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Overview

 This page is an extremely high level attempt to look at some of the basic terminology and its definition in addition to some basic units, equations, and laws.  There are many, many other factors that are needed when looking at electricity.  Hopefully this page might have some EE's laughing at some of the rudimentary things listed.

Definitions

(The definitions below are taken from a couple different sources [3], [4], & [5] and will be mixed as to help provide better examples)


Alternating Current (AC)

  • Also known as AC. A flow of electricity through a conductor that continuously reverses its direction of flow, in contrast to direct current (DC). Nearly all electricity generated in the United States is alternating current.
  • An electric current that reverses its direction of flow periodically (see Frequency) as contrasted to Direct Current (DC) that constantly flows in one direction. In the US this direction change occurs 60 times a second (60 cycles or 60 hertz).
  • Advantages: As compared with DC, the advantage of AC is the reduced cost of transmission by use of high voltage transformers.
  • Disadvantages: As compared with DC, the disadvantages of AC are: The high voltage which renders it dangerous and requires more efficient insulation; alternating current cannot be used for such purposes as electroplating, charging storage batteries, etc.
  • Effects: There are several effects of the AC to consider in determining the size of wires. Accordingly, allowance must be made for: Self induction, mutual induction, power factor, skin effect, eddy currents, frequency, resistance, electric hysteresis, etc..

Ampere

  • The unit of measurement for the rate of flow of electric current. It is proportional to the quantity of Electrons flowing through a Conductor past a given point in one second. It is analogous to gallons per minute of water flowing in a water piping system. It is the unit current produced in a Circuit by one volt acting through a Resistance of one ohm.
  • If a one ohm resistance is connected to a one volt source, one ampere will flow.

Capacitor

  • A device used to boost the voltage to a motor. Running capacitors are used in starting winding to increase the running torque of the motor.
  • Starting capacitors are used in the starting winding to increase the starting torque of the motor. Two electrodes or sets of electrodes in the form of plates, separated from each other by an insulating material called the dielectric.

Conductor

  • An electrical path which offers comparatively little resistance. A wire or combination of wires not insulated from one another, suitable for
    carrying a single electric current.
  • A Wire, Cable, Busbar, Rod, or Tube that serves as a "path" for electrical flow.

Current

  • The movement of electrons through a conductor; measured in amperes, milliamperes, and microamperes.


Direct Current (DC)

  • Also known as DC. Electricity that flows through a conductor in a single direction. In contrast to alternating current or AC, which continually reverses the direction of flow.
  • Electricity that flows continuously in one direction as contrasted with Alternating Current that flows in one direction than reverses. A Battery produces Direct Current.



Drop

  • The voltage drop developed across a resistor due to current flowing through it.


Extra High-Voltage (EHV)

  • A term applied to voltage levels of Transmission Lines that are higher than the voltage levels commonly used. At present, the electric utility industry generally considers EHV to be any voltage greater than 345,000 volts (345 kW).


Frequency

  • The number of periods occurring in the unit of time periodic process, such as in the flow of electric charge. The number of complete cycles per second existing in any form of wave motion; such as the number of cycles per second of an alternating current.


Generating Station, Generating Plant, or Power Plant

  • A facility (or operation) for converting mechanical, chemical, and/or nuclear energy into electric energy.


Grid

  • A system of interconnected high-voltage transmission lines and power-generating facilities that allows bulk-power suppliers to share resources on a regional basis. This system provides emergency generation and transmission.


Impedance

  • The total opposition which a circuit offers the flow of alternating current at a given frequency; combination of resistance and reactance, measured
    in ohms.



Joule's Law

  • The law first stated by Joule, that the quantity of heat developed in a conductor by the passage of an electric current is proportional to the resistance of the conductor, to the square of the strength of the current, and to the duration of the flow.



Kilovolt (kv)

  • A unit of pressure equal to one thousands volts.


Kilowatt (kW)

  • A unit of electrical power, equal to one thousands watts. Electric power is usually expressed in kilowatts. As the watt is equal to 1/746
    horsepower, the kilowatt or 1,000 watts = 1.34 hp. Careful distinction should be made between kilowatts and kilovolt amperes.


Kilowatt-hour (kWh)

  • The quantity of electrical energy (1000 watts) operating for one hour. For example, a 100-watt light bulb burning for 10 hours uses one kilowatt-hour. Kilowatt-Hour is the basic measure of electric energy generation or us. Electric energy is commonly sold by the kilowatt hour.


Line Loss

  • Can refer to the amount of voltage, power, or energy lost when carrying-current over a "conductive path" due the Resistance of the "conductive path."


Line Transformer

  • A device used to raise or lower voltage in electric distribution or transmission lines.

Load

  • The amount of electric power delivered (or required), at any specified point(s) on a system. Load originates primarily at the power-consuming equipment of the customers. (See Demand.)


Load Factor

  • The "ratio" of the average load in kilowatts applied during a designated period to the peak or maximum load in kilowatts occurring in that period. Multiplying the kilowatt-hours in the period by 100 and dividing by the product of the maximum demand in kilowatts and the number of hours in the period may also derive Load Factor in Percent.


Ohm

  • The unit of electrical resistance. Resistance is one ohm when a DC voltage of one volt will send a current of one ampere through.


