Something to do with the Y/D voltages and the difference between the two ratings I posted, so I don't have to look it up and explain, as it will probably be second nature to you!
A Thought Experiment
- Thread starter Sidewinder
- Start date
Help Support Talk Electrician Forum:
Was it that the 240/415 motors were what were called " Universal " which was the USA market they would connect it in mesh and their supply is 3ph 240v ....in the UK we would connect it in Star on 415v
is not to do with the current reading when only two phases are connected and how much it goes down by when you connect the third one or even if it will run with only two phases connceted
Thing is poni, you can't connect it up correctly and safely unless you know whether it is Y or D wound...
On the subject of learning etc .....I worked for a rewind firm once (contracting dept) I remember being told that you can only wind a motor for certain speeds .......can't remember the standard ones now ...possibly 950 RPM , then 1500 RPM and so on ...so standard set speeds . For other speeds you need pullies , controllers, gearbox etc .
You are correct Deke, they are the 2 pole speed based on 50 Hz, circa 3000 rpm less design losses & slip, then the 4 pole speed @ 1500 etc.
why do you need to know how its wound to connect it up? don't you have all you need with the cables coming out of the motor just like a single phase motor has only 3 cores to connect?
- Joined
- Oct 22, 2010
- Messages
- 14,521
- Reaction score
- 1,086
I seem to remember something akin to
4.44 f n fi. ( or phi? That circle thing with a vertical line through it )....... However this was from almost 40 years ago so,it is probably all done with Facebook or something now
just saying
poni,
Like the title of the thread it is a thought experiment, plus, I have not said anything about connecting it up, I have said we need to know if it is Y or D.
There are more reasons to know this than just how to connect 3 or 4 wires.
Why be so restrictive in your thought processes?
Like the title of the thread it is a thought experiment, plus, I have not said anything about connecting it up, I have said we need to know if it is Y or D.
There are more reasons to know this than just how to connect 3 or 4 wires.
Why be so restrictive in your thought processes?
Its speed=50 x 50/p where p= pairs of poles per phase
quite right its 60x 50/p
quite right its 60x 50/p
Last edited by a moderator:
steady on there I was only saying
this was not meant for Canoeboy
this was not meant for Canoeboy
Last edited by a moderator:
It is to do with the number of poles and the frequency, which is 50 Hz in the UK.
ω = 2 · 60 · f / n
Where:
ω = the rotational speed in rpm,
f = supply frequency, as said in the UK, 50Hz,
n = number of poles.
This gives the SYNCHRONOUS speed as follows, for 50 Hz:
2 pole 3k rpm
4 pole 1k5 rpm
6 pole 1k rpm
8 pole 750 rpm
10 pole 600 rpm
12 pole 500 rpm
A squirrel cage motor develops no torque @ synchronous speed, thus they run slower striving to achieve synchronous speed, thus developing rotational torque.
So you will see speeds such as 2880, 1470 740, 980 rpm, etc. on motor rating plates.
ω = 2 · 60 · f / n
Where:
ω = the rotational speed in rpm,
f = supply frequency, as said in the UK, 50Hz,
n = number of poles.
This gives the SYNCHRONOUS speed as follows, for 50 Hz:
2 pole 3k rpm
4 pole 1k5 rpm
6 pole 1k rpm
8 pole 750 rpm
10 pole 600 rpm
12 pole 500 rpm
A squirrel cage motor develops no torque @ synchronous speed, thus they run slower striving to achieve synchronous speed, thus developing rotational torque.
So you will see speeds such as 2880, 1470 740, 980 rpm, etc. on motor rating plates.
Beaten to it, it seems.
I think /know I have descoob sidewinder could some one reset sorry done by a slip of the mouse thanks
I will have to have a go with a motor tomorrow and see what difference I get in star and delta use a 9v battery and a multimeter
poni,
You can't use a battery as it will have a drooping voltage as it is depleted, this will affect your results.
You have to use a constant current source to get accurate readings, the current drawn through the windings will deplete the charge in the battery thus affecting your results.
Plus experiments only tell half the story, they can be used to disprove a theory, but, they need to be reinforced with the theory to prove the rule.
You can't use a battery as it will have a drooping voltage as it is depleted, this will affect your results.
You have to use a constant current source to get accurate readings, the current drawn through the windings will deplete the charge in the battery thus affecting your results.
Plus experiments only tell half the story, they can be used to disprove a theory, but, they need to be reinforced with the theory to prove the rule.
Canoe your driving the 300kw motor at 55Hz
Previously, you did, yes, to me.
However, I can't afford one!
As much as I would like one, and IF it is the one I am thinking of, it would be very useful for other motor tests.
I still think it is worth pursuing the first principles investigation.
However, I can't afford one!
As much as I would like one, and IF it is the one I am thinking of, it would be very useful for other motor tests.
I still think it is worth pursuing the first principles investigation.
could I not use one of new LED consent current drivers for this?
Canoe is it a lift going down?
Canoe is it a lift going down?
Last edited by a moderator:
- Joined
- Oct 22, 2010
- Messages
- 14,521
- Reaction score
- 1,086
