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

[Lancie1]

If there's voltage and measured impedance...

They have not tried an analogue meter - just a Fluke digital one -

For motors, it really depends on with WHAT the "measured impedance" was measured. Matt stated that it was measured with a Fluke meter, which can only put out about 9 volts as it measures the resistance (unless it is a Fluke Process Meter which can go up to 24 volts).

These levels are not nearly enough potential to determine if 400 volt motor windings have a thin spot on the insulation (9 volts is only about 1.7% of the 537 peak volts for a 380-volt alternating current). In other words the operating peak voltage is 60 times more than the voltage being used to measure the windings. Voltage potential is like water pressure in a water line - at 2 PSI there may be no leaks at all - impedance looks normal, but at 60 times that pressure or 120 PSI, there could be water spraying from several pinholes - impedance is shorted to ground.

Motor windings are often not "all bad" or "all good". The windings are insulated with varnish, and it does not all deteriorate at the same time. Hot spots can cause it to crumble away at some points, and often a motor will check good (with a 9-volt ohmmeter) under low humidity, but once things get wet again, it will check bad. The ultimate test is what happens when you put normal voltage on it. The best test (short of applying line voltage that DickDV recommended) is using a Megohm meter.

 

[Lancie1]

Error correction: I realized that the voltage is 230 VAC phase-to-phase, so my above calcuations are not correct, although the message is not changed. 230 X 2^0.5 = 325 peak volts, which is only 36 times more than the Fluke meter voltage being used to measure the windings. This is still not enough potential to detect partially bad windings.

 

[leitmotif]

The different statements regarding line voltage bug me. Here is how I would go about it.
1. Find out if line voltage is 230 or 460 or whatever
2. Double check to see if all components are rated for that line voltage.
3. Check motor with Fluke for open windings and severe ground.
4. If you really want to know winding resistance put 6 or 12 VDC across a winding and using a shunt measure the current. R = E/I
5. Disconnect motor from soft start at soft start. Megger line to motor and motor all at once. IF all good leave alone. If not split again to find problem
6. Check to see if pump and motor turn freely. If not fix mechanical problem.
7. Put discharge pressure gage on pump.
8. Set unloader for minimum pressure or better yet put in bypass.
9. Jumper out soft start.
10. Make sure existing overcurrent protection will suffice or adapt to ensure it is correct. I would not get too exacting on this since I would only run motor for 5 or 10 second to see if it will run.
IF it runs then I may get overcurrent protection set correctly and run across line for hour or so under normal operating conditions to ensure no pump or motor problems.

Dan Bentler

 

[matt_sd]

Error correction: I realized that the voltage is 230 VAC phase-to-phase, so my above calcuations are not correct, although the message is not changed. 230 X 2^0.5 = 325 peak volts, which is only 36 times more than the Fluke meter voltage being used to measure the windings. This is still not enough potential to detect partially bad windings.

A megger will prove this when they check it. Do you think that is is unusual for a new ABB motor that has been running probably 20 hours maximum over the last few months to fail or have you seen this occur before?


Thanks Lacie.

 

[matt_sd]

The different statements regarding line voltage bug me. Here is how I would go about it.
1. Find out if line voltage is 230 or 460 or whatever
2. Double check to see if all components are rated for that line voltage.
3. Check motor with Fluke for open windings and severe ground.
4. If you really want to know winding resistance put 6 or 12 VDC across a winding and using a shunt measure the current. R = E/I
5. Disconnect motor from soft start at soft start. Megger line to motor and motor all at once. IF all good leave alone. If not split again to find problem
6. Check to see if pump and motor turn freely. If not fix mechanical problem.
7. Put discharge pressure gage on pump.
8. Set unloader for minimum pressure or better yet put in bypass.
9. Jumper out soft start.
10. Make sure existing overcurrent protection will suffice or adapt to ensure it is correct. I would not get too exacting on this since I would only run motor for 5 or 10 second to see if it will run.
IF it runs then I may get overcurrent protection set correctly and run across line for hour or so under normal operating conditions to ensure no pump or motor problems.

