question archive A 208 - V four - pole 10 - hp 60 - Hz Y - connected three - phase induction motor develops its full - load induced torque at 3

A 208 - V four - pole 10 - hp 60 - Hz Y - connected three - phase induction motor develops its full - load induced torque at 3

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A 208 - V four - pole 10 - hp 60 - Hz Y - connected three - phase induction motor develops its full - load induced torque at 3.8 percent slip when operating at 60 Hz and 208 V. The per - phase circuit model impedances of the motor are R = 0.33ohm Xm = 16ohm X1 -0.42ohm X2- 0.42ohm

Mechanical, core, and stray losses may be neglected in this problem. 

a) Find the value of the rotor resistance R2

(b) Find Tmax,Smax, and the rotor speed at maximum torque for this motor

(c) Find the starting torque of this motor

(d) What code letter factor should be assigned to this motor? 

 

When it is necessary to stop an induction motor very rapidly, many induction motor controllers reverse the direction of rotation of the magnetic fields by switching any two stator leads. When the direction of rotation of the magnetic fields is reversed, the motor develops an induced torque opposite to the current direction of rotation, so it quickly stops and tries to start turning in the opposite direction. If power is removed from the stator circuit at the moment when the rotor speed goes through zero, then the motor has been stopped very rapidly. This technique for rapidly stopping an induction motor is called plugging. The motor of problem upper is running at rated conditions and is to be stopped by plugging,

(e) What is the slips before plugging?

 (f) What is the frequency of the rotor before plugging?

 (g) What is the induced torque Tind before plugging? 

(h) What is the slips immediately after switching the stator leads?

 (i) What is the frequency of the rotor immediately after switching the stator leads?

(j)  What is is the induced torque Tind immediately after switching the stator leads?

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