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Definitions of Electrical Symbols

Definitions of Electrical Symbols

Resistor

o  Resistor in an electrical circuit reduce the current that travels through the circuit

from a higher to a lower level. A variable lamp contains a resistor to dim the bulb.

Capacitor

o  A capacitor accepts current in a circuit into a conducting plate and stores it until

released to another plate separated from the first by some element that does notconduct electricity.

Diode

o  A diode can convert alternating current into direct current by preventing the

alternating part of the current from continuing past the diode, thus producing direct

current.

Fuse

o  A fuse acts as a safety device in an electrical current by containing a thin wire that

will break if the current exceeds a specified amount.

Groundo  An electrical ground is a connection to the Earth or some metal object that has zero

potential (energy) so if some part of the circuit in a device fails, it will not create adangerous shock.

Circuit Symbols

Circuit symbols are used in circuit diagrams which show how a circuit is connected

together. The actual layout of the components is usually quite different from the

circuit diagram. To build a circuit you need a different diagram showing the layout

of the parts on stripboard or printed circuit board. 

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Wires and connections

Component Circuit Symbol Function of Component

WireTo pass current very easily from onepart of a circuit to another.

Wires joined

A 'blob' should be drawn where wires

are connected (joined), but it is

sometimes omitted. Wires connected at

'crossroads' should be staggered

slightly to form two T-junctions, as

shown on the right.

Wires not joined

In complex diagrams it is often

necessary to draw wires crossing even

though they are not connected. I prefer

the 'bridge' symbol shown on the right

because the simple crossing on the left

may be misread as a join where you

have forgotten to add a 'blob'!

Power Supplies

Component Circuit Symbol Function of Component

Cell

Supplies electrical energy.

The larger terminal (on the left) is positive

(+).

A single cell is often called a battery, butstrictly a battery is two or more cells joined

together.

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Battery

Supplies electrical energy. A battery is

more than one cell.

The larger terminal (on the left) is positive

(+).

DC supply

Supplies electrical energy.

DC = Direct Current, always flowing in

one direction.

AC supply

Supplies electrical energy.

AC = Alternating Current, continually

changing direction.

Fuse

A safety device which will 'blow' (melt) if 

the current flowing through it exceeds a

specified value.

Transformer 

Two coils of wire linked by an iron core.

Transformers are used to step up (increase)

and step down (decrease) AC voltages.

Energy is transferred between the coils by

the magnetic field in the core. There is no

electrical connection between the coils.

Earth

(Ground)

A connection to earth. For many electronic

circuits this is the 0V (zero volts) of the

power supply, but for mains electricity and

some radio circuits it really means the

earth. It is also known as ground.

Output Devices: Lamps, Heater, Motor, etc.

Component Circuit Symbol Function of Component

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Lamp (lighting)

 

A transducer which converts electrical

energy to light. This symbol is used for

a lamp providing illumination, for

example a car headlamp or torch bulb.

Lamp (indicator)

 

A transducer which converts electrical

energy to light. This symbol is used for

a lamp which is an indicator, for

example a warning light on a car

dashboard.

HeaterA transducer which converts electrical

energy to heat.

MotorA transducer which converts electrical

energy to kinetic energy (motion).

BellA transducer which converts electrical

energy to sound.

Buzzer

 

A transducer which converts electrical

energy to sound.

Inductor

(Coil, Solenoid)

 

A coil of wire which creates a

magnetic field when current passes

through it. It may have an iron core

inside the coil. It can be used as a

transducer converting electrical energy

to mechanical energy by pulling on

something.

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Switches

Component Circuit Symbol Function of Component

Push Switch (push-to-

make)

A push switch allows current to flowonly when the button is pressed. This is

the switch used to operate a doorbell.

Push-to-

Break Switch 

This type of push switch is normally

closed (on), it is open (off) only when

the button is pressed.

On-Off 

Switch 

(SPST)

SPST = Single Pole, Single Throw.An on-off switch allows current to

flow only when it is in the closed (on)

position.

2-way Switch 

(SPDT)

SPDT = Single Pole, Double Throw.

