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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)
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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