|Electric power generators|
|Tuesday, 05 September 2006|
Electrical generators are devices which transform mechanical energy into electrical energy. A typical generator set includes an engine, driven by a fuel such as gasoline, and a rotating shaft driven by the engine. The rotating shaft develops electric power, which is then used to power an electrical load. An electric power generator generally includes a rotor that rotates within a stator core to convert mechanical energy into electrical energy. A frame-supported stator core provides a high permeability path for magnetism and a rotor assembly positioned to rotate continuously within the stator core so as to induce electrical current through rotor-borne conductors moving through magnetic fields set up within the stator. The resulting current is carried by high-current conductors through and out from a housing surrounding the power generator, to connectors that provide the current to a plant bus for power distribution to consumers, commercial establishments, and other users of electrical power. The stator often includes a set of parallel rings which attach to at least one lead. The lead carries the power generated by the power generator typically to a bus adapter connected to connectors that convey electric power to a plant bus for distribution to residential, commercial, and other consumers of electric power. Power generators generally have an exciter positioned adjacent thereto to provide excitation to the power generators. Electrical power can be generated by electromagnetic induction using a generator having a rotor which in response to mechanical energy supplied to the generator turns within a stator core. Power generators employing magnetic fluids are magnetically driven generators, while most other types of power generators are electrically driven. Magnetically driven generators have two primary advantages over electrically driven generators. They are not subject to any catastrophic failures analogous to electrical breakdown, and second, they have a higher energy density.
Synchronous power generators are commonly used by power utilities to produce electrical energy. Synchronous power generators generally have a magnetic rotor that is surrounded by a stationary stator having conductive windings. A stator of a synchronous generator comprises a number of conductors in which an alternating current is induced by the rotor as it rotates within the stator, generating a rotating magnetic field in the narrow airgap between the stator and rotor. Rotating magnetic field from the spinning rotor creates electric current in the armature windings in a stationary stator that surrounds the rotor. The current from these windings is output as electrical power from the generator. Such generators are synchronous in that the rotor is rotated at a constant speed synchronous with the rotation of the magnetic field induced in the stator, thereby producing alternating current with a constant frequency. Synchronous power generators are often driven by gas turbines. Virtually all large turbine-driven generators used in the production of electrical power are synchronous generators. Induction generators differ from synchronous generators in that the rotor comprises a number of conductors in which alternating current flow is induced as a result of the rotor being rotated at a speed higher than the rotating magnetic field of the stator. While less efficient, induction generators have many advantages over synchronous generators, including simplicity, robustness, and cost. However, a major disadvantage of induction generators is that they must be supplied with reactive power.
A turbine power generator generates electric power by converting mechanical energy into electrical energy. The turbine power generator typically includes a stator and rotor to generate electrical power as the rotor turns within the stator. A turbine electric power generator has a plurality of rotor windings formed in an axial direction in which the windings are disposed. These windings are formed by superimposing a winding conductor by a plurality of turns in a radial direction, and insulation layers are provided between the turns. The rotor is driven by the rotation of a drive shaft that connects to and turns the rotor. The drive shaft of the turbine power generator is, in turn, driven by steam or combustion supplied within a turbine section of the turbine power generator. In a steam turbine generator, the shaft is driven by high-pressure saturated steam produced by a boiler and supplied to the turbine section. The boiler is fired by a fossil fuel or heated by a nuclear reactor. With a combustion turbine, the shaft is turned by an expansion of hot gas within the turbine section where air enters an inlet, is compressed by an air compressor, and then supplied to a combustor where fuel is burned to produce the hot gas. To start the gas turbine, the generator may be temporarily operated as a motor that is powered from an auxilary electrical power source. Once the generator/motor accelerates the rotational speed of the drive shaft sufficiently to start the gas turbine, the gas turbine is started.
