EECE-259

Electrical and

Electronics Technology

Credit 4.00

Contact Hours 4.00

Course Outline Sec A

DC Generator

Principles

Types

Performances and characteristics

DC Motor

Principles

Types

Performances and characteristics

Speed control and starters of motors

Course Outline Sec A

AC Generator/Alternator

Principles

Performances and characteristics

Induction Motor

Principles

Performances and characteristics

Synchronous Motor

Principles

Performances and characteristics

AC Motor

Course Outline Sec A

Transformer

Principles

Single phase transformer

Equivalent circuit and laboratory testing

Losses

Introduction to three phase transformers

Book References A Text Book of Electrical Technology (AC, DC

Machines) – B.L Theraja & A.K. Theraja; S.

Chand & Company Ltd.

Electrical Machinery Fundamental - Stephan

J. Chapman; McGraw-Hill.

Direct and Alternating Current Machhinery-

Rosenblatt; Friedman

What is Electricity?

Electricity is energy transported by

the motion of electrons

**We do not make electricity, we

CONVERT other energy sources into

electrical energy**

Energy Conversion Options for Electricity Non-Thermal Paths

• Source to Electrical

Source Converter

Sun Photovoltaic (photon to electron)

Chemical Fuel Cell

• Source to Potential/Kinetic to Mechanical to Electrical

Source Converter Kinetic to Mechanical Mech to Electrical

Dam Penstocks Turbine (water) Generator

Tides Machine Turbine (air or water) Generator

Wind N/A Turbine (air) Generator

Energy Conversion Options for Electricity Thermal Paths

• Heat to Mechanical to Electrical

Source Heat to Mechanical Mech to Electrical

Geothermal Turbine (vapor) Generator

OTEC Turbine (vapor) Generator

• Stored Energy to Heat to Mechanical to Electrical

Source Reactor Heat to Mechanical Mech to Electrical

Fuel Combustor Turbine (gas or vapor) Generator

U, Pu Reactor Turbine (gas or vapor) Generator

Sun Collector* Turbine (gas or vapor) Generator

H, H2, H3Reactor Turbine (gas or vapor) Generator

* More a modifier or concentrator than a reactor

Energy Transfer

Chemical

Electrical

Sound

(mechanical)

Light

(Electromagnetic)

Thermal Mechanical

Where do we get our Electricity?

• Fossil – Coal, Natural

Gas, Oil – 550 Gigawatts

(GW)

• Nuclear – 200 GW

• Hydro – 75 GW

• Geothermal – 2.3 GW

• Other Renewable –

Wind, Solar, OTEC – 13.6

GW

Electrical Machine

• What is Electrical Machine?

An electrical machine is the apparatus that

converts energy in three categories: Generators

which convert mechanical energy to electrical

energy, Motors which convert electrical energy

to mechanical energy, and Transformers which

changes the voltage level of an alternating

power.

Faraday Effect

• Faraday Effect

• Basic Concepts • Voltage – V – Potential to Move Charge (volts)

• Current – I – Charge Movement (amperes or amps)

• Resistance – R – V = IxR (R in =ohms)

• Power – P = IxV = I2xR (watts)

Faradays Law • The EMF generated is proportional to the rate

of change of the magnetic flux.

aabbbbbbbbbbbbbbb

Lenz’s Law

Lenz’s law: If an induced current flows, its direction is always such that it will oppose the change which produced it.

Flux decreasing by right move induces loop flux to the left.

N S

Left motion

I

Induced B

Flux increasing to left induces loop flux to the right.

N S

Right motion I

Induced B

John Ambrose Fleming Rule

Electric Generator

Electric Motor

Electric Generator

G Mechanical

Energy Electrical

Energy

Stationary magnets - rotating magnets - electromagnets

DC Generator Principle

An electrical generator is a machine which converts mechanical energy (or power) into electrical energy (or power).

DC Generator Principle

The energy conversion is based on the principle of the production of dynamically (or motionally) induced e.m.f. whenever a conductor cuts magnetic flux, dynamically induced e.m.f. is produced in it according to Faraday’s Laws of Electromagnetic Induction. This e.m.f. causes a current to flow if the conductor circuit is closed.

SINGLE LOOP GENERATOR

Motion is parallel to the flux.

No voltage is induced.

N

S

N

S

Motion is 45° to flux. Induced voltage is 0.707 of maximum.

SINGLE LOOP GENERATOR

x

N

S

Motion is perpendicular to flux.

Induced voltage is maximum.

SINGLE LOOP GENERATOR

Motion is 45° to flux.

N

S

Induced voltage is 0.707 of maximum.

SINGLE LOOP GENERATOR

N

S

Motion is parallel to flux.

No voltage is induced.

