Download An Introduction to Electrical Technology

Unit 3 – Lesson 5
AN INTRODUCTION TO
ELECTRICAL TECHNOLOGY
Electrical Technology
 Electrical technology is the technology of
producing, storing, controlling, transmitting
and getting work from electrical energy.
(Example applications: power plant
generator, flashlight, electric motor in a can
opener, doorbell, electric heater, hair dryer.)
Electronic Technology
 Electronic technology as the technology of
using small amounts of electricity for
controlling; detecting; and information
collecting, storing, retrieving, processing, and
communicating. (Example applications:
thermostat for controlling temperature, a
metal detector, video tape recorder,
computer, pocket calculator, telephone,
radio, television.)
Important Concepts
 Resistance - The opposition to the flow of
electrical charge.
 Conduction - The movement of electrically
charged particles through a transmission
medium.
 Conductor - A material containing many free
electrons that move through the material
easily.
Important Concepts
 Semi-conductor - Materials whose electrical
conductivity can be precisely altered by appropriate
manufacturing processes. A semiconductor behaves
as an insulator at very low temperature, and has an
appreciable electrical conductivity at room
temperature although much lower conductivity than
a conductor. Semiconductor materials are the
foundation of modern electronics, including radio,
computers, telephones, and many other devices.
Such devices include transistors, solar cells, many
kinds of diodes including the light-emitting diode,
the silicon controlled rectifier, and digital and analog
integrated circuits.
Important Concepts - Current
 Current - The force that moves electrons
 Direct Current - current that starts at one place and flows in
one direction to the end destination, hence the name
Direct.
 Alternating Current - current flows in one direction for a
period of time and then switches direction, going the
opposite way. It switches diretion over and over again
continuously. In the united states the AC current in power
lines goes switches direction, forward to backward, then
backward to forward, 60 times each second. This is a
frequency of 60 Hertz and is called 60Hz AC electricity.
Important Concepts - Current
 One major reason for using ac rather than dc is
the need for long range transmission.
Transmission line power loss is proportional to
the square of the current. To keep the current to
a minimum while keeping the energy
transmission at a high enough level it is
necessary to use transformers. These raise the
voltage to a very high level and lower the current
accordingly. Direct current cannot be
transformed so transmission would have to be at
the low voltage safe for customer usage.
Important Concepts
 When electric generation first started (before
1900), there was competition between ac
(Westinghouse) and dc (Edison). However the
need for long distance transmission killed off
the dc generation industry.
Important Concepts - Current
 Microelectronics use DC because they are
composed, essentially, of transistors. Transistors
are small "switches" which use voltages as
control signals. If the control signals were
changing polarity many times a second, the
switches would open and close many times a
second, leading to, well, a mess. It'd be very hard
to make a digital computer which could use AC.
Important Concepts
 Voltage - the difference in the electrostatic
charge that exists between two points. It is
this imbalance in the electrostatic charge that
causes electrons to flow from one point to the
next. Known as potential difference.
Important Concepts
 Power - The rate of doing work or the rate of
transferring energy
 Circuits - A complete path of an electric
current including the source of electrical
energy. Electric circuits provide a means of
transferring and using electrical energy to
produce heat, light, and sound as well as
chemical changes.
Important Concepts
 Magnetism - A force that exists around magnets that
attracts ferrous materials and is used in motors and
generators.
 Ferrous materials - Ferrous is derived from the Latin term
which means iron (hence the elemental symbol "Fe") . A
non-ferrous metal is any metal which is not iron or any alloy
of metals which does not contain iron as a component.
Most (but not all) ferrous alloys are magnetic and even
those which vary in magnetic attraction due to the amount
of iron in the alloy. Stainless steel is not always
magnetically attracted because the process of making it
"stainless" removes a great deal of the iron (it is put in nitric
acid to remove the iron leaving only a small amount of iron
and mostly nickel).
Important Concepts
 Ohm’s law - The linear relationship between
voltage and current through an electrical
device. Ohm's law states that the current
through a conductor between two points is
directly proportional to the potential
difference across the two points. Introducing
the constant of proportionality, the
resistance, one arrives at the usual
mathematical equation that describes this
relationship: I = V/R
Important Concepts
 Ratio - The relationship in quantity, amount,
or size between two or more things
Horsepower
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Horsepower calculation - James Watt performed experiments and determined
that a horse could lift 550 pounds at a rate of one foot per second.
Mechanical horsepower
hp(I) ≡ 33,000 ft-lbf/min = 550 ft·lbf/s
= 745.699872 W
Metric horsepower
hp(M) ≡ 75 kgf·m/s
≡ 735.49875 W
Electrical horsepower
hp(E) ≡ 746 W
Boiler horsepower
hp(S) ≡ 33,475 BTU/h = 9,809.5 W
Hydraulic horsepower = flow rate (US gal/min) × pressure (psi) × 7/12,000
or
= flow rate (US gal/min) × pressure (psi) / 1714
= 550 ft·lbf/s
= 745.699872 W
Electromagnet
 Electromagnet – A core of magnetic material
surrounded by a coil of wire through which an
electric current is passed to magnetize the
core.