# Altivar 71 drive giving motor short cct



## Safari (Jul 9, 2013)

We have this drive 15kw/20hp.that we use in our 10tonne crane for hoist motor.the drive gives motor short cct fault.though when I take megavalues and resistance the motor is ok.
The manual says in such a case you decrease the switching frequency I decrease it from 4 to 3khz but still.

When the fault is reset the drive. runs for about 20mins then gives the short cct error.

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## thorax181 (Aug 29, 2015)

How far away is the motor from the vfd? Did u megger the wires?

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## triden (Jun 13, 2012)

Had it happen before, bad cable. Megger the conductors.

You have to remember that VFD load transients can easily reach 2000 volts, so bad insulation can easily cause a shorting fault. Make sure your megger is capable of of higher voltages required to test inverter rated motors and cable.


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## JRaef (Mar 23, 2009)

I doubt it's a short in the cable, because it would trip immediately, not after 20 minutes. If the cable gets wet after 20 minutes that might be an issue maybe, but in a crane, not likely. 

Cable distance can indeed be an issue, because the cables begin to act like capacitors and the charging current for them looks like a short circuit to the drive. That's why they recommended lowering the carrier frequency. Try that again and if it doesn't work, you might need to add a dv/dt filter on the output of the drive.


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## thorax181 (Aug 29, 2015)

I would agree. Add a filter or move the drive closer if possible if everything meggers fine

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## Safari (Jul 9, 2013)

thorax181 said:


> How far away is the motor from the vfd? Did u megger the wires?
> 
> Sent from my SCH-I605 using Tapatalk


Took megger values after disconnecting from drive.. values are at infinity.

The motor is 8M away from drive.

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## Safari (Jul 9, 2013)

triden said:


> Had it happen before, bad cable. Megger the conductors.
> 
> You have to remember that VFD load transients can easily reach 2000 volts, so bad insulation can easily cause a shorting fault. Make sure your megger is capable of of higher voltages required to test inverter rated motors and cable.


The crane is 4yrs old.has not happened before. My megger has a maximum of 5000vdc.but I set it at 500vdc mostly.

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## thorax181 (Aug 29, 2015)

What voltage did u megger at?

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## Safari (Jul 9, 2013)

JRaef said:


> I doubt it's a short in the cable, because it would trip immediately, not after 20 minutes. If the cable gets wet after 20 minutes that might be an issue maybe, but in a crane, not likely.
> 
> Cable distance can indeed be an issue, because the cables begin to act like capacitors and the charging current for them looks like a short circuit to the drive. That's why they recommended lowering the carrier frequency. Try that again and if it doesn't work, you might need to add a dv/dt filter on the output of the drive.


Let me add also a resistor box 14ohm is added on the drive for breaking purposes.

Yes am also of the opinion a direct short should not take that long for a drive to trip.



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## thorax181 (Aug 29, 2015)

And did this just start happening or was something worked on?

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## Safari (Jul 9, 2013)

thorax181 said:


> And did this just start happening or was something worked on?
> 
> Sent from my SCH-I605 using Tapatalk


Recently preventive maintenance was done on it.....nothing else.

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## triden (Jun 13, 2012)

JRaef said:


> I doubt it's a short in the cable, because it would trip immediately, not after 20 minutes. If the cable gets wet after 20 minutes that might be an issue maybe, but in a crane, not likely.
> 
> Cable distance can indeed be an issue, because the cables begin to act like capacitors and the charging current for them looks like a short circuit to the drive. That's why they recommended lowering the carrier frequency. Try that again and if it doesn't work, you might need to add a dv/dt filter on the output of the drive.


Last bad cable I had that faulted an altivar 61 would fail intermittently over a period of about 45 minutes.


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## triden (Jun 13, 2012)

What's the motor voltage? 500v probably isn't enought. Did you also megger the motor?


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## John Valdes (May 17, 2007)

I once had a motor in the shop that was reported as "ground fault" on the drive.
We megged it, surge tested it and used a Hi-Pot on it and could not find the short or ground.

Hook it up to a drive and see "ground fault" immediately on start.
For a motor shop with everything we had, we could not locate where the ground or short was or even existed.
Put another motor on the drive and no fault occurred.

We ended up selling the customer a new motor while we sent the original faulting motor back to Baldor for inspection.
Indeed they did come back with a motor issue a few weeks later.

The point I'm trying to make is drives do sense faults and are very careful about what they will allow to run and what they will fault on.
I would try operating the drive without motor first. If it starts, you know the cable is good. I say its in your motor.
And I bet if you hooked this motor up to an across the line starter, it would run just fine.
Drives are very particular about what will run and what will not.
Its in your motor.


