Question4 1 pts A three-phase, 460V, 60Hz, 1760rpm, wound-rotor induction motor

Question

Question4 1 pts A three-phase, 460V, 60Hz, 1760rpm, wound-rotor induction motor has the following equivalent circuit parameters R1- 0.25 ohm R2-0.2 ohm: X1 1.33 ohm : X2' 1 ohm : XM 35 ohm. The motor is connected to a 3ph, 460V, 60Hz supply and is star-connected. Use the simplified equivalent circuit. The external rotor resistance is set to value which gives maximum torque at standstill. Calculate the required external rotor resistance in ohms (referred to the stator). Question5 1 pts 7.16. Constant volts-per-Hertz control is applied to an induction motor which is rated at 460V and 60Hz in order to keep the flux in the motor at its rated value. Calculate the required stator voltage corresponding to a stator frequency of 20Hz.

Explanation / Answer

Question 4)

asper simplified equivalent circuit . The maximum torque occurs at when lR3'/Sl = lR1+j(X1+X2')l

So R3'/S= ?(R1^2)+(X1+X2)^2

Since at stand still S= 1

R3'=?(0.25^2)+(1.33+1)^2

R3'=2.34 ohm

So R3' = R2'+Rx' Rx'=2.34-0.2=2.14

Rx'= 2.14 ohm

Question 5)

Let V1= 460 . f1=60hz

So f2=20hz

So . V2/V1 = f2/f1

V2= 460*(20/60) =153.33

So voltage corresponding to stator frequency is V2= 153.33 volts

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