Electric Drives:
Generators (Description and Applications)
The primary power of the world's electricity is generated in three-phase synchronous generators with machines with power up to 1500 MW or more. Design rules Despite the variety of electric generators is not as big as the wide range of electric motors available, they obey similar and most of the operating principles used in the various classes of electric motors, are also applicable to electrical generators. The vast majority of generators are machines (alternators), with a smaller number of DC generators (Zamalek).
Voltage and Frequency Regulation:
The primary power of the world's electricity is generated in three-phase synchronous generators with machines with power up to 1500 MW or more. Design rules Despite the variety of electric generators is not as big as the wide range of electric motors available, they obey similar and most of the operating principles used in the various classes of electric motors, are also applicable to electrical generators. The vast majority of generators are machines (alternators), with a smaller number of DC generators (Zamalek).
Voltage and Frequency Regulation:
Most applications require some way control the generator output voltage and, in the case of an AC machine control method of the frequency. Voltage and frequency regulation is normally attained in the field of large machines that carry very high currents, controlling the excitation of the generator and the speed of the first engine driving the generator.
In smaller systems, particularly those designed to capture energy from intermittent energy flows such as wind and wave power voltage and frequency control can be done electronically. In principle, these control systems are similar to the engine controls and the various components are described in that section.
Generator Types
AC Generators (Alternators) :
Generator Types
AC Generators (Alternators) :
Stationary Field Synchronous AC Generator In a stationary field generator, the stator in a fixed permanent magnets (or electromagnets powered by direct current) provides the magnetic field and current is generated in the windings of the rotor.
When the coil rotor rotates at constant speed in this field between the two poles of the stator the emf generated in the coil will be approximately sinusoidal, the actual waveform depends on the size and shape of the magnetic poles. The peak voltage occurs when the conductor is moving through the center line of the magnetic pole. Decreases to zero when the conductor is the space between the posts and increased to a peak in the opposite direction as the driver approaches the center line of the opposite pole of the magnet. The frequency of the waveform is directly proportional to the speed of rotation. The wave amplitude is proportional to the speed until the magnetic circuit saturates while the rate of increase of tension, as the speed increases, slows dramatically.
The output frequency is proportional to the number of poles and the rotor speed in the same way as a motor sychronous. See Table of engine speeds.
The current output generated alternating the rotor can be connected to external circuits via slip rings and does not need a switch.
Typical applications are portable AC generator with output power up to 5 kilowatts.
The rotating field synchronous AC generator The power management capabilities of a machine brushed, it is usually limited by the current handling capacity of the rings to slip in a car AC (or even more, the switch in a DC machine). Since the load current source is generally much higher than the current field, it is usually appropriate to use the rotor to create the field and take power from the generator stator to minimize the load on the rings slip .
Exchanging fixed and moving elements in the example above a generator rotating field is created in which the CEM is instead generated in the stator windings. In this case, in its simplest form, the field is provided by a permanent magnet (or electromagnet) that is rotated within a fixed cycle or coil of wire in the stator. The magnetic field in motion due to rotation of the rotor magnet will then cause a sinusoidal current flowing in the coil stator fixed the field moves beyond the stator conductors. If the field of rotor is provided by an electromagnet, will need to direct excitation current supplied through slip rings. Does not need a switch.
If instead of a single coil, three independent coils or the stator windings, spaced 120 degrees apart around the periphery of the machine are used, then the output of these coils are three-phase alternating current.
Series Wound Generator Classified as a generator at constant speed, they have poor voltage regulation and few are in use.
Shunt Wound Generator Classified as a constant voltage, the output voltage can be controlled by varying the field current. Reasonably good voltage regulation in the range of machine speed.
Brushless excitation Industry rotating machines are used for high power generation plants, in most systems of the world, the national grid. The power of excitement on the ground, these machines can be as large as 2.5% of the power (25 kW in a 1.0 MW generator), although this reduces the efficiency improves with the size so that a generator of 500 MW to 2.5 MW needs (0.5%) of power of excitation. If the voltage field is 1000 volts, the required field current will be 2500 Amps. Provide through the rings of excitement this shift is a technical challenge that was overcome by generating the necessary energy into the box itself by means of a pilot, three phase, stationary field generator on the same tree. The AC current generated in the windings of the pilot generator is rectified and fed directly to the windings of the rotor to provide excitation for the main machine.