A 2-way changeover switch directs the

flow of current to one of two routes

according to its position. Some SPDT

switches have a central off position and

are described as 'on-off-on'.

Dual On-Off 

Switch 

(DPST)

DPST = Double Pole, Single Throw.

A dual on-off switch which is often

used to switch mains electricity

because it can isolate both the live and

neutral connections.

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Reversing

Switch 

(DPDT)

DPDT = Double Pole, Double Throw.

This switch can be wired up as a

reversing switch for a motor. Some

DPDT switches have a central off 

position.

Relay

 

An electrically operated switch, for

example a 9V battery circuit connected

to the coil can switch a 230V AC

mains circuit.

NO = Normally Open,

COM = Common, NC = Normally

Closed.

Resistors

Component Circuit Symbol Function of Component

Resistor 

A resistor restricts the flow of current,

for example to limit the current

passing through an LED. A resistor is

used with a capacitor in a timing

circuit.

Some publications still use the old

resistor symbol:

Variable Resistor(Rheostat)

 

This type of variable resistor with 2

contacts (a rheostat) is usually used to

control current. Examples include:

adjusting lamp brightness, adjusting

motor speed, and adjusting the rate of 

flow of charge into a capacitor in a

timing circuit.

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Variable Resistor

(Potentiometer) 

This type of variable resistor with 3

contacts (a potentiometer) is usually

used to control voltage. It can be used

like this as a transducer converting

position (angle of the control spindle)

to an electrical signal.

Variable Resistor

(Preset) 

This type of variable resistor (a preset)

is operated with a small screwdriver or

similar tool. It is designed to be set

when the circuit is made and then left

without further adjustment. Presets are

cheaper than normal variable resistorsso they are often used in projects to

reduce the cost.

Capacitors

Component Circuit Symbol Function of Component

Capacitor

 

A capacitor stores electric charge. A

capacitor is used with a resistor in a

timing circuit. It can also be used as

a filter, to block DC signals but pass

AC signals.

Capacitor,polarised

 

A capacitor stores electric charge.

This type must be connected the

correct way round. A capacitor is

used with a resistor in a timing

circuit. It can also be used as a filter,

to block DC signals but pass AC

signals.

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Variable Capacitor

 

A variable capacitor is used in a

radio tuner.

Trimmer

Capacitor 

This type of variable capacitor (a

trimmer) is operated with a small

screwdriver or similar tool. It is

designed to be set when the circuit is

made and then left without further

adjustment.

Diodes

Component Circuit Symbol Function of Component

Diode 

A device which only allows

current to flow in one direction.

LED

Light Emitting Diode 

A transducer which converts

electrical energy to light.

Zener Diode 

A special diode which is used tomaintain a fixed voltage across its

terminals.

Photodiode A light-sensitive diode.

Transistors

Component Circuit Symbol Function of Component

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Transistor NPN

 

A transistor amplifies current. It can be used

with other components to make an amplifier or

switching circuit.

Transistor PNP

 

A transistor amplifies current. It can be used

with other components to make an amplifier or

switching circuit.

Phototransistor A light-sensitive transistor.

Audio and Radio Devices

Component Circuit Symbol Function of Component

MicrophoneA transducer which converts sound to

electrical energy.

EarphoneA transducer which converts electrical

energy to sound.

Loudspeaker

 

A transducer which converts electrical

energy to sound.

Piezo Transducer

 

A transducer which converts electrical

energy to sound.

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Amplifier

(general symbol)

An amplifier circuit with one input. Really it

is a block diagram symbol because it

represents a circuit rather than just one

component.

Aerial

(Antenna)

A device which is designed to receive or

transmit radio signals. It is also known as an

antenna.

Meters and Oscilloscope

Component Circuit Symbol Function of Component

Voltmeter 

A voltmeter is used to measure voltage.

The proper name for voltage is 'potential

difference', but most people prefer to say

voltage!

Ammeter  An ammeter is used to measure current.

Galvanometer 

A galvanometer is a very sensitive meter

which is used to measure tiny currents,

usually 1mA or less.

Ohmmeter  

An ohmmeter is used to measure

resistance. Most multimeters have an

ohmmeter setting.

