FUNDAMENTALS OF ELECTRICAL ENGINEERING ENT 163 LECTURE 8

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FUNDAMENTALS OF ELECTRICAL ENGINEERING [ ENT 163 ] LECTURE #8 INTRODUCTION TO AC CIRCUITS

FUNDAMENTALS OF ELECTRICAL ENGINEERING [ ENT 163 ] LECTURE #8 INTRODUCTION TO AC CIRCUITS HASIMAH ALI Programme of Mechatronics, School of Mechatronics Engineering, Uni. MAP. Email: hashimah@unimap. edu. my

CONTENTS • IMPEDANCE AND ADMITTANCE • AC POWER ANALYSIS

CONTENTS • IMPEDANCE AND ADMITTANCE • AC POWER ANALYSIS

IMPEDANCE AND ADMITTANCE Element Impedance Admittance R Z=R Y=1/R C Z=jωL Y=1/jωL L Z=1/jωC

IMPEDANCE AND ADMITTANCE Element Impedance Admittance R Z=R Y=1/R C Z=jωL Y=1/jωL L Z=1/jωC Y=jωC • When ω=0 (dc source), ZL=0 and Zc=∞ (confirm- inductor acts like short circuit, capacitors acts like open circuit). • When ω=∞ (high frequencies ) ZL= ∞ and Zc=0 (indicate- inductor acts like open circuit, capacitors acts like short circuit).

IMPEDANCE AND ADMITTANCE Impedance in rectangular and polar form: Admittance: Y the reciprocal of

IMPEDANCE AND ADMITTANCE Impedance in rectangular and polar form: Admittance: Y the reciprocal of impedance, measured in Siemens (S) As complex quantity: Where,

IMPEDANCE COMBINATIONS Consider the N series-connected impedances: 1. The same current will flows through

IMPEDANCE COMBINATIONS Consider the N series-connected impedances: 1. The same current will flows through the impedance; applying KVL The equivalent impedance: For N=2,

IMPEDANCE COMBINATIONS Consider the N parallel-connected impedances: For N=2, Current in the impedances are:

IMPEDANCE COMBINATIONS Consider the N parallel-connected impedances: For N=2, Current in the impedances are:

IMPEDANCE COMBINATIONS The Conversion Formulas are as Follows: circuit Delta-wye The delta-to-wye transformation For

IMPEDANCE COMBINATIONS The Conversion Formulas are as Follows: circuit Delta-wye The delta-to-wye transformation For a ∆-Y balanced circuit: Z∆=3 ZY

AC POWER ANALYSIS • Power analysis- important-usage in electric utilities. Instantaneous power (in Watts)

AC POWER ANALYSIS • Power analysis- important-usage in electric utilities. Instantaneous power (in Watts) is the power at any instant of time. p(t)=v(t)i(t) Average power (in Watts) is the average of the instantaneous power over one period. P=S cos(θv-θi) • A resistive load (R) absorbs power at all times, while reactive load (L or C) absorb zero average power. Apparent power (VA) is the product of the rms value of voltage and current S=Vrms. Irms

AC POWER ANALYSIS Reactive power (Var) is the power kept by reactive elements (L

AC POWER ANALYSIS Reactive power (Var) is the power kept by reactive elements (L and C) Q=S sin (θv-θi) Power factor is the cosine of the phase difference between voltage and current, or the cosine of the angle of the load impedance. Power factor= P/S = cos (θv-θi)

FURTHER READING… Fundamentals of electric circuit. (2 th Edition), Alexander, Sadiku, Magraw. Hill. (chapter

FURTHER READING… Fundamentals of electric circuit. (2 th Edition), Alexander, Sadiku, Magraw. Hill. (chapter 9 & 11). Electric Circuits. (8 th edition), Nilsson & Riedel, Pearson. (Chapter 9).