Transformers and Electrical System Design

Transformer types and system design

1. EET 323 –Electrical System Design
Lecture 14: Transformers
Radian Belu, PhD

3. Lecture Objectives

8. A transformer consists of two or more windings
coupled by mutual magnetic flux.
-Primary Winding
-Secondary Winding(s)

9. Transformer Equation
Faraday’s Law states that,
◦If the flux passes through a coil of wire, a voltage will be
inducedin the turns of wire. This voltage is directly proportional
to the rate of change in the flux with respect of time.
If we have Nturns of wire,dt
td
EmfV
indind
)(
 dt
td
NEmfV
indind
)(

Lenz’s Law

13. Apparent Power Conservation E1*I1 = E2*I2

14. Transformer Equationa
I
I
N
N
E
E
Therefore 
1
2
2
1
2
1
,
Where,‘a’is the Voltage Transformation Ratio; which will
determine whether the transformer is going to be step-up or
step-down
E
1> E
2For a > 1
For a < 1 E
1< E
2 Step-Up
Step-Down
For a = 1 E
1= E
2 Impedance
Transformer

23. Low-Voltage Transformers
•LV Transformers Ratings: 600 V or less for booth primary
and secondary windings
•Typically Transformer Ratings: 480-120/240 V, or
480-208 Y/120 V
•Indoor installations and dry-type construction

36. Loading Calculations

43. Floating Υ–ΔConnections
•Rule of Thumb –Lighting Transformer Leg Load:
2/3 Single-Phase Load + 1/3 3-Phase Load

52. Transformer Voltage Taps
•The taps are made to high-voltage side to adjust for the
variations in the supply voltage

67. THE END of the Lecture
Thank you for listening
•Questions?
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