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How does a Variable speed transmission work?
Assume a 3 phase AC Induction motor. The speed of the motor is derived by the formula N = (120/f)/P. N speed, f - frequency, P number of poles. In an induction motor P is fixed by the winding. f system frequency. Variable speed drives change the system frequency so that the speed (N) can be varied. Drive is a power electronic device through which the system frequency can be varied
What type of machine that use asynchronous motor?
Typically a synchronous motor is applied in constant speed applications where the higher cost of the motor is offset by the improved power factor realized
How does a furnace multi speed motor work?
Mutli speed furnace motors work on a basis of horse power verses work load. The motor actually contains multiple windings or you could say multiple motors. Each of the windings has a specific horse power rating at a given work load. For example, a 3 speed 1/2 horse power motor is actually 3 different horse powers. High is 1/2 hp - medium is 1/3 hp - low is 1/4 hp. As the motor horse power is decreased the motor will slow down under a given or constant work load. Technically there is no such thing as a multi speed motor but in actuality a multi horse power motor.
What is the working principle of rolling mill machine?
The workpiece is holding on the worktable of the machine. The table movement controls the feed of workpiece against the rotating cutter. The cutter is mounted on a spindle or arbor and revolves at high speed. Except for rotation the cutter has no other motion. As the workpiece advances, the cutter teeth remove the metal from the surface of workpiece and the desired shape is produced.
What is the principle operation wound rotor induction motor?
Considering a split phase single phase motor: The basic motor has a run winding uses 2 poles (or some equivalent), so the motor is activated by the single phase at 180 degree times. This needs a spin to get it started. The direction is according to the direction of the starting spin. It is an induction motor, meaning the rotor has shorting bars. The stator field is connectd to the supply, and induces the required magnetic field in the rotor by transformer action, as for other induction motors. The starting circuit has the purpose of getting the motor to spin up to sufficient speed for the run winding to take over. The rotation needs some sort of flywheel (inertial) action to carry it through the periods of zero magnetic reaction. It might use a rotor with a commutator for starting, with a centrifugal device that shorts the rotor once the speed is sufficient, so it converts to an induction motor. This method is not used much nowadays. It can have high starting torque for use with compressors for example. A common approach is to have a second field winding for starting, with poles at 90 degrees to the run winding, so there are four (or equivalent) poles. This is a two phase motor, with a separate field winding for each phase. It can be used as a 2 phase motor with the phases separated by 90 degrees. The second phase is derived from the supply using a capacitor or inductor to cause the current to lead or lag by approximately 90 degrees. The inductor type might use the different inductance of the two windings to get some current separation, and so the starting torque might be lower as this is less than 90 degrees. These were popular because capacitors were expensive. The capacitor type has a capacitor in series with the start winding, and is the most likely type nowadays. Once the rotor is up to speed the start winding can be disconnected by a centrifugal or current operated switch. Some motors run with both windings continuously connected. Another principle now out of favour because of efficiency issues is used on small motors like fans. It is called a shaded pole motor. Here a special shading pole, part of each stator field pole, is fitted with a shorting winding which causes the field to shift as it builds up on each half cycle, so there is a flick in the correct rotational direction. This has low starting torque.
What will happen to speed-torque characteristics of an induction motor is the rotor resistance is increased?
If Rotor resistance is increased torque is increased
Performance curve of a single phase induction motor?
The performance curve can be a graph of torque versus speed. The torque is zero at zero speed and also at the synchronous speed. Normally an induction motor operates at 90-97% of the synchronous speed, where the slip is between 10% and 3%. In this region the torque is proportional to the slip. As the torque is increased the speed falls until the motor stalls and the speed drops to zero. Below the stalling speed the torque rises between zero speed and the stalling speed. Because the torque is 0 at 0, a single-phase induction motor needs a separate starting winding fed by a starting capacitor to produce a little positive torque that starts the motor.
Why induction motor current increase when load increase?
The slip is proportional to the load torque in an induction motor. This can also be seen as a reduction in speed causing extra current to be induced in the rotor to supply the increased torque.
Speed of the stator field of an Induction motor is?
synchronous speed
What are the advantages of induction motor?
1. Induction motor has high starting torque, therefore use for operate pump which need high starting torque. 2. Induction motor operate on variable speed. 3. It can be used as generator when speed of motor is higher than synchronous speed.
Application of induction motor in industry?
Induction motor used in industries for variable speed machines . Induction motor has always lagging power factor. Less cost compared to syn. Motor.
Difference between induction motor and induction generator?
in case of induction motor the rotor speed is less than synchronous speed giving positive slip but in case of generator the rptor speed is greater than synchronous speed giving negative slip.......
What are convectional and non convectional methods of speed control of a induction motor?
The flux control method is the convectional and the non-convectional method of speed control of an induction motor.
If a three phase induction motor runs at a speed greater than synchronous speed?
When an induction motor is pushed over synchronous speed it will become a generator and will deliver power back to the utility.
What is speed controller?
It is used for sensorless motor control. With vf speed control u can control speed of any induction motor.
What did mean by standstill in induction motor?
rotor speed = 0
Why doesn't an induction motor run at synchronous speed?
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