Oscilloscope

 

An oscilloscope is used to display the

shape of electrical signals and it can be

used to measure their voltage and time

period.

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Sensors (input devices)

Component Circuit Symbol Function of Component

LDR

 

A transducer which converts brightness(light) to resistance (an electrical

property).

LDR = Light Dependent Resistor

Thermistor 

A transducer which converts temperature

(heat) to resistance (an electrical property).

Logic Gates

Logic gates process signals which represent true (1, high, +Vs, on) or false (0, low,

0V, off).

For more information please see the Logic Gates page.

There are two sets of symbols: traditional and IEC (International Electrotechnical

Commission).

Gate

Type

Traditional

SymbolIEC Symbol Function of Gate

NOT 

A NOT gate can only have one

input. The 'o' on the output means

'not'. The output of a NOT gate is

the inverse (opposite) of its input,

so the output is true when the input

is false. A NOT gate is also called

an inverter.

AND 

An AND gate can have two or more

inputs. The output of an AND gate

is true when all its inputs are true.

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NAND  

A NAND gate can have two or

more inputs. The 'o' on the output

means 'not' showing that it is

a Not AND gate. The output of a

NAND gate is true unless all its

inputs are true.

OR

 

An OR gate can have two or more

inputs. The output of an OR gate is

true when at least one of its inputs

is true.

NOR

 

A NOR gate can have two or moreinputs. The 'o' on the output means

'not' showing that it is

a Not OR gate. The output of a

NOR gate is true when none of its

inputs are true.

EX-

OR 

An EX-OR gate can only have two

inputs. The output of an EX-OR

gate is true when its inputs are

different (one true, one false).

EX-

NOR 

An EX-NOR gate can only have

two inputs. The 'o' on the output

means 'not' showing that it is

a Not EX-OR gate. The output of an

EX-NOR gate is true when its

inputs are the same (both true or

both false).

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Electrical Symbol Descriptions:

  Circuit Symbols 

  Switch Symbol 

Electrical Symbol Descriptions  

Electric circuits are made with the use of electronic components connected to each

other by conductors such as wires or solder. The purpose of the components is tomanipulate and control current by performing operations such as storing,

switching, blocking and amplifying.

Electrical symbols are used to represent electronic components in circuits. They

are a quick and easy way that makes it easier to design circuits or read a schematic

someone else has created. 

1.  Basic Symbols

o  The most basic components are resistors, capacitors and inductors. Other basic

symbols include voltage sources and measurement devices.

Resistors

o 

Resistors are components made from conductors or semiconductors such as tightly

wound metal wires or carbon. They are used as current limiters and voltage

dividers or reducers. Regular ones are usually represented by a series of triangles

that are open at the bottom. Variable ones have an arrow drawn through thetriangles.

Capacitors

o 

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Capacitors are composed from two parallel conductors, called plates. These plates

are separated by a dielectric such as glass, air or paper. They have the ability to

store a charge. This ability allows them to perform functions such as smoothing

voltage spikes that are caused by lightning or by electrical switches opening and

closing. Ordinary capacitors are symbolized by two parallel lines.

Inductors

o 

Inductors are made from coils of wire, and are used to produce magnetic fields.

They may have many coils, be placed in casings, or are just single bare coils on

circuit boards. They are an essential part of devices such as tuners, transformers

and motors. A solenoid, which is a wire in the form of a helix, is an example of aninductor. Inductors are symbolized by a series of coils.

Voltage Sources

o  Credit: Jleedev 

Voltage sources may be batteries or alternating currents such as those drawn from

an electrical outlet. Long and short parallel lines usually represent batteries. AC

sources are usually circles with swirls inside.

Multimeters

o 

Multimeters measure the strength of signals in a circuit. When placed on a

voltmeter setting, it measures the amount of AC or DC voltage in a circuit. When

operating as an ammeter, it measures the strength of current. A circle with a V

inside represents a voltmeter, while a circle with an A inside represents an

ammeter.

Miscellaneous

o 

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The symbol for ground is usually a group of several short parallel lines.

