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Explains why a 3-phase induction motor develops no torque when running at synchronous speed?
Wiki User
∙ 14y ago
When rotor speed becomes equal to Synchronous speed in an induction motor, it means that the slip is zero. Which means that there is no cutting of magnetic lines by rotor bars and hence no torque is generated.
To generate Torque, rotor speed should always be less than the synchronous speed. That is why, you must have seen in your dailty life that all induction motors are rated below 3000 RPM(sync speed for a 2 pole machine).
Sync speed (Ns) = 120f/P
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∙ 14y ago
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What is the importance of slip in a 3-phase induction motor?
Slip is a measure of the difference in relative motion between the rotor and the magnetic field set up by the field windings.In very simple terms, without slip an induction motor would not be able to develop any torque! A slip of zero means that the rotor is turning at synchronous speed; in other words it is running at the same speed as the rotating field set up by the field windings, so there is no relative movement between the field and the rotor. To develop torque, the voltages must be induced into the rotor, and this can only happen if there is relative movement between the field and the rotor -in other words, the rotor MUST be running more slowly than synchronous speed. That is, there must be some degree of slip.
Why a pure single phase induction motor does not have starting torque but has running torque?
A single-phase induction motor can be considered as running on two oppositely-rotating magnetic fields. In normal running just below synchronous speed, the slip is perhaps 0.05 on one of these rotating fields and 1.95 on the other. The first field supplies the major part of the torque. When the motor is stationary with power supplied, both fields have a slip of 1 and they produce contrary torques so the motor remains stalled. If the motor is spun in one direction, the slip becomes unbalanced and there is a net torque from the direction with the least slip, so the motor runs up in that direction.
What is the rotor speed of synchronous motor?
It depends on the number of poles and the frequency of the power. A two pole motor running on 60 Hz would rotate at 1800 RPM.
What type of induction motor is used in table fan?
Motor used in Table Fan is Split phase Motor(Continuous Running with Capacitor).It has Two winding Running coil + Starting Coil. Running coil connected Direct to Supply Starting coil Connected is series with capacitor than parallel with power.
How is direction of rotation for single phase induction motor determined?
A single phase induction motor is not self starting; thus, it is necessary to provide a starting circuit and associated start windings to give the initial rotation in a single phase induction motor. The normal running windings within such a motor can cause the rotor to turn in either direction, so the starting circuit determines the operating direction.
Why induction motor does not runs at synchronous speed?
An induction motor cannot run at synchronous speed because it is the "slippage" of the rotor relative to the rotaing magnetic field that generates the current in the windings contained within the rotor. This induced (hence the term induction) current sets up the opposing magnetic fields that cause the rotor to rotate.
What will happen if excitation of a running synchronous motor suddenly cuts off?
something cool
Why do you give DC excitation to AC Synchronous motor?
If the synchronous motor is running near synchronous speed, it will begin rotating at synchronous speed when DC is applied to the rotor. Source: Electrical Machines, Drives, and Power Systems Theodore Wildi Section 17.3
Differences of induction motors and synchronous motors?
An induction motor is a type of electric motor. It uses alternating current (AC) electricity and induces (hence the name) a current in the rotating part to make it move. You might call it a rotating transformer. A hydraulic motor is powered by a fluid. Typically this might be an oil, The oil forces round some gears or vanes to make the motor shaft turn. A hydraulic motor requires an external supply of pressurised fluid, e.g. oil. Large earthmoving equipment or diggers use hydraulic power as it is compact and powerful for its size.
What is induction motor slip?
The slip measures the percentage by which the actual speed is less than the synchronous speed. AC motors have a synchronous speed of 3000 rpm on a 50 Hz system, or 3600 rpm on 50 Hz. Some motors might have a synchronous speed half or a third of those speeds (or less), because the synchronous speed must be divided by the number of pole-pairs. For a 50 Hz motor running at 2850 rpm the slip is (3000-2850)/3000 or 5%. The slip speed is 2850 rpm.
What happen to 440v motor running at 480v?
Depends on the motor. If it is a synchronous motor it will run too fast.
When induction motor is switched on the rotor frequency is?
The induction motor rotor has different frequency compared to it's stator. The rotor has slip ( s ) frequency. slip = ( Synchronous speed - rotor speed ) / Synchronous speed Synchronous speed = ( 120 * f ) / P where f = supply frequency to the stator. p = no of poles rotor speed is the actual speed the motor is running. Frequency in the rotor = slip * frequency in the stator At starting rotor speed is zero, so slip is one. Let us take the supply frequency is 50 Hz, then rotor frequency is also 50 Hz at starting. The motor attains speed and runs with its full speed at a point of time. Then let us take the slip is 0.04 then the rotor frequency will be 2 Hz.
What voltage is suitable for running a 180 kw motor?
380v 60 hz is suitable for running 180kw induction motor
What is the importance of slip in a 3-phase induction motor?
Slip is a measure of the difference in relative motion between the rotor and the magnetic field set up by the field windings.In very simple terms, without slip an induction motor would not be able to develop any torque! A slip of zero means that the rotor is turning at synchronous speed; in other words it is running at the same speed as the rotating field set up by the field windings, so there is no relative movement between the field and the rotor. To develop torque, the voltages must be induced into the rotor, and this can only happen if there is relative movement between the field and the rotor -in other words, the rotor MUST be running more slowly than synchronous speed. That is, there must be some degree of slip.
Why synchronous motor is not a self starting motor?
As per the operating principle of the Synchronous motor, due to continuous & rapid rotation of stator poles,the rotor is subjected to a torque which is rapidly reversing i.e. in quick succession,the rotor is subjected to torque which tends to move it first in one direction & then in the opposite direction.Owing to its large inertia,the rotor cannot instataneously respond to such quickly-reversing torque,with the result that it remains stationary or in other words it is not self starting.
How is single phase induction motor is constructed?
An induction motor is an alternating current (only) motor that has one or more coils of wire wound on a metal frame that induces a current in the conductors in the rotor when the rotor is moving at a different than synchronous speed. Synchronous speed it determined by the line frequency and the number of poles the motor has. For example, a two pole motor with a 60 Hz line frequency would have a synchronous speed of 3600 RPM. When used with single phase, the magnetic field generated in the stator needs to be caused to rotate around the rotor. In most cases this is initiated by a separate starting winding that is fed out of phase with the running winding(s). Once the rotor is rotating, the stator's field rotation has been established and the starting circuit is generally switched off.
Will a singl phase induction motor start if only the running or the starting winding is excited?
No.
