Asynchronous generator uses the air gap between stator and rotor to rotate magnetic field andRotor windingininduced currentInteractionalternator。It is also called according to the working principle“Induction generator”。The speed is slightly higher than the synchronous speed.The output power increases or decreases with the slip.It can be magnetized by power grid or self magnetized by power capacitor.
Asynchronous generator is also called“Induction generator”。Use the air gap between stator and rotor to rotate the magnetic field andRotor windingininduced currentInteractionalternator。The rotation direction of the rotor is the same as that of the rotating magnetic field, but the speed is slightly higher than the synchronous speed of the rotating magnetic field.Commonly used as small powerHydro generator。
AC excited generatorAlso known asDoubly fed generator。AC excitation generator adopts AC voltage due to rotor sideexcitation, so that it has a flexible operation modePower frequency overvoltageVariable speed constant frequency power generation, electric power of pumped storage power station-Generator SetHas a tradition in terms of speed regulationSynchronous generatorIncomparable advantages.There are three main operation modes of AC excited generator: 1) Variable speed constant frequency operation;2) Operating in the way of reactive power regulation in a large range;3) It operates in the power generation electric mode.
Production process
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With the power systemTransmission voltageThe increase ofTransmission powerlower thanNatural powerThe line and power station will have continuousPower frequency overvoltageIn order to improve the operation characteristics of the system, many technologically advanced countries began to study the application of asynchronous generators in large power systems in the early 1960s, and believed that the use of asynchronous generators in large systems could improve the stability, reliability and operation economy of the system
Advantages and disadvantages
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Main advantages
The cage rotor asynchronous generator has simple and firm structure, and is especially suitable for high peripheral speed motors.nothingCollector ringandCarbon brushIt has high reliability and is not limited by the use place.Because there is no rotorexcitationThe magnetic field does not need synchronization and voltage regulation devices, and the power station equipment is simplified.The load control is very simple. In most cases, the turbine governor is not required, and the turbine can operate at full speed or at a certain speed range with a locked wicket gate opening.Although the asynchronous generator may have power swing, there is noSynchronous generatorSimilar oscillations andOut of stepProblem, the operation of grid connection is simple.
Main disadvantages
Large capacity asynchronous generator must be connected withSynchronous generatorParallel operationOr connect to the power grid for operation, and the synchronous generator or power grid will provideexcitationReactive power, so the asynchronous generator is the power gridReactive load。Although in principle, asynchronous generators can use capacitorsIsolated operationstaySelf excitationHowever, the voltage regulating capacity of the generator is very weak when the generator reaches the critical loadVoltage collapse。Generally speaking, the excitation of asynchronous generator can be provided by synchronous generator, power grid or static capacitor.The specific excitation supply mode is determined by the type of power station or grid operation conditions.Although it may be a defect that the asynchronous generator cannot provide the reactive power required by itself and the load, it can be used as the power grid when it is properly usedReactive power optimizationA means of.It will bring obvious technical and economic benefits to the power station and power grid.[1]
Economy
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(1) The power station equipped with asynchronous generator does not need DCExcitation system，Synchronizing deviceThe investment cost of the power station is low.
⑶ The rotor of asynchronous generator is non salient pole and non salient poleSynchronous generatoralliedRotor windingTherefore, the efficiency is generally higher than that of synchronous generators with the same capacity and speed. Under the same water source, asynchronous generators can generate more power.
⑷ The above economic advantages of asynchronous generator will be due to the demand of asynchronous generatorexcitation(or additional synchronous capacity or additional capacitor) is partially offset.
(5) The size of the excitation required by the asynchronous generator and theRated speedIn inverse proportion (that is, in direct proportion to the number of poles of the motor), the higher the speed, the lower the per unit excitation.
(6) Area comparison of asynchronous generator power plantSynchronous generatorThe powerhouse area is small.
alternator
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A generator is a device that converts mechanical energy into electrical energy.The first set was made by the Frenchman, Ippolit PixeiPermanent magnet generator。
In Pichia's generator, the magnetic field is generated by a fixed permanent magnet.A winding wound on the plate assembly rotates in this magnetic field. One end of the winding is connected to the ground wire of the permanent magnet generator, and the other end is connected to the wire pole of the generator.The closed circuit of the winding forms the armature of induced current.When the winding coil rotates in the magnetic field, it will be generated in the winding coil due to cutting the magnetic line of forceInduced electromotive force。If the generator is externally connected with load, current will be generated.Here we call the rotating winding the rotor armature and the permanent magnet the stator pole.In 1831, Michael Faraday, an Englishman, gave a demonstration performance in this way.This is the earliest induction generator and the earliest device to convert mechanical energy into electrical energy.The current generated by this generator is alternating current, so it is also called alternator.
Until July 17, 1871, the Belgian Zinab Gram invented the first machine that uses mechanical energy to generate electricityDC generator。Gram's generator is designed as follows: the wire is wound around the ring and rotates in the magnetic field perpendicular to the rotation axis of the ring. The two ends of each winding wire are connected to two pieces of commutator, and two electric brushes contact with the commutator to form positive electrode and negative electrode.Gram was very excited because he was just an ordinary worker who had attended night school before. At the Vienna Expo, he suddenly became a world famous person.In 1878, he invented the alternator.At that time, people could only convert mechanical energy into electricity. Gram began to manufacture the DC generator in 1832. Strictly speaking, Gram invented the commutator generator in 1869.
