construction and working

1. TRANSFORMER
S

2. introduction
 A transformer is a static (or stationary) piece of
apparatus by means of which electric power in
one circuit is transformed into electric power of
the same frequency in another circuit.
 Works on the principle of mutual induction.

3. Types of transformers
 Core Type Transformer (for low voltage
applications)
 Shell Type Transformer(for High voltage
applications)
 Berry Type Transformer

4. Construction
 Core
 Windings
 Bushings
 Insulation

5. Core
 Square or rectangular in size
 Made up of sheet steal laminations assembled
(high permeability and low hysteresis loss).
 Core sheet dimensions [0.35mm to 0.5mm]
 Laminations in the form of long strips of L’s , I’s ,
E’s

6. Laminations
(Yoke)
Limbs(windin
gs)
Cor
e

7. windings
 Cylindrical type
 Sandwich type

8. Core Type Transformers
 Cylindrical wound type windings used
 Insulation may be mica , paper or cloth
 For Small size – rectangular core with rectangular
cylindrical coils
 For Large size – Square core with circular
cylindrical coils

9. Shell Type Transformers
 Sandwich or Multilayer disc type coils are used
 Windings consists of stacked disc with insulation
space between the coils
 Windings are placed in central limbs

10. Comparison
Core type Shell type
Winding encircles the core Core encircles most of the
winding.
Cylindrical type Multilayer type or
Sandwich Type
Natural Cooling is provided Natural Cooling not
possible. Cooling Fans are
used
Coils are easily removed
for maintenance
Coils are not easily
removed for maintenance
For Low Voltage
transformers
For High Voltage
transformers

11.  Transformer are housed in tightly fitted sheet metals.
 Oil are used as insulation. Its free from alkaline and
sulphur.
 Moisture presence which reduces dielectric strength
in oil.
 Breathers are used in large size transformers to relax
the oil inside the expand or contract bcoz of temp
increase or decrease.
 Transformer leads are brought out of their cases
through suitable bushings. (Porcelain , oil-filled and
capacitor type).
 Cooling methods