A transformer is a static device that changes alternating current (AC) electrical power at one voltage level to another voltage level through magnetic induction. It does this without changing the frequency, and can either step up or step down the voltage. Transformers work based on mutual inductance between two inductively coupled coils. Transformers can be classified based on their core type, cooling system, number of phases, and whether they are ideal or practical. The main types are core type, shell type, air cooled, oil cooled, single phase, and three phase transformers.

1. BY
D.RAJESHWARI
147Q1A0213

2. DEFINITION
A transformer is a static device.
 The word ‘transformer’ comes form the word
‘transform’.
Transformer is not an energy conversion device, but it
is device that changes AC electrical power at one
voltage level into AC electrical power at another
voltage level through the action of magnetic field but
with a proportional increase or decrease in the current
ratings., without a change in frequency.
It can be either to step-up or step down

3. WORKING
 The main principle of operation of a transformer is mutual inductance
between two circuits which is linked by a common magnetic flux. A
basic transformer consists of two coils that are electrically separate and
inductive, but are magnetically linked through a path of reluctance.
The working principle of the transformer can be understood from the
figure below

4. CLASSIFICATION OF
TRANFORMER
single phase
As per phase
Three phase
Core type
As per core
Shell type
Self-cooled
As per cooling system Air cooled
Oil cooled

5. TRANSFORMER CLASSIFIED AS PER CORE
 CORE TYPE TRONSFORMER
 The general arrangement of the core-type transformer with
respect to the core is shown below. Both low-voltage (LV) and high
voltage (HV) windings are shown.

6. The low voltage windings are placed nearer to the core as it is the easiest
to insulate. The effective core area of the transformer can be reduced with
the use of laminations and insulation

7.  SHELL TYPE TRONSFORMER
 In shell-type transformers the core surrounds a considerable portion
of the windings. The comparison is shown in the figure below.
 The coils are form-wound but are multi layer disc type usually wound
in the form of pancakes. Paper is used to insulate the different layers of
the multi-layer discs. The whole winding consists of discs stacked with
insulation spaces between the coils.

8. A strong rigid mechanical bracing must be given to the cores and coils of the
transformers. This will help in minimizing the movement of the device and also
prevents the device from getting any insulation damage. A transformer with
good bracing will not produce any humming noise during its working and will
also reduce vibration

9. CLASSIFICATION ON THE BASIS OF
COOLING EMPLOYED
OIL FILLED SELF-COOLED TYPE
 Oil filled self cooled type uses small and medium-sized
distribution transformers. The assembled windings and core of
such transformers are mounted in a welded, oil-tight steel tanks
provided with a steel cover. The tank is filled with purified, high
quality insulating oil as soon as the core is put back at its proper
place.
OIL FILLED WATER-COOLED TYPE
 This type is used for much more economic construction of large
transformers, as the above told self cooled method is very
expensive. The same method is used here as well- the windings and
the core are immersed in the oil.
AIR BLAST TYPE
 This type is used for transformers that use voltages below 25,000
volts. The transformer is housed in a thin sheet metal box open at
both ends through which air is blown from the bottom to the top

10. Transformer classified as per Phase
 SINGLE PHASE TRONSFORMER
 A single phase transformer two or more winding , coupled
by a common magnetic core.

11.  THREE PHASE TRONSFORMER
 Since each single-phase transformer has a primary and a secondary
winding, then 3 single-phase transformers will have the required 3
primary and 3 secondary windings and can be connected in the field
either Delta-Delta or Delta-Wye to achieve the required three-phased
transformer bank

12.  IDEAL TRONSFORMER
 An ideal transformer is a transformer which has no loses, i.e. it’s
winding has no ohmic resistance, no magnetic leakage, and therefore
no I2R and core loses.
 However, it is impossible to realizesuch a transformerin practice.
 Yet, the approximate characteristic of ideal transformer will be used in
characterized the practical transformer