Transformers transfer energy from one circuit to another through electromagnetic induction. They work by using a primary and secondary winding to induce an electromotive force. Transformers are used for impedance matching, electrical isolation, and increasing or decreasing voltages for power transmission. Some key points are that transformers were first invented by Michael Faraday and have since been improved. Their behavior is based on Faraday's law of induction. Real transformers experience losses such as copper and core losses.

1. TRANSFORMERS
MARK LEAKEY
KOK WAI, WONG
WAN HAZLIN ZAINI
Reference : http://www.osha.gov/SLTC/etools/electric_power/images/transformer2.jpg

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
• 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: http://www.tpub.com/doeelecscience/electrical
%20science2_files/image1053.jpg

7. TRANSFORMER MODELS
Ideal Transformer
ip(t)
Np
Ns
is(t)
+
+
Vp(t)
-
Vs(t)
-
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
ip(t)
Lp
Rp
Vp(t)
Ls
jXm
Rc
Np
Ns
• Copper losses (I^2 R)
• Leakage Flux losses
• Core losses
 Eddy
currents
 Hysteresis losses
Rs
Vs(t)
is(t)

11. EQUIVALENT CIRCUIT
Leqp
Vp
Rc
Reqp
jXm
Approximate Transformer Model referred
to the primary side
Is/a
aVs

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

13. TYPES
Three Phase Transformers
Three phase transformers
can be constructed in two
different ways i.e. :1. A three phase bank consists
of three single phase
transformers.
2. 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)
Wye – delta (Y- Δ)
Delta – delta (Δ – 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 V O
at no load to VO at full load.
• An Ideal transformer has a voltage regulation,
VR = 0%
Reference : http://en.wikipedia.org/wiki/Voltage_regulation