Dan Bentler

Thanks Dan, will run through this with them.

Matt

 

[shoelesscraig]

While it is pretty rare that a new motor has got some kind of problem, I wouldn't rule it out completely. I have seen new equipment, be it motor or starter, that could have some sort of defect from the factory. Usually in this case, it would fail immediately upon starting, but I have seen a new motor run for a few hours and then die. I'm just saying, when troubleshooting something like this, I would never say "never".

As was stated before, disconnect the motor from the soft starter and meg it from there. That would check the motor and wiring going to the motor all at once. It is possible to have a wire that will short out when voltage is applied to it yet still look ok when tested with a regular meter. The megger is the way to go.

 

[electroferoza]

Hi Matt

what worries me the most is that you said there is 230V reading between the phases. When talking about a 3 phase delta connected load we should keep in mind that voltage line equals voltage phase. In other words what we read between any two line terminals must be 415v not 230v.

Hopefully a capable Sparky shoud be able to perform all mandatory tests like the Insulation Resistance (Megger) tests others suggested and have this sorted out.

 

[electroferoza]

Hi Matt

what worries me the most is that you said there is 230V reading between the phases. When talking about a 3 phase delta connected load we should keep in mind that voltage line equals line voltage. In other words what we read between any two line terminals must be 400v not 230v.

Hopefully a capable Sparky shoud be able to perform all mandatory tests like the Insulation Resistance (Megger) tests others suggested and have this sorted out.

 

[silva.foxx]

I get really impatient waiting for outcomes

.

 

[Lancie1]

Do you think that is is unusual for a new ABB motor that has been running probably 20 hours maximum over the last few months to fail or have you seen this occur before?

It is rare, but over the past 40 years, I have seen about 2 new motors fail (out of hundreds). I suspected that these were just cases of weak spots on the winding insulation, right out of the box.

I have seen quite a few others fail quickly, but it turned out that dual-voltage motors had been wired with 480 volts applied to the 240-volt coil configuration. That doesn't help the motor at all!

In another case I heard of a 40-horsepower 480-volt SEW brand motor that burned out 2 expensive Allen-Bradley variable speed drives. The installer was blaming it on poor grounding, but it sounded awfully like a short circuit to me. Upon replacing the second drive, the owner called for help. I discovered that one of the spade terminal lugs in the motor had a loose stray wire that was lying over against another phase. The wire was burned black and had a little ball of melted copper on the tip.

 

[benjie007]

i can't hardly wait for the result of this thread, but its all been said outloud. i strongly agree with Lancie1 about using multimeter instead of megger on motor problems. its a common fault of some technicians.
once again, disconnect the softstarter from the motor, and try to run the softstarter w/o load, if it runs, make note the output voltage/phase. from here, you have 99% the problem is the load side.

 

[The Plc Kid]

A little OT but somewhat related.

How do you guys feel about meggering a motor from the control panel when the run is under 150 feet and the motor is in a difficult location.

I haw quite a few of these cases.

Will a 150 foot of lead resistance make that much difference in the test.

I look at it as it is good to test the leads also.

We just do it on the motors that are hard to get to the pecker head.

We use MSA and ESA tests most of the time instead of using a megger but some of our guys still like the megger only.

 

[Lancie1]

Megging the leads is killing two birds with one meter. If either the cable or the motor is shorted to ground, it usually shows up.

If not, then you go out to the motor and disconnect the wires and meg the wires again. It wires good, then meg motor because it is probably shorted.

 

[benjie007]

yes, motor pecker head is the right way to test motors. wether it be megger or any other form of testing. we want to isolate the part being tested alone, so we can get right result.

 

[Lancie1]

Benjie,

Yes, if you are testing motors. What if you are just trying to find why a piece of machinery won't run, or why it trips the breaker?
It could be the motor, or the cable, or both, or something else. I say start at the top with the mostest and work down to the leastest.