PesWiki.com

Menu

PowerPedia:Electrical generator

Lasted edited by Andrew Munsey, updated on June 14, 2016 at 9:26 pm.

  • 53 errors has been found on this page. Administrator will correct this soon.
  • This page has been imported from the old peswiki website. This message will be removed once updated.

An electrical generator is a device that converts mechanical energy to There was an error working with the wiki: Code[9] may be a reciprocating or turbine There was an error working with the wiki: Code[10], an Internal combustion engine, a Wind Turbine, a hand crank, or any other source of mechanical energy.

Historic developments

Electrostatic generators are used for scientific experiments requiring high voltages. Because of the difficulty of insulating machines producing very high voltages, electrostatic generators are made only with low power ratings and are never used for generation of commercially-significant quantities of electric power. Before the connection between Magnetism and Electricity was discovered, generators used electrostatic principles. The Wimshurst machine used electrostatic induction or "influence". Some electrostatic machines (such as the more modern Van de Graaff generator) uses either of two mechanisms:

Charge transferred from a high-voltage electrode

Charge created by the There was an error working with the wiki: Code[11]s (the belt leaving the lower pulley)

Faraday

In There was an error working with the wiki: Code[24]-There was an error working with the wiki: Code[25] Michael Faraday discovered that a There was an error working with the wiki: Code[26] is generated between the ends of an electrical conductor that moves perpendicular to a Magnetic field. He also built the first electromagnetic generator called the 'Faraday disc', a type of Homopolar generator, using a There was an error working with the wiki: Code[27] disc rotating between the poles of a horseshoe There was an error working with the wiki: Code[28]. It produced a small DC voltage, and large amounts of current.

Dynamo

The Dynamo was the first electrical generator capable of delivering power for industry. The dynamo uses Electromagnetism principles to convert mechanical rotation into an alternating electric Current (electricity). A dynamo machine consists of a stationary structure which generates a strong magnetic field, and a set of rotating windings which turn within that field. On small machines the magnetic field may be provided by a permanent magnet larger machines have the magnetic field created by electromagnets.

The first dynamo based on Faraday's principles was built in There was an error working with the wiki: Code[12], Pixii was able to convert the alternating current to direct current.

Unlike the Faraday disc, many turns of wire connected in series can be used in the moving windings of a dynamo. This allows the terminal voltage of the machine to be higher than a disc can produce, so that electrical energy can be delivered at a convenient voltage. The relationship between mechanical rotation and electric current in a dynamo is reversible the principles of the electric motor were discovered when it was found that one dynamo could cause a second interconnected dynamo to rotate if current was fed through it.

Jedlik's dynamo

In 1827, There was an error working with the wiki: Code[13] and There was an error working with the wiki: Code[14]. In essence the concept is that instead of permanent magnets, two electromagnets opposite to each other induce the magnetic field around the rotor.

Gramme dynamo

Both of these designs suffered from a similar problem: they induced "spikes" of current followed by none at all. There was an error working with the wiki: Code[15] one, which he created by wrapping an iron ring. This meant that some part of the coil was continually passing by the magnets, smoothing out the current. There was an error working with the wiki: Code[29] reinvented this design a few years later when designing the first commercial power plants, which operated in There was an error working with the wiki: Code[30] in the There was an error working with the wiki: Code[31]. His design is now known as the There was an error working with the wiki: Code[32]. Various versions and improvements have been made since then, but the basic concept of a spinning endless loop of wire remains at the heart of all modern dynamos.

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 itself. Other types of electrical generator exist, based on other There was an error working with the wiki: Code[16] such as There was an error working with the wiki: Code[33], and There was an error working with the wiki: Code[34]. The construction of a dynamo is similar to that of an Electric motor, and all common types of dynamos could work as motors.

