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2 speed 3 phase motor question....

Evening all, Im confused (seems to be happening a lot lately) by the motor on my mill.

its a 2 speed 3 phase induction motor. the configuration has a name, which I cant find now, hopefully the ascii art will help:

u1 / \ / \ u2 ---/ \--- v2 / \ w1 /________\ v1 | w2

Low speed is run by delta connection to u1,v1,and w1. High speed is star connection by joining u1, v1, w1 together and feeding into u2, v2, and w2. this gives a 2:1 speed ratio (4 pole and 2 pole). There is no neutral connection. The motor runs ok in low speed, but wont fully start in high speed. There is much clattering from both the convertor and the mill as the motor tries to spin up, and it does move, but not upto synchronous speed. I suspect this is because the converter isnt man enough to provide the starting current? This is one source of confusion, as although the star is 2 coils in parallel I thought that the star connection reduced starting current, thus I wouldnt expect such a problem? The motor is rated at 1.8KW low and 2.5KW high, and the converter is a

3KW rotary. Its fed from 6mm^2 cable, 237V idle but I havent yet managed to measure the volts when trying to start (only 1 pair of hands...) Ill phone the manufacturer tommorow, but as I bought it secondhand (*MUCH* cheaper) they arent under any obligation as far as I can see (although its only 1 year old), so any help from here would be gratefully received

cheers

Dave

Reply to
dave sanderson
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Dave,

I hate to rain on your parade, but I never did get my Colchester Student dual speed working satisfactorily on a static converter. It was ok on the lower speed in all gears, but high speed in the higher gears gave all the symptoms that you describe. As you have a rotary, you may get some joy from wiring a larger pilot motor to start first. (BTW if it's a Transwave converter, you'll find them very helpful wherever you got it from)

AWEM

Reply to
Andrew Mawson

Dahlander is the word you are searching for,also known as PAM type winding.One set of three windings,six tails and two speeds. Mark.

Reply to
mark

I had very similar problems on my Holbrook C10, which has a 3 speed 2 HP motor. The lower 2 speeds were OK, the top speed (2850) gave the symptoms you describe. I tried with a 5.5kW transwave static (they were very helpful but we gave up eventually) and with a 5HP pilot motor on the Transwave - no luck. I then used a 415V in/out inverter (fed single phase 415 from the transwave) and had the same problem (although it gave many benefits in the other 2 speeds). Interestingly, with the inverter I could run the 2850 winding up to just over 30Hz (or the 1450 winding to about 80Hz) but with higher frequencies the currents would become excessive. I'm resigned to pulling-out the motor at some time and probably replacing it with a modern one because I don't understand what's going on.

Dave

Reply to
NoSpam

yep, thats the word, you know how it is with the internet, find something, look away and its gone...

Dave

Reply to
dave sanderson

well, if I cant get it to go fast I only actually loose 4500 and 2800 rpm, the rest of the speeds interleave with the slow speed. Not had a chance to speak to Boost yet (its a Booster), but it is the model that they suggested when I initially contacted them, so there is a possibility that it'll turn out ok. Ill let you all know how I get on. Dave

Reply to
dave sanderson

Two speed motors are notorious for trouble when driven from from a phase converter or VFD because of the high starting current and abnormal power factor. Westinhouse recommend starting in the low speed connection and only changing to high speed AFTER the motor has reached low speed revs.

From Westinghouse:-

"The PAM motor should be started on its low-speed winding to limit the inrush current. This prolongs motor life by keeping rotor and core temperatures to a minimum. Starting on the low speed is also more desirable for driven equipment considerations. When starting the motor with the speed changing switch at the low-speed setting, the main breaker is closed. To change speed once the motor is operating, the main breaker must be opened, the switch transferred to the other three leads, and the main breaker closed again. It is important, however, to allow the magnetic flux in the air gap to decay before finally closing the main breaker. This pause will usually take about one to two seconds, depending on motor size."

Jim

Reply to
pentagrid

Hmm, I had thought of that, but discounted it as it seemed 'wrong' or possibly dangerous. However I guess its a bit like a star delta starter, where the motor runs up and then switches to the other configuration. I guess Ill give it a go, though the speed switch is round the back, and the start button is on the front, which could make it interesting...

Dave

Reply to
dave sanderson

im also in the same position ,

having just aquired a smart and brown 1024 lathe ,with a 3speed 440 motor . i have the offer of a transwave 5hp box ,but it sounds like that won do the job !. thanks for opening this subject david its just what i needed .

looks like a rotary phase converter and a big transformer is the bes chance of success , so its either a 240 to 440 tranny and then rpc, or rpc and then 3 p tranny ?.... wonder which is cheaper ? regards rober

-- ivanhoe

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