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The Power Transformer
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The Power Transformer
Transformer BasicsWhat is a transformerTransformer Basic TheoryPower TransformerConstruction of a Power Transformer
Ideal TransformerPractical TransformerThe Equivalent Circuit of a Power TransformerThe Power Transformer Phasor DiagramWinding Connections & Vector Groups
Protection of a Power Transformer
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The Power Transformer
Transformer Basics
What is a transformer It may be defined as a piece of static apparatus, which by e.m. indu
transforms a.c. voltage &b current between 2 or more windings @ frequency, and usually at different values of V & I.
In its basic form, it consists of 2 coils wound on a single magnetic
Transformer Basic Theory Faraday Newman Laws: Statements Basic Principle of operation: by mutual induction between 2 or mo
windings, which are linked by a common B-field, have energy tranbetween the 2 ccts without direct electrical or galvanic actio
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The Power Transformer
Transformer BasicsWhat is a transformer
Basic Circuits : (a) Tx on No Load, (b) Tx on Load The coupling efficiency & hence depends to a large exte
degree to which the common B- field links both circuits, i.e deof magnetic leakage. For this reason, the use of materials with , mainly steel based reduces the reluctance .
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The Power TransformerTransformer Basics
Tx Operation (ctd) On Load - see fig.02
I2 creates a flux 2 which opposes m . The demagnetizing effeweakens the balance between V 1 & E1, V1 E1. To compensatweakening, I 1 must increase appropriately so as to produce a flux
whichis = & opposite to 2 , i.e.
1 = 2 For any load
1 = 2This is known as the ampere turns balance
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The Power Transformer
Transformer BasicsBasic Tx Equation It relates the induced e.m.f E & m . = If the supply voltage is sinusoidal, K = 4.44, so = . Can re- write equn thus: = .
Tx Relations It can be shown that = =
To maintain magnetic balance in the circuit, the secondary ampereturns must be balanced by the opposite polarity ampere primary windings, i.e. =
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The Power Transformer
Transformer BasicsTx Relations (ctd)
Combining the above =
= =
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The Power TransformerThe Power TransformerWhat is a power tx
The term Power Transformer generally refers to all types of transformers exclcontrol txs .
Function: Transfers electrical energy from 1 voltage level to another: Can have step up or step- down tx : turns ratio
The need of a power tx in a power system
The tx allows electrical energy to be supplied to the load @ a pre-determined vollevel. Thus the coupled energy is transformed from 1 level to another It serves as an economical means of transporting the product to the con
(consumers) are very far away from the generating stns (the factory), i.e. Power Losses Safety to the consumer
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The Power TransformerThe Power TransformerPower Transformer Classification (ctd)
Application(a) Gen Tx(b) Grid - Tx(c) Distribution
Note :
(i) Power txs refers to the above(ii) have other types of txs(d) Control : VT, CT(e) isolation tx(f) communications
Construction: (a) Core, (b) Shell
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The Power Transformer
Transformer Construction Basics Core Tank Windings: Primary and Secondary Cooling Medium Bushings Reservoir etc
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The Power TransformerThree Phase Transformer Winding Connections
Wye Wye (Y - Y) Delta Delta ( - ) Wye Delta (Y - ) Delta Wye ( - Y)
Wye - Delta - Wye (Y - - Y) : tertiary winding Auto TxNote :1) Advantages & disadvantages See Notes2) Double Wound (2 winding)Tx vs Series (One) Winding Tx
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The Power Transformer
Three Phase Transformer Vector Groups Star - Star Connection: (Yy0) Delta Delta Connection: (Dd0) - Exercise Wye Delta Connection: (Yd11) Delta Wye Connection: (Dy11) Table
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The Power TransformerThe Ideal Transformer
What is an ideal tx? Hypothetical: Loss free
Pin = PoutWinding Resistance = 0
Eddy Current Loss = 0Hysteresis Loss = 0No flux leakage
We use the ideal tx model to approximate the behaviour of a real txpower system
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The Power TransformerThe Ideal 1 Phase Transformer : No LoadSteady State Behaviour
