For induction motors, the following is true: a: Should be essentially a constant speed motor b; Its speed reduces to some extent with increase in load c; Does not need to be synchronized d; All of these

Derive the torque equation for a three phase induction motor, with the help of torque speed characteristics curve briefly explain how an induction motor can operate in stable region.

A 50-KW, 220V, 50 Hz, squirrel-cage three-phase induction motor is needed to rotate a mine conveyor belt drive. The motor starts sometimes under load, but most of the time is needed to run at rated speed and slip of 3.5%. Propose an appropriate design of this drive motor in order to suit the application. Motivate and then illustrate your design with suitable drawings and speed (slip)-torque graphs.

A value of magnetizing current in a 3-phase induction motor * gives power factor smaller .. larger smaller. .poor large . better O large...poor O

An 3-phase induction motor(IM) has full load slip = 0.5%. If the rotor circuit resistance is increased so that R2new =2R2old, then the slip at which the motor develops the same full load torque is=.. * ......

23) In the speed current characteristics of DC series motor, the speed is increasing when the current decreases. Select one: True False

A 80 kW, 480-V, 60-Hz, six pole induction motor has a slip of 5 percent when operating at fullload conditions. At full-load conditions, the friction and windage losses are 300 W, and the core losses are 400 W. For full-load conditions, compute the induced torque,T-ind, in N-m.

f The simplicity in construction of a single-stack VR step motor is due to.... 1. Low number of phases, 2. Low used voltage, 3. N, N, 4. Bidirectional rotation, 5- None of previous. g- The synchronous inductor motor has the ability to step when the phase windings are .............. 1. Connected in parallel, 2. Connected in series, 3. Connected in star, 4. Energized with dc, 5- None of previous. h- The speed of multiple-stack VR step motor with continuous stepping is 3.120, 4.5 5- None of previous. 60f T T Resonance conditions distort the torque/speed curve causing a Drop, 3. Ripple, 4. Fluctuation, 5- None of previous. ********** 1. 120f 2p 2. 60f 2p " in torque. 1. Increase, 2. j- The frequency of armature current in 1-phase series motor is 1. =f, 2. f, 4. Zero, 5- None of previous. (f is the supply frequency)

Q4) What is the effect in series motor if you assume V = Eb , with low resistance fielding winding ? a) b) The given information about series motor on full – load (with that the flux is proportional to the field current) is a ) takes ( 78A) and runs at (850 r.p.m) , the series winding resistance is (0.04 2) , with diverter in parallel with the field winding is a (0.18 2) and the armature resistance is (0.09 S2). ( 220 V Neglected the iron, friction and windage losses. Determine the efficiency , speed when developing full load torque ,the maximum efficiency .

1- To control the speed of an induction motor, the supply frequency is reduced by 10%. For the same magnetizing current to remain constant, the supply voltage must be....... a) Reduced by 10%, b) Reduced by 20%, c) Increased by 10%, d) Increased by 20% 2. When maximum starting torqua ic ohtoinod