What Is The Difference Between Synchronous And Asynchronous Motor Pdf
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- Synchronous motor
- What is the differences between synchronous and asynchronous motor?
- What is the differences between synchronous and asynchronous motor?
- The difference between asynchronous and synchronous generator
In the electrical systems, we use either in industries, power stations or domestic needs, motors and generators have become a common thing. With the demand for high energy efficient and less power consuming systems, the invention of new models of these electrical devices is seen. The basic calculating factor for motors and generators reliable operation is the Power factor. It is the ratio of applied power over the required power.
A synchronous electric motor is an AC motor in which, at steady state ,  the rotation of the shaft is synchronized with the frequency of the supply current ; the rotation period is exactly equal to an integral number of AC cycles. Synchronous motors contain multiphase AC electromagnets on the stator of the motor that create a magnetic field which rotates in time with the oscillations of the line current. The rotor with permanent magnets or electromagnets turns in step with the stator field at the same rate and as a result, provides the second synchronized rotating magnet field of any AC motor.
A synchronous motor is termed doubly fed if it is supplied with independently excited multiphase AC electromagnets on both the rotor and stator. The synchronous motor and induction motor are the most widely used types of AC motor. The difference between the two types is that the synchronous motor rotates at a rate locked to the line frequency since it does not rely on current induction to produce the rotor's magnetic field.
By contrast, the induction motor requires slip : the rotor must rotate slightly slower than the AC alternations in order to induce current in the rotor winding. Small synchronous motors are used in timing applications such as in synchronous clocks , timers in appliances, tape recorders and precision servomechanisms in which the motor must operate at a precise speed; speed accuracy is that of the power line frequency , which is carefully controlled in large interconnected grid systems.
Synchronous motors are available in self-excited sub-fractional horsepower sizes  to high power industrial sizes. These machines are commonly used in analog electric clocks, timers and other devices where correct time is required. In higher power industrial sizes, the synchronous motor provides two important functions.
First, it is a highly efficient means of converting AC energy to work. Second, it can operate at leading or unity power factor and thereby provide power-factor correction. Synchronous motors fall under the more general category of synchronous machines which also includes the synchronous generator.
Generator action will be observed if the field poles are "driven ahead of the resultant air-gap flux by the forward motion of the prime mover ". Motor action will be observed if the field poles are "dragged behind the resultant air-gap flux by the retarding torque of a shaft load ". There are two major types of synchronous motors depending on how the rotor is magnetized: non-excited and direct-current excited.
In non-excited motors, the rotor is made of steel. At synchronous speed it rotates in step with the rotating magnetic field of the stator, so it has an almost-constant magnetic field through it. The external stator field magnetizes the rotor, inducing the magnetic poles needed to turn it. The rotor is made of a high- retentivity steel such as cobalt steel. These are manufactured in permanent magnet , reluctance and hysteresis designs: .
These have a rotor consisting of a solid steel casting with projecting salient toothed poles. Typically there are fewer rotor than stator poles to minimize torque ripple and to prevent the poles from all aligning simultaneously—a position that cannot generate torque.
This creates a torque pulling the rotor into alignment with the nearest pole of the stator field. Thus at synchronous speed the rotor is "locked" to the rotating stator field. This cannot start the motor, so the rotor poles usually have squirrel-cage windings embedded in them, to provide torque below synchronous speed.
The machine starts as an induction motor until it approaches synchronous speed, when the rotor "pulls in" and locks to the rotating stator field. Reluctance motor designs have ratings that range from fractional horsepower a few watts to about 22 kW.
Very small reluctance motors have low torque , and are generally used for instrumentation applications. Moderate torque, multi-horsepower motors use squirrel cage construction with toothed rotors.
When used with an adjustable frequency power supply, all motors in the drive system can be controlled at exactly the same speed. The power supply frequency determines motor operating speed. These have a solid smooth cylindrical rotor, cast of a high coercivity magnetically "hard" cobalt steel. The rotating stator field causes each small volume of the rotor to experience a reversing magnetic field. Because of hysteresis the phase of the magnetization lags behind the phase of the applied field.
As long as the rotor is below synchronous speed, each particle of the rotor experiences a reversing magnetic field at the "slip" frequency which drives it around its hysteresis loop, causing the rotor field to lag and create torque.
There is a 2-pole low reluctance bar structure in the rotor. Therefore, it is self-starting and doesn't need an induction winding to start it, although many designs do have a squirrel-cage conductive winding structure embedded in the rotor to provide extra torque at start-up. Hysteresis motors are manufactured in sub-fractional horsepower ratings, primarily as servomotors and timing motors.
More expensive than the reluctance type, hysteresis motors are used where precise constant speed is required. A permanent-magnet synchronous motor PMSM uses permanent magnets embedded in the steel rotor to create a constant magnetic field.
