied in the
transformer core
• Eddy current losses due to (oule heating in the core that are proportional to
the s"uare of the transformer%s applied voltage.
• $n addition to this there will be copper loss.
• oule losses due to resistance in the primary and secondary windings
• eakage flu) that escapes from the core and passes through one winding
only resulting in primary and secondary reactive impedance.
38
http://en.wikipedia.org/wiki/Linearityhttp://en.wikipedia.org/wiki/Magnetic_couplinghttp://en.wikipedia.org/wiki/Transformer#Energy_Losseshttp://en.wikipedia.org/wiki/Fluxhttp://en.wikipedia.org/wiki/Magnetic_corehttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Magnetomotive_forcehttp://en.wikipedia.org/wiki/Electromotive_forcehttp://en.wikipedia.org/wiki/Magnetic_core#Core_losshttp://en.wikipedia.org/wiki/Magnetic_core#Core_losshttp://en.wikipedia.org/wiki/Joule_heatinghttp://en.wikipedia.org/wiki/Linearityhttp://en.wikipedia.org/wiki/Magnetic_couplinghttp://en.wikipedia.org/wiki/Transformer#Energy_Losseshttp://en.wikipedia.org/wiki/Fluxhttp://en.wikipedia.org/wiki/Magnetic_corehttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Magnetomotive_forcehttp://en.wikipedia.org/wiki/Electromotive_forcehttp://en.wikipedia.org/wiki/Magnetic_core#Core_losshttp://en.wikipedia.org/wiki/Magnetic_core#Core_losshttp://en.wikipedia.org/wiki/Joule_heating
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.2.3 CORE AND SHELL FORM OF TRANSFORMERS
losed-core transformers are constructed in %core form% or %shell form%. When
windings surround the core, the transformer is core form when windings are
surrounded by the core, the transformer is shell form. &hell form design may be more
prevalent than core form design for distribution transformer applications due to the
relative ease in stacking the core around winding coils. ore form design tends to, as
a general rule, be more economical, and therefore more prevalent, than shell form
design for high voltage power transformer applications at the lower end of theirvoltage and power rating ranges *less than or e"ual to, nominally, 768 k? or
=> M?!+. !t higher voltage and power ratings, shell form transformers tend to be
more prevalent. &hell form design tends to be preferred for e)tra-high voltage and
higher M?! applications because, though more labor-intensive to manufacture, shell
form transformers are characteri#ed as having inherently better k?!-to-weight ratio,
better short-circuit strength characteristics and higher immunity to transit damage.
.2.4 INDING
The conducting material used for the windings depends upon the application,
but in all cases the individual turns must be electrically insulated from each other to
ensure that the current travels throughout every turn. 9or small power and signal
transformers, in which currents are low and the potential difference between ad(acent
turns is small, the coils are often wound from enameled magnet wire, such as t wire.arger power transformers operating at high voltages may be wound with copper
rectangular strip conductors insulated by oil-impregnated paper and blocks
of pressboard is shown in 9ig.>.7.
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9ig.>.7. Winding
.2. COOLING
To place the cooling problem in perspective, the accepted rule of thumb is that
the life e)pectancy of insulation in all electric machines including all transformers is
halved for about every = to ;8 increase in operating temperature, this life
e)pectancy halving rule holding more narrowly when the increase is between about
= to : in the case of transformer winding cellulose insulation. &mall dry-type
and li"uid-immersed transformers are often self-cooled by natural convection
and radiation heat dissipation. !s power ratings increase, transformers are often
cooled by forced-air cooling, forced-oil cooling, water-cooling, or combinations of
these. arge transformers are filled with transformer oil that both cools and insulates
the windings.
.3 TYPES OF TRANSFORMER
• !utotransformer G Transformer in which part of the winding is common to
both primary and secondary circuits.
• apacitor voltage transformer G Transformer in which capacitor divider is
used to reduce high voltage before application to the primary winding.
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• 'istribution transformer, power transformer G $nternational standards make a
distinction in terms of distribution transformers being used to distribute
energy from transmission lines and networks for local consumption and
power transformers being used to transfer electric energy between the
generator and distribution primary circuits.
• 0hase angle regulating transformer G ! speciali#ed transformer used to
control the flow of real power on three-phase electricity transmission
networks.