Switches are represented by a line with a piece that is held at an angle to the rest of 

the line. They are used to stop and start the flow of current in a circuit.

Tip: Once you become comfortable recognizing the most common elements of a

circuit, you may proceed to learn the symbols of the most common semiconductorcomponents. These include the diode, transistor and op-amp.

Designator Component Type

AT Attenuator 

BR Bridge rectifier 

BT Battery 

C Capacitor 

CN Capacitor network

D Diode (including zeners, thyristors and LEDs)

DL Delay line

DS Display

F Fuse

FB or FEB Ferrite bead

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FD Fiducial

J Jack connector (female)

JP Link (Jumper)

K Relay

L Inductor

LS Loudspeaker or buzzer

M Motor

MK Microphone

MP Mechanical part (including screws and fasteners)

P Plug connector (male)

PS Power supply

Q Transistor (all types)

R Resistor

RN Resistor network

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RT Thermistor

RV Varistor

S Switch (all types, including push-buttons)

T Transformer

TC Thermocouple

TUN Tuner

TP Test point

U Integrated circuit

V Vacuum Tube

VR Variable Resistor (potentiometer or rheostat)

X Transducer not matching any other category

Y Crystal or oscillator

Z Zener Diode

Component name abbreviations widely used in industry:

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  AE: aerial, antenna

  B: battery

  BR: bridge rectifier

  C: capacitor

  CRT:cathode ray tube

  D or CR: diode

  DSP:digital signal processor

  F: fuse

  FET:field effect transistor

  GDT: gas discharge tube

  IC: integrated circuit

  J: wire link ("jumper")

  JFET: junction gate field-effect transistor

  L: inductor

  LCD:Liquid crystal display

  LDR: light dependent resistor

  LED: light emitting diode

  LS: speaker

  M: motor

  MCB: circuit breaker

  Mic: microphone

  MOSFET:Metal oxide semiconductor field effect transistor

  Ne: neon lamp

  OP: Operational Amplifier

  PCB: printed circuit board

  PU: pickup

  Q: transistor

  R: resistor

  RLA: RY: relay

  SCR: silicon controlled rectifier

  SW: switch

  T: transformer

  TFT:thin film transistor(display)

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  TH: thermistor

  TP: test point

  Tr: transistor

  U: integrated circuit

  V: valve (tube)

  VC: variable capacitor

  VFD: vacuum fluorescent display

  VLSI:very large scale integration

  VR: variable resistor

  X: crystal, ceramic resonator

  XMER: transformer

  XTAL: crystal

  Z or ZD: Zener diode

Phone jacks 

TM 5-3895-382-24HARNESS AND WIRE ELECTRICAL SCHEMATIC

SYMBOLSELECTRICAL SCHEMATIC SYMBOLS AND DEFINITIONS

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FUSE -A component in an electrical circuit that will open the circuit if too much current

flows through it.

REED SWITCH -A switch whose contacts a controlled by a magnet. A magnet closes the

contacts of anormally open reed switch; It opens the contacts of a normally closed reed

switch.SENDER -A component that is used with a temperature or pressure gauge.The sender measures thetemperature or pressure. Its resistance changes to give an

indication to the gauge of the temperature orpressure.

RELAY (Magnetic Switch) -A relay is an electrical component that is activated by

electricity It has a coil thatmakes an electromagnet when current flows through it. The

electromagnet can open or close the switchpart of the relay.

CIRCUIT BREAKER (C/B) -A component in an electrical circuit that will open the circuit

if too much currentflows through it. This does not destroy the circuit breaker and it can be

reset to become part of the circuitagain.

SOLENOID -A solenoid is an electrical component that is activated by electricity. It has a

coil that makes anelectromagnet when current flows through it. The electromagnet can

open or close a valve or move a pieceof metal that can do work.

Electric generatorFrom Wikipedia, the free encyclopedia

(Redirected from Electrical generator) 

U.S. NRC image of a modern steam turbine generator

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In electricity generation, an electric generator is a device that converts mechanical energy to electrical energy. 