Cooling The efficiency of a generator of large size can be as high as 98% or 99%, but for a generator of 1000 MW, with a loss efficiecy of just 1% means 10 megawatts of losses must be dissipated, primarily as heat. To avoid overheating, cooling, special precautions must be taken and the two forms of cooling are usually used simultaneously. The cooling water is circulated through copper bars in the stator windings and hydrogen is passed through the casing of the generator. Hydrogen has the advantage that its density is only 7% of air density with consequent loss of derivation of the rotor turning out less because the air in the machine and its thermal capacity is 10 times greater than air give him the ability to remove the heat higher.
Permanent Magnet AC Generators Smaller versions of both cars above can be used permanent magnets to provide magnetic field of the machine and the power is used to supply the industry, this means that the machines are simpler and more efficient. The disadvantage is however that there is no easy way to control this type of machine. Permanent magnet synchronous generators (PMSGs) are typically used in low-cost "power generators" to provide emergency power.
The voltage and output frequency of the permanent magnet generator is proportional to rotation speed, and although this may not be a problem for applications powered by a fixed speed drive mechanic, many applications such as wind turbines, require an output voltage fixed frequency, but are powered by variable speed prime movers. In these cases, complex control systems, feedback or external power conditioning may be required to provide the desired output stabilized.
In general, the output will be rectified and the output voltage variable supplied through the DC link to a dollar - reinforce that provides a fixed voltage regulator together with an inverter that provides a fixed output frequency.
Variable / Switched Reluctance Generators Similar in construction of the reluctance motor running, the generator is a doubly salient machine without magnets or brushes. As inert, iron poles of the generator rotor reluctance poles are pushed over the stator, the reluctance of the magnetic circuit evolution of the source is accompanied by a corresponding change in inductance of the stator poles, which in turn causes a current to be induced in the stator windings.
When the coil rotor rotates at constant speed in this field between the two poles of the stator the emf generated in the coil will be approximately sinusoidal, the actual waveform depends on the size and shape of the magnetic poles. The peak voltage occurs when the conductor is moving through the center line of the magnetic pole. Decreases to zero when the conductor is the space between the posts and increased to a peak in the opposite direction as the driver approaches the center line of the opposite pole of the magnet. The frequency of the waveform is directly proportional to the speed of rotation. The wave amplitude is proportional to the speed until the magnetic circuit saturates while the rate of increase of tension, as the speed increases, slows dramatically.
The output frequency is proportional to the number of poles and the rotor speed in the same way as a motor sychronous. See Table of engine speeds.
The current output generated alternating the rotor can be connected to external circuits via slip rings and does not need a switch.
Typical applications are portable AC generator with output power up to 5 kilowatts.
The rotating field synchronous AC generator The power management capabilities of a machine brushed, it is usually limited by the current handling capacity of the rings to slip in a car AC (or even more, the switch in a DC machine). Since the load current source is generally much higher than the current field, it is usually appropriate to use the rotor to create the field and take power from the generator stator to minimize the load on the rings slip .
Exchanging fixed and moving elements in the example above a generator rotating field is created in which the CEM is instead generated in the stator windings. In this case, in its simplest form, the field is provided by a permanent magnet (or electromagnet) that is rotated within a fixed cycle or coil of wire in the stator. The magnetic field in motion due to rotation of the rotor magnet will then cause a sinusoidal current flowing in the coil stator fixed the field moves beyond the stator conductors. If the field of rotor is provided by an electromagnet, will need to direct excitation current supplied through slip rings. Does not need a switch.
If instead of a single coil, three independent coils or the stator windings, spaced 120 degrees apart around the periphery of the machine are used, then the output of these coils are three-phase alternating current.
Series Wound Generator Classified as a generator at constant speed, they have poor voltage regulation and few are in use.
Shunt Wound Generator Classified as a constant voltage, the output voltage can be controlled by varying the field current. Reasonably good voltage regulation in the range of machine speed.