Overload

  • A demand for more current than the circuit wires or electrical device was designed to carry. An overload will cause a fuse to blow or circuit breaker to trip if they are on the circuit; otherwise, the wire will likely overheat and may cause serious damage.


Peak Demand

  • The maximum amount of electrical power produced-or used by-a system during a specified time period.


Power (Electric)

  • The ability to do work; the "rate" of generating, transferring, or using electrical energy usually expressed in watts, kilowatts, or megawatts.


Power Factor

  • The "ratio" of Real Power (kW) to Apparent Power


Step-Down

  • The process of lowering a Circuit's voltage from a higher-to-lower voltage.


Substation

  • An electrical facility containing equipment for controlling the flow of electricity from supplier to user.
  • An assemblage of equipment for the purpose of switching and/or changing or regulating the voltage and flow of electricity. It consists of small buildings (or fenced-in yards) containing Switches, Transformers, other equipment, and structures. Adjustments of voltage, monitoring of Circuits, and other service functions take place in this installation.


Transmission

  • The act or process of transporting electric energy in bulk from a source(s) of supply to other principal parts of the system or to other Utility Systems. Transmission Lines are Lines with voltages exceeding 39,000 volts (39 kV).


Voltage

  • The unit of "electromotive force" or "electric pressure" analogous to water pressure in a water piping system that is a measure of the push or force which causes electricity to flow. It is the "electromotive force" of one (1) volt that, if steadily applied to a Circuit having a Resistance of one ohm, will produce a current of one (1) ampere.


Watts

  • The electrical unit of power or "rate" of doing work in the metric system; the "rate" of energy transfer equivalent to one (1) ampere flowing under a pressure of one (1) volt at unity power factor. It is analogous to horsepower of "mechanical power" in the English system of units. One horsepower equals 746 watts.




Units, Equations, & Laws

Math Info


 (Source: "FHSST Physics Electricity:Important Equations and Quantities")

 Equations

(Equations are from sources [2] & [6])

DC Circuits:  Equations & Laws

Ohm's Law

     V = I*R

     I = V/R

     R = V/I


Joule's Law

Note:  P = Power (watts)
     P = I*V

     P = V²/R

     P = I²*R


Power Loss

     Po (Power Loss)  = I²*R

Putting it to use [6]

The key to operating electric transmission lines is to keep the current as low as possible and also to keep the amount of power lost at a minimum.  From the definition above, keeping the current low avoids excessive loss and keeps the lines at a lower temperature, will help avoid overloads in the transmission lines themselves.  There are many other things at the stations, sub-stations, etc. that need to make sure that they do not overload also.

Current (Amps)

As mentioned above to avoid overloading a line, you need to keep the current low.  From the equation Power = Volt * Current, then that means that you need to increase the amount of voltage needed; hence the step-up stations to step the voltage to kilo-volts.  Here's a quick math example to show it in use:

     Power (P):  5,000 MW (Mega Watts:  5,000,000,000 watts)

     Voltage (V):  250 V

     Current (I):  ?

     P = I*V (*Note: solve for 'I' & use watts not MW)

     I = 20,000,000 amps

With that many amps, the lines would be overloaded, we need to increase the voltage to lower the current (amperage).

     Power (P):  5,000 MW (Mega Watts:  5,000,000,000 watts)

     Voltage (V):  5,000 kV (kilo-volts: 5,000,000 volts)

     Current (I):  ?

     P = I*V (*Note: solve for 'I' & use volts not kV)

     I = 10,000 amps

That's much more acceptable to use.  The next thing to look at is power loss.

Power Loss

The equation for power loss is:  Po (Power Loss)  = I²*R

As you can see from the equation, the current does play a huge role in power loss.  If the current were to double then the resistance would need to be reduced by a four times the original value.  If the current were to be tripled then the resistance would need to be reduced by nine time the original value.

Example:

     Power (watts) = ?

     Current (amps) = 10

     Resistance (ohms) = 50

        P = 10² * 50
        P = 5,000

     Power (watts) = ?

     Current (amps) = 20

     Resistance (ohms) = 50

       P = 20² * 50
       P = 20,000

Let's say we want to keep the power at 5,000 watts and the current at 20 amps.  What does the resistance need to be?

     Power (watts) = 5,000

     Current (amps) = 20

     Resistance (ohms) = ?

        5,000 = 20² * R
        R = 12.5

In the original equation we had 10 amps and 50 ohms to produce 5,000 watts.  In the second equation when the current doubled and the resistance stayed the same, the power increased by 4 times the original.  If we wanted to keep the same power output of 5,000 watts and having the current double, we would need to reduce the resistance by 4 times the original from 50 ohms to 12.5 ohms.

Home

Sources 

[1] "FHSST Physics Electricity:Important Equations and Quantities"
http://en.wikibooks.org/wiki/FHSST_Physics_Electricity:Important_Equations_and_Quantities

[2] "Lessons In Electric Circuits - Volume V"
http://openbookproject.net//electricCircuits/Ref/REF_1.html#xtocid107701

[3] "Electrical Definitions"
http://www.outlawnet.com/~oclass/electricity/definitions.htm

[4] "Glossary of Terms"
http://www.gcec.net/electricity/documents/GlossaryofTerms_000.pdf

[5] "Definition of Electrical Terms"
http://www.cmsquared.com/electrical/definitions.html


[6] "Power Transmission and Usage"
http://www.outlawnet.com/~oclass/electricity/definitions.htm




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