In 1959, the first electromagnetic fluid power generator was successfully manufactured by the research experiment in Afko, Massachusetts, USA. It can directly convert heat energy into electric energy.In an MHD generator, the burner converts the fuel intoPlasmaThe combustion can reach 2500-3000 ℃.Plasma is a highly ionized gas composed of countless positive ions.It is composed of innumerable atoms that have lost electrons.Under the action of a strong magnetic field, free electrons move towards the positive electrode and generate current for the positive electrode to absorb.Since there is no "intermediate procedure" for the MHD generator, its power is large and its efficiency is high.For example, there is no intermediate procedure for steam driven turbines, which can reduce generator efficiency by 40%.The use of electromagnetic fluid power generator can not only improve the efficiency, but also save half of the combustion supporting agent.In addition, the temperature reached is beyond the usual range.In the turbine, the temperature cannot exceed 800-900 ℃. If the temperature exceeds this limit, the turbine will be damaged.Unfortunately, there are still some serious problems in the high temperature resistance of the electrode of the MHD generator.It should be mentioned here that the manufacturing of electro-hydraulic power generators includes the theoretical results of the research work of Swedish physicist Alfen in the previous decade.[2]
alternator
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A machine that uses the principle of electromagnetic induction to obtain alternating electromotive force.On October 28, 1831, the scientist Faraday made the disk rotate in the magnetic field of a large magnet, thus obtaining continuous current, and made the world's first generator with the principle of electromagnetic induction.
The generator model in the middle school physics textbook can only be used for demonstration, and has no practical value.In practical application, in order to increase the electromotive force of the generator so as to increase the output voltage, two measures need to be taken: first, the magnetic field in the generator must be strengthened, so the coil generating the electromotive force is always wound around the iron core, and a strong magnet is used to replace the permanent magnet to generate the magnetic field;Second, in order to improve the electromotive force, multi turn coils must be used instead of single turn coils.
An alternator is a device that converts mechanical energy into electrical energy.Ampere force plays an important role in the process of energy conversion.fromAmpere's lawIt can be seen that the current carrying wire is subject to ampere force in the magnetic field.Ampere force pairArmature windingThe electromagnetic resistance moment is provided.When the external circuit is not loaded (the external circuit is open), there is no current in the armature winding. At this time, the armature winding is not subject to ampere force.In order to maintain uniform angular speed ω rotation of the armature, the external torque only needs to be equal to the friction resistance torque, and the work of the external torque is all converted into the heat generated by friction, which is calledNo load operation。When the generator is loaded (the external circuit is connected), there is current passing through the armature winding, and it will suffer the electromagnetic resistance moment of ampere force. At this time, in order to keep the armature winding rotating at a uniform angular speed ω, the external torque must be equal to the sum of friction resistance moment and electromagnetic resistance moment.The work of the external torque will be all converted into the electrical energy consumed by the load except for the part generated by friction.It can be seen that the ampere force plays a key role in the process of energy conversion.Generally, the devices that provide external torque to the generator mainly include steam turbine, water turbine, etc., and correspondingly there are thermal power generation and hydraulic power generation.In order to have a strong power output of modern generators, the voltage of armature winding is as high as several thousand volts or even up to ten thousand volts, and the current is as high as several thousand amperes.In order to avoid serious sparks caused by high voltage and large current between the slip ring and the brush, generators with power of more than tens of kilowatts generally exchange the armature and electromagnet to make the armature fixed while the magnetic pole rotates.After the transformation, the armature winding can be directly connected to the load, and the excitation winding of the electromagnet with low voltage and current can be connected to the external DC power through the slip ring and brush.Such generators are called rotating pole generators.Generators in modern power plants are generally of this type.
Synchronous generator
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The prime mover drives the magnetic pole rotor with DC excitation to rotate, so that the stator winding of the stationary part induces the AC electromotive force to output poweralternating current dynamo。It is a rotating machine that uses the principle of electromagnetic induction to transform mechanical energy into electrical energy.The ratio of its output current frequency to speed is a constant value. When generating power in parallel with other synchronous generators, the frequency must be equal, that is, it must rotate synchronously.
Development History Synchronous generators were originally single-phase and were used for electric lighting in the early 1980s;Late 1880sThree phase asynchronous motorAfter the invention, the synchronous generator was also changed to three-phase.In the early days, synchronous generators were driven by steam engines, diesel engines, water turbines or steam turbines, and their capacity was not large. Later, the capacity of turbine generators and water turbine generators increased rapidly, and they were increasingly widely used in the power industry.
typeSynchronous generatorPrime moverCome on, there areTurbine generator、Hydro generator、Diesel generatorEtc.According to the structural characteristics of rotorsSalient pole generatorandConcealed pole generatorTwo basic types.Due to the simple magnetic pole structure of salient pole type, most small and medium-sized synchronous generators use salient pole rotor.The speed of hydro generator is relatively low, generally only tens to hundreds of revolutions per minute, with many poles, so the rotor of hydro generator also adopts salient pole structure.Because of the high speed of the turbine generator, if salient pole pole is used, its centrifugal force is too large, so the structural form is changed, and the excitation winding is embedded in the slot on the surface of the cylinder rotor, which is called the hidden pole type.
working principleThe working principle of synchronous generator is the same no matter what kind of prime mover drives it or whether the rotor is salient pole or implicit pole.The excitation winding of the hydro generator is sleeved on the iron core of the convex magnetic pole, and the excitation magnetic field is generated after the DC current is connected.When the water turbine drives the generator rotor to rotate, like the turbine generator, the AC electromotive force is induced in the stator winding of the water turbine generator, and the current is output to the load to do work.[3]
