3. Working principle
Physical basis of a transformer is mutual induction
between two circuits linked by a common
magnetic flux.
If one coil is connected to a source of
alternating voltage, an alternating flux is set up in
the laminated core, most of which is linked with
the other coils in which it produces mutually
induced emf
4. A transformer is a static device which is used to step up
or step down voltages at constant frequency
It consists of two coils, that are electrically isolated but
magnetically linked
The primary coil is connected to the power source and
the secondary coil is connected to the load
Voltage is stepped up or stepped down proportional to
turns ratio
The turn’s ratio is the ratio between the number of
turns on the secondary (Ns)to the number of turns on
the primary (Np).
5. Turn’s Ratio = No. windings in Secondary
No. Windings in Primary
= Voltage in Secondary
Voltage in Primary
V s = N s
V p N p
6. Transformer classification
Based on construction
Core type
Shell type
Berry type
Based on application
Power transformer
Distribution transformer
Based on cooling
Oil filled self cooled
Oil fill water cooled
Air blast type
7.
8. Losses in a transformer
No load losses or core losses
Load losses or copper losses
9. No load losses
No load losses remains the same irrespective of the load
connected to the transformer
It is the power consumed to sustain the magnetic field in the transformer’s
core
It is of two types – hysteresis loss and eddy current loss
Hysteresis loss is the energy lost by reversing the magnetizng field in
the core as the AC changes direction in every cycle.
Eddy current loss is a result of induced currents circulating in the core
Hysteresis loss is minimized by using steel of high silicon content for
the core
Eddy current loss is minimized by using very thin laminations
polished with varnish
No load loss = IL( Va / Vr ) ²
10. Load losses
It is associated with load current flow in the transformer windings
Copper loss is power lost in the primary and secondary windings of
a transformer due to the ohmic resistance of the windings
load loss = I ² R
11. Problem
Find the total losses taking place in a 250 KVA
transformer operating at 60% of its rated capacity
whose No load loss = 500 W and
Full load loss = 4500 W
12. Problem
Transformer Rating 5 0 0 kVA, PF is 0 . 8, No
Load Loss =3.5 kW, Full Load Loss = 4 . 5 kW
No. of
hrs
Load kW PF
6 4 0 0 0 . 8
1 0 3 0 0 0 . 7 5
4 1 0 0 0 . 8
4 0 0
13. How to improve the efficiency of
transformer
By operating the transformer at optimum load
By operating the transformers in parallel
Voltage regulation of transformer
At optimum loading no load loss = Full load loss
Thus during max. efficiency no load loss = Full load loss
No Load Loss = 1600 W, Full Load Loss = 2 845 W
X = 100 √(No Load Loss/ Full Load Loss)
Load at max Eff = ( 1 6 0 0 / 2 8 4 5 ) 0 . 5
= 7 5 . 0 %
14. Parallel operation of transformer
This is done for fluctuating loads, so that the load
can be optimized by sharing the load between the
transformers
This way of operation provides high efficiency
For parallel operation, both the transformers
should be technically identical and should have
the same impedance level.
15. Problem
Power Required : 8 0 0 kVA
( 4 0 0 kVA x 2 )
No of Transformers : 2
Rated Capacity : 1 2 5 0 kVA each
No Load Loss : 2 k W
Load Loss : 1 5 k W
16. Transformer selection
Calculate the connected load and diversity factor
Multiply Diversity Factor with connected load
applicable to particular industry and arrive at
kVA rating of transformers
Diversity factor is the ratio of sum of individual
maximum demand of various equipment to the
overall maximum demand of the plant
It will be always greater than one
17. Voltage regulation
When the supply voltage changes, it causes tripping of
voltage sensitive load devices
The voltage regulation in transformers is done by
altering the voltage transformation ratio with the help
of tapping
There are two methods of tap changing facility
available
Off-circuit tap changer
On-load tap changer
18. System Distribution losses and
Optimization
Relocating transformers and substations near to the
load centres
Re-routing the feeders and cables, where the line
losses and voltage drops are higher
Power factor improvement by incorporating capacitors
at the load end.
Optimum loading of the transformers in the system
Opting for low resistance All Aluminium Alloy
Conductors (AAAC) instead of conventional
Aluminium Cored Steel Reinforced (ACSR) lines
19. Capacity
( kVA )
C o n v e n t i o n a l A m o r p h o u s
No Load
Loss
Copper a
Loss at
No Load
Loss
Copper
Loss at FL
W
1 0 0 2 6 0 1 7 6 0 6 0 1 6 3 5
2 5 0 6 0 0 3 6 0 0 1 6 0 3 2 8 0
5 0 0 8 4 0 5 7 0 0 2 4 0 5 6 0 0
7 5 0 1 1 0 0 7 5 0 0 3 6 0 7 2 0 0
1 0 0 0 1 3 0 0 9 8 0 0 4 3 0 9 0 0 0
E N E R G Y L O S S E S C O N V E N T I O N A L
T R A N S F O R M E R V I S - A - V I S
A M O R P H O U S T R A N S F O R M E R
20. Energy conservation in transformer
% Loading of Transformer
Transformer Efficiency
No Load Losses
Operating Power Factor
Power Factor improvement in capacitor installation
On Load Tap Changer ( OLTC )
Parallel operation of Transformers
Idle transformer
Separate transformer for lighting
