EET 251
Electricity and Electronics
Lesson Five
SOURCES OF ELECTRICAL ENERGY
Electrical energy sources convert some other form of
energy into electrical energy. Batteries and electrical generators are two
major sources of electrical energy. Batteries convert chemical energy into
electrical energy. Electrical generators rely on the principle of
electromagnetic induction to convert mechanical energy into electrical energy.
The types of electrical generators include single-phase ac generators,
three-phase ac generators, and dc generators. Batteries, generators, and other
sources of electrical energy are discussed in this lesson.
5.1 Chemical Sources
Chemical
cells
Electrolyte
Primary
cells: operation principles; electrodes; ions; dry
cell; types of primary cells used today (ex: carbon-zinc cell)
Secondary
cells: principle and common types
(1) Lead-acid cells: construction,
chemical process, specific gravity test to measure amount of charge, hydrometer
to test electrolyte solution.
(2) Nickel-cadmium cells:
construction, common use
(3) Nickel-metal-hybride cell:
construction, use and advantages
5.2 Battery Connections
Series
connection
Parallel
connection
Combination
(series-parallel) connection
5.3 Light Sources
Photovoltaic
or solar cells
5.4 Heat sources
Seebeck
effect
thermocouples
5.5 Pressure sources
Piezoelectric
effect: change of mechanical pressure into electrical energy
Pressure-sensitive
crystals
Applications
of the piezoelectric principle (ex: vinyl recording sound systems)
5.6 Electromagnetic
Induction
Principles
of electromagnetic induction
Cycle
Frequency
5.7 Generating a VoltageAmount of voltage induced into a conductor cutting
across a magnetic field depends on:
(1)
speed of the relative motion between the magnetic field and the conductor
(2)
strength of the magnetic field
(3)
length of the conductor
5.8 Electrical Generator Basics
Parts
of the generator: stator and rotor;
prime mover, slip ring or commutator and brush assembly.
5.9 Single-Phase AC
Generators
Sine-wave
voltage
Methods
to convert mechanical energy into electrical energy: rotating-armature and
rotating-field
5.10 Three-Phase AC
Generators
Methods
to connect alternator output windings: wye and delta connection
Use
of three-phase power
5.11 Direct-Current
Generators
Uses
of direct current
Construction
and operation of the generator
Types
of generators:
(1) Permanent magnet dc generators
(2) Separately excited dc generators
(3) Self-excited generators:
series-wound dc generators, shunt-wound dc generators, compound-wound dc
generators
Generator
operating characteristics:
(1) armature reaction
(2) neutral plane
(3) running neutral plane
(4) interpoles
(5) voltage regulation
REVIEW
1.List
eight sources of electrical energy.
2.
What are the two types of electrical current produced by energy sources called?
3.
What are two classifications of chemical cells, and hos are they different?
4.
Discuss the operation of a carbon-zinc cell.
5.
Discuss the operation of a lead-acid cell.
6.
How do nickel-cadmium cells differ from carbon-zinc cells?
7.
How is light energy used to produce electrical energy?
8.
How is heat energy used to produce electrical energy?
9.
How is pressure used to produce electrical energy?
10.
Discuss electromagnetic induction.
11.
What three factors determine the amount of voltage induced into a conductor
inside a magnetic field?
12.
What are the differences between slip rings and a commutator used for
electrical generators?
13.
What is a sine wave?
14.
If the maximum voltage of a generator is 50 V and the angle of rotation is 240
degrees, what is the instantaneous voltage?
15.
If the speed of ratation of a four-pole generator is 1800 rpm, what is its
ouptu frequency?
16.
What are the two methods used to produce voltage ouptput in generators, and how
do they differ?
17.
Discuss the two types of three-phase connections used for stator windings in
three-phase generators.
18.
Discuss the construction of a dc generator.
19.
What are the types of dc generators?
20.
Discuss armature reaction.
21.
If a generator has a no-load voltage output of 100V and a full-load voltage
output of 90 V, what is its voltage regulation percentage?
22. If a generator has a power output of 2000W and a power input of 3 hp, what if its efficiency?