SINGLE LOOP GENERATOR

N

S

Notice current in the

conductor has reversed. Induced voltage is

0.707 of maximum.

Motion is 45° to flux.

SINGLE LOOP GENERATOR

N

S

Motion is perpendicular to flux.

Induced voltage is maximum.

SINGLE LOOP GENERATOR

N

S

Motion is 45° to flux.

Induced voltage is 0.707 of maximum.

SINGLE LOOP GENERATOR

Motion is parallel to flux. N

S

No voltage is induced.

Ready to produce another cycle.

SINGLE LOOP GENERATOR

COMMUTATION

For making the flow of current unidirectional in the external circuit, the slip-rings are replaced by split-rings .The split-rings or commutator are made out of a conducting cylinder which is cut into two halves or segments insulated from each other by a thin sheet of mica or some other insulating material. the coil ends are joined to these segments on which rest the carbon or copper brushes.

COMMUTATION

It is seen (a) that in the first half revolution current flows along (ABMLCD) i.e. the brush No. 1 in contact with segment ‘a’ acts as the positive end of the supply and ‘b’ as the negative end. In the next half revolution (b), the direction of the induced current in the coil has reversed. But at the same time, the positions of segments ‘a’ and ‘b’ have also reversed with the Fig. result that brush No. 1 comes in touch with the segment which is positive i.e. segment ‘b’ in this case. Hence, current in the load resistance again flows from M to L. The waveform of the current through the external circuit is as shown in Fig. This current is unidirectional but not continuous like pure direct current.

Practical Generator

1. Magnetic Frame or Yoke

2. Pole-Cores and Pole-Shoes

3. Pole Coils or Field Coils

4. Armature Core 5. Armature Windings

or Conductors 6. Commutator 7. Brushes and Bearings

DC Machine Construction

DC Machine Construction

DC Machine Construction

DC Machine Construction

Armature Windings Lap and Wave Windings

Two types of windings mostly employed for drum-type armatures are known as Lap Winding and Wave Winding. The difference between the two is merely due to the different arrangement of the end connections at the front or commutator end of armature. Each winding can be arranged progressively or retrogressively and connected in simplex, duplex and triplex.

Armature Windings Uses of Lap and Wave Windings

The advantage of the wave winding is that, for a given number of poles and armature conductors, it gives more e.m.f. than the lap winding.

Conversely, for the same e.m.f., lap winding would require large number of conductors which will result in higher winding cost and less efficient utilization of space in the armature slots.

Hence, wave winding is suitable for small generators especially those meant for 500-600 V circuits.

Another advantage is that in wave winding, equalizing connections are not necessary whereas in a lap winding they definitely are.

However, when large currents are required, it is necessary to use lap winding, because it gives more parallel paths.

Hence, lap winding is suitable for comparatively low-voltage but high-current generators whereas wave-winding is used for high-voltage, low-current machines.

Types of Generators

E.M.F. Equation of a Generator

E.M.F. Equation of a Generator

Iron / Core Loss in Armature

(i) Hysteresis Loss (Wh)

If the magnetic field applied to a magnetic material is increased and then decreased back to its original value, the magnetic field inside the material does not return to its original value. The internal field 'lags' behind the external field. This behaviour results in a loss of energy, called the hysteresis loss, when a sample is repeatedly magnetized and demagnetized.

Iron / Core Loss in Armature (ii) Eddy Current Loss (We)

When the armature core rotates, it also cuts the magnetic flux. Hence, an e.m.f. is induced in the body of the core according to the laws of electromagnetic induction. This e.m.f. though small, sets up large current in the body of the core due to its small resistance. This current is known as eddy current. The power loss due to the flow of this current is known as eddy current loss. This loss would be considerable if solid iron core were used.

Losses in a Generator

Usually, magnetic and mechanical losses are collectively known as Stray Losses. These are also known as rotational losses for obvious reasons.

Power Stages

Condition for Maximum Efficiency

46

DC Generator Characteristics

In general, three characteristics specify the steady-state

performance of a DC generators:

1. Open-circuit characteristics: generated voltage versus field

current at constant speed.

2. External characteristic: terminal voltage versus load current

at constant speed.

3. Load characteristic: terminal voltage versus field current at

constant armature current and speed.

DC Generator Characteristics

Open-Circuit and Load Characteristics

The terminal voltage of a dc

generator is given by

aa

mf

aaat

RI

dropreactionArmatureIf

RIEV

,

DC Generator Characteristics

It can be seen from the external

characteristics that the terminal

voltage falls slightly as the load

current increases. Voltage regulation

is defined as the percentage change

in terminal voltage when full load is

removed, so that from the external

characteristics,

External characteristics

100V

VEregulationVoltage

t

ta

Uses of D.C. Generators