The document discusses the basics of transformers, including their components, ratings, losses, efficiency, cooling methods, and oil properties. It describes how a basic transformer consists of two electrically isolated coil windings, and how AC voltage applied to the primary winding induces voltage in the secondary winding. The document outlines different objectives related to transformer losses, efficiency, ratings, cooling, and oil testing. It provides formulas for calculating copper losses, iron losses, efficiency based on test results, and defines different transformer cooling classifications based on the cooling medium and flow type.

1. Electrical Machines
LSEGG216A
9080V

2. Transformer

3. Basic of Transformer
• A basic transformer consists of two sets of coils
or windings.
• Each set of windings is simply an inductor. AC
voltage is applied to one of the windings, called
the primary winding.
• The other winding, called the secondary
winding, is positioned in close proximity to the
primary winding,
• but is electrically isolated from it.

4. Transformer
Losses & Efficiency

5. Objectives
1. Describe the power losses which occur in a
transformer
2. Describe the tests which allow the power losses of a
transformer to be calculated
3. Calculate transformer losses and efficiency using test
results
4. Define the all day efficiency of a transformer
5. Calculate the all day efficiency of a transformer

6. 5. Calculate the all day efficiency of a transformer
6. Describe the relationship between transformer cooling and
rating
7. Describe the methods of cooling
8. List the properties of transformer oil
9. Describe the tests conducted on transformer oil
Objectives

7. Transformer Ratings
Transformers are rated to supply a given output in
Volt Amps
or
VA
at a specified frequency and terminal voltage.

8. Transformer Ratings
They are NOT rated in Watts
The load power factor is unknown
I
V
S 

PF
S
Power 

PF
Power
S 

9. Transformer Ratings
They are NOT rated in Watts
The load power factor is unknown

10. Student Exercise 1

11. Efficiency
Power
Input
Power
Output
η 
Losses
Output
Input 

Losses
Power
Output
Power
Output
η


Ratio between Input power and Output Power
Power
Input
Losses
Power
Input
η



12. Efficiency
100
Power
Input
Power
Output
η% 

Efficiency is normally expressed as a percentage

13. Transformer Efficiency
Power
In
Power
Out
Overcome
Iron
Losses
Overcome
Copper
Losses
Some Power
is used to:

14. Transformer Losses
Copper Losses (Cu)
•Varies with load current
•Produces HEAT
•Created by resistance of windings
•Short circuit test supplies copper losses

15. Short Circuit Test
  100
0.5
loss
Copper
2


Copper Losses (Cu)
•Finds Cooper losses at full load
•Copper losses vary with the square of the load
Full load Cu loss = 100 W
Transformer loaded at 50%
PCu = 25 W
100
0.25
loss
Copper 


16. 0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
0 10 20 30 40 50 60 70 80 90 100 110
Copper Losses (Cu)
% Load
Cu
Losses
(W)

17. Transformer Losses
Iron Losses (Fe)
•Fixed
•Always present
•Related to transformers construction
Eddy Currents
Reduced by laminations
Produces HEAT
Hysteresis
Reduced by using special
steels in laminations

18. Open Circuit Test
Finds Iron Losses (Fe)
Full Supply
Voltage
Secondary
Open Circuit
Wattmeter indicates Iron Losses (Fe)

19. 100
Losses
Output
Power
Output
η% 


Sout = 30 kVA Fe = 220 W
Cu FL= 840 W
Calculate η%at 75%Load
 
  100
0.22
0.75
22.5
22.5
η% 2





84
.
0
η% = 97%
100
0.22
0.4725
22.5
22.5
η% 



5
.
22
30
75
.
0 


out
S
  5
.
472
840
75
.
0
2



75%
Cu

20. 0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0 10 20 30 40 50 60 70 80 90 100 110
96.00
97.00
% Load
Losses
(W)
η%
Cu Losses
Fe Losses
η%
Fe = Cu =Max η

21. Transformer Cooling
• Transformer ratings can be increased if their windings are cooled by some
external means
• The most common cooling mediums are in direct with transformer
windings;
and/or
Air Oil
• The most common methods of circulation are
Forced and/or Natural

23. Transformer Classification
• Transformers are allocated symbols which indicate the type of cooling
used
• Can consist of up to 4 letters indicating the cooling system
1st Letter 2nd Letter 3rd Letter 4th Letter
The cooling medium in contact
with the windings
The cooling medium in contact
with the external cooling system
Kind of Medium Circulation type Kind of Medium Circulation type

24. Transformer Classification
Type AN
Dry Transformer with
Natural Air Flow
Air Natural

25. Transformer Classification
Type AF
Dry Transformer with
Forced Air Flow
Air Forced

26. Transformer Classification
Type ONAF
Oil Tank Cooling Natural Oil Flow - Forced Air Flow
Oil Natural Air Forced

27. Transformer Classification
Type OFAF
Oil Tank Cooling Forced Oil Flow – Forced Air Flow
Oil Forced Air Forced

28. Transformer Oil
• Low Viscosity
• High Flash point
• Chemically inert
• Good insulator
Acts as Coolant & Insulator

29. THE END