When the rotor coil is rotated at constant speed in the field between the stator poles the EMF generated in the coil will be approximately sinusoidal, the actual waveform being dependent on the size and shape of the magnetic poles. In a stationary field generator, the stator in the form of fixed permanent magnets (or electromagnets fed by DC) provides the magnetic field and the current is generated in the rotor windings. Stationary Field Synchronous AC Generator.Voltage and frequency regulation correct for minor deviations in the generator output as noted above but large changes in the load demand (current) can only be accommodated by adjusting the torque of the prime mover driving the generator since generally, in electric machines, torque is proportional to current or vice versa. Where ω is the speed in radians per second and T is the torque in Newton metres.Īs with electric motors, the maximum power handling capability of the generator is determined by its maximum permissible temperature. The mechanical shaft power P in Watts applied to a generator is given by: See more details about, and examples of voltage and frequency regulation of grid connected systems on the Wind Power page. When connecting a generator to the grid, it's speed should be run up so that it's output frequency matches the grid frequency before the connection is made. Changing the energy output from the prime mover does not affect the frequency and voltage but will cause the output current to increase resulting in an equivalent change in the generator output power. In grid connected systems the generator voltage and frequency are locked to the grid system. In principle these control systems are similar to Motor Controls and the various components are outlined in that section. In smaller, stand alone systems particularly those designed to capture energy from intermittent energy flows such as wind and wave power the voltage and frequency control may be carried out electronically. Voltage and frequency regulation is normally accomplished in very large machines carrying very high currents, by controlling the generator excitation and the speed of the prime mover which drives the generator. Most generator applications require some way controlling the output voltage and in the case of AC machines a method of controlling the frequency. The vast majority of generators are AC machines (Alternators) with a smaller number of DC generators (Dynamos). Though the variety of electric generators is not as great as the wide variety of electric motors available, they obey similar design rules and most of the operating principles used in the various classes of electric motors are also applicable to electric generators. The primary supply of all the world's electrical energy is generated in three phase synchronous generators using machines with power ratings up to 1500 MW or more. Woodbank does not monitor or record these emailsĮlectrical Machines - Generators (Description and Applications)
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