Detect shorted turns in motor windings...

[Tor Tveitane]

Hi,

Can I use a LCR bridge in inductance mode to measure difference in
inductance if I suspect one of the windings in an electrical motors to have
shorted turns...?

What is the preferred way to check for shorted turns within an inductor...?

Thanks for clues

Tpr

 

[CJT]

Hi,

Can I use a LCR bridge in inductance mode to measure difference in
inductance if I suspect one of the windings in an electrical motors to have
shorted turns...?

What is the preferred way to check for shorted turns within an inductor...?

Thanks for clues

Tpr

I don't know what's preferred, but one way might be to ring it like
a flyback and look at the response.

 

[NSM]

| Hi,
|
| Can I use a LCR bridge in inductance mode to measure difference in
| inductance if I suspect one of the windings in an electrical motors to
have
| shorted turns...?

Sure. Compare the ratio of inductance to resistance.

| What is the preferred way to check for shorted turns within an
inductor...?

For shorted turns in a motor use a growler.

N

 

[Tom MacIntyre]

I don't know what's preferred, but one way might be to ring it like
a flyback and look at the response.

That was my thought/guess as well.

Tom

 

[Tor Tveitane]

That was my thought/guess as well.

Any urls and info to show how to setup this and to diagnose the response..?

Tor

 

[NSM]

| "Tom MacIntyre" <[email protected]> skrev i melding
| |
| > >I don't know what's preferred, but one way might be to ring it like
| > >a flyback and look at the response.
| >
| > That was my thought/guess as well.
|
| Any urls and info to show how to setup this and to diagnose the
response..?

http://repairfaq.ece.drexel.edu/REPAIR/F_appfaqi.html

What sort of motor? What's shorted, field or rotor?

N

 

[CJT]

"Tom MacIntyre" <[email protected]> skrev i melding




Any urls and info to show how to setup this and to diagnose the response..?

Tor

This is the kind of thing I had in mind:

http://repairfaq.ece.drexel.edu/sam/flytest.htm#flyadv

 

[N Cook]

Hi,

Can I use a LCR bridge in inductance mode to measure difference in
inductance if I suspect one of the windings in an electrical motors to have
shorted turns...?

What is the preferred way to check for shorted turns within an inductor...?

Thanks for clues

Tpr

I've never used one but isn't a growler used for this purpose.

electronic hints and repair briefs
http://homepages.tcp.co.uk/~diverse

 

[Ross Herbert]

I've never used one but isn't a growler used for this purpose.

electronic hints and repair briefs
http://homepages.tcp.co.uk/~diverse

Or perhaps the modern day equivalent might work on motor windings,..
http://members.ozemail.com.au/~bobpar/fbt.htm

 

[Sam Goldwasser]

I've never used one but isn't a growler used for this purpose.

Yes, though it would be hard to justify the expense to fix one small
motor.

See, for example: http://www.sotcher.com/mre/520.html

It's just the primary of a transformer connected to 60 Hz along with
a hacksaw blade, so you could probably build one or improvise from
something else.

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[Jim Adney]

Yes, though it would be hard to justify the expense to fix one small
motor.

Yes, but any electric motor shop, or automotive electric shop will
have a growler and would charge only a very small fee to test an
armature for you.

Disassemble the motor and just take in the rotor, so that they don't
have to do any significant work.

If you bring it over here, it would take me less than 2 minutes to
check it out. ;-)

-

 

[Charles Schuler]

Disassemble the motor and just take in the rotor, so that they don't
have to do any significant work.

IF, it's a wound rotor motor. Most ac rotors are of the squirrel cage
variety.

 

[Jim Adney]

IF, it's a wound rotor motor. Most ac rotors are of the squirrel cage
variety.

I was wondering about that. Wouldn't a squirrel cage motor still have
the same magnetic properties? I'm not sure, but I'd bet that such a
rotor would still pass the growler test, but it's hard to imagine a
squirrel cage rotor with a short in it, which, I believe is what the
OP asked about.

Does anyone know if this happens?

-

 

[NSM]

| On Tue, 9 Nov 2004 16:41:01 -0500 "Charles Schuler"
|
| >> Disassemble the motor and just take in the rotor, so that they don't
| >> have to do any significant work.
| >
| >IF, it's a wound rotor motor. Most ac rotors are of the squirrel cage
| >variety.
|
| I was wondering about that. Wouldn't a squirrel cage motor still have
| the same magnetic properties? I'm not sure, but I'd bet that such a
| rotor would still pass the growler test, but it's hard to imagine a
| squirrel cage rotor with a short in it, which, I believe is what the
| OP asked about.

I don't know how to 'growl' a squirrel cage motor. I'd just fire it up and
check the amps on each leg.

NM

 

[James Sweet]

I was wondering about that. Wouldn't a squirrel cage motor still have
the same magnetic properties? I'm not sure, but I'd bet that such a
rotor would still pass the growler test, but it's hard to imagine a
squirrel cage rotor with a short in it, which, I believe is what the
OP asked about.

Does anyone know if this happens?

I've never even heard of a rotor failure on any type of induction motor,
usually it's the starting switch, capacitor, or bearings that fail. The
stator windings can burn out but it's rare.

 

[Sam Goldwasser]

I was wondering about that. Wouldn't a squirrel cage motor still have
the same magnetic properties? I'm not sure, but I'd bet that such a
rotor would still pass the growler test, but it's hard to imagine a
squirrel cage rotor with a short in it, which, I believe is what the
OP asked about.

By definition, a squirrel cage rotor is all shorts.

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[Sam Goldwasser]

I've never even heard of a rotor failure on any type of induction motor,
usually it's the starting switch, capacitor, or bearings that fail. The
stator windings can burn out but it's rare.

The only way a squirrel cage rotor could fail would be for one or more
of the shorting bars to open. A quirrel cage rotor is based on all
the bars being shorted at the end-plates.

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[Jim Adney]

By definition, a squirrel cage rotor is all shorts.

Right, but so is a regular commutator rotor. The only difference, I
think, is that the squirrel cage rotor is wound with much more rugged
"wire."

-

 

[Sam Goldwasser]

Right, but so is a regular commutator rotor. The only difference, I
think, is that the squirrel cage rotor is wound with much more rugged
"wire."

Nah. A commutator motor happens to be shorted but that is a byproduct
of how it's wound, not a requirement. A squirrel cage rotor is a bunch
of copper bars embedded just under the surface of a solid steel rotor
running length-wise. They are shorted at the end plates. Since these
are induction motors, they depend on the current flowing in the bars
as the secondary of a transformer to provide the torque.

For brush-type motors, current is applied to the rotor windings via the
brushes. It's possible to build such a motor without "shorted" windings.

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[Asimov]

"Jim Adney" bravely wrote to "All" (11 Nov 04 20:57:04)
--- on the heady topic of "Re: Detect shorted turns in motor windings..."

JA> From: Jim Adney <[email protected]>

By definition, a squirrel cage rotor is all shorts.

JA> Right, but so is a regular commutator rotor. The only difference, I
JA> think, is that the squirrel cage rotor is wound with much more rugged
JA> "wire."

The squirrel cage rotor is really a rotating transformer with a very
low resistance secondary. Any phase difference (slip) between the
applied field and the transformed field generates very high currents
in the range of 100's of amperes. To say the rotor is wound with much
more rugged wire is really an understatement. It is this high current
that causes a counter emf, applying a mechanical torque to the shaft,
and results in the desired motor action.

A*s*i*m*o*v

.... Electrical engineers deal with current events.