In general, each of hydraulic power equipment, thermal power equipment, and atomic power equipment are widely known as electric power generator equipment. There are many types of power generators. Some use mechanical or physical means to generate power, and the others employ electronic or electric circuit design to accomplish power generation. Electrical energy for general use is being generated primarily by natural water flow, by burning fossil fuels and by nuclear generation. These methods have associated environmental problems and in the case of fossil fuels, an unacceptable depletion rate. Hydroelectric power generation is one of the most inexpensive and cleanest methods for generating large amounts of electric power. The use of hydroelectric power generation, however, is limited because it requires the availability of vast quantities of water and the feasibility of constructing a large dam to store the large amount of water. To generate electricity, hydraulic power, thermal power or atomic power is utilized, which involves disadvantages such as natural destruction with a dam, fuel shortage, air pollution and radioactivity injuries. In recent years, varying attention has been given to generating electricity from renewable, pollution-free, energy sources such as the sun, wind and water. For example, an oceanic thermal power generator generates electric power by utilizing a temperature difference between warm sea water at high temperature in an oceanic surface layer and cold sea water at low temperature in an oceanic deep layer. Clean natural energy such as solar generation, wind power generation, geothermal power generation, tidal power generation has been employed over the whole world.
Among these power generations, wind power generation produces electric power utilizing natural wind and has advantages in that installation cost is inexpensive compared with other power generating plants, and further the wind power generation can be performed individually in a unit of home or local community. Wind power is the conversion of wind energy into more useful forms, usually electricity using wind turbines. Wind power is generated in the form of electricity by converting the rotation of turbine blades into electrical current by means of an electrical generator. The power in the wind can be extracted by allowing it to blow past moving wings that exert torque on a rotor. The amount of power transferred is directly proportional to the density of the air, the area swept out by the rotor, and the cube of the wind speed. The wind power generator system includes a generator which is driven by rotation of a wind turbine and a battery which is charged by power supply from the generator. In this wind power generator system, power can be supplied to loads such as an electric device while the battery is charged by the rotation of the wind turbine. Wind turbines require steady breezes to function and the size of the towers and blades can be problematic to the environment and costly to build. Wind energy is abundant, renewable, widely distributed, and clean. Wind power was the most rapidly growing means of alternative electricity generation and provides a valuable complement to large-scale base-load power stations.
Another source of clean energy is sunlight. Photovoltaic panels (also called solar panels) are well known and are used to generate electricity from sunlight. Solar power generation uses solar photovoltaic arrays or solar cells to provide electricity for human activities. Sunlight is free and so the cost of electricity generated by a photovoltaic panel is extremely low. Photovoltaic cells are devices or banks of devices that use the photovoltaic effect of semiconductors to generate electricity directly from sunlight. Sunlight falling on the semiconductor material of the cell generates free electrons in the material, thereby creating an electric current. Some systems for generating electricity using solar energy require a concentrator and a receiver, the concentrator intercepting the solar radiation and focusing it on the receiver, the receiver absorbing the focused solar radiation, convening the radiation to heat and transferring the heat to a working fluid. Typically, photovoltaic panels are currently fixedly attached to the roof of a house and wired directly into the home's electrical system. Solar arrays are increasingly incorporated into new domestic and industrial buildings as a principal or ancillary source of electrical power.
In situations where utility power is not available, it is common to use an portable electrical generator to supply electrical power, often on a temporary basis but sometimes as a main source of electrical power. Portable power generators incorporating a generator driven by an internal combustion engine are popular for many uses. Typically, the generator, the engine and other components related to the generator and the engine are surrounded with an insulator cover for suppressing noise. Recently, private use cogeneration type generator apparatuses which can be interconnected with electric power networks for improvement of the efficiency of operation are getting popular. A cogeneration type private use generator apparatus comprises a small generator driven by a gasoline engine or a gas engine fueled with gas fuel. The cogeneration system driven by a gasoline engine or a gas engine includes a controller unit for purifying the exhaust gas.