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TRANSFORMERS
Mustafa Gkhan Gnay
150609027
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DEFINITION
Device used to transfer energy from primarywinding to secondary winding by
electromagnetic induction.
Based on Faradays Law of induction
Where:-
EMF (V)
B Magnetic flux (Wb)
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TRANSFORMER USES
Impedance matching
Electrical Isolation
AC power transmission
STEP-UP Transformer
STEP-DOWN Transformer
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HISTORY
1831Michael Faraday invented the
Induction Ring.
1881Lucien Gaulard and John Gibbs
exhibited a device called secondary generator.
1885William Stanley developed the fist
commercially used practical device while
working for Westinghouse Electric Companyin US.
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INDUCTION THEORY
Transformers behaviour is based on
Faradays Law of Induction
Where:-
EMF (V)N No of turns of wire
B Magnetic flux (Wb)
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INDUCTION THEORY
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POWER GENERATION AND
TRANSMISSION
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TRANSFORMER MODELS
Ideal Transformer
-
Vs(t)
Np Ns
+
Vp(t)
ip(t)
-
+
is(t)
Np = No of windings on the primary Ns = No of windings on the secondaryip = Current into the primary is = Current out from the secondaryVp = Voltage across the primary Vs = Voltage across the secondary
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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, P
= S=
Primary and Secondary Relationship
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Transformers have losses and these losses
must come into consideration.
Copper losses (I^2 R)
Leakage Flux losses
Core losses
Eddy currents
Hysteresis losses
LOSSES
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REAL TRANSFORMER LOSSES
Vp(t) jXm
Rp
Vs(t)Rc
is(t)Lp Ls
Np
Rsip(t)
Ns
Copper losses (I^2 R)
Leakage Flux losses Core losses
Eddy currents
Hysteresis losses
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EQUIVALENT CIRCUIT
jXm aVsRc
Is/aLeqpReqp
Vp
Approximate Transformer Model referredto the primary side
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TYPES
Auto-TransformerUsed to change a desirable voltage by only a small
amount. For example: 120/132 V
IH +
-
+
-
VL
VSE
NC
NSE
VH
ISE
IL
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TYPES
Three Phase TransformersThree 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.
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THREE PHASE TRANSFORMER
CONNECTIONS
Deltawye ( Y)
Wye delta (Y- )
Deltadelta ( )
Wye wye (Y Y)
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TYPES
Two types of special purpose transformers usedin power systems for taking measurements.
Potential Transformer
Current Transformer
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EFFICIENCY
Efficiency () is the ratio of the power out to the
power in of a transformer.
in anIdeal transformer, no power losses
PIN = VPIP cos P
POUT = VSIS cos S
PIN = POUT = VPIP cos P = VSIS cos S
SOUT = SIN = VPIP = VSIS Ideal = 100%
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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, Real = POUT x 100%
PIN
= POUT x 100%
POUT + PLOSS
= VSIScosS_________
VSIS cos S + i2R + (VP/a)2 RC
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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.
VOLTAGE REGULATION
An Ideal transformer has a voltage regulation,
VR = 0%
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