A generator forces electric charge (usually carried by electrons) to flow through an external electrical circuit. It

is analogous to a water pump, which causes water to flow (but does not create water). The source of

mechanical energy may be a reciprocating or turbine steam engine, water falling through a turbine or

waterwheel, an internal combustion engine, a wind turbine, a hand crank, compressed air or any other source

of mechanical energy.

Early 20th century alternator made inBudapest, Hungary, in the power generating hall of a hydroelectric station

Early Ganz Generator in Zwevegem,West Flanders, Belgium 

The reverse conversion of electrical energy into mechanical energy is done by an electric motor, and motors

and generators have many similarities. In fact many motors can be mechanically driven to generate electricity,

and very frequently make acceptable generators.

Contents

[hide] 

1 Historical developments 

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o  1.1 Jedlik's dynamo 

o  1.2 Faraday's disk 

o  1.3 Dynamo 

o

  1.4 Alternator 

o  1.5 Other rotating electromagnetic generators 

o  1.6 MHD generator 

2 Terminology 

3 Excitation 

4 Equivalent circuit 

5 Vehicle-mounted generators 

6 Engine-generator 

7 Human powered electrical generators 

8 Linear electric generator 

9 Tachogenerator 

10 See also 

11 References 

12 External links 

[edit]Historical developments

Before the connection between magnetism and electricity was discovered, electrostatic generators were

invented that used electrostaticprinciples. These generated very high voltages and low currents. They operated

by using moving electrically charged belts, plates and disks to carry charge to a high potential electrode. The

charge was generated using either of two mechanisms:

  Electrostatic induction 

  The triboelectric effect, where the contact between two insulators leaves them charged.

Because of their inefficiency and the difficulty of insulating machines producing very high voltages, electrostatic

generators had low power ratings and were never used for generation of commercially significant quantities of

electric power. The Wimshurst machine and Van de Graaff generator are examples of these machines that

have survived.

[edit]Jedlik's dynamo

Main article:  Jedlik's dynamo  

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In 1827, Hungarian Anyos Jedlik started experimenting with electromagnetic rotating devices which he called

electromagnetic self-rotors. In the prototype of the single-pole electric starter (finished between 1852 and 1854)

both the stationary and the revolving parts were electromagnetic. He formulated the concept of the dynamo at

least 6 years before Siemens andWheatstone but didn't patent it as he thought he wasn't the first to realize this.

In essence the concept is that instead of permanent magnets, two electromagnets opposite to each other

induce the magnetic field around the rotor. It was also the discovery of the principle of self-excitation.[1]

 

[edit]Faraday's disk

Faraday disk, the first electric generator. The horseshoe-shaped magnet (A) created a magnetic field through the disk (D).

When the disk was turned this induced an electric current radially outward from the center toward the rim. The current

flowed out through the sliding spring contact m , through the external circuit, and back into the center of the disk through the

axle.

In the years of 1831 –1832, Michael Faraday discovered the operating principle of electromagnetic generators.

The principle, later calledFaraday's law, is that an electromotive force is generated in an electrical conductor

that encircles a varying magnetic flux. He also built the first electromagnetic generator, called the Faraday disk, 

a type of homopolar generator, using a copper disc rotating between the poles of a horseshoe magnet. It

produced a small DC voltage.

This design was inefficient due to self-cancelling counterflows of current in regions not under the influence of

the magnetic field. While current was induced directly underneath the magnet, the current would circulate

backwards in regions outside the influence of the magnetic field. This counterflow limits the power output to the

pickup wires and induces waste heating of the copper disc. Later homopolar generators would solve this

problem by using an array of magnets arranged around the disc perimeter to maintain a steady field effect in

one current-flow direction.

Another disadvantage was that the output voltage was very low, due to the single current path through the

magnetic flux. Experimenters found that using multiple turns of wire in a coil could produce higher more useful

voltages. Since the output voltage is proportional to the number of turns, generators could be easily designed

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to produce any desired voltage by varying the number of turns. Wire windings became a basic feature of all

subsequent generator designs.

