THE ELECTRIC GENERATOR GUIDE |
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Frequent blackouts in recent years increased demand for backup power
solutions among homeowners and businesses. A power outage is more
than spoiled food, loss of light or just an inconvenience; it is a potential
life-threatening situation such as loss of air conditioning in the
summer or heat in the winter, not to mention loss of power for electrically operated
medical equipment.  This site is dedicated to information about various types of the generators. |
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WHAT IS A GENERATOR?In power industry, this term refers to a device that produces electrical energy. Although electricity does occur naturally, it does not exist in the forms that currently can be practically used. For practical use electricity is converted from other forms of energy. Since energy cannot be created but can only be transferred from one form to another, a generator obviously needs an energy source. In electric generators such source is mechanical energy. The mechanical energy in turn is converted from so-called primary sources, such as chemical or nuclear energy in various types of fuel, or obtained from renewable resources such as wind or falling water. The machine that converts primary energy into mechanical energy is called prime mover. Steam turbines, internal-combustion engines, gas combustion turbines, water and wind turbines are the common types of prime movers. HOW IT WORKS.
The operation of power generators is based on the phenomenon of
electromagnetic induction: whenever a conductor moves relative to a
magnetic field, voltage is induced in the conductor. Particularly, if a
magnet is spinning inside a coil, AC voltage is induced in the coil.
For more details, see How generators work
tutorial with an animation that illustrates the basic operation. The induced voltage (called electromotive force or emf) will create a current through an external circuit connected to the coil, resulting in energy being delivered to the load. Thus, the mechanical energy that rotates the source of the magnetic field is converted into electrical energy. Note that the load current in turn creates a magnetic field that opposes the change in the flux of the coil, so the coil opposes the motion. The higher the current, the larger the force that must be applied to the magnet to keep it from slowing down. In practice, the magnetic field is most often induced by an electromagnet rather then a permanent magnet. In AC systems, usually the electromagnet is spinning, and the power-producing armature is stationary. The armature normally comprises of a set of coils that form a cylinder. The electromagnet consists of so called field coils mounted on an iron core. A current flow in the field coils is required to produce magnetic field. This current may be obtained from an external source or from the system's own armature. Most modern AC sources with field coils are self-excited: the current for field coils is supplied by an additional exciting winding in the armature. The initial magnetic field is produced by residual magnetism in the electromagnet's cores. When the prime mover starts turning the armature, at first the armature rotates in a very weak magnetic field and produces small emf. This emf creates a current in field coils, which increases magnetic flux, which in turn increases emf in the armature. This process continues until the rated output voltage is reached. If the electromagnet's core lost its residual magnetism, the rotor will spin, but no output voltage will be produced. In this case, to start the device you may need to do so called field flashing. EMERGENCY BACKUP GENSETS.In power plants the generators are most often driven by steam or hydraulic turbines or by diesel engines. The same concept of converting mechanical energy into electric energy is widely used in small privately owned generators as well. In commercially available devices an electric generator head is usually integrated with an internal-combustion engine into a single appliance. The resulting device is referred to as an engine-generator set or a genset. It is the most common type of backup power source for home or business. A genset is often casually called just a generator even though it also includes an engine. There are two main types of such devices that differ by their connection and activation methods: standby and portable. Standby gensets are permanently connected to the house wiring system via a transfer switch and are also permanently connected to a fuel source, such as a natural gas line or a large propane or diesel tank. They cost more than portables and require professional installation, but they can provide continuous power for as long as the fuel is available (see standby brands and ratings). Portable devices are intended primarily for a temporary connection to several appliances via extension cords. They are normally fueled from an on-board tank and therefore need frequent refueling. Some more expensive portable models can also be powered from an external source for extended run time (see portable brands and ratings). A portable genset is generally cheaper then a standby and does not need a professional installation unless you want to connect it directly to the house wiring (in which case you need to install a transfer switch). Choosing the best genset for your application involves selecting the right type and sizing based on the amount of power you may need during an emergency. |
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© 2008 Lazar Rozenblat |
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