• &cott-T transformer G Transformer used for phase transformation from three-
phase to two-phase and vice versa.
• 0olyphase transformer G !ny transformer with more than one phase.
• Lrounding transformerG Transformer used for grounding three-phase circuits
to create a neutral in a three wire system, using a wye-delta transformer or
more commonly, a #ig#ag grounding winding.
• eakage transformer G Transformer that has loosely coupled windings.
• Aesonant transformer G Transformer that uses resonance to generate a high
secondary voltage.
•!udio transformer G Transformer used in audio e"uipment.
• Cutput transformer G Transformer used to match the output of a valve
amplifier to its load.
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• $nstrument transformer G 0otential or current transformer used to accurately
and safely represent voltage, current or phase position of high voltage or
high power circuits.
.4 LOSSES IN TRANSFORMER
!n ideal transformer is the one which is ;88N efficient. This means that the
power supplied at the input terminal should be e)actly e"ual to the power supplied
at the output terminal, since efficiency can only be ;88N if the output power is
e"ual to the input power with #ero energy losses. 3ut in reality, nothing in this
universe is ever ideal. &imilarly, since the output power of a transformer is never
e)actly e"ual to the input power, due a number of electrical losses inside the core
and windings of the transformer, so we never get to see a ;88N efficient
transformer. Transformer is a static device, i.e. we do not get to see any movements
in its parts, so no mechanical losses e)ist in the transformer and only electrical
losses are observed. &o there are two primary types of electrical losses in the
transformerG
1 opper losses
7 $ron losses
Cther than these, some small amount of power losses in the form of Ostray losses@
are also observed, which are produced due to the leakage of magnetic flu).
.4.1 COPPER LOSS
These losses occur in the windings of the transformer when heat is
dissipated due to the current passing through the windings and the internal
resistance offered by the windings. &o these are also known as ohmic losses or $7A
losses, where O$@ is the current passing through the windings and A is the internal
resistance of the windings.
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These losses are present both in the primary and secondary windings of the
transformer and depend upon the load attached across the secondary windings
since the current varies with the variation in the load, so these are variable losses.
Mathematically, these copper losses can be defined asG
0ohmic P $ pA p F $sA s
.4.2 IRON LOSS
These losses occur in the core of the transformer and are generated due to
the variations in the flu). These losses depend upon the magnetic properties of the
materials which are present in the core, so they are also known as iron losses, as
the core of the Transformer is made up of iron. !nd since they do not change like
the load, so these losses are also constant.
There are two types of $ron losses in the transformerG
1 Eddy urrent losses
7 Hysteresis oss
.4.2.1 EDDY CURRENT LOSS
When an alternating current is supplied to the primary windings of the
transformer, it generates an alternating magnetic flu) in the winding which is then
induced in the secondary winding also through 9araday@s law of electromagnetic
induction, and is then transferred to the e)ternally connected load. 'uring this
process, the other conduction materials of which the core is composed of also gets
linked with this flu) and an emf is induced.
3ut this magnetic flu) does not contribute anything towards the e)ternally
connected load or the output power and is dissipated in the form of heat energy. &o
such losses are called Eddy urrent losses and are mathematically e)pressed asG
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0e P 5 e fQ 5 f Q 3mQ
Where
•
5 e P onstant of Eddy urrent
• 5 f Q P 9orm onstant
• 3m P &trength of Magnetic 9ield
.4.2.2 HYSTERESIS LOSS
Hysteresis loss is defined as the electrical energy which is re"uired to realign
the domains of the ferromagnetic material which is present in the core of the
transformer.
These domains lose their alignment when an alternating current is supplied
to the primary windings of the transformer and the emf is induced in the
ferromagnetic material of the core which disturbs the alignment of the domains and
afterwards they do not realign properly. 9or their proper realignment, some
e)ternal energy supply, usually in the form of current is re"uired. This e)tra energy
is known as Hysteresis loss.
Mathematically, they can be defined as
R0h P 5 h 3m;.B f?
These are the different kinds of losses happened to occur in transformer and
an electrical engineer must take care of their losses and try to reduce them as low
as possible.
Transformer has two states of operations, one is without load and the other is
with load. Most of these errors appear when the load is applied on the transformer.
&o it is essential to read the behaviour of transformer when load is applied on it,
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