Brushless excitation Industry rotating machines are used for high power generation plants, in most systems of the world, the national grid. The power of excitement on the ground, these machines can be as large as 2.5% of the power (25 kW in a 1.0 MW generator), although this reduces the efficiency improves with the size so that a generator of 500 MW to 2.5 MW needs (0.5%) of power of excitation. If the voltage field is 1000 volts, the required field current will be 2500 Amps. Provide through the rings of excitement this shift is a technical challenge that was overcome by generating the necessary energy into the box itself by means of a pilot, three phase, stationary field generator on the same tree. The AC current generated in the windings of the pilot generator is rectified and fed directly to the windings of the rotor to provide excitation for the main machine.
Cooling The efficiency of a generator of large size can be as high as 98% or 99%, but for a generator of 1000 MW, with a loss efficiecy of just 1% means 10 megawatts of losses must be dissipated, primarily as heat. To avoid overheating, cooling, special precautions must be taken and the two forms of cooling are usually used simultaneously. The cooling water is circulated through copper bars in the stator windings and hydrogen is passed through the casing of the generator. Hydrogen has the advantage that its density is only 7% of air density with consequent loss of derivation of the rotor turning out less because the air in the machine and its thermal capacity is 10 times greater than air give him the ability to remove the heat higher.
Permanent Magnet AC Generators Smaller versions of both cars above can be used permanent magnets to provide magnetic field of the machine and the power is used to supply the industry, this means that the machines are simpler and more efficient. The disadvantage is however that there is no easy way to control this type of machine. Permanent magnet synchronous generators (PMSGs) are typically used in low-cost "power generators" to provide emergency power.
The voltage and output frequency of the permanent magnet generator is proportional to rotation speed, and although this may not be a problem for applications powered by a fixed speed drive mechanic, many applications such as wind turbines, require an output voltage fixed frequency, but are powered by variable speed prime movers. In these cases, complex control systems, feedback or external power conditioning may be required to provide the desired output stabilized.
In general, the output will be rectified and the output voltage variable supplied through the DC link to a dollar - reinforce that provides a fixed voltage regulator together with an inverter that provides a fixed output frequency.
Variable / Switched Reluctance Generators Similar in construction of the reluctance motor running, the generator is a doubly salient machine without magnets or brushes. As inert, iron poles of the generator rotor reluctance poles are pushed over the stator, the reluctance of the magnetic circuit evolution of the source is accompanied by a corresponding change in inductance of the stator poles, which in turn causes a current to be induced in the stator windings.
It would therefore be in a pulsed waveform appears at each pole of the stator. In machines polyphase results of each phase are fed to a converter that allows you to pass each stage sequentially to the DC link to provide a DC voltage. The system needs to detect the rotor position to control the timing of triggering the converter switches. These position sensors also allow the current to be controlled by varying the turn on and off the corners of the output current depending on the position of the rotor. As for the permanent magnet generator, Buck - boost regulators are also used to provide control over production.
The car unfortunately is not in itself self-exciting and different methods were adopted to enable the start, including the provision of an excitation current from a battery backup through the stator windings during start up or using small permanent magnets embedded in some of the poles of the rotor.
Features Compact, rugged design:
Variable speed operation.
The phases of the generator are completely independent.
Inexpensive to produce.
Because they have simple, inert without rotor windings or magnets embedded that can be driven at very high speeds and can operate in conditions of high temperature.
Suitable for models up to megawatts of capacity and speed of more than 50,000 rpm.
Applications:
The car unfortunately is not in itself self-exciting and different methods were adopted to enable the start, including the provision of an excitation current from a battery backup through the stator windings during start up or using small permanent magnets embedded in some of the poles of the rotor.
Features Compact, rugged design:
Variable speed operation.
The phases of the generator are completely independent.
Inexpensive to produce.
Because they have simple, inert without rotor windings or magnets embedded that can be driven at very high speeds and can operate in conditions of high temperature.
Suitable for models up to megawatts of capacity and speed of more than 50,000 rpm.
Applications:
Hybrid electric vehicle (HEV) drive systems, automotive starter generators, the generation of aircraft auxiliary power, wind generators, gas generators, high-speed turbine.
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