electrical motor will not run -no current - phases & voltage present

[matt_sd]

Hello all,

I am on the phone to someone who is remotely trying to diagnose a motor problem

it is a 30kW 4 pole, 400VAC ABB motor connected to a ABB softstarter. It is wiring in an 'inside delta' configuration. 6 wire connection to the motor. It has been working for a time months before it failed to run, the wiring has not been touched and there is another one next to it the same that is working without problem.

Now it is not running, completely silent, the motor is windings have been checked that are all 4 ohms (U1 to U2, v1 to v2 & W1 to W2) They have confirmed 230VAC between phases.

They have also swapped over the softstarters and still doesn't run. They are suggesting it is the motor but if there is resistance and voltage across it - surely there should be some motor movement or if not current increase??

Any ideas??

 

[nic00]

Have all the field cables been checked?

 

[JeffKiper]

Use an analog meter NOT a digital and see if the voltage is still there. You can add a couple of 100watt light bulbs in series place them across the line and see if you have voltage.
Think leakage voltage

 

[Christoff84]

Where did they confirm the voltages? Line side of the soft start? Load side? Motor windings?

You say the confirmed 230V between phases, but you said its a 400V motor? There should be some current flow somewhere, no current flow makes me think you have more then 1 wire broken, even with 1 wire broken you should still single phase the motor and trip the overload.


Do they have another small motor they can hook up to the end of the wire run to see if it runs?

 

[matt_sd]

hi guys, thanks for your quick replies,

• the field collection is directly from the starter panel to the motor about 2 metres away - this is correctly connected.

• They have not tried an analogue meter - just a Fluke digital one - should this make a difference?

the motor is collected as shown on page 53 inside delta

http://www05.abb.com/global/scot/scot209.nsf/veritydisplay/2985284834bcff7fc1256f3a00274038/$File/1SFC132002M0201.pdf

I asked them to disconnect the wiring to the motor at the starter (before the connections to the motor) and check between each phase and also between each winding (starter side after the softstarter)
They say they have 230VAC between each phase and between terminals that connect to each winding.

I agree with you 100% they should have some current, the resistance is in the windings and not all 3 windings could be open circuit but measuring 4ohms closed circuit...

I will suggest to try a small motor.
I am not there and the person is suppose to he a competent electrical engineer so I am really itching my head and starting to think that either there is something else I have not though of or he is not telling me correct information.

 

[jrwb4gbm]

With the motor windings disconnected it is very possible that the voltage will appear, if it is due to it being an eletronic soft start instead of a mechanical soft start. This is normal leakage. Here is another test that can be done with the motor connected. With the starter energized (Attempting to run) check from line "A" (L1) and load "A" (T1) of the soft starter. There should be zero volts or very nearly so. Repeat the procedure for phase "B" (L2) to (T2) and "C" (L3) to (T3).
Another option is to connect the suspect motor to a known good working starter. If it runs that would eliminate the motor being at fault.

 

[Christoff84]

Personally, even though the collection point is 2m away, I would still want to verify voltage inside the motor box. I would check each phase, phase-to-phase and phase-to-ground inside the motor box. I've not dealt with soft starters before so you may not see full line voltage from it.

Is it possible for them to uncouple the load and try starting the motor across the line? That's probably the simplest way to find out if the motor is bad.

If they have an amp-clamp handy, check each phase when they try to start it, then clamp all 3 phases and look for a ground fault. I doubt the ground fault due to no current flow but one can never be sure.

I really do doubt its the motor though, if it was bad bearings you'd be tripping overloads, if it was open windings you wouldn't have 4 ohms between them, if it was shorted windings, fuses would be blowing.

This reads like you've lost 2 of 3 phases somewhere along the line as even single phasing would draw something.

Edit: If they have a megger handy it might not hurt to test the wiring/windings from the load side of the soft starter (after they've disconnected them of course.

It's a tricky one, let us know how it turns out.

 

[gas]

This has to be in either the soft start unit or the external control.
A 30kw/40hp motor will make lots of smoke or sparks if there is a power side failure. If all the terminations are tight test the control side.
Are you sure the control in enabled?

