POWER GENERATOR

tarih: 29/8/2007 Saat: 05:21 : - Yorum Yaz

In electricity generation, an electrical generator is a device that converts kinetic energy to electrical energy, generally using electromagnetic induction. The reverse conversion of electrical energy into mechanical energy is done by a motor, and motors and generators have many similarities. 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, or any other source of mechanical energy.

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 triboelectric effect using the separation of two insulators (the belt leaving the lower pulley)

   In 1831-1832 Michael Faraday discovered that a potential difference 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 copper disc rotating between the poles of a horseshoe magnet. 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 electromagnetic principles to convert mechanical rotation into an alternating electric current. 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 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. The construction of a dynamo is similar to that of an electric motor, and all common types of dynamos could work as motors.

An engine-generator is the combination of an electrical generator and an engine mounted together to form a single piece of equipment. This combination is also called an engine-generator set or a gen-set. In many contexts, the engine is taken for granted and the combined unit is simply called a generator.

In addition to the engine and generator, engine-generators generally include a fuel tank, an engine speed regulator and a generator voltage regulator. Many units are equipped with a battery and electric starter. Standby power generating units often include an automatic starting system and a transfer switch to disconnect the load from the utility power source and connect it to the generator.

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 temporary installations of lighting, sound ampliification systems, amusement rides etc.

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).The generator voltage (volts), frequenc (Hz) and power (watts) ratings are selected to suit the load that will be connected.

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).

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.

Portable engine-generators may require an external power conditioner to safely operate some types of electronic equipment.

Hand portable emergency generators

Hand-held direct current generators supply energy to discharged car batteries. They are called emergency vehicle generators and includes batteries, to store energy.

A prefered hand-held generator is one that has an inverter. They are the smallest, quietest, and most fuel-efficient generators. Small portable generators have a standard A.C. alternator and run at a faster R.P.M. to generate power. Inverter models can run at slower RPMs to generate the power that is necessary, thus reducing the noise of the engine and making it more fuel-efficient. Inverter generators are best to power sensitive electronic devices such as computers and lights that use a ballast. The power output of an inverter is more stable and is equal to or better than household electrical power. Regular generators that do not have AVR (Automatic Voltage Regulation) can damage electronics such as computers and sound systems due to their varying voltage.

The mid-size stationary engine-generator pictured here is a 100 kVA set which produces 415 V at around 110 A per phase. It is 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. Diesel engines in the UK run on red diesel and rotate at 1500 rpm. This produces power at a frequency of 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 peak 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.