Dept of Electrical & Electronics

ELE 1001: Basic Electrical Technology

Lecture 02

Resistance &Star-Delta Transformation

Dept of Electrical & Electronics

We will learn here… Fundamentals of Resistor Star & Delta connections Star-Delta & Delta-Star Transformations

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

+ -

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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Resistive Circuits

Resistors in parallel:

Resistors in series:

R1

R2

R3

+ +

+ +

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Current Division in Parallel Circuits

R1

R2V

I I 2I 1

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Voltage Division in Series Circuits

R 1

R 2

V

+ V1 -

- V2 +

I

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Star & Delta ConnectionsA

BC

Rab

Rbc

Rca

BC

Ra

RbRc

A

Star Connection Delta Connection

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Star-Delta Transformation

BC

Ra

RbRc

AA

BC

Rab

Rbc

Rca

Delta to Star Transformation:

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Star-Delta Transformation contd… Star to Delta Transformation:

BC

Ra

RbRc

AA

BC

Rab

Rbc

Rca

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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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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

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.