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 Describe the power losses which occur in a transformer
Describe the tests which allow the power losses of a transformer to be calculated
Calculate transformer losses and efficiency using test results
Define the all day efficiency of a transformer
Calculate the all day efficiency of a transformer
Describe the relationship between transformer cooling and rating

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

7. Transformer Ratings Volt Amps VA
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

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

10. Student Exercise 1

11. Ratio between Input power and Output Power
Efficiency
Ratio between Input power and Output Power

12. Efficiency is normally expressed as a percentage

13. Transformer Efficiency
Power In
Power Out
Overcome Copper Losses
Overcome Iron 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. Transformer loaded at 50%
Short Circuit Test
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

16. Copper Losses (Cu)
Cu Losses (W)
% Load

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

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

19. Cu FL= 840 W
Fe = 220 W
Sout = 30 kVA
Calculate η%at 75%Load
η% = 97%

20. η%
Cu Losses
Fe Losses
Losses (W) η%
% Load
Fe = Cu =Max η

21. Air Oil Forced Natural Transformer Cooling and/or and/or
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;
Air
Oil
and/or
The most common methods of circulation are
Forced
Natural
and/or

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

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

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

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

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

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

29. THE END