Terminology

The parts of a dynamo or related equipment can be expressed in either mechanical terms or electrical terms. Although distinctly separate, these two sets of terminology are frequently used interchangeably or in combinations that include one mechanical term and one electrical term. This causes great confusion when working with compound machines such as a brushless alternator or when conversing with people who are used to working on a machine that is configured differently than the machines that the speaker is used to.

Mechanical

Rotor: The rotating part of an alternator, generator, dynamo or motor.

Stator: The stationary part of an alternator, generator, dynamo or motor.

Electrical

Armature: The power-producing component of an alternator, generator, dynamo or motor. The armature can be on either the rotor or the stator.

Field: The magnetic field component of an alternator, generator, dynamo or motor. The field can be on either the rotor or the stator and can be either an electromagnet or a permanent magnet.

Equivalent circuit

To determine the generator's V_G and R_G parameters, follow this procedure: -

Before starting the generator, measure the resistance across its terminals using an There was an error working with the wiki: Code[35]. This is its DC internal resistance R_{GDC}.

Start the generator. Before connecting the load R_L, measure the voltage across the generator's terminals. This is the open-circuit voltage V_G.

Connect the load as shown in the diagram, and measure the voltage across it with the generator running. This is the on-load voltage V_L.

Measure the load resistance R_L, if you don't already know it.

Calculate the generator's AC internal resistance R_{GAC} from the following formula:

R_{GAC} = {R_L} \left( There was an error working with the wiki: Code[1]-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 R_{GAC} and assume that R_{GAC} and R_{GDC} are equal.

Note 2: If the generator is an AC type (distinctly not a dynamo), use an AC voltmeter for the voltage measurements.

Maximum power

The There was an error working with the wiki: Code[36] applies to generators as it does to any source of electrical energy. This 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. However, under this condition the power transfer efficiency is only 50%, which means that half the power generated is wasted as heat and Lorentz force or back emf inside the generator. For this reason, practical generators are not usually designed to operate at maximum power output, but at a lower power output where efficiency is greater.

Low-power

Early motor vehicles tended to use DC generators with electromechanical regulators. These were not particularly reliable or efficient and have now been replaced by There was an error working with the wiki: Code[17] and There was an error working with the wiki: Code[37], which places a high load on the electrical system. Commercial vehicles are more likely to use 24 V to give sufficient power at the There was an error working with the wiki: Code[38] to turn over a large Diesel engine without the requirement for unreasonably thick cabling. Vehicle alternators usually do not use permanent magnets they can achieve efficiencies of up to 90% over a wide speed range by control of the field voltage. Motorcycle alternators often use permanent magnet There was an error working with the wiki: Code[39]s made with There was an error working with the wiki: Code[40] magnets, since they can be made smaller and lighter than other types.

Some of the smallest generators commonly found are used to power There was an error working with the wiki: Code[18]. These tend to be 0.5 A 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 There was an error working with the wiki: Code[41]s and are designed and manufactured with great precision. 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 There was an error working with the wiki: Code[42], Wind Turbine or There was an error working with the wiki: Code[43] is connected to a low-power alternator and rectifier to supply currents of up to 12 A at typical cruising speeds.

Engine-generator

An engine-generator is the combination of an electrical generator and an There was an error working with the wiki: Code[19] regulator. Many units are equipped with a battery and electric starter. Standby power generating units often include an automatic starting system and a There was an error working with the wiki: Code[44] to disconnect the load from the utility power source and connect it to the generator.

Engine-generators produce alternating current power that is used as a substitute for the power that might otherwise be purchased from a utility power station. The generator Volt (volts), There was an error working with the wiki: Code[20] (watts) ratings are selected to suit the load that will be connected. Both There was an error working with the wiki: Code[45] and There was an error working with the wiki: Code[46] models are available. There are only a few portable three-phase generator models available in the US. Most of the portable units available are single phase power only and most of the three-phase generators manufactured are large industrial type generators.

