Overcurrent tripping

[bob]

Hi,

 

Iam looking for urgent help on Asirobicon SVTL600 VSD. The drive is driving a 400 kW electric motor. Below 8 Hz the drive run well and the output current is very stable but as soon as the frequency is increased above this limit , the current became unstable and it tripped on overcurrent. I have tried to get hold of the tech people in Italy but one of the guy is on vacation and the technical mailbox is full and all my msgs are returning back to me.

The drive is set on V/hz mode and is actually driving a non-loaded load.

Any help welcome.

 

Bob

[marke]

Hi Bob

 

Is this a new installation, or has this motor and drive performed corectly before?

I do not know my way around these drives, but I have found similar problems where there is a resonant interaction between the motor and the drive. This can sometimes be improved by changing the carrier frequency or the output. - came across a small motor the other day, that just refused to run on the output of a drive. Runs fine on normal supply, but was tried on two different drive and gave the same result. It was a brand new motor.

 

Best regards,

[bob]

Hi Marke,

Thanks for your reply. No its not a new installation but some slight modifications have been done on the mechanical side. There is no jamming of the load and the drive works very well below 8 hz.

In v/Hz the tuning is quite complex for Asirobicon drive.

 

Regards.

 

Bob

[Tua]

Hello Bob!

May be you should try to restore manufacture settings and parameters and after that try to start your motor once agan?

Did you try to do a ID test when the AC driver automatically defines any parameters of the motor?

[jraef]

"Tuning" in a V/Hz drive? Why?

[kens]

Hi Bob, i am not very familiar with this paticular drive but have had a similar experiance with another brand. Are you certain that the load is not binding? The situation that i had was on a 315 kW motor on a crushing plant. Had been running fine for 6 months then after a maint shutdown began tripping on overcurrent. After i had been told constantly that there was nothing different on the load side i set up a scope on the output of the drive and logged currents it took 12 hrs of monitoring before I caught it but it was a mechanical transient that caused the over current. So when the engineers admitted that maybe the changes they had made to their side may be at fault i not so calmly told them that perhaps they might like to change things back so we could all go home and get some sleep. They did just that and the machine has been fine ever since. This is what concerns me when you say that there have been slight modification done on the load side. I would setup a logging device on the current and try to see exactly what is happening when the drive trips.

Is the drive current limiting before the trip or is it instant? What type of load is connected?

 

Ken

[bob]

Hi,

 

Thanks for the comments. It is common on Asirobicon drive that the current oscillates at low frequency and the drive has got in built current regulator to damp the oscillation. However, the same settings which worked well some months ago is now proving unstability. I have resetted the parameters to default and have plugged in the same settings but without any success. The mechanical people is claiming that there is no problem on their side which I believe is true because on two attempts I succeeded to raise the speed to maximum and the crusher run well without any transient.

I am at a loss.

 

Bob

[marke]

Hello Bob

 

It is quite common for some motors/drives to exhibit an instability at particular frequencies. They often have skip frequencies to cause the drive to skip through these resonances. Is this a possibility??

 

Best regards,

[bob]

Hi Marke,

 

Yes the drive has provision for skip frequency ranges. I shall try later, but do you think resonance could trip the drive on overcurrent ? It works very well at low frequency with stable output current but as soon as the frequency is increased above 10 Hz , you can see the current oscillation until it tripped. There is no current limitation which proves that there is no overloading on the mechanical side.

I shall keep you inform.

 

Bob

[marke]

Hi Bob

 

Yes, resonance can certainly cause the drive to trip on over current and also on over voltage.

The question is is this problem occuring at particular frequencies, or over a frequency range. If it occurs at spot frequencies, then it is a resonance type issue and can be sorted by using skip frequencies. If it ocurs over a frequency range, i.e. 10 - 20 HZ, then there is another problem.

 

Have you tried palying with the carrier frequency??

 

Best regards,

[bob]

Hi Marke,

 

I have skipped the 10-25 Hz range and the drive succeeded to pass this range without tripping. But, between this range the output current of the drive is very unstable but once this range is skipped the current dropped to 25 % and the drive operation is very much stable. Resonance range ?

Thanks again Marke for your expert advice.

Bob

[marke]

Hi Bob

 

Well if that gets rid of the problem, then thats good news.

I would not normally expect to skip such a wide frequency range, usually around 2 - 3 Hz is all that is required.

I would sugest that you consult with the suppliers to see if you can get a more definative answer, but at least this has got you going in the mean time.

I am concerned that the problem seems to have evolved and may continue to evolve. It may indicate an issue with the motor such as a damaged rotor bar or similar.

 

Best regards,

[mariomaggi]

Dear bob,

how can we suggest to you a good solution if you don't explain your application?

Load is a fan, a roller, a piston pump, what?

 

What kind of drive? Nominal main supply voltage for that unit? True main voltage?

What kind of mechanical modification was done?

 

Regards

Mario (Milan - Italy)

 

 

 

 

[bob]

Dear Mario,

 

It is not the application which is the problem but most is the particular drive. I have got other drives( PDL ) ding the same job and which are not giving any trouble at all. I am actually querying the manufacturer to sort out things.

 

Bob