5 a 20 kw 6 pole 400 v 50 hz 3 phase induction motor has a...

5) A 20 kW, 6 pole, 400 V, 50 Hz, 3-phase induction motor has a full-load slip of 0.02. If the torque lost is 20 N-m, find (a) the rotor ohmic losses, (b) motor input and (c) efficiency. Stator losses total 900 watts. 6) A 4 pole, 8 kW, 50 Hz, 3 phase induction motor develops rated torque at 1,440 rpm. In case load torque is reduced to one-fourth, find (a) the motor speed and (b) the power output. Assume linear torque torque-slip characteristics near the operating range.

Transcript

00:01 Hello student, let us note down the given data here.

00:05 Power output 20 kilowatt, pole number 6, 400 volt and frequency 50 hertz, phase is 3 phase.

00:20 Here then stator speed will become 120 into f that is frequency 50 divided by pole number 6 which is equal to 1000 rotation per minute.

00:37 Then rotor speed will be ns into 1 minus s.

00:44 Here slip is 0 .02.

00:49 Substituting for that rotor speed will become 1000 into 1 minus 0 .02 from this 980 rotation per minute.

01:04 Then to find power loss we consider torque loss into omega r.

01:12 Torque loss is given in the question 20 newton meter.

01:17 Omega r is given by 2 pi nr divided by 60.

01:23 Then 20 into 2 pi nr is 980 divided by rotation per minute is there so convert to second.

01:34 From this we get power loss will be 2052 .50 watts.

01:45 Then given that stator loss is 900 watts to find power input we consider power output plus power loss plus stator loss.

02:03 Here power loss nothing but rotor loss.

02:07 Substituting the values here 20 kilowatt plus 20052 plus 900 from all this the power input will be equal to 22952 watts.

02:29 It is written in 22 .952 kilowatt.

02:34 Then efficiency can be find out by using the formula eta is equal power out divided by power in into 100.

02:45 That is power out is 20 kilowatt power in is 22 .95 kilowatt into 100.

02:54 From this the efficiency will be equal to 87 .13 percent.

03:02 Next question given that motor develops rotational torque at 1440 rotation per minute then stator speed is equal to 120 into 50 divided by 4 which is equal to 1500 rotation per minute.

03:33 Then stator speed is equal to rotor speed into 1 minus s...

Question

Please give Ace some feedback