Engine-generators are available in a wide range of power ratings. These include small, hand-portable units that can supply several hundred watts of power, hand-cart mounted units, as pictured above, that can supply several thousand watts and stationary or trailer-mounted units that can supply over a million watts. The smaller units tend to use gasoline (petrol) as a fuel, and the larger ones have various fuel types, including diesel, natural gas and propane (liquid or gas).

When using engine-generators, you must be aware of the quality of the electrical wave it outputs. This is particularly important when running sensitive electronic equipment. A There was an error working with the wiki: Code[47] can take the square waves generated by many engine-generators and smooth it out by running it through a battery in the middle of the circuit. Engine-generators are often used to supply electrical power in places where utility power is not available and in situations where power is needed only temporarily. Small generators are sometimes used to supply power tools at construction sites. Trailer-mounted generators supply power for lighting, amusement rides etc. for traveling carnivals.

Standby power generators are permanently installed and kept ready to supply power to critical loads during temporary interruptions of the utility power supply. Hospitals, communications service installations, sewage pumping stations and many other important facilities are equipped with standby power generators. Small and medium generators are especially popular in third world countries to supplement grid power, which is often unreliable. Trailer-mounted generators can be towed to disaster areas where grid power has been temporarily disrupted.

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

Mid-size stationary engine-generator

The mid-size stationary engine-generator pictured here is a 100 kVA set which produces 415 V at around 110 A per phase. It's powered by a 6.7 litre turbocharged Perkins Phaser 1000 Series engine, and consumes approximately 27 litres of fuel an hour, on a 400 litre tank. Stationary generators used in the US are used in size up to 2800 kW. These diesel engines are run in the UK on There was an error working with the wiki: Code[48] and rotate at 1500 rpm. This produces power at 50 Hz, which is the frequency used in the UK. In areas where the power frequency is 60 Hz (United States), generators rotate at 1800 rpm or another even multiple of 60. Diesel engine-generator sets operated at their best efficiency point can produce between 3 and 4 kilowatthours of electrical energy for each litre of diesel fuel consumed, with lower efficiency at part load.

Related

There was an error working with the wiki: Code[49]

Solar cell

There was an error working with the wiki: Code[50]

There was an error working with the wiki: Code[51]

Windmill

External articles and references

There was an error working with the wiki: Code[2] -- Magneto-Electric Machines : There was an error working with the wiki: Code[21] dynamo. The device's nickname was the "long-legged Mary-Ann". This device has large bipolar magnets. It is inefficient.

There was an error working with the wiki: Code[3] -- There was an error working with the wiki: Code[52] : Edison's improved dynamo which includes an extra coil and utilizes a field of force.

There was an error working with the wiki: Code[4] -- Dynamo Electric Machine - Nikola Tesla's construction of the Alternating current Induction motor / generator.

There was an error working with the wiki: Code[5] -- Dynamo Electric Machine - Tesla's "Unipolar" machine (i.e., a disk or cylindrical conductor is mounted in between magnetic poles adapted to produce a uniform magnetic field).

There was an error working with the wiki: Code[6] -- Armature for Electric Machines -Tesla's construction principles of the armature for electrical generators and motors. (Related to patents numbers US327797, US292077, and GB9013.)

There was an error working with the wiki: Code[7] -- Method of Operating Arc-Lamps - Tesla's alternating current generator of high frequency alternations (or pulsations) above the auditory level.

There was an error working with the wiki: Code[8] -- Alternating Electric Current Generator - Tesla's generator that produces alternations of 15000 per second or more.

Electus Distribution Reference Data Sheet: Impedance Matching Primer (PDF)

Build an AC gen from scratch

Hamster-powered night light

Simple generator

There was an error working with the wiki: Code[1], Wikipedia: The Free Encyclopedia. Wikimedia Foundation.

There was an error working with the wiki: Code[22]

There was an error working with the wiki: Code[23]

There was an error working with the wiki: Code[53]

Comments