3 phase motor problem 1

[antonym]

Hi, I've come across a strange problem with a couple the tiny (0.089kw/0.12hp) motors at work.
Both motors are identical. We run them on 220V 50hz. According to the name plate they should draw 0.72A, but they don't. Even without a load one draws 1A and the other 1.2A. To make things more fun the name plate shows a 6 wire connection, but there is 12 wires that come out of the motor. I'm not sure how long they have been doing this for as we are only fitting them with overloads now. Both motors are connected in wye wye.

The motor that draws 1A has just been rewound (low insulation resistance), but i didn't think to check the current before it was sent away.
I tried a few different connection options for the motor drawing 1.2A (wye wye, DELTA, and delta delta) but the current only got higher.

I've considered that the windings could be polarised incorrectly, but since one has just been rewound and the other has been checked by our rewinder I don't think that is very likey.

We might have some other motors that are identical, but the machines need to be turned over to see the motor so I can't confirm that right now. And yes these motors do have a terrible power factor (0.32 by my calculation)

Anyone have any ideas as to what the problem could be?

 

[itsmoked]

Got a picture of one of these motors?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[antonym]

Should have a photo of the motors name plate with this post. I'll be able to get the whole motor tomorrow.

 

[zlatkodo]

Do you have a FLA (full load Amps) and rewind data?
Two things more:
- something is wrong with:

We run them on 220V 50hz ..........Both motors are connected in wye wye.

-

I tried a few different connection options for the motor drawing 1.2A (wye wye, DELTA, and delta delta) but the current only got higher

Can not be correct because the NLA at 1Delta should be lower then at 2Wye

Motor Repair and Design

 

[antonym]

Can not be correct because the NLA at 1Delta should be lower then at 2Wye

That's what I expected too. We have other 12 wire motors which are connected in 1delta to run on 220v and are fine. but this one drew 2.6A, which is a step in the wrong direction.

Only data I have on the motor current is what they should draw from the nameplate and what they do draw. Although I could make some measurements.
Don't have much on the rewind other than the guy winds them the same as he found them. (doesn't mean it was correct when he got it though)

 

[flexoprinting]

Hello

Would an ohm reading of winding comparing one motor to the other bring things to light?

Chuck

 

[zlatkodo]

A lot of unexplained things.
If the motor works well, do not change anything.
Otherwise, the winding data can be recalculated according to nameplate to 6 leads, 380 V; 50 Hz; Wye ( same as 220V; 50 Hz, Delta).
More at:
[URL unfurl="true"]http://winding.wixsite.com/design/winding-data-calculation[/url]

 

[antonym]

If the motor works well, do not change anything.

They do seem to work ok. they just get alot hotter than the other motors of the same type.

Strange thing is I checked the resistance of the windings in the motors.
the 1.2a motor is 35.5ohm, the 1a motor comes in at 50ohm, and a third motor of the same type drawing 0.7a has 68ohm windings. the different resistances explains the current difference. No idea why the motors seem to have different windings in them though.

 

[electricpete]

the different resistances explains the current difference.

The different resistances don't in themselves explain the current difference (stator winding resistance does not play any role in determining current) but does suggest the motors are not identical as you say.

=====================================
(2B)+(2B)' ?

 

[roydm]

The nameplate shows Star Delta connection.

 

[lukin1977]

on your 1st post you said that the motors are connected 220V wye
but on the nameplate shows the it must be connected in delta to 220V ...

 

[Parchie]

(Electrical)(OP)15 Sep 16 04:57
They do seem to work ok. they just get alot hotter than the other motors of the same type.

Strange thing is I checked the resistance of the windings in the motors.
the 1.2a motor is 35.5ohm, the 1a motor comes in at 50ohm, and a third motor of the same type drawing 0.7a has 68ohm windings. the different resistances explains the current difference. No idea why the motors seem to have different windings in them though.

Your motor windings are not getting enough voltage because you got your motor connection wrong. Wire the motors in delta and supply with 220VAC or wire your motor in wye and supply with 380V.

 

[antonym]

Seems that the motors have been rewound in the past, but whoever did it changed the winding setup. It's the only way to explain why they are 12 wore not 6, and why the windings differ from motor to motor.