2. CONSTRUCTION OF
TRANSFORMER :
The Transformer mainly consist of Core and Windings
(Coils).
With Increase in the Capacity, it also need other parts such
as –
1.Transformer Tank
2.Terminal Bushings
3. Conservator
4. Breather
5. Explosion Vent
6. Buchholz relay
4. Mangnetic Core may be either Square or Rectangular
in size
Vertical portion on which coils (windings) are wound is
called ‘Limb” while the top & bottom horizontal portion is
called ‘Roke’.
The core is made up of Laminations to minimize losses.
Generally L- shaped or I- shaped laminations are used
as shown in figure
6. 2. TYPES OF WINDINGS :-
As we disscussed earlier, the windings are
seperately wound on each Limbs.
In this method the losses are higher hence to
avoid this the two coils are wound on both the limits
adjecently, the structure is called “Cylindrical
concentric”.
7. SANDWICH COILS
The other type of coil which is very commonly
used is sandwich coils .
Each high voltage coil is lies between the two low
voltage coils i.e two low voltage coils sandwiching
the high voltage coil, it reduces leakage flux.
8. 3. TRANSFORMER TANK :-
In Large size transformer, while transformer
assembly is placed in Fabricated sheet metal tank
& immersed in oil .
Oil is used for insulation as well as cooling .
The heat generated in the winding & the core is
carried by the oil to the external surface of the tank.
9. 4. TERMINAL BUSHINGS :-
The leads of the transformer brought out from the
tank are insulated from it with the help of porcelain
bushings .
10. 5. CONSERVATOR :-
In transformer provision of some space above the oil
level is always essential to take up the expansion and
contraction of the oil with changes of temperature in
service .
When transformer becomes warm, the oil expands and
air at the top of the oil expelled .
When it cools, oil contracts and outside air is drawn into
the tansformer. This process is known as breathing of
transformer .
11. 6. BREATHER :-
the dispalcement of air above the oil level in the
conservator during the breathing process of the
transformer takes place through the aparatus known as
Breather.
It conatains a drying agent such as silica gel or calcium
chloride which extracts the moisture from the air.
The breather also cleans the air by removing the dust
particles present in it. Thus only dry & clean air is
allowed to come in contact with the oil in the tansformer.
12. 7. BUCHHOLZ REALY :-
It is a protective device mounted in the pipeline
connecting the main tank to the conservator.
Due to excessive heat developed during the fault
condition, the oil in the tank gets decompased &
different types of gases are liberated.
These gases operate the Buchholz realy which in the
initial condition gives alarm to the operator.
If fault is severe then this relay trips off the main circuit
breaker .
13. EXPLOSION VENT :-
It is the bent up pipe fitted on the upper surface of the
tank is known as explsion vent or relief valve.
It provided with a diaphragm made out of glass sheet,
aluminium foil or a bakelite sheet.
In the event of the fault conditon, it the exessive
pressure is developed inside the tank due to liberated
gases, the diaphrag in the explosion vent bursts and
releases the pressure, thus avoiding damage to the
transformer.
14. WORKING PRINCIPLE OF 1
PHASE TANSFORMER
Transformer is static device which transforms electrical
power from one circuit to another circuit with desire
change in volatage and current and without change in
the frequency also there is no any electrical connection
between two circuits.
Transformer works on the principle fo Mutual Induction
i.e when two coils is changed uniformely the an emf gets
induced in the other coil, this e.m.f can drive a current, if
closed path is provided .
15. Any one of the two coils is connected to a source
of alternating voltage & the other coil (winding) is
connected to load.
i. The winding which is connected to
source(supply) is called primary winding (p)
ii. The winding which is connected to load is called
secondary winding(s).
17. When A.C (alternating) voltage or supply is given to the primary
winding, it circulates a current which produces an alternating
flux(Ø) which completes its path through common magnetic iron.
This flux links with the secondary windings(s) as flux is
alternating, according to Faradays law of electromagnetic
induction, mutually induced emf gets developed in the secondary
winding .
Now if load is connected to secondary winding this e.m.f drives a
current through it.
Hence without any electrical cotact between the two windigs an
electrical energy gets transferred from primary winding to the
secondary winding.
