Anyone good with motors - for I, am poo

[wade88]

Alright lads,

As brief as i can - Screw auger dosing head, driven by a Carpanelli 0.37KW (1/2 HP) 3 phase 415V 1380max RPM induction motor . Under very little stress, is dosing a material into the feed heads, with a consistency of that of play doh or floury lard - soft and very pliable, can see no reason why a motor of this spec would have a hard time.

However, the auger screw is indexed so the motor will complete a turn say every 0.5 seconds, i know very little about motors, fortunately im off on a course soon to become a little more acquainted. That being said however i understand enough about induction motors to be a little perplexed as to what may have gone wrong. The electrical connections are fine, no loose terminations which may be causing a phase imbalance - so the paired coils should be getting the electricity they need to energise the aluminium rods and turn the rotor. But this is appears to be the issue, when the motor is turned on it would appear there is movement within the motor and the coils are energized, but the screw thread at the end of the rotor is turning inconsistently, sometimes it will complete several turns in a row, other times it will turn once, then stutter or complete half turns.

What may be causing this inconsistency?

Thanks lads

Ben

 

[malcolmsanford]

Have you checked the windings ? what are the values of the 3 windings, they should be the same.

Sometimes Wade if you have a winding that is failing and it's trying to start on it, it move intermittently and fails, or judders as if trying to start.

In olden days I've seen lads give small motors a little half turn tweak and off they go. Not saying this is it definately but it's a start Try testing the windings see what you have.

 

[wade88]

Is this done as a no load test Malcom? Disconnect the load then test. How would i test for a jammed or damaged rotor?

 

[malcolmsanford]

First off test the windings and see what you have it maybe a winding breaking down. If you have a "blind" spot on your rotor then you have to do the old tweak it and see.

You can sometimes semi prove this by taking it off load and if it starts up ok then, your pretty certain it's a winding/rotor problem

You did say you checked all the connections, and your not single phasing. Ie a contactor not making properly or a loose connection

 

[telectrix]

could it also be stripped teeth in gearbox, if there is one?

 

[wade88]

First thought was stripped teeth in gear box so i checked that first, teeth are fine and screw is fine.

Now i just tested it - but its highly likley i have tested it incorrectly as that was my first time testing a motor. So bare with me here.

Results were as follows:

Voltage test showed - 160V at winding 1, 160V at winding 2, 0 volts at winding 3
Resistance test showed - -2.54 Mohms winding 1, -2.65 Mohms winding 2, 0Mohms at winding 3.

I am assuming the third winding is kapoot

 

[wade88]

This diagnosis appears to be exactly what is occuring:

"One of the common faults occurring with motor windings is a turn to turn fault. This occurs when the insulation between two turns in the same coil breaks down and reduces the coil’s ability to produce a balanced magnetic field. Unbalanced magnetic fields result in vibration, which can then cause degradation of the insulation as well as bearing failures. Localized heating around the short can also spread to other coils, resulting in a coil to coil short. Excessive heating will eventually not only destroy the motor windings, but will also damage the insulation between the laminations of the stator core."

My results would confirm this i believe?

 

[telectrix]

where did you measure resistance? to E, or end/end of windings?

 

[wade88]

End to end of windings. Was that a boo boo

 

[telectrix]

would normally expect only a few ohms, so looks like both 1 and 2 are buggered. try a continuity on 3 ( low ohms or multimeter. should only read a few omegas.

 

[Knobhead]

Motor tests

IR
With links in place:
All windings to earth
With links removed:
Test between A1/B1, B1/C1, C1/A1

CR
A1/A2, B1/B2, C1/C2

IR high as you would expect for any such test
CR should be equal

Supply with motor disconnected:
CR from starter through isolator
IR all phases.

 

[Knobhead]

I think it’s time I did a thread covering three phase motor testing. but give me a day or two.