Transcript The Science Behind Direct Current & Alternating Current

ENERGY INDUSTRY FUNDAMENTALS: MODULE 1, UNIT A --The Evolution of the Power
Industry and Its Regulatory Structure
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Static electricity = an imbalance of positively and
negatively charged atoms. Electrons then jump
from atom to atom, releasing energy.
Examples of static electricity
 Lightning
 Shocks from scuffing your feet across the carpet on a
dry day and then touching a metal surface such
as a doorknob
ENERGY INDUSTRY FUNDAMENTALS: MODULE 1, UNIT A --The Evolution of the Power
Industry and Its Regulatory Structure
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Current = a flow of electrons along a pathway
Direct current (DC) means that electrons flow in
one direction. Batteries provide DC.
Batteries consist of two or more cells filled with
chemicals. As the chemicals react, electrons are
removed, leaving behind positively charged ions.
The separation between the electrons and
the ions creates voltage.
ENERGY INDUSTRY FUNDAMENTALS: MODULE 1, UNIT A --The Evolution of the Power
Industry and Its Regulatory Structure
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The voltage produced depends on the chemicals
used. A “D” cell flashlight battery uses an alkaline
reaction. A car battery uses a lead-acid reaction.
The voltage of a cell drops over time as the
chemical reaction slows down and the battery
dies.
ENERGY INDUSTRY FUNDAMENTALS: MODULE 1, UNIT A --The Evolution of the Power
Industry and Its Regulatory Structure
ENERGY INDUSTRY FUNDAMENTALS: MODULE 1, UNIT A --The Evolution of the Power
Industry and Its Regulatory Structure
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1 Coulomb = 6.25 x 1018 electrons; symbol is C
1 Ampere of current = the movement of
1 Coulomb of electrons past one point, in one
second; symbol is A
Load: device or customer that receives power
from the electric system. Load should not be
confused with demand, which is the
measure of power that a load requires
ENERGY INDUSTRY FUNDAMENTALS: MODULE 1, UNIT A --The Evolution of the Power
Industry and Its Regulatory Structure
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Voltage is the “push” behind the movement of
electrons (current flow)
Unit is the Volt
Symbols
DC Voltage
Source
AC Voltage
Source
ENERGY INDUSTRY FUNDAMENTALS: MODULE 1, UNIT A --The Evolution of the Power
Industry and Its Regulatory Structure
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Resistance is the opposition to current flow
Unit is Ohm (Ω)
resistor : A component used
to limit current flow in a
circuit or to provide a
voltage drop
Symbol : R
ENERGY INDUSTRY FUNDAMENTALS: MODULE 1, UNIT A --The Evolution of the Power
Industry and Its Regulatory Structure
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A simple DC Circuit consists of a source, a load,
control and conductors connecting the three
parts.
ENERGY INDUSTRY FUNDAMENTALS: MODULE 1, UNIT A --The Evolution of the Power
Industry and Its Regulatory Structure
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A series circuit has a single path for current to
flow. (When the switch is open, the circuit is
incomplete and the electrons cannot flow.)
ENERGY INDUSTRY FUNDAMENTALS: MODULE 1, UNIT A --The Evolution of the Power
Industry and Its Regulatory Structure
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A Parallel circuit has multiple paths for current to
flow.
ENERGY INDUSTRY FUNDAMENTALS: MODULE 1, UNIT A --The Evolution of the Power
Industry and Its Regulatory Structure
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Capacitor: a device with the ability to store electric
charge (Ex: condenser in a car) and release it; used in
electronic circuits for blocking DC while allowing AC
to pass
Transformer: transfers electricity from one circuit to
another with an increase or decrease in voltage
Inductor: a coil of wire that can store energy in its
magnetic field and resists any change in the amount
of current flowing through it; when the current
flowing through an inductor changes, it
will create an opposing or reverse voltage
ENERGY INDUSTRY FUNDAMENTALS: MODULE 1, UNIT A --The Evolution of the Power
Industry and Its Regulatory Structure
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Alternating current (AC) means that electrons flow
in two directions. Power plants provide AC.
AC current is generated when a conductor—often a
coil of wire—is rotated in a magnetic field.
The magnetic field has polarity (north and south
poles). As the coil rotates between the opposing
poles, the change in polarity causes a change in
direction of the current flow.
The directional change happens at regular intervals.
In the U.S., 60 full 360º rotations through the field
(cycles) happen every second.
ENERGY INDUSTRY FUNDAMENTALS: MODULE 1, UNIT A --The Evolution of the Power
Industry and Its Regulatory Structure
ENERGY INDUSTRY FUNDAMENTALS: MODULE 1, UNIT A --The Evolution of the Power
Industry and Its Regulatory Structure
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Thomas Edison’s power plants provided DC to
customers but could only send it about 1 mile
before it lost power. Edison hired Nikola Tesla to
find a solution and Tesla delivered, but then
Edison allegedly refused to pay him.
Tesla quit and investors helped him establish a
competing industrial laboratory where he
manufactured the prototype for today’s AC
generation and transmission system.
ENERGY INDUSTRY FUNDAMENTALS: MODULE 1, UNIT A --The Evolution of the Power
Industry and Its Regulatory Structure
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DC was difficult to convert from higher to lower
voltages and required separate transmission lines for
different voltages; AC could be “stepped down”
easily through the use of transformers
Separate transmission lines meant great cost and
more danger to the public from overhead lines
DC required power plants to be located close to the
end user (electric load); AC could transmit high
voltage over long distances requiring fewer plants
AC motors are simpler in design than
DC motors
ENERGY INDUSTRY FUNDAMENTALS: MODULE 1, UNIT A --The Evolution of the Power
Industry and Its Regulatory Structure
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Economies of scale in generation, when cost of
production falls because output has increased
Load diversity, when the peak demands of a
variety of electric customers occur at different
times
ENERGY INDUSTRY FUNDAMENTALS: MODULE 1, UNIT A --The Evolution of the Power
Industry and Its Regulatory Structure
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Batteries and power systems
http://www.eng.cam.ac.uk/DesignOffice/mdp/
electric_web/DC/DC_11.html
Electrical components and systems
http://science.howstuffworks.com/electricitychannel.htm
Inventor Nikola Tesla
http://www.pbs.org/tesla/
ENERGY INDUSTRY FUNDAMENTALS: MODULE 1, UNIT A --The Evolution of the Power
Industry and Its Regulatory Structure