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Early 20th century alternator made in Budapest, Hungary, in the power generating hall of a hydroelectric station
Early 20th century alternator made in Budapest, Hungary, in the power generating hall of a hydroelectric station
Generator in Zwevegem, West Flanders, Belgium
Generator in Zwevegem, West Flanders, Belgium

In electricity generation, an electrical generator is a device that converts mechanical energy to electrical energy, generally using electromagnetic induction. The twentieth century of the Common Era began on alternator is an electromechanical device that converts mechanical energy to Alternating current electrical energy Budapest ( also /ˈbʊ-/) is the capital city of Hungary. As the largest city of Hungary it serves as the country's principal Political, Hungary (Magyarország 'mɔɟɔrorsaːg) officially in English the Republic of Hungary ( Magyar Köztársaság, literally Magyar (Hungarian Republic Hydroelectricity is electricity generated by Hydropower, ie the production of power through use of the gravitational force of falling water Zwevegem is a Municipality located in the Belgian province of West Flanders. West Flanders (West-Vlaanderen is the westernmost province of the Flemish Region also named Flanders, in Belgium. The Kingdom of Belgium is a Country in northwest Europe. It is a founding member of the European Union and hosts its headquarters as well as those Electricity generation is the process of converting non-electrical Energy to Electricity. In Physics, mechanical energy describes the Potential energy and Kinetic energy present in the components of a mechanical system. Electric energy is the potential energy associated with the conservative Coulomb forces between Charged particles contained within a system, where Faraday's law of induction describes an important basic law of electromagnetism which is involved in the working of Transformers Inductors and many forms of The reverse conversion of electrical energy into mechanical energy is done by a motor, and motors and generators have many similarities. An electric motor uses Electrical energy to produce Mechanical energy. 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, the sun or solar energy, compressed air or any other source of mechanical energy. A steam engine is a Heat engine that performs Mechanical work using Steam as its Working fluid. Hydropower, hydraulic power or water power is power that is derived from the Force or Energy of moving water which may The internal combustion engine is an engine in which the Combustion of Fuel and an Oxidizer (typically air occurs in a confined space called a A wind turbine is a rotating machine which converts the Kinetic energy in Wind into Mechanical energy. A crank is an arm at right angles to a shaft (an Axle or spindle by which motion is imparted to or received from the shaft it is also used to change circular into Reciprocating The Sun (Sol is the Star at the center of the Solar System. Solar energy is the Light and radiant heat from the Sun that powers Earth 's Climate and Weather and sustains Life Compressed air

Contents

Historic developments

Before the connection between magnetism and electricity was discovered, electrostatic generators were invented that used electrostatic principles. In Physics, magnetism is one of the Phenomena by which Materials exert attractive or repulsive Forces on other Materials. An electrostatic generator, or electrostatic machine, is a mechanical device that produces Static electricity, or electricity at High voltage Electrostatics is the branch of Science that deals with the Phenomena arising from what seems to be stationary Electric charges Since Classical These generated very high voltages and low currents. Electrical tension (or voltage after its SI unit, the Volt) is the difference of electrical potential between two points of an electrical Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. They operated by using moving electrically charged belts, plates and disks to carry charge to a high potential electrode. Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction. The charge was generated using either of two mechanisms:

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. An insulator, also called a Dielectric, is a material that resists the flow of Electric current. The Wimshurst machine and Van de Graaff generator are examples of these machines that have survived. The Wimshurst machine is an electrostatic device for generating high Voltages developed between 1880 and 1883 by British Inventor James Wimshurst A Van de Graaff generator is an electrostatic machine which uses a moving belt to accumulate very high electrostatically stable Voltages on a hollow metal globe

Faraday's disk

Faraday disk
Faraday disk

In 1831-1832 Michael Faraday discovered the operating principle of electromagnetic generators. Year 1831 ( MDCCCXXXI) was a Common year starting on Saturday (link will display the full calendar of the Gregorian Calendar (or a Year 1832 ( MDCCCXXXII) was a Leap year starting on Sunday (link will display the full calendar of the Gregorian Michael Faraday, FRS ( September 22 1791 – August 25 1867) was an English The principle, later called Faraday's law, is that a potential difference is generated between the ends of an electrical conductor that moves perpendicular to a magnetic field. Faraday's law of induction describes an important basic law of electromagnetism which is involved in the working of Transformers Inductors and many forms of In Physics, the potential difference or pd between two points is the difference of the points' Scalar potential, equivalent to the line integral In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges He also built the first electromagnetic generator, called the 'Faraday disc', a type of homopolar generator, using a copper disc rotating between the poles of a horseshoe magnet. A homopolar generator is a DC Electrical generator that is made when a magnetic electrically conductive rotating disk has a different Magnetic field passing Copper (ˈkɒpɚ is a Chemical element with the symbol Cu (cuprum and Atomic number 29 A magnet (from Greek grc μαγνήτης λίθος " Magnesian stone" is a material or object that produces a Magnetic field. It produced a small DC voltage, and large amounts of current.