[edit]Dynamo

Main article:  Dynamo  

Dynamos are no longer used for power generation due to the size and complexity of the commutator needed for high power

applications. This large belt-driven high-current dynamo produced 310 amperes at 7 volts, or 2,170 watts, when spinning at

1400 RPM.

Dynamo Electric Machine [End View, Partly Section] (U.S. Patent 284,110) 

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The dynamo was the first electrical generator capable of delivering power for industry. The dynamo

uses electromagnetic principles to convert mechanical rotation intopulsed DC through the use of a commutator. 

The first dynamo was built by Hippolyte Pixii in 1832.

Through a series of accidental discoveries, the dynamo became the source of many later inventions, including

the DC electric motor, the AC alternator, the AC synchronous motor, and the rotary converter. 

A dynamo machine consists of a stationary structure, which provides a constant magnetic field, and a set of

rotating windings which turn within that field. On small machines the constant magnetic field may be provided

by one or more permanent magnets; larger machines have the constant magnetic field provided by one or

more electromagnets, which are usually called field coils.

Large power generation dynamos are now rarely seen due to the now nearly universal use of alternating

current for power distribution and solid state electronic AC to DC power conversion. But before the principles of

AC were discovered, very large direct-current dynamos were the only means of power generation anddistribution. Now power generation dynamos are mostly a curiosity.

[edit]Alternator

Without a commutator, a dynamo becomes an alternator, which is a synchronous singly fed generator. When

used to feed anelectric power grid, an alternator must always operate at a constant speed that is precisely

synchronized to the electrical frequency of the power grid. A DC generator can operate at any speed within

mechanical limits, but always outputs direct current.

The primary advantage of the alternator is that the field windings can be swapped from the exterior non-rotating

shell to the interior rotating shaft, and the current producing windings are on the exterior shell. This allows for

extremely thick current producing windings that stay in a fixed position with permanent non-moving wiring.

The rotating field coil by contrast can operate at high voltage and low current so that only small, simple, and

low-cost slip rings are needed. For example, automotive alternators commonly only use a single carbon brush

to supply power to the field coil; the other end of the coil is attached to the vehicle ground by way of the rotor

bearings.

By using a rotary transformer to convey power to the rotating field coil, no rubbing physical contacts are needed

at all, and the alternator becomes an almost maintenance-free power generation device.

[edit]Other rotating electromagnetic generators

Other types of generators, such as the asynchronous or induction singly fed generator, the doubly fed

generator, or the brushless wound-rotor doubly fed generator, do not incorporate permanent magnets or field

windings (i.e., electromagnets) that establish a constant magnetic field, and as a result, are seeing success in

variable speed constant frequency applications, such as wind turbines or other renewable energy technologies. 

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The full output performance of any generator can be optimized with electronic control but only the doubly fed

generators or the brushless wound-rotor doubly fed generator incorporate electronic control with power ratings

that are substantially less than the power output of the generator under control, a feature which, by itself, offers

cost, reliability and efficiency benefits.

[edit]MHD generator

Main article:  MHD generator  

A magnetohydrodynamic generator directly extracts electric power from moving hot gases through a magnetic

field, without the use of rotating electromagnetic machinery. MHD generators were originally developed

because the output of a plasma MHD generator is a flame, well able to heat the boilers of a steam power plant. 

The first practical design was the AVCO Mk. 25, developed in 1965. The U.S. government funded substantial

development, culminating in a 25 MW demonstration plant in 1987. In the Soviet Union from 1972 until the late

1980s, the MHD plant U 25 was in regular commercial operation on the Moscow power system with a rating of25 MW, the largest MHD plant rating in the world at that time.

[2] MHD generators operated as a topping

cycle are currently (2007) less efficient than combined-cycle gas turbines. 

[edit]Terminology

The two main parts of a generator or motor can be described in either mechanical or electrical terms.

Mechanical:

  Rotor: The rotating part of an electrical machine 

  Stator: The stationary part of an electrical machine

Electrical:

  Armature: The power-producing component of an electrical machine. In a generator, alternator, or dynamo

the armature windings generate the electric current. The armature can be on either the rotor or the stator.

  Field: The magnetic field component of an electrical machine. The magnetic field of the dynamo or

alternator can be provided by either electromagnets or permanent magnets mounted on either the rotor or

the stator.

