Bit of fun for you....

[mickys86]

1) The synchronous speed of the rotating magnetic field in a four pole 50hz synchronous motor is?
A) 12.5
B) 16.6
C) 25
D) 50

Btw I already know the answers, just for those that are interested

 

[mickys86]

2) A four pole 50hz three phase induction motor is connected to a 400v supply. If the motor has 4% slip the rotor speed will be?
A) 12.5
B) 12
C) 25
D) 24

 

[mickys86]

I'll post the formulas later if no one beats me to it although I'm very sure somebody will

 

[mickys86]

3) calculate the frequency of the rotor current on an eight pole squirrel cage induction motor, Synchronous speed is 12.5 revs/s with a 2% slip

(a bit trickier)

 

[johnboy6083]

1= a, 2= b, c= 102.

not confident with C.

 

[mickys86]

1= a, 2= b, c= 102.

not confident with C.

1 wrong 2 wrong 3 wrong

 

[johnboy6083]

lol, shows how much i know!

 

[mickys86]

lol, shows how much i know!

Your kind of on the right path for the first two.

 

[johnboy6083]

i chose A for question 1,becausethe answer i was expecting (750) wasnt there, and i assumed that you didnt want the seed converted to revs per min. Im interested to see the correct answer and the equation used.

 

[brman]

isn't it 2f/n? so C, D for the 1st two. Not sure about squirrels though

Assuming the answer is in revs per second rather than rpm......

 

[Knobhead]

1440rpm

 

[mickys86]

Your looking for the frequency which is Hz

 

[Knobhead]

The frequency doesn't change. 50Hz
Speed does change.

 

[mickys86]

The frequency doesn't change. 50Hz
Speed does change.

I'll look at what I got written down when back in class, we wasn't given the 50Hz for question 3, it was 3 separate questions

 

[telectrix]

i didn't understand the q. until i realised the answers weren't in rpm. is this rps some new metric thing?