This design was inefficient due to self-cancelling counterflows of current in regions not under the influence of the magnetic field. While current flow 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.

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.
Dynamos are no longer used for power generation due to the size and complexity of the commutator needed for high power applications. A dynamo, originally another name for an Electrical generator, now means a generator that produces Direct current with the use of a commutator. 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 )
Dynamo Electric Machine [End View, Partly Section] (U.S. Patent 284,110 )

The Dynamo was the first electrical generator capable of delivering power for industry. The dynamo uses electromagnetic principles to convert mechanical rotation into a pulsing direct electric current through the use of a commutator. Electromagnetism is the Physics of the Electromagnetic field: a field which exerts a Force on particles that possess the property of Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. A commutator is an electrical Switch that periodically reverses the current direction in an Electric motor or Electrical generator The first dynamo was built by Hippolyte Pixii in 1832. Hippolyte Pixii (1808–1835 was an instrument maker from Paris, France.

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. An electric motor uses Electrical energy to produce Mechanical energy. alternator is an electromechanical device that converts mechanical energy to Alternating current electrical energy A synchronous electric motor is an AC motor distinguished by a rotor spinning with coils passing magnets at the same rate as the Alternating current A rotary converter is a type of Electrical machine used to convert one form of electrical power into another form

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. An alternating current ( AC) is an Electric current whose direction reverses cyclically as opposed to Direct current, whose direction remains constant But before the principles of AC were discovered, very large direct-current dynamos were the only means of power generation and distribution. Now power generation dynamos are mostly a novelty.

Other Rotating Electromagnetic Generators

Without a commutator, the dynamo is an example of an alternator, which is a synchronous singly-fed generator. A commutator is an electrical Switch that periodically reverses the current direction in an Electric motor or Electrical generator alternator is an electromechanical device that converts mechanical energy to Alternating current electrical energy Singly-fed electric machines (ie Electric motors or Electric generators belong to a category of electric machines that incorporate one multiphase winding set which With an electromechanical commutator, the dynamo is a classical direct current (DC) generator. The alternator must always operate at a constant speed that is precisely synchronized to the electrical frequency of the power grid for non-destructive operation. The DC generator can operate at any speed within mechanical limits but always outputs a direct current waveform.

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. Singly-fed electric machines (ie Electric motors or Electric generators belong to a category of electric machines that incorporate one multiphase winding set which Doubly-fed electric machines (ie Electric motors or Electric generators belong to a category of electric machines that incorporate two multiphase Doubly-fed electric machines (ie Electric motors or Electric generators belong to a category of electric machines that incorporate two multiphase 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. A wind turbine is a rotating machine which converts the Kinetic energy in Wind into Mechanical energy. Renewable energy is Energy generated from Natural resources mdashsuch as Sunlight, Wind, Rain, tides and geothermal

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, which by itself offer cost, reliability and efficiency benefits. Doubly-fed electric machines (ie Electric motors or Electric generators belong to a category of electric machines that incorporate two multiphase Doubly-fed electric machines (ie Electric motors or Electric generators belong to a category of electric machines that incorporate two multiphase

MHD generator

A magnetohydrodynamic generator directly extracts electric power from moving hot gases through a magnetic field, without the use of rotating electromagnetic machinery. The MHD ( magnetohydrodynamic) generator or dynamo transforms Thermal energy or Kinetic energy directly into Electricity 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 Rankine cycle is a thermodynamic cycle which converts heat into work A power station (also referred to as generating station, power plant or powerhouse) is an industrial facility for the generation of The first practical design was the AVCO Mk. 25, developed in 1965. The U. S. government funded substantial development, culminating in a 25Mw demonstration plant in 1987. MHD generators operated as a topping cycle are currently (2007) less efficient than combined-cycle gas turbines. A combined cycle is characteristic of a power producing engine or plant that employs more than one Thermodynamic cycle. A gas turbine, also called a combustion turbine, is a rotary Engine that extracts energy from a flow of Combustion gas

Concepts

The generator moves an electric current, but does not create electric charge, which is already present in the conductive wire of its windings. It is somewhat analogous to a water pump, which creates a flow of water but does not create the water inside. Other types of electrical generators exist, based on other electrical phenomena such as piezoelectricity, and magnetohydrodynamics. Electrical phenomena are commonplace and unusual events that can be observed which illuminate the principles of the Physics of Electricity and are explained by them Piezoelectricity is the ability of some materials (notably Crystals and certain Ceramics including bone to generate an Electric potential in response to Magnetohydrodynamics (MHD ( magnetofluiddynamics or hydromagnetics) is the Academic discipline which studies the dynamics of electrically The construction of a dynamo is similar to that of an electric motor, and all common types of dynamos could work as motors. An electric motor uses Electrical energy to produce Mechanical energy.

