TRANSFORMER

1. Transformers & Accessories
Presentation On

2. Approach
 Need
 Introduction
 Types of Transformers
 Constructions forms
 Active parts/components of
Transformer
 Transformer Accessories

3. WHY TRANSFORMER
• TO OPTIMISE COST OF BULK TRANSMISSION
OF POWER FROM GENERATORS TO
CONSUMERS
• REDUCTION IN TRANSMISSION LOSS
• TO REDUCE OR INCREASE VOLTAGE IN AC
SYSTEM
• ENABLES SAFE SUPPLY VOLTAGE TO
CONSUMERS
• ISOLATION OF TWO SYSTEMS

4. Definition of Transformer
Need
Introduction
Types of Transformers
Constructions forms
Active parts/components of
Transformer
Transformer Accessories

5. IEC 60076-1
A static piece of apparatus with two or
more windings which are electrically isolated
but Magnetically coupled with a path of Low
reluctance for transferring power from one
circuit to other circuit with out change in
frequency.
It Can Raise or lower the voltage with
corresponding decrease or increase of current.
Being Static “No rotational loss & hence High
Efficiency “

6. Working Principle
If a time-varying voltage is applied to the primary
winding of turns, a current will flow in it producing a
magnetomotive force (MMF). Just as an electromotive
force (EMF) drives current around an electric circuit,
so MMF tries to drive magnetic flux through a
magnetic circuit.
The primary MMF produces a varying magnetic flux
in the core, and, with an open circuit secondary
winding, induces a back electromotive force (EMF). In
accordance with Faraday's law of induction, the voltage
induced across the primary winding is proportional to
the rate of change of flux:

7. Working Principle
Vp/Vs = Np/Ns
Where
• Vp and Vs are the voltages across the
primary winding and secondary winding.
• Np and Ns are the numbers of turns in the
primary winding and secondary winding.

10. Classifications
Transformers are adapted to numerous
engineering applications and may be
classified in many ways:
• By power level:
(From fraction of a volt-ampere(VA) to over
a thousand MVA),
• By application:
(Power supply, impedance matching, circuit
isolation),
• By frequency range:
(Power, audio, radio frequency(RF))
• By voltage class:
(A few volts to about 765 kilovolts)

11. Classifications
• Isolating
• Intended to transform from one voltage to
the same voltage. The two coils have
approximately equal numbers of turns,
although often there is a slight difference in
the number of turns, in order to compensate
for losses (otherwise the output voltage
would be a little less than, rather than the
same as, the input voltage).
• Variable
• The primary and secondary have an
adjustable number of turns which can be
selected without reconnecting the
transformer.

12. Basic Components of a
Transformer
Current conductors – Primary &
Secondary Windings
•Magnetic flux conductor - Laminated
Steel Core
and
Insulation :
•Cooling
•Protection
•Supporting accessories

13. COMPONENTS - CORE
Core
The “conductor” for the flux
 The skeleton for mechanical rigidity of
the active part .
 The core, an unbroken path for magnetic
flux
CRGO or Cold Rolled Grain Oriented Steel
is available in various grades

14. Types
The transformers are of two
general types distinguished from
each other by the manner in
which the primary and secondary
coils are placed around the
laminated steel core. They are
(a) shell type and
(b) core type.

16. Transformer Construction

17. CORE Type Transformer

18. SHELL Type Transformer

19. Transformer Insulation
Minor insulation Like inter turn insulation,
is achieved using cellulosic paper.
Major insulation Between primary and
secondary, phase to phase and inner coil
to core. This is achieved by Bakelite,
wooden blocks, cellulosic paper
cylinders.
Transformer Oil: derivative or petroleum
crude. This has good dielectric strength.
also a good cooling medium and absorbs
heat from the windings in transformer.

20. Transformer Oil
• NAPTHANIC BASE OILS GENERALLY HAVE
HIGHER RESISTIVITY VALUES WHEN
COMPARED TO PARAFFINIC BASE OILS AND
HAVE BETTER OXIDATION STABILITY.
• EQUALLY GOOD PARAMETERS CAN BE
ACHIEVED WITH PARAFFINIC BASE OILS
ALSO, WHEN PROPERLY REFINED.
• OIL PARAMETERS ARE IMPORTANT. BASE
OF OIL IS NOT IMPORTANT(NONE OF THE
STANDARDS SPECIFY THE BASE OF OIL).

21. Transformer Insulation
–Thus mineral oil has a flash point of
140°C and 160°C fire point. This also
'can Sustain the combustion with its
own energy, once it catches fire. Thus
this is unsuitable for the transformer
located indoors.
–The indoor transformers are filled
with a synthetic liquid known as
silicate liquid. This is fire assistant and
has flash point well above 300°C.

22. Accessories & Auxiliaries
• Tank ( Low carbon Steel)
• Radiators
• cooling fans, oil pumps, oil to water heat exchangers
(Cooling ONAN / ONAF/ OFAF/ OFWF external
coolers)
• Bushings
• Buchholz Relay/Oil Surge Relay
• Temperature Indicators- WTI , OTI
• Oil Level Indicators
• Pressure Relief Device
• Marshalling Box/Control cubicle
• Oil Preservation Systems: Conservators (gas sealed,
Bellows/membrane sealed) Breathers

24. Buchholz Relay

25. RADIATORS

26. Buchholz's Relay
• This has two Floats, one of them with surge catching baffle and
gas collecting space at top. This is mounted in the connecting
pipe line between conservator and main tank. This is the most
dependable protection for a given transformer.
• Gas evolution at a slow rate, that is associated with minor faults
inside the transformers gives rise to the operation of top float
whose contacts are wired for alarm. There is a glass window with
marking to read the volume of gas collected in the relay. Any
major fault in transformer creates a surge and the surge element
in the relay trips the transformer. size of the relay varies with oil
volume in the transformer and the mounting angle also is
specified for proper operation of the relay.

27. BUCHHOLZ PROTECTION
• Alarm element Operates When a specified volume of gas
gets collected in Chamber during
Broken down core bolt insulation
 Shorted Laminations
 Bad Contacts
 Overheating of winding parts
• Trip element Operates by Oil surge in the event of serious
fault
– Short Circuit between Winding Phases or
within Windings
– Puncture of Bushing

29. Conservator
• Conservator With the variation of
temperature there is corresponding
variation in the oil volume. To account for
this, an expansion vessel called
conservator is added to the transformer
with a connecting pipe to the main tank.
In smaller transformers this vessel is
open to atmosphere through dehydrating
breathers (to keep the air dry). In larger
transformers, an air bag is mounted inside the
conservator with the inside of bag open to
atmosphere through the breathers and the
outside surface of the bag in contact with the
oil surface.

30. Location of Buchholz Relay

31. Breather
Both transformer oil and cellulosic paper are
highly hygroscopic. Paper being more
hygroscopic than the mineral oil The
moisture, if not excluded from the oil surface
in conservator, thus will find its way finally
into the paper insulation and causes
reduction insulation strength of transformer.
To minimize this the conservator is allowed
to breathe only through the silica gel
column, which absorbs the moisture in air
before it enters the-conservator air surface.

32. SILICAGEL BREATHER

33. Temperature Indicator

34. Pressure Relief Device/Expansion vent
The pressure relief device allows for
the rapid release of excessive
pressure that may be generated in
the event of a serious fault
A pressure relief device is a spring
loaded device which provides rapid
amplification of its actuating force

35. Pressure Relief Device( PRD)

36. Magnet Oil Level Guage
Magnetic oil level gauge is fitted on
the main conservator which can give
alarm in the event of the oil level
falling below the pre-set levels due
to any reason.