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What are the advantages of skewed slots in the rotor of a squirrel cage rotor?
It helps to put on a little more traction. The rotor will stay on better because it is not as slippery.
Why are the rotor bars of a squirrel cage induction motor usually slanted i.e. not entirely parallel with the shaft?
The squirrel cage is skewed so that the force applied to the rotor it continuous. If they were straight then the force would be jerky, as whole of the bar is cutting the magnetic field lines at the same time. With the bars skewed the amount of the bar cutting the field line grows continuously and the next bar starts cutting the field lines as the first finishes. also, slots are skewed to get uniform torque ,reduce the magnetic locking (also called COGGING EFFECT) between stator and rotor,and thirdly to reduce the magnetic humming noise during running condition
Why rotor slots is more than stator slots in induction motor?
rotor slot more. it is to get a large rotor inductance value of inductance the stator windings
What are slots in dc generator?
Slots are teeth shaped portions made on outer periphery of rotor and coils are placed in these slots.
What is squirrel cage in motors?
When the number of rotor and stator poles are equal in the motor and if these rotor poles have opposite polarity with respect to the stator poles magnetic locking occurs. This magnetic locking is know as "Cogging" in 3 phase squirrel cage induction motor. In order to avoid this problem, the rotor slots housing the conductors are skewed by an angle of 5 degrees over the surface.
Define gap contraction factor for slots?
It is nothing but the effect of flux which is reduced slightly due to fringing effect. it depends on the material used for the stator and rotor design. as well as shape of the slots.
What is cogging and crawling in case of 3 phase induction machines?
CoggingInduction motors have a series of slots in the stator and in the rotor. These slots should not be equal in number because if they are, there is a good chance that the motor will not start at all due to a characteristic known as cogging. The slots will align like a stepper motor. For this reason, there are an unequal number of slots in the rotor and in the stator, but there can still be situations where the slot frequencies coincide with harmonic frequencies and this can cause torque modulations. The slots are skewed to keep an overlap on all slots to reduce this problem.CrawlingAnother characteristic of induction motors, is crawling. There are harmonic fluxes developed in the gap due to the magnetics of the motor. These harmonics create additional torque fields. A common problem is with the seventh harmonic where the seventh harmonic creates a forward rotating torque field at one seventh of the synchronous speed. There will be a maximum torque just below 1/7 Ns and if this is high enough, the net torque can be higher than the torque due to the line frequency where at 1/7 Ns, the slip is high. This can cause the motor to crawl at just below 1/7 synchronous speed. There is another crawl speed at 1/13 Ns.
What is construction of cage induction motor?
The rotor is manufactured from a stack of circular silicon-steel lamination clamped together around a shaft, with open or closed slots running along the length of the rotor through which the rotor conductors ('bars') pass. The rotors are then interconnected at opposite ends with conducting end-rings. In some cases, the rotor bars are poured into the (enclosed) slots as molten metal. If the bars were visible, they would resemble a gerbil's exercise wheel.
Why rotor of an induction motor has slots around periphery filled with copper or aluminium?
The slots in the rotor of an induction motor are filled with copper or aluminum because those copper or aluminum filled slots are conductors. They constitute multiple one-turn transformers, setting up an induced magnetic field, induced from the field windings, that creates a differential magnetic flux, i.e. a torque, that causes the rotor to turn.This has little to do with the fact that the field windings are pulsing from the AC current, because the rotor "windings" are pulsing in turn - what is happening is that the rotor and field "windings" attract or repel each other as a function of their distance from each other, which is related to slippage induced by torque.
What is inductor alternator?
The armature and the field windings of an inductor alternator are both accommodated in the stator. The three phase ac armature windings are distributed in small slots and the dc field windings are concentrated in two slots in the stator. Each field coil spans half the total number of stator slots. Armature coils are connected in star and field coils are connected in series. The rotor resembles a cogged wheel, with no winding. The core of the stator, which is completely embraced by the field coils, will retain a residual magnetism if excited once. When the rotor is rotated, the passage of the rotor teeth alternatively under the field offers a varying reluctance path for the flux produced by the field coils. This flux, which varies periodically, links with the armature coils and induces an emf in them. The frequency of the induced emf depends on the speed of the rotor. The magnitude depends on the speed of the rotor as well as on the level of excitation. The armature and the field windings of an inductor alternator are both accommodated in the stator. The three phase ac armature windings are distributed in small slots and the dc field windings are concentrated in two slots in the stator. Each field coil spans half the total number of stator slots. Armature coils are connected in star and field coils are connected in series. The rotor resembles a cogged wheel, with no winding. The core of the stator, which is completely embraced by the field coils, will retain a residual magnetism if excited once. When the rotor is rotated, the passage of the rotor teeth alternatively under the field offers a varying reluctance path for the flux produced by the field coils. This flux, which varies periodically, links with the armature coils and induces an emf in them. The frequency of the induced emf depends on the speed of the rotor. The magnitude depends on the speed of the rotor as well as on the level of excitation.
What is winding and rewinding?
Winding: To wind the coils into the slots on the stator or rotor and connecting them up to form a winding. Re-winding. Is to remove the old winding and doing what I explained above.
Working principle of three phase drivers?
An electrical motor is such an electromechanical device which converts electrical energy into a mechanical energy. In case of three phase AC operation, most widely used motor is Three phase induction motor as this type of motor does not require any starting device or we can say they are self starting induction motor.For better understanding the principle of three phase induction motor, the basic constructional feature of this motor must be known to us. This Motor consists of two major parts: Stator: Stator of three phase induction motor is made up of numbers of slots to construct a 3 phase winding circuit which is connected to 3 phase AC source. The three phase winding are arranged in such a manner in the slots that they produce a rotating magnetic field after 3Ph. AC supply is given to them. Rotor: Rotor of three phase induction motor consists of cylindrical laminated core with parallel slots that can carry conductors. Conductors are heavy copper or aluminum bars which fits in each slots & they are short circuited by the end rings. The slots are not exactly made parallel to the axis of the shaft but are slotted a little skewed because this arrangement reduces magnetic humming noise & can avoid stalling of motor.