Because power transferred into the field circuit is much less than in the armature circuit, AC generators nearly

always have the field winding on the rotor and the stator as the armature winding. Only a small amount of field

current must be transferred to the moving rotor, using slip rings. Direct current machines (dynamos) require

a commutator on the rotating shaft to convert the alternating current produced by the armature to direct current, 

so the armature winding is on the rotor of the machine.

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[edit]Excitation

A small early 1900s 75 KVA direct-driven power station AC alternator, with a separate belt-driven exciter generator.

Main article:  Excitation (magnetic) 

An electric generator or electric motor that uses field coils rather than permanent magnets requires a current to

be present in the field coils for the device to be able to work. If the field coils are not powered, the rotor in a

generator can spin without producing any usable electrical energy, while the rotor of a motor may not spin at

all.

Smaller generators are sometimes self-excited , which means the field coils are powered by the current

produced by the generator itself. The field coils are connected in series or parallel with the armature winding.

When the generator first starts to turn, the small amount of remanent magnetism present in the iron core

provides a magnetic field to get it started, generating a small current in the armature. This flows through the

field coils, creating a larger magnetic field which generates a larger armature current. This "bootstrap" process

continues until the magnetic field in the core levels off due to saturation and the generator reaches a steady

state power output.

Very large power station generators often utilize a separate smaller generator to excite the field coils of the

larger. In the event of a severe widespread power outage where islanding of power stations has occurred, the

stations may need to perform a black start to excite the fields of their largest generators, in order to restore

customer power service.

[edit]Equivalent circuit

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Equivalent circuit of generator and load.

G = generator

VG=generator open-circuit voltage

RG=generator internal resistance

VL=generator on-load voltage

RL=load resistance

The equivalent circuit of a generator and load is shown in the diagram to the right. The

generator's V G and RG parameters can be determined by measuring the winding resistance (corrected to

operating temperature), and measuring the open-circuit and loaded voltage for a defined current load.

[edit]Vehicle-mounted generators

Early motor vehicles until about the 1960s tended to use DC generators with electromechanical regulators.

These have now been replaced byalternators with built-in rectifier circuits, which are less costly and lighter for

equivalent output. Moreover, the power output of a DC generator is proportional to rotational speed, whereas

the power output of an alternator is independent of rotational speed. As a result, the charging output of an

alternator at engine idle speed can be much greater than that of a DC generator. Automotive alternators power

the electrical systems on the vehicle and recharge the battery after starting. Rated output will typically be in the

range 50-100 A at 12 V, depending on the designed electrical load within the vehicle. Some cars now have

electrically powered steering assistance and air conditioning, which places a high load on the electrical system.

Large commercial vehicles are more likely to use 24 V to give sufficient power at the starter motor to turn over

a largediesel engine. Vehicle alternators do not use permanent magnets and are typically only 50-60% efficient

over a wide speed range.[3]

Motorcycle alternators often use permanent magnet stators made with rare

earth magnets, since they can be made smaller and lighter than other types. See also hybrid vehicle. 

Some of the smallest generators commonly found power bicycle lights. These tend to be 0.5 ampere,

permanent-magnet alternators supplying 3-6 W at 6 V or 12 V. Being powered by the rider, efficiency is at a

premium, so these may incorporate rare-earth magnets and are designed and manufactured with great

precision. Nevertheless, the maximum efficiency is only around 80% for the best of these generators—60% is

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more typical—due in part to the rolling friction at the tyre –generator interface from poor alignment, the small

size of the generator, bearing losses and cheap design. The use of permanent magnets means that efficiency

falls even further at high speeds because the magnetic field strength cannot be controlled in any way. Hub

generators remedy many of these flaws since they are internal to the bicycle hub and do not require an

interface between the generator and tyre. Until recently, these generators have been expensive and hard to

find. Major bicycle component manufacturers like Shimano and SRAM have only just entered this market.

However, significant gains can be expected in future as cycling becomes more mainstream transportation and

LED technology allows brighter lighting at the reduced current these generators are capable of providing.