The stator carries windings connected to an AC supply to produce a rotating magnetic field as in an asynchronous motor. At synchronous speed the rotor poles lock to the rotating magnetic field. Permanent magnet synchronous motors are similar to brushless DC motors. Neodymium magnets are the most commonly used magnets in these motors. Permanent magnet motors have been used as gearless elevator motors since Most PMSMs require a variable-frequency drive to start. Permanent magnet synchronous motors are mainly controlled using direct torque control  and field oriented control.
Usually made in larger sizes larger than about 1 horsepower or 1 kilowatt these motors require direct current DC supplied to the rotor for excitation. This is most straightforwardly supplied through slip rings , but a brushless AC induction and rectifier arrangement may also be used. A permanent magnet synchronous motor and reluctance motor requires a control system for operating VFD or servo drive. There are a large number of control methods for PMSM, which is selected depending on the construction of the electric motor and the scope.
Control methods can be divided into: . The synchronous speed of a synchronous motor is given:  in RPM , by:. The number of pole-pairs is 2, so the synchronous speed is:. The number of pole-pairs is 6, so the synchronous speed is:. To determine the number of coil groups per phase in a 3-phase motor, count the number of coils, divide by the number of phases, which is 3. The coils may span several slots in the stator core, making it tedious to count them.
For a 3-phase motor, if you count a total of 12 coil groups, it has 4 magnetic poles. For a pole 3-phase machine, there will be 36 coils. The number of magnetic poles in the rotor is equal to the number of magnetic poles in the stator. The principal components of a synchronous motor are the stator and the rotor.
In some machines or when a large number of poles are needed, a salient pole rotor is used. This type of construction as an advantage than dc motor type where the armature used is of rotating type. The operation of a synchronous motor is due to the interaction of the magnetic fields of the stator and the rotor. Its stator winding, which consists of a 3 phase winding, is provided with a 3 phase supply, and the rotor is provided with a DC supply.
The 3 phase stator winding carrying 3 phase currents produces 3 phase rotating magnetic flux and therefore a rotating magnetic field. The rotor locks in with the rotating magnetic field and rotates along with it. Once the rotor field locks in with the rotating magnetic field, the motor is said to be in synchronization. A single-phase or two-phase derived from single phase stator winding is possible, but in this case the direction of rotation is not defined and the machine may start in either direction unless prevented from doing so by the starting arrangements.
Once the motor is in operation, the speed of the motor is dependent only on the supply frequency. When the motor load is increased beyond the breakdown load, the motor falls out of synchronization and the field winding no longer follows the rotating magnetic field.
Since the motor cannot produce synchronous torque if it falls out of synchronization, practical synchronous motors have a partial or complete squirrel-cage damper amortisseur winding to stabilize operation and facilitate starting.
Because this winding is smaller than that of an equivalent induction motor and can overheat on long operation, and because large slip-frequency voltages are induced in the rotor excitation winding, synchronous motor protection devices sense this condition and interrupt the power supply out of step protection.
Above a certain size, synchronous motors are not self-starting motors. This property is due to the inertia of the rotor; it cannot instantly follow the rotation of the magnetic field of the stator.
Since a synchronous motor produces no inherent average torque at standstill, it cannot accelerate to synchronous speed without some supplemental mechanism. Large motors operating on commercial power frequency include a squirrel-cage induction winding which provides sufficient torque for acceleration and which also serves to damp oscillations in motor speed in operation.
Very large motor systems may include a "pony" motor that accelerates the unloaded synchronous machine before load is applied. Very small synchronous motors are commonly used in line-powered electric mechanical clocks or timers that use the power line frequency to run the gear mechanism at the correct speed. Such small synchronous motors are able to start without assistance if the moment of inertia of the rotor and its mechanical load is sufficiently small [because the motor] will be accelerated from slip speed up to synchronous speed during an accelerating half cycle of the reluctance torque.
See Shaded-pole synchronous motor for how consistent starting direction is obtained. The operational economics is an important parameter to address different motor starting methods. By varying the excitation of a synchronous motor, it can be made to operate at lagging, leading and unity power factor. Excitation at which the power factor is unity is termed normal excitation voltage.
This causes a demagnetizing effect due to armature reaction. The V curve of a synchronous machine shows armature current as a function of field current. With increasing field current armature current at first decreases, then reaches a minimum, then increases.
The minimum point is also the point at which power factor is unity. This ability to selectively control power factor can be exploited for power factor correction of the power system to which the motor is connected. Since most power systems of any significant size have a net lagging power factor, the presence of overexcited synchronous motors moves the system's net power factor closer to unity, improving efficiency.
Such power-factor correction is usually a side effect of motors already present in the system to provide mechanical work, although motors can be run without mechanical load simply to provide power-factor correction. In large industrial plants such as factories the interaction between synchronous motors and other, lagging, loads may be an explicit consideration in the plant's electrical design. If load is applied further then the motor will lose its synchronism, since motor torque will be less than load torque.
From Wikipedia, the free encyclopedia. Main article: Reluctance motor. Main article: Synchronous condenser. Electric Machinery, 3rd Ed.
What is the differences between synchronous and asynchronous motor?