Property 1 : An ideal tx is lossless (hypothetical)MeaningWinding Resistance = 0: Rp = Rs = 0Eddy Current Loss = 0Hysteresis Loss = 0Pin = Pout
Voltage EquationsThe Transformer E.M.F Equation
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The Power TransformerThe Ideal 1 Phase Transformer : No Load
Property 2 : In an ideal tx all flux links all turns of all windings, i.flux leakage
Meaning Induced e.m.fs Transformation ratio: a - definition Equivalent Circuit on no load No Load current Voltage equations Phasor Diagram
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The Power TransformerThe Ideal 1 Phase Transformer : On Load
Demagnetizing Effect of i2
due N2i2
Additional current in N 1 to neutralize demagnetizing effect of i 2( ) = ( )
Balance of mmfs: ( ) = ( ) Property 3 : In an ideal tx, the permeability is infinite ( = )Meaning = ( ) = ( )
( )( )
=
=
Power Invariance Principle: For an ideal tx, Pin = Pout, i.e. VARs are cons
i.e. CLE
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The Power TransformerThe Ideal 1 Phase Transformer : On Load
Property 4 : Load reflected to the source: If an ideal tx isconnected to a load impedance Z, the apparent, Z, presented to thsource is
=
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The Power TransformerThe Real/Practical 1 Phase Transformer
Tx Losses C 0
Stray inductance: this affects the induced emfs
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The Power TransformerThe Real/Practical 1 Phase Transformer : Effect of Windin
Resistance Losses Distortion in the output voltage
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The Power TransformerThe Steady State Behaviour Real/Practical 1 Phase Tra
Real Tx on No - Load Equivalent Circuit Circuit Parameters: Primary: = Secondary: = Phasor Diagram
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The Power TransformerThe Steady State Behaviour Real/Practical 1 Phase Tra
Real Tx On- Load Equivalent Circuit Equivalent circuit referred to the primary Primary: = ( ) Secondary: = Phasor Diagram
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The Power TransformerTransformer Parameters
R1 R2 X1 X2 Rm Xm
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The Power TransformerDetermination of Transformer Parameters
Open Circuit (OC) Test Also called No Load Test Test performed by applying rated voltage at terminals of 1 wdg (of
V. wdg) while the terminals of the other wdg is kept open. This shouresult in rated voltage appearing on the HV wdg. Current drawn to blow s.t. I 2R loss 0 & power measured is almost all from core los
Aim is to determine (i) P c, (ii) Rm, (iii) Xm and a Measurements: (i) V 1 & V2, (ii) INL, (iii) Pc = = + Calculations
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The Power TransformerDetermination of Transformer Parameters
Short Circuit (S.C.) Test Test performed by shorting out one wdg (often LV) and apply
voltage at the other wdg (often HV) & adjusted until rated curr(IFL) flows in the HV wgd, at which time rated current should the LV wdg
Following are measured: (i) V sc, (ii) Isc, (iii) Psc Aim: To determine (i) R eq , (ii) Xeq , (iii) Load loss (P L,FL) Calculations
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The Power TransformerTransformer Performance
This addresses (i) Tx Efficiency and Tx V.R. Tx Efficiency What is the P in for a required P out ? = =
=
=
+
+ + = Maximum Efficiency: P cu = Pc
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The Power TransformerTransformer Performance
Tx Voltage Regulation (V.R.) Defined as the change in magnitude of the sec voltage from N.
condition to F.L. expressed as a %age of F.L. value Expression
Transformer Cooling ONAN ONAF ODAF OFAF, etc
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The Power TransformerTransformer Ratings (Specifications)
This gives nominal operating parameters These are No. of phases Frequency Winding Connections and Vector Group
Method of cooling Rated Apparent Power Voltage Ratio Tappings Rated voltage and current @ primary & secondary
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The Power TransformerTransformers Operating in Parallel
UJ APK campus 11 kV network Conditions (Some) The e.m.fs should be = in magnitude & phase ( vector
order to circulating currents & permit good load sharing The per unit impedances should be = in magnitude & have the
same angle, i.e. X/R ratios should be the same
h f
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The Power TransformerTransformers Protection
Bucholtz Winding Temperature Oil temperature E/F O/C, etc