syncronous condensor/motor rotor design

Thread Starter

l0vot

Joined Apr 29, 2013
107
I am going to try to convert a 3 phase induction motor into a syncronous condensor, the motor is 2 pole. Would the rotor need to have 2 poles, or 4 in order to work properly? If I had a 2 pole DC excited syncronous motor on hand, I would pop it open and see for myself, or possibly use it instead if it were the right size.
 

Thread Starter

l0vot

Joined Apr 29, 2013
107
Two for each phase. per electrical revolution.
Max.
Are you telling me it needs 6 poles, like the field windings have? The way it's set up I can't fit 6, only 2 or 4 on the squirrel cage rotor (which I need to keep so it's self starting). All the drawings appear to have a 2 or 4 pole rotor in the middle when paired with 2 pole power windings. Am I even using the termonology correctly? What's the DC excited spinny bit in the middle called on a rotating syncronous device?
 
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Thread Starter

l0vot

Joined Apr 29, 2013
107
In an induction motor the number of rotor poles equals the number of stator poles.
Max.
the objective here is to have it function as an induction motor to get it up to speed, then feed power to coils in the rotor via slip rings to make it into a syncronous rotor, so the DC coils in the middle need to be configured the same way as the ones in a syncronous motor/generator. There are holes in the rotor that should be able to accept 2 or 4 windings, that should, when energized make the rotor into a 2 or 4 pole syncronous motor stator.
 

MaxHeadRoom

Joined Jul 18, 2013
25,973
That was done some decades ago in large motors, some around 100hp, the motor was ran up as a AC induction motor, with a rotor winding connected to slip rings, the winding was used to record the slip frequency, when the slip was within 4-5cyles, DC was then fed into the rotor via the same slip rings and the motor came up to synchronism.
Max.
 

Thread Starter

l0vot

Joined Apr 29, 2013
107
That was done some decades ago in large motors, some around 100hp, the motor was ran up as a AC induction motor, with a rotor winding connected to slip rings, the winding was used to record the slip frequency, when the slip was within 4-5cyles, DC was then fed into the rotor via the same slip rings and the motor came up to synchronism.
Max.
I have seen squirrelcage windings on syncronous stator before, they weren't actually inside the motor, and I didn't have the nameplate to figure out how many poles it had, but they definately had the squirrelcage windings, and stator windings. My question is how many stator poles do I need to have to make this work. Pretty sure it's 4, but I don't really have enough data to be sure, drawings don't always match reality.
 
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