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Join Date: Sep 2009
Posts: 69

VSD Altivar 61 Ground Short Circuit

05/14/2012 12:06 PM

We have a Altivar 61 45kw VSD that trips on Ground short circuit, especially when we start up some other equipment (motor)... anyone have any ideas... (Motor insulation is ok). our switching frequency is 12kHz.

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#1

Re: VSD Altivar 61 Ground Short Circuit

05/14/2012 1:12 PM

Yes I have an idea. Most circuits don't work well when a short circuit happens. It sounds to me like your protection circuitry is doing the right thing. I think that we might have a ESO condition here.

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#2
In reply to #1

Re: VSD Altivar 61 Ground Short Circuit

05/14/2012 2:08 PM

Problem is that I do not have a short.... the drive and motor work ok ... but when I start another unrelated motor .. the drive faults... with " Ground Short Circuit".. again .. this does not always happen... we have about 8 of these drives and I only have this problem with two of the drives.

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#3
In reply to #2

Re: VSD Altivar 61 Ground Short Circuit

05/14/2012 2:31 PM

OK have you used any troubleshooting tools like an oscilloscope and current transformer to compare a working and a tripping motor and driver combination to diagnose your problem?

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#4

Re: VSD Altivar 61 Ground Short Circuit

05/14/2012 3:08 PM

RTFM

In the ATV61 drive, the fault designated as "Ground Short Circuit" (SCF3) is related to the OUTPUT of the drive, not the input. They don't (as per typical for Schneider) go onto detail as to how this fault detection functions, but one of the interesting solutions they offer it to add a reactor to the output. That may indicate that the drive is sensitive to rise time issues on the ouput wave form. If you start a large amount of other equipment and tax your supply transformer more, you may be creating a voltage drop on the input side and create a steep wave front on the output current because the load has not changed. Putting in a load reactor may be the best solution because it will slow down any rapid changes in current by increasing the inductive time constant.

But also, why the heck are you running at 12kHz? Totally wasteful and possibly another contributing factor. High carrier frequencies only provide the benefit of reducing audible noise in things like office fans where people will hear the high pitched whine of the motor through the air ducts. In most machines, it's likely that the machine itself is making so much noise that you would never hear the motor anyway. High carrier frequencies increase the switching losses in the drive, cutting down on the drive's energy efficiency benefits and in fact often result in the need to de-rate the VFD because of the extra heat. By the way, that is another suggestion for mitigating the SCF3 fault in the manual, "Lower the carrier frequency".

"• Check the cables connecting the drive to the motor, and the

insulation of the motor

• Perform the diagnostic tests via the [1.10 DIAGNOSTICS]

menu.

• Reduce the switching frequency

• Connect chokes in series with the motor

• Check the adjustment of speed loop and brake"

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#5
In reply to #4

Re: VSD Altivar 61 Ground Short Circuit

05/15/2012 1:24 PM

hi JRaef... Thanks for your reply.. today I adjusted the switching frequency from 12 to 8 then to 6Khz.. but the drive continued to fault... I did notice that if I limited the max freq to 58hz the drive seemed to behave, however above that we had various shutdowns... could you explain the reason for this ..Thanks..(I have ordered chokes to install.)

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#6
In reply to #5

Re: VSD Altivar 61 Ground Short Circuit

05/15/2012 2:40 PM

If the output speed affects the trip and this is above maximum voltage level, it sounds like the motor vibration is causing these faults. The coincidence other switching (switching off??) may have is if the DC voltage is increased in the drive's DC link, causing higher voltages to arrive at the motor terminals which in turn triggers the earth current to trip level when the motor is at these higher speeds.

Have you swapped out the problem drive / motors and where does the problem stay? I'd suspect the motor which tests OK statically but fails under dynamic conditions, i've seen this many times with VFD.

However, a process of elimination should resolve whether it is VFD, motor cable or motor causing the problem.(by swapping out)

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#7

Re: VSD Altivar 61 Ground Short Circuit

05/15/2012 5:09 PM

Hi,

I also recommend you swap the VSD with another similar one then try to replicate .

See if the fault remains with the same VSD or the motor.

Once the VSd is tuned on it will do a self check on the IGBTS to detect any short circiut faults .You do not see this but we do this on power up. if the test is ok then VSD is ready. From your description, the fault may be related to :

Motor insulation fault: I have seen cases where motors passed megger test but. when we turne the rotor it failed. you can also check the winding resistance while turnining the motor .the resistance should be the same on three phases. If the motor is in Delta then you may need to remove the delat shorts and redo the megger test as Delta windings can be misleading.

I also recommend you swap the VSD with another similar one then try to replicate .

See if the fault remains with the same VSD or the motor.

Earth leakage current: this usually related to high switching frequency .You are opertaing at 12khz which is very high unless the the motor is very small. however you need to wind down the switching frequency and see if the fault is gone.One way to know if your switching frequency is higher than normal is look for hissing noise neear the motor , the lower the switching frequency the lower this noise would be.

Can you send me your VSD single line drawings including earthing arrangements. I hope yoiu are using the EMC plate .

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#8

Re: VSD Altivar 61 Ground Short Circuit

05/16/2012 2:07 PM

Hi everyone.. just thought I´d fill you in.... I had a meeting with a schneider engineer today who informed me that a few years ago.. (roughly when we purchased our vfd) they had a bad batch of vfd that faulted with exactly the same fault.. the drives had leaking IBGT, (In one sale of about 15 drives 8 had this problem).. I hope this is the end of this story.. I will let you know how their technicians visit goes.. Thanks to all

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