Christian Cavallo. Electric motors come in hundreds of sizes, shapes, and varieties, and the sheer amount of choices can be paralyzing when looking for the best option. The first step in finding any motor is determining its power source; is it powered by AC current, or DC? However, both of these categories still contain many kinds of machines, so this article will help further differentiate the AC motor class our article on brushless vs. AC motors can be split into synchronous motors and induction motors , and this article will give a brief explanation of both, and compare their working characteristics and applications. Induction motors are considered one of, if not the most prolific AC motor used in industry today. They were one of the first electric motors invented, and so have had ample time to be optimized to work in many applications.
Many people often get confused with the terms Synchronous and Asynchronous motors and what exactly are their applications. Check it below:. The following information deals with the general working principles of Synchronous and Asynchronous motors, their advantages and where are they normally used and what can be achieved using each of these motors. This is a typical AC electrical motor that is capable of producing synchronous speeds. In these motors, both the stator and the rotor rotate at the same speed thus achieving synchronization.
is a machine whose rotor speed and the speed of the stator magnetic field is equal.
What is the differences between synchronous and asynchronous motor?
The Difference Between Synchronous and Asynchronous Motor are explained considering factors like its type, slip, requirement of additional power source, requirement of slip ring and brushes, their cost, efficiency, power factor, current supply, speed, self starting, effect in torque because of change in voltage, their operational speed and various applications of both Synchronous and Asynchronous motor. Difference Between Synchronous and Asynchronous Motor are explained below in the tabulated form. Synchronous motor is a motor that operates at synchronous speed, i.
Register now or log in to join your professional community. Synchronous motor runs only at one speed i. If load exceeds the maximum value that the motor can take, it will come to halt.
The difference between asynchronous and synchronous generator
Each peak of the sinusoidal waveform corresponds to a physical position of the rotor. A synchronous generator is essentially the same machine as a synchronous motor. The magnetic field of the rotor is supplied by direct current or permanent magnets. If the RPM is held constant, the frequency varies depending on the power level. The peaks of the waveform have no fixed relationship with the rotor position.
A synchronous electric motor is an AC motor in which, at steady state ,  the rotation of the shaft is synchronized with the frequency of the supply current ; the rotation period is exactly equal to an integral number of AC cycles. Synchronous motors contain multiphase AC electromagnets on the stator of the motor that create a magnetic field which rotates in time with the oscillations of the line current. The rotor with permanent magnets or electromagnets turns in step with the stator field at the same rate and as a result, provides the second synchronized rotating magnet field of any AC motor. A synchronous motor is termed doubly fed if it is supplied with independently excited multiphase AC electromagnets on both the rotor and stator. The synchronous motor and induction motor are the most widely used types of AC motor. The difference between the two types is that the synchronous motor rotates at a rate locked to the line frequency since it does not rely on current induction to produce the rotor's magnetic field.
Synchronous motor is a machine whose rotor speed and the speed of the stator magnetic field is equal. Asynchronous motor is a machine whose rotor rotates at the speed less than the synchronous speed. A synchronous motor is a doubly excited machine, whereas an induction motor is a single excited machine. In case of Synchronous motor its armature winding is energized from an AC source and its field winding from a DC source, whereas in case of Induction motor its stator winding is energized from an AC source. An induction motor or asynchronous motor is an AC electric motor in which the electric current in the rotor needed to produce torque is obtained by electromagnetic induction from the magnetic field of the stator winding. An induction motor can therefore be made without electrical connections to the rotor.
What does asynchronous motor mean?
All rotary electric motors, ac, and dc, operate because of the interaction of two magnetic fields. Rotation is caused by the interaction between the two fields. In a simple dc motor, there is a rotating magnetic field whose polarity is reversed every half turn by means of a brush-commutator combination. Brushes — basically conductive carbon rods which brush against the conductors on the rotor as they turn — also serve the purpose of getting the electrical current into the spinning armature. The situation is a bit different in the dc brushless motor.
Энсей Танкадо отдал кольцо, надеясь обнародовать ключ. И теперь - во что просто не верится - какой-то ни о чем не подозревающий канадский турист держит в своих руках ключ к самому мощному шифровальному алгоритму в истории. Сьюзан набрала полные легкие воздуха и задала неизбежный вопрос: - И где же теперь этот канадец. Стратмор нахмурился: - В этом вся проблема. - Офицер полиции этого не знает.
Час сорок пять ночи. Он в недоумении посмотрел на двухцветного. - Ты сказал - в два ночи.
Сьюзан рассеянно подняла на нее глаза, безучастная к царившему вокруг нее безумию. Все в комнате дружно повернули головы. Диаграмма чем-то напоминала бычий глаз. В центре находился красный кружок с надписью БАЗА, вокруг которого располагались пять концентрических окружностей разной толщины и разного цвета. Внешняя окружность была затуманена и казалась почти прозрачной.
Мы с ним какое-то время переписывались, - как бы невзначай сказал Хейл. - С Танкадо.