01․ During no load test, an induction motor draws power
No load test is similar to the open-circuit test on a transformer. The motor is made run at no load, the input power is measured by the 2-wattmeter method. No load current is measured by an ammeter and the normal rated supply voltage is measured by a voltmeter. Since no load current is 20 - 30 % of full load current, the I2R losses in the primary may be neglected as they vary with the square of the current. Since the motor is running at no load, total input power is equal to constant iron loss, friction and windage losses of the rotor.
If the supply voltage to a 3 - φ IM is unbalanced and the it is delta connected, then a counter rotating magnetic field is formed. This counter rotating field results in the formation of a negative sequence current.
Unlike that of a power transformer the magnetic circuit of an induction motor has an air gap. Therefore the exciting current of an induction motor ( 30 % - 40 % of full load current) is much higher than that of a power transformer.
04․ If starting current of a 3 - ÃŽÂ¦ induction motor is 5 times the rated current, while rated slip is 4 %, then ratio of starting torque to full load torque is
05․ In travelling cranes for hoisting and lowering which type of motor is preferred?
For hoisting and lowering of crane requires high starting torque. Hence ac slip ring induction motor, Ward Leonard controlled DC shunt motors are preferred.
06․ In travelling cranes for crane travel, trolley and boom hoist which motor is preferred?
For crane travel, trolley travel and boom hoist of traveling crane requires high starting torque and constant speed in operation. Hence slip ring induction motor is preferred.
07․ In travelling cranes for swing action which motor is preferred?
AC slip ring or DC shunt motors are preferred for slew and swing action of traveling cranes.
08․ Which of following motor is preferred for belt conveyor?
Normal starting current and high starting torque double cage IM with DOL starter or slip ring ring induction motors are preferred for belt conveyors.
09․ A crusher is equipped with
A crusher is a machine designed to reduce large rocks into smaller rocks, gravel, or rock dust. Belted slip ring induction motor are employed in jaw crushers because of their high starting torque.
10․ In shapers and slotters which motor are preferred?
A shaper is another machine tool that is used to plane metal. It is smaller than a planer and has a cutting action opposite to that of the planer. Constant speed squirrel cage induction motors are prefer for shapers and slotters.