45_6575_EE328_2014_1__1_1_EE 328 _lect_01

Electric Power & Machines “Dr. Ahmed El-Shenawy”

Electrical Power and MachinesLecture 1

<Dr Ahmed El-Shenawy><Dr Hadi El Helw>


Course Contents

Review on electric circuits & Magnetic circuits.The law of motor and generator action.DC Motors and DC Generator.Core Loss, transformer model and regulation.AC rotating field.3-phase induction motor.Synchronous machines.Single phase and small motors.Electric power system.Plant distribution system.Protective devices and distribution of electricity in buildings.System protection & PF correction.


Power System Objectives?

• Provide energy services

• System criteria– Safe

– Reliable

– Cheap

– Clean

– any more?


Major Elements of Power Systems• Power Plant– Fossil fuel powered

– Renewable energy

• Transformers

• Transmission Lines

• Distribution Lines

• Protection and Control

• Customers


Power Systems Componentselectric generatoris a device that converts mechanical energy to electrical energy In a

generator, moving a conductor through a stationary magnetic field generates voltage. If a coil is rotated through a magnetic field as shown, an alternating voltage will be produced.


A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core, and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF) or "voltage" in the secondary winding. This effect is called mutual induction.


An electric motor uses electrical energy to produce mechanical energy, very typically through the interaction of magnetic fields and current-carrying conductors.


A power cable is an assembly of two or more electrical conductors, usually held together with an overall sheath. The assembly is used for transmission of electrical power. Power cables may be installed as permanent wiring within buildings, buried in the ground, or run overhead.


Introduction

The present day machines are based on the electro-magnetic principles. Though one sees a variety of electrical machines in the market, the basic fundamental principles of all these are the same. To understand, design and use these machines the following laws must be studied.

1. Electric circuit laws - Kirchoff′s Laws

2. Magnetic circuit law - Ampere′s Law

3. Law of electromagnetic induction - Faraday′s Law


Review on electric circuits & Magnetic circuits

Kirchhoff’s Current Lawat every instant of time the sum of the currents flowing into any node of a circuit must equal the sum of the currents leaving the node,


Example: Using Kirchhoff’s Current Law. A node of a circuit is shown with current direction arrows chosen arbitrarily.

Having picked those directions, i1 = −5 A, i2 = 3 A, and i3 = −1 A. Write an expression for Kirchhoff’s current law and solve for i4.

so that


Kirchhoff’s Voltage Law

the sum of the voltages around any loop of a circuit at any instant is zero.


Power

Energy

is the total amount of work done, energy is just the integral of power:

Time rate of expending or absorbing energy



Series connection

Neq RRRRR 321

R1

R3R2 Req

R1

R2

-+

+

-

+

-

v

i

v1

v2

21

11 RR

Rvv

21

22 RR

Rvv

Voltage division:


Parallel connection

21

21

RRRRR eq

21

21 RR

Rii

21

12 RR

Rii

Current division:

R1 R2

+

-

v

i

i1 i2


Three-Phase Circuit

Three sinusoidal voltages form a set of balanced voltages when they have the same amplitudes and frequency.

These voltages are shifted in phase by 120o with each other

The standard practice is to name those phases by a, b and c and use phase a as reference.

These voltages represent phase a voltage, phase b voltage and phase voltage.


Three-Phase Circuit

Y-connected source ∆-connected source


Three-Phase Circuit

a) a wye-connected load b) a delta-connected load


Three-Phase Circuit


Phasor Representation of R,L and C CircuitsResistance

Both the current and voltage vary sinusoidally, and are in phase with each other.

The root-mean-square


Phasor Representation of R,L and C Circuits

Inductive Reactance

Capacitive Reactance


Impedance: RLC Circuits

45_6575_EE328_2014_1__1_1_EE 328 _lect_01

Documents

Transcript of 45_6575_EE328_2014_1__1_1_EE 328 _lect_01