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The Science Behind Direct Current & Alternating Current. Static Electricity. Static electricity = an imbalance of positively and negatively charged atoms. Electrons then jump from atom to atom, releasing energy. Examples of static electricity Lightning - PowerPoint PPT Presentation
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ENERGY INDUSTRY FUNDAMENTALS: MODULE 1, UNIT A --The Evolution of the Power Industry and Its Regulatory Structure
THE SCIENCE BEHIND DIRECT CURRENT & ALTERNATING CURRENT
ENERGY INDUSTRY FUNDAMENTALS: MODULE 1, UNIT A --The Evolution of the Power Industry and Its Regulatory Structure
Static Electricity 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
Current Electricity 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
Batteries 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
Batteries
ENERGY INDUSTRY FUNDAMENTALS: MODULE 1, UNIT A --The Evolution of the Power Industry and Its Regulatory Structure
Vocabulary 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
Voltage 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
Resistors 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
Circuits 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
Series DC Circuit 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
Parallel DC Circuit 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
Vocabulary 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
Current Electricity 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
AC Circuit
ENERGY INDUSTRY FUNDAMENTALS: MODULE 1, UNIT A --The Evolution of the Power Industry and Its Regulatory Structure
The War of Currents: General Electric (DC) vs. Westinghouse (AC) 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
AC electricity is more efficient and more cost effective than DC 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
An AC power system benefits from: 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
For More About… Batteries and power systems
http://www.eng.cam.ac.uk/DesignOffice/mdp/electric_web/DC/DC_11.html
Electrical components and systemshttp://science.howstuffworks.com/electricity-channel.htm
Inventor Nikola Teslahttp://www.pbs.org/tesla/