 

[Lancie1]

A soft starter can protect against high-voltage partially shorted motor windings. The protection electronics will detect the high starting current and prevent a start, where as an old across-the line contactor will go ahead and apply the voltage and create a short and the fuse or breaker will then trip. The soft starter never applies full voltage to a bad motor, because the current goes above the overload point in first 1/2 second. Remember that a soft starter is similar to a Variable Speed Drive - it starts off at 0 volts output and increses the voltage over some time period, but if its current sensor hits the overload point, it shuts down. A bad motor winding or a wire with bad insulation will cause an immediate shut-down and it will appear that nothing happened.

Check the windings with a 500 volt or 1000 volt Megohm meter ("megger"). Often partially shorted or burned windings will show up where they will not with a 9 volt ohmmeter.

Also check the power leads between soft starter and the motor. Best check is to disconnect the motor supply wires from the soft starter and connect megohm meter between each phase wire and ground, then run test.

 

[silva.foxx]

No amp flow = no motor go!

If there's voltage and measured impedance...

The inside delta diagram, you directed us to, shows a contactor and overload. Is this contactor closing? Is the overload intact?

The other thing I'm thinking is: are the windings across phases?

ie. L1 thru Softstarter thru motor to L2 via o/l and contactor.
.

 

[DickDV]

With proper branch circuit fusing in place, I would remove the softstarter from the circuit, reconnect the motor leads in delta as would be normal in a direct-on-line start. Attempt to start the motor unloaded. If it runs, the softstarter is causing the problem. If it doesn't, its the motor.

To repeat, be sure the branch circuit fusing is in place and functioning since a shorted or grounded motor needs to be released quickly to prevent a fire.

 

[moggie]

Have you a copy of the schematics for the contactor and softstart?
As Silva-Foxx suggested - is the contactor energising? If yes then it is possibly a faulty soft start, if no then check to see if the overload has tripped.
Have the fuses in the soft-start been checked?

 

[shoelesscraig]

I have dozens and dozens of soft-starters all across our plant. Usually, the motor is the problem, and it will present the same symptoms you are speaking of...no movement from the motor at all. It is b/c, as was previously mentioned, the starter limits the current that it will output when a short circuit is detected.

Best bet is to MEG the motor to check for shorted windings in the motor. I have seen bad soft-starters before (on more than one occasion), but more often that not, its the motor.

 

[Andrew Evenson]

What about the load??

What is the motor driving?? I know at our plant, we multiple multi-armature drive setups where we drive "rolls". There is a common bus where the armature of multiple motors are driven from a common drive, while the fields are controlled seperately. Lots of time, the drive is healthy, field controller is healthy and field contactor is closed, but there is no load current. This is usually due to the roll to motor coupling being broken.

Just wanted to give and example of where it is not a controls issue. Do you have a mechanical issue??

Just a thought...

 

[matt_sd]

Thanks for the replies

I will ask them to get a Megger tomorrow to check the winders continuity and insulation resistance.

They have confirmed to me that the softstarter is ok as swapped with the identical working one. They have confirmed that the overload is in and voltage to the motor from the overload side (cant be from the softstarter via motor as checked voltage when motor tails removed.


hi silva.foxx, yes - I thought the isolator or overload would be open but they have confirmed it isn't and voltage when motors disconnected. They assume me that the wiring is correct as same as the other one and has been working for weeks as wired without problems before this. Would be so much easier if there to confirm what I'm being told but the other side of the world.

I will upload the wiring diagram tomorrow. If they could connect a smaller motor just to prove all the wiring it would be good.

Interesting shoelesscraig, i.e motor at fault. Megger will fully test the windings, it is only a few months old and would suspect they would have had some serious smoke/heat with a 30kw motor.

The motor is driving an hydraulic pump. This is unloaded when starting. When commissioning, even if the pump was not unloaded (unload solenoid was not energised) the motor would still start but labour more.

Will speak to them tomorrow and do some more tests as suggested.
Thanks for the replies and will let you know how they get on.

Matt