A 3-phase, Y - connected induction motor has a full load slip of 4%. An autotransformer is used to limit the starting current to 4 times the full load current. For such limitation, determine the ratio of the starting torque to full load torque

6- In a stepper motor, how is the speed of rotation determined? a) By the current supplied to the motor. b) By the magnitude of the voltage applied. c) By the load applied to the motor. d) By the frequency of the waveforms used. 7- A transformer core is laminated to a) reduce hysteresis loss b) reduce eddy current losses c) reduce copper losses d) reduce all above losses 8- An induction motor with 580 r.p.m. speed at 60 Hz will have a) 8 poles b) 6 poles c) 4 poles d) 2 poles 9- If any two phases for an induction motor are interchanged a) the motor will run in reverse direction b) the motor will run at reduced speed c) the motor will not run d) the motor will burn 10- No-Load speed of which of the following motor will be highest? a) Shunt motor b) Series motor c) Short-Shunt compound motor d) Long-Shunt compound motor

A three-phase induction motor, operating at rated voltage and frequency, has a startingtorque of 1.35 times and a maximum torque of 2.2 times, both with respect to its rated-loadtorque. Ignoring the effects of the stator resistance and rotational losses and assumingconstant rotor resistance, determine the slip rated load, and the rotor current at starting (as a percentage of the rotor current at rated load). The slip at maximum torque is 0.343 if that helps.

The maximum torque of 3-phase induction motor occurs at a slip of 11 percent. The motor has anequivalent secondary resistance of 0.08 ohm/phase. Calculate the equivalent load resistance RL theequivalent load voltage VL and the current at this slip if the gross power output is 8 kW.

A synchronous motor has a synchronous reactance of 0.8 pu and a transient reactance of 0.25 pu. The motor is connected to an infinite bus. The field current is adjusted such that the unloaded motor draws half the rated current at zero power factor lagging. With the field current left unchanged find the following: a) Find the maximum per-unit torque that can be applied gradually without losing synchronism b) Find the maximum per-unit torque that can be applied suddenly without losing synchronism.

A 3-phase, 6-pole induction motor is con- nected to a 60 Hz supply. The voltage in- duced in the rotor bars is 4 V when the ro- tor is locked. If the motor turns in the same direction as the flux, calculate the approxi- mate voltage induced and its frequency: a. At 300 r/min b. At 1000 r/min c. At 1500 r/min

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The standstill reactance of each phase of a three-phase induction motor with star-connected rotor are 0.06 ohms and 0.4 ohms respectively. The full-load slip is 4%. Calculate the resistance per phase of a star-connected rheostat, which when connected to the rotor, will give a pull out torque at one half of the full-load speed. What is then the power factor?

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.

A single-phase, 120 V, 60 Hz, four-pole, split-phase induction motor has the following standstill impedances:Main winding: Zm =5+j6.25Auxiliary winding: Za =8+j6a) Determine the value of capacitance to be added in series with the auxiliary winding to obtainmaximum starting torque.b) Compare the starting torques and starting current with and without the added capacitance in theauxiliary winding circuit when operated from a 120V, 60Hz supply