1. MARK LEAKEY KOK WAI, WONG WAN HAZLIN ZAINI
TRANSFORMERS
MARK LEAKEY
KOK WAI, WONG
WAN HAZLIN ZAINI
Reference :

2. DEFINITION
Device used to transfer energy from primary winding to secondary winding by electromagnetic induction.
Based on Faraday’s Law of induction
Where:-
ε – EMF (V)
ΦB – Magnetic flux (Wb)

3. TRANSFORMER USES Impedance matching Electrical Isolation
AC power transmission
STEP-UP Transformer
STEP-DOWN Transformer

4. HISTORY 1831 – Michael Faraday invented the Induction Ring.
1881 – Lucien Gaulard and John Gibbs exhibited a device called secondary generator.
1885 – William Stanley developed the fist commercially used practical device while working for Westinghouse Electric Company in US.

5. INDUCTION THEORY ε – EMF (V)
Transformers behaviour is based on Faraday’s Law of Induction
Where:-
ε – EMF (V)
N – No of turns of wire
ΦB – Magnetic flux (Wb)

6. INDUCTION THEORY
Reference:

7. TRANSFORMER MODELS Ideal Transformer
Np = No of windings on the primary Ns = No of windings on the secondary
ip = Current into the primary is = Current out from the secondary
Vp = Voltage across the primary Vs = Voltage across the secondary

8. Primary and Secondary Relationship
VP = NP = a = iS
VS NS iP
Note; a < 1 = Step up transformer
a > 1 = Step down transformer
Voltage and current angles are NOT affected hence, θP = θS = θ

9. LOSSES
Transformers have losses and these losses must come into consideration.
Copper losses (I^2 R)
Leakage Flux losses
Core losses
Eddy currents
Hysteresis losses

10. REAL TRANSFORMER LOSSES
Copper losses (I^2 R)
Leakage Flux losses
Core losses
Eddy currents
Hysteresis losses

11. Approximate Transformer Model referred to the primary side
EQUIVALENT CIRCUIT
Approximate Transformer Model referred to the primary side

12. TYPES Auto-Transformer
Used to change a desirable voltage by only a small amount. For example: 120/132 V IH VL
VSE NC
NSE VH
ISE IL

13. Three Phase Transformers
TYPES
Three Phase Transformers
Three phase transformers
can be constructed in two
different ways i.e. :-
A three phase bank consists of three single phase transformers.
Three windings wrapped around a common core.
Reference : Electric Machinery and Power System Fundamentals, Stephen J. Chapman

14. THREE PHASE TRANSFORMER CONNECTIONS
Delta – wye (Δ – Y)
Delta – delta (Δ – Δ)
Wye – delta (Y- Δ)
Wye – wye (Y – Y)
Reference : Electric Machinery and Power System Fundamentals, Stephen J. Chapman

15. TYPES
Two types of special purpose transformers used in power systems for taking measurements.
Potential Transformer
Current Transformer
Reference : Electric Machinery and Power System Fundamentals, Stephen J. Chapman

16. EFFICIENCY
Efficiency (η) is the ratio of the power out to the power in of a transformer.
η in an Ideal transformer, no power losses
PIN = VPIP cos θP
POUT = VSIS cos θS
PIN = POUT = VPIP cos θP = VSIS cos θS
SOUT = SIN = VPIP = VSIS
ηIdeal = 100%

17. Efficiency for a single phase real transformer
As mentioned previously, losses occur in a real transformer and these losses must be taken into count.
Hence, ηReal = POUT x 100%
PIN
= POUT x 100%
POUT + PLOSS
= VSIS cos θS_________
VSIS cos θS + i2R + (VP/a)2 RC

18. VOLTAGE REGULATION
Voltage regulation (VR) is the ability of a system to provide near constant voltage over a wide range of load conditions. Also it compares the VO at no load to VO at full load.
An Ideal transformer has a voltage regulation,
VR = 0%
Reference :