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1. CURRENT TRANSFORMER AND POTENTIAL
TRANSFORMER
 Current transformers, together with potential
transformers (PT) are known as instrument
transformers.
 When current in a circuit is too high to directly apply
to measuring instruments, a current transformer
produces a reduced current accurately proportional to
the current in the circuit, which can be conveniently
connected to measuring and recording instruments.
 Potential Transformer or Voltage Transformers are
used in electrical power system for stepping down the
system voltage to a safe value which can be fed to low
ratings meters and relays. Commercially available
relays and meters used for protection and metering,
are designed for low voltage.

2. ELECTRIC POWER PATH THROUGH A
TYPICAL SUB-STATION

3.  Main Components of Transformer
are:
 Magnetic core
 Primary and secondary windings
 Insulation of windings
 Expansion tank or conservator
 Tank, oil, cooling arrangement, temperature gauge, oil gauge
 Buchholz relay
 Silica gel breather

4. 1) MAGNETIC CORE
 Magnetic core consists of an iron core. The core is laminated and made of
silicon steel.
 Thickness varies from 0.35 mm to 0.5 mm.
 Laminations are insulated from each other by coating then with a thin coat of
varnish.
 Various types of stampings and laminations employed in the construction of
transformers.
There are two types of transformer cores, they are
A) Shell type B) Core type
Shell type – Two windings are carried by central limb. Core is made up of E and I
stampings and has three limbs. Has two parallel paths for magnetic flux.
Core type – Has two limbs for two windings and is made up of two L-type
stampings. Has only one magnetic path.

5. 2) WINDING
 There are two windings in a transformer
 They are primary and secondary windings.
 Made up of copper.
3) INSULATING OIL
 The coil used in transformer protects the paper from dirt and moisture and
removes the heat produced in the core and coils.
 It also acts as insulating medium.
 Oil must possess following properties:
 High dielectric strength
 Free from inorganic acid, alkali and corrosive Sulphur.
 Low viscosity to provide good heat transfer.
 Good resistance to emulsion so that the oil may throw down any moisture
entering the tank instead of holding it.

6. TESTING IN TRANSFORMER
Testing
Indirect
Open
Circuit Test
Short
Circuit Test
Direct
Load Test

7. THANK YOU !