Terminology

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

Mechanical:

Electrical:

Since 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 necessarily have the commutator on the rotating shaft, so the armature winding is on the rotor of the machine. In Mathematics, the commutator gives an indication of the extent to which a certain Binary operation fails to be Commutative.

Excitation

A small early 1900s 75 KVA direct-driven power station AC alternator, with a separate belt-driven exciter generator.
A small early 1900s 75 KVA direct-driven power station AC alternator, with a separate belt-driven exciter generator. A volt-ampere in electrical terms means the amount of Apparent power in an Alternating current circuit equal to a current of one Ampere at an

Main article Excitation (magnetic)

An electric generator or electric motor that uses field coils rather than permanent magnets will require a current flow to be present in the field coils for the device to be able to work. An electric generator or electric motor that uses field coils rather than permanent magnets will require a current flow 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. 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. A power outage (also known as power cut, power failure, power loss, or blackout) is the loss of the Electricity supply to an A black start is the process of restoring a Power station to operation without relying on external energy sources

Equivalent circuit

Equivalent circuit of generator and load.G = generatorVG=generator open-circuit voltageRG=generator internal resistanceVL=generator on-load voltageRL=load resistance
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. To determine the generator's VG and RG parameters, follow this procedure: -

R_{GAC} = {R_L} \left( {{{V_G}\over{V_L}}-1} \right)

Note 1: The AC internal resistance of the generator when running is generally slightly higher than its DC resistance when idle. The above procedure allows you to measure both values. For rough calculations, you can omit the measurement of RGAC and assume that RGAC and RGDC are equal.

Note 2: If the generator is an AC type, use an AC voltmeter for the voltage measurements.

The maximum power theorem states that the maximum power can be obtained from the generator by making the resistance of the load equal to that of the generator. In Electrical engineering, the maximum power (transfer theorem states that to obtain maximum external power from a source with a finite internal resistance This is inefficient since half the power is wasted in the generator's internal resistance; practical electric power generators operate with load resistance much higher than internal resistance, so the efficiency is greater.

Vehicle-mounted generators

Further information: V2G

Early motor vehicles until about the 1960's tended to use DC generators with electromechanical regulators. Vehicle-to-grid (V2G describes a system in which power can be sold to the electrical power grid by an electric-drive motor vehicle that is connected to the grid when it is not These were not particularly reliable or efficient and have now been replaced by alternators with built-in rectifier circuits. alternator is an electromechanical device that converts mechanical energy to Alternating current electrical energy These 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. Power steering is a system for reducing the Steering effort on vehicles by using an external power source to assist in turning the roadwheels. The term air conditioning refers to the cooling and dehumidification of indoor air for Thermal comfort. Commercial vehicles are more likely to use 24 V to give sufficient power at the starter motor to turn over a large diesel engine without the requirement for unreasonably thick cabling. An automobile self-starter (commonly "starter motor" or simply "starter" is an Electric motor that initiates rotational motion in a car's Internal A diesel engine is an Internal combustion engine which operates using the Diesel cycle (named after Dr Vehicle alternators do not use permanent magnets and are typically only 50-60% efficient over a wide speed range. Motorcycle alternators often use permanent magnet stators made with rare earth magnets, since they can be made smaller and lighter than other types. The stator is the stationary part of an Electric generator or Electric motor. Rare earth elements and rare earth metals are according to IUPAC, the collection of seventeen Chemical elements in the Periodic table, namely See also hybrid vehicle. A hybrid vehicle is a vehicle that uses two or more distinct power sources to propel the vehicle

Some of the smallest generators commonly found power bicycle lights. Bicycle lighting has two purposes seeing and being seen There are many types of Bicycle lights available each with its own advantages and disadvantages 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. Rare-earth magnets are strong permanent magnets made from Alloys of Rare earth elements Rare-earth magnets are substantially stronger than Nevertheless, the maximum efficiency is only around 60% for the best of these generators - 40% is more typical - due to the use of permanent magnets. A battery would be required in order to use a controllable electromagnetic field instead, and this is unacceptable due to its weight and bulk.

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. A propeller is essentially a type of fan which transmits power by converting Rotational motion into Thrust for propulsion of a vehicle such as an A wind turbine is a rotating machine which converts the Kinetic energy in Wind into Mechanical energy. An impeller is a rotor inside a tube or conduit to increase the pressure and flow of a fluid

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. An engine-generator is the combination of an Electrical generator and an Engine (prime mover mounted together to form a single piece of equipment An engine is a mechanical device that produces some form of output from a given input 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.

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). Self-powered equipment is a term used for Electrical appliances which can be powered by human muscle power as an alternative to conventional sources of electricity such as

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 as large as 12 volts, and in some cases are designed with an integral inverter. Portable radio receivers with a crank are made to reduce battery purchase requirements, see clockwork radio. A clockwork radio or windup radio is a radio that is powered by human muscle power rather than batteries or the Electrical grid.

Patents

References

See also

External links

A wind turbine is a rotating machine which converts the Kinetic energy in Wind into Mechanical energy.
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