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]

Ok here's what I got:

f = frequency
ns = synchronous speed
p = number of pairs of poles

Two pairs make one pole

ns = f/p

For question one that makes 2/50 = 25
(fairly simple)

 

[Webman176]

1) C
2) D
3)1hz

 

[mickys86]

Q2
2/50 = 25 (-4%) which gives us 24

 

[telectrix]

2/50 = 0.04!!!

 

[mickys86]

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

Hi tony, this is what I have as notes.

Speaking to the tutor he says that the rotor creates a slight current which will have its own frequency,

 

[mickys86]

2/50 = 0.04!!!

My bad tel :-( 50/2

 

[Knobhead]

It’s one reason why I’m not doing you collage work.

Slip frequency in the cage is higher than the supply frequency.

Just checked my little red book. Your right at 1Hz. but if thats taken in contect with rotation?

 

[mickys86]

It’s one reason why I’m not doing you collage work.

Slip frequency in the cage is higher than the supply frequency.

I'm not asking you to do my college work?? I've learnt what I have learnt this morning everything I know is on two pieces of paper, I'm not asking for answers, we already have them in front of us. Like the topic says, 'bit of fun'

 

[mickys86]

And all I have been told is that the rotor creates a slight current (emf?) and that the frequency of that current is 1Hz
Like i said, This is all I know and I'm not saying I know more than anyone else. Just some fun?

 

[Knobhead]

You can tell you tutor the rotor can generate very heavy currents. Have a look at the size of the bars in a rotor cage. Their big for a reason.

 

[Silly Sausage]

When it comes to motors, I'm not going to argue with Tony!

 

[mickys86]

Neither am I, this was what I was told in this instance and I posted it on here for fun

All he has done is taught us the formula, a couple of examples. And that's it. The rest is on us to look up etc

 

[telectrix]

nor me.

 

[Knobhead]

Micky, do you work with any motors?

An interesting experiment if you can get access to a slip-ring motor is to put a clamp meter on the rotor tails. Trying to read it if it’s analogue will send you cross-eyed. It pulses with the slip, so at your 4% slip it will be pulsing at 2Hz. Last time I did this I used a digital with peak hold, it was the only way I could get any sense out of the readings.

As for rotor current. The motor I was taking the readings on the peak current at normal load was 1750A. Had it been a squirrel cage it would have been much higher. I’ve known them melt a 1x¼” copper bar.

I’ll help you where I can with motors.

 

[High Tower]

I got the first two!, and I'm in the same camp as the others!!, tony is the daddy with this kind of thing!if he told me that motors are made of mash mallows and run on fairy dust, lubricated with squirrels tears I would believe him!!.