Sailing yachts may use a water or wind powered generator to trickle-charge the batteries. A

small propeller, wind turbine or impeller is connected to a low-power alternator and rectifier to supply currents

of up to 12 A at typical cruising speeds.

[edit]Engine-generator

Main article:  Engine-generator  

An engine-generator is the combination of an electrical generator and an engine (prime mover) mounted

together to form a single piece of self-contained equipment. The engines used are usually piston engines, but

gas turbines can also be used. Many different versions are available - ranging from very small

portable petrol powered sets to large turbine installations.

[edit]Human powered electrical generators

Main article:  Self-powered equipment  

A generator can also be driven by human muscle power (for instance, in field radio station equipment).

Human powered direct current generators are commercially available, and have been the project of

some DIY enthusiasts. Typically operated by means of pedal power, a converted bicycle trainer, or a foot

pump, such generators can be practically used to charge batteries, and in some cases are designed with an

integral inverter. The average adult could generate about 125-200 watts on a pedal powered generator, but at a

power of 200 W, a typical healthy human will reach complete exhaustion and fail to produce any more power

after approximately 1.3 hours.[4]

 Portable radio receivers with a crank are made to reduce battery purchase

requirements, see clockwork radio. 

[edit]Linear electric generator

In the simplest form of linear electric generator, a sliding magnet moves back and forth through a solenoid - a

spool of copper wire. An alternating current is induced in the loops of wire byFaraday's law of induction each

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time the magnet slides through. This type of generator is used in the Faraday flashlight. Larger linear electricity

generators are used in wave powerschemes.

[edit]Tachogenerator

Tachogenerators are frequently used to power tachometers to measure the speeds of electric motors, engines,

and the equipment they power. Generators generate voltage roughly proportional to shaft speed. With precise

construction and design, generators can be built to produce very precise voltages for certain ranges of shaft

speeds

BusbarFrom Wikipedia, the free encyclopedia

(Redirected from Bus bar) 

This article needs additional citations for verification. Please help improve this

article by adding citations to reliable sources. Unsourced material maybe challenged and removed. (November 2009) 

1500 ampere busbars within a power distribution rack for a large building

In electrical power distribution, a busbar is a strip of copper or aluminium that conducts electricity within

a switchboard, distribution board, substation or other electrical apparatus.

The size of the busbar determines the maximum amount of current that can be safely carried. Busbars can

have a cross-sectional area of as little as 10 mm2

but electrical substations may use metal tubes of 50 mm in

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diameter (1,963 mm2) or more as busbars. An aluminum smelter will have very large busbars used to carry

tens of thousands of amperes to the electrochemical cells that produce aluminum from molten salts.

[edit]Design and placement

Busbars are typically either flat strips or hollow tubes as these shapes allow heat to dissipate more efficiently

due to their high surface area to cross-sectional area ratio. The skin effect makes 50 –60 Hz AC busbars more

than about 8 mm (1/3 in) thick inefficient, so hollow or flat shapes are prevalent in higher current applications. A

hollow section has higher stiffness than a solid rod of equivalent current-carrying capacity, which allows a

greater span between busbar supports in outdoor switchyards.

A busbar may either be supported on insulators, or else insulation may completely surround it. Busbars are

protected from accidental contact either by a metal earthed enclosure or by elevation out of normal

reach. Neutral busbars may also be insulated. Earth busbars are typically bolted directly onto any metal

chassis of their enclosure. Busbars may be enclosed in a metal housing, in the form of bus duct or busway,

segregated-phase bus, or isolated-phase bus. 

Busbars may be connected to each other and to electrical apparatus by bolted, clamp, or welded connections.

Often joints between high-current bus sections have matching surfaces that are silver-plated to reduce the

contact resistance. At extra-high voltages (more than 300 kV) in outdoor buses, corona around the connections

becomes a source of radio-frequency interference and power loss, so connection fittings designed for these

voltages are used.

Busbars are typically contained inside switchgear, panelboards, or busway. Distribution boards split the

electrical supply into separate circuits at one location. Busways, or bus ducts, are long busbars with a

protective cover. Rather than branching the main supply at one location, they allow new circuits to branch off

anywhere along the route of the busway.

[edit]See also