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Dept of Electrical & Electronics
ELE 1001: Basic Electrical Technology
Lecture 02
Resistance &Star-Delta Transformation
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Dept of Electrical & Electronics
We will learn here… Fundamentals of Resistor Star & Delta connections Star-Delta & Delta-Star Transformations
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Dept of Electrical & Electronics
Resistors Resistance
Property which opposes the flow of current
R = V/I Unit – Ohms () Power P = VI = V2/R = I2R
Conductance Reciprocal of resistance Symbol: G Unit – Siemens (S)
R
V
I
+ -
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Dept of Electrical & Electronics
Resistivity & Temperature Coefficient For a homogeneous material:
where, ρ= resistivity, l= length & a= cross-sectional area of the materialwhere, α0 = Temp coefficient of resistivity at 0°CR0 = Resistance at 0°C
Positive temp coeff: Aluminum, Copper, Gold, TungstenNegative temp coeff: Carbon, Germanium (pure), Silicon (pure)
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Dept of Electrical & Electronics
Resistive Circuits
Resistors in parallel:
Resistors in series:
R1
R2
R3
+ +
+ +
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Dept of Electrical & Electronics
Current Division in Parallel Circuits
R1
R2V
I I 2I 1
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Dept of Electrical & Electronics
Voltage Division in Series Circuits
R 1
R 2
V
+ V1 -
- V2 +
I
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Dept of Electrical & Electronics
Star & Delta ConnectionsA
BC
Rab
Rbc
Rca
BC
Ra
RbRc
A
Star Connection Delta Connection
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Dept of Electrical & Electronics
Star-Delta Transformation
BC
Ra
RbRc
AA
BC
Rab
Rbc
Rca
Delta to Star Transformation:
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Dept of Electrical & Electronics
Star-Delta Transformation contd… Star to Delta Transformation:
BC
Ra
RbRc
AA
BC
Rab
Rbc
Rca
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Dept of Electrical & Electronics
Example 1For the circuit shown, determine the power supplied to the resistive network ( all resistor values are in ’s)
1 0 V
+-
36
93
6
9Psupplied =47.06 W
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Dept of Electrical & Electronics
Example 2Find the potential difference across 10Ω resistor. Also, find the power consumed by it.
+-
8
2
5
6
101 0 V
5 A
V10Ω= 14.14V; P10Ω= 20W
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Dept of Electrical & Electronics
SummaryWe started with
Resistance and its properties
Then discussed Resistive circuits Current Division in Parallel Circuit Voltage Division in Series Circuit Star-Delta Transformation
Concluded with Application of star-delta & source transformation
concepts.