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## MDShunk (Jan 7, 2007)

Drives are pretty self-diagnostic. If they say ground fault, I tend to believe them. If it was a simple overcurrent or high dc bus voltage, I might say it's a capacitive charging issue that could be corrected with a load reactor. In the case of ground fault, methinks you have a ground fault... you just haven't found it yet. Are there collectors involved between the drive and the hoist motor? Dirty/dusty/poorly maintained collectors and bus bars, even in one little spot, are very common sources of a ground fault error on hoists and cranes.


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## Safari (Jul 9, 2013)

triden said:


> What's the motor voltage? 500v probably isn't enought. Did you also megger the motor?


415V

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## JRaef (Mar 23, 2009)

triden said:


> What's the motor voltage? 500v probably isn't enought. Did you also megger the motor?





Safari said:


> 415V
> 
> Sent from my HUAWEI Y330-U01 using Tapatalk


What he meant by that (if I may), is that because the DC pulses coming out of a VFD are at a higher potential, and the possibility exists for them to be even HIGHER than normal of you end up with what are called "reflected waves" of up to 2000V, a 500V megger may be insufficient to see the possible effects. I recommend using a 1000V megger on the output cables and windings of VFD fed motors in the 400V class and above. A 500V megger would be fine for a 240V motor and drive, but up to that point you had not said what it was.


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## Safari (Jul 9, 2013)

JRaef said:


> What he meant by that (if I may), is that because the DC pulses coming out of a VFD are at a higher potential, and the possibility exists for them to be even HIGHER than normal of you end up with what are called "reflected waves" of up to 2000V, a 500V megger may be insufficient to see the possible effects. I recommend using a 1000V megger on the output cables and windings of VFD fed motors in the 400V class and above. A 500V megger would be fine for a 240V motor and drive, but up to that point you had not said what it was.


Thanks for clarifying jraef.just to update on the progress.a colleague said on sunday it tripped on overcurrent.they tried to reset the fault but it didn't.until they disconnected motor cables from drive then return back that's when it responded.

The crane operators mainly reset themselves.when they have a load and the hoist fails.they quickly reset and finish the task.

When they call us it actually means they have reset in vain.when I check the fault history it confirms.

Iet me go see if it has faulted again on motor short cct.

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## RIVETER (Sep 26, 2009)

Safari said:


> Recently preventive maintenance was done on it.....nothing else.
> 
> Sent from my HUAWEI Y330-U01 using Tapatalk


Check the grease points on the pulleys.


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## Safari (Jul 9, 2013)

JRaef said:


> What he meant by that (if I may), is that because the DC pulses coming out of a VFD are at a higher potential, and the possibility exists for them to be even HIGHER than normal of you end up with what are called "reflected waves" of up to 2000V, a 500V megger may be insufficient to see the possible effects. I recommend using a 1000V megger on the output cables and windings of VFD fed motors in the 400V class and above. A 500V megger would be fine for a 240V motor and drive, but up to that point you had not said what it was.


I just did with 1000V









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## Safari (Jul 9, 2013)

I just called up again it had faulted.on checking it was an undervoltage fault.since changing the switching frequency from 4khz to 2.1khz.it has not faulted by motor short cct.









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## thorax181 (Aug 29, 2015)

You said the motor was 415. Is the vfd set to that? I've seen some weird things happen when the drive was set higher than nameplate. Also is your incoming voltage correct?

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## John Valdes (May 17, 2007)

Will the drive run without the motor connected?
If it will, chances are very good its the motor.


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## macmikeman (Jan 23, 2007)

My opinion is 71 is too old for any Altivar to be driving.


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## Safari (Jul 9, 2013)

thorax181 said:


> You said the motor was 415. Is the vfd set to that? I've seen some weird things happen when the drive was set higher than nameplate. Also is your incoming voltage correct?
> 
> Sent from my SCH-I605 using Tapatalk


Incoming voltage and voltage parameter settings are all set ok.the drive has been ok for almost 4yrs now. Without having any issues.I willhave to install a load reactor 

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## Safari (Jul 9, 2013)

John Valdes said:


> Will the drive run without the motor connected?
> If it will, chances are very good its the motor.


Disconnected the motor and ran the drive.the drive gave a fault motor flux.because the motor was not connected.

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## John Valdes (May 17, 2007)

Safari said:


> Disconnected the motor and ran the drive.the drive gave a fault motor flux.because the motor was not connected.


Do you have a motor, any motor to try out in place of the existing motor?
Trying a different motor and seeing if it runs will answer the question and verify if its a drive problem or a motor/wiring issue.

Most drives (standard volts/Hz) will run without a motor. But some require some programming changes to run without one.


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