Overcurrent Tripping of VFD

Does the pronoun <...We...> include the drive manufacturer’s and the motor manufacturer’s technical helplines?

There certainly could be several reasons for this inconvenient tripping of the drive...no other course but to work through the possibilities one at a time...That's why we get the big bucks...lol

https://www.electriciantalk.com/threads/drive-tripping-on-over-current.63820/

https://forums.mikeholt.com/threads/vfd-tripping-on-instantaneous-overcurrent.76955/

Thanks...But they have also not found out the root cause ;)

Check the inverter

Would it not have tripped immediately had there been any problem within VFD?

A few years ago, several VFD mfrs used Hall effect current transducers made by Honeywell that had a high premature failure rate, right in this size range. The failure mode was in an internal A-D converter that they would randomly go to all bits high, which would report a current value based on a digital value of 65536 (binary 16 bit word, all 1s) then it would cool down and act normal again.

Several of the affected mfrs had recalls because of it, some chose to see if they would fail in the field and then replace them. You may have that situation.

Dear sir, the CT is of LEM Swiss make LF 305 series.Do you suspect any issue on motor/ drive.

Girl, that is exactly who you must ask. Email them or get a phone number. If it is a stock fault they will be the ones to tell you the remedy.

Is this a new problem on a previously well behaved installation?

What is the driven machine? Looking for possible high frequency current/torque reversals?

What is the actual trip current programmed in the ACS800? What is the hardware limit amperes of the inverter? Wondering if IET instantaneous electronic trip rather than machine mechanical load, even though you did good check of external, perhaps internal VFD problem such as bad gate on timing resulting from noisy phase timing signal due to harmonics in the source power.

What other loads are on the local power supply that sources your VFD? Possible harmonic generators?

The current sensors would be the next logical item since you have changed the control board.

Yes sir.This is a new problem being faced in a 10 yer old system where the motor is rewounded once as per our records.The driven machine is a fan and being run at 50% speed in a cyclic operation.

The current limit set on the drive is 225A.There are 5 nos. similar rating drives nearby.The rest of the things you suggest would be clear only when we replace the drive.?

It certainly appears that the drive is the cause of the problem, as you suspect. Especially if you have several others performing acceptably. It seems unlikely that a fan and/or bearings could be exciting the drive enough to cause a trip. The only other thing I can think of is some drives have software to derate the motor full load ampere rating based on speed. If that parameter got set accidentally, I’ve had that happen where we’d get overload trips at half rated current. Usually these start derating the motor at 20% speed and lower, but the ACS800 might have a higher threshold.

Actually the suspicion is that insufficient phone calls have been made to the manufacturer of both the drive and the motor.

Do you have a line reactor installed? Might be worth the investment. I've seen them cure lots of odd/strange drive troubles.

https://www.rae.ca/wp-content/uploads/Line%20Reactor%20White%20Paper%20AN0032.pdf

There is no line reactor...the VFD to motor length is approximately 300mtr...As per the practice here in India, for distance more than 300mtr , the vfd OEM recommends reactor as per the discussion with them.

While the installation is old about 10 years , this problem is new.Yes the motor is resounded once as per records years back.

I would certainly install a line reactor. The incoming line power has somehow changed and now it's advantageous to install the line reactor. I am uncertian as to weather you have the load reactor installed or not as per your practice. I would install the load reactor as the OEM recommends if it has not been done.

The reactor they would recommend is certainly to be mounted at or near the motor, due to standing waves on the 300 meter motor leads. Perhaps some change in the driven machine is exciting the motor circuit, something has to have changed.

It is unlikely that a reactor before or after the drive will eliminate the problem, though certainly easier to install. You may want to experiment with changing the PWM frequency, it could be that simple. I think lower is the direction you want to go.

I find that a load reactor is now recommended typically to be at the drive, and not the motor. My experience was with a long line PWM going to a non-inverter rated motor, so perhaps local ground plane was more important for dvdt protection in that case, like applying surge arresters....

Can you share standards/ general guideline / best practices followed on requirement of reactors because it would attract initial investment & result would only be known later.

Output reactors are used to protect motor and not nuisance tripping if iam not wrong.

Here's a few to look at:

https://www.wolfautomation.com/blog/wp-content/uploads/tci-reactor-benefits-techpaper.pdf

https://acim.nidec.com/drives/kbelectronics/-/media/kbelectronics/documents/white-papers/applications-of-line-and-load-reactors-with-variable-frequency-drives.ashx?la=en

The last page of this one has easy instructions about sizing the reactors:

https://literature.rockwellautomation.com/idc/groups/literature/documents/wp/drives-wp016_-en-p.pdf

This link gives you an idea of the pricing for a 77 amp 480 volt 3 phase reactor:

https://www.wolfautomation.com/line-reactor-3-ph-77a-480vat-60hp/

This YouTube has useful information: https://www.youtube.com/watch?v=qQ8iJaJaPtA

So does this one: https://www.youtube.com/watch?v=89_aY5wXnZg

And this one: https://www.youtube.com/watch?v=redfKSwkUI0

Usually you would use a "LowZ" (3%) on the line and a "HighZ" (5%) on the load. The other parameters are the working voltage and the Full Load Amps.

Be sure and size the reactors amps close to the FLA. I usually go just a little high on the reactor amps, nothing extravagant.

The reactors are relatively inexpensive and well worth the money just for the safety factor.

Thank you...

In addition to the suggestion of a line reactor (between the drive and the incoming power) I suggest the inclusion of a load reactor (3%) mounted adjacent to the drive (or as close as other equipment permits) and wired between the drive's output terminals and the motor.

Also, if your PC does not do a good enough monitoring of current, rent or borrow a good recorder to simultaneously record all three phases of current and voltage. It will help to identify the probable events at the time of a trip. Most of the good ones will also allow you to look at the harmonic distortion in the line to the motor.

--JMM

I did see a VFD trip for "high current" alarm where the current "seemed" to be within the +/-20% manufacturer's nominated values and all items tested "OK" in static tests.

Situation was something like the drive was being used simultaneously at low frequency and plus 20% voltage. The combination of low frequency and high excitation voltage provided a current that was outside the parameters. A 132kw motor operating at 20% overvoltage and 20% reduced impedance would produce an effective 190kVA load and would show as an overcurrent. The VFD was protecting the load motor for the parameters that had been loaded.

The designer had selected the controller by treating each tolerance independently and had not utilised the total operating envelope.

For our situation, the displayed fault was the overcurrent fault, but the device was operating outside the parameter envelope for the pump motor that was being driven. I suppose that a better description should have been "over-power" fault.

Maybe the overcurrent fault is the first in the diagnostic software lookup table.

A 132kw motor operating at 20% overvoltage and 20% reduced impedance would produce an effective 190kVA load and would show as an overcurrent.

How can we say that the drive is running at 20% overvoltage and 20% reduced impedance.And why this problem now.The drive is generally run at 50% speed that is at around 750rpm.

I wonder if something has changed in the air load your fan is moving. A number of possibilities come to mind:

• First, the drive was near the limit of its time to ramp from one speed to another
• Possibly a bearing or two on the fan, that are adding friction (have you done an infra-red scan on the bearings, including the motor bearings and compared this to the other fans you mention)
• Possibly a lower duct resistance to the air flow, such as adding another branch to it or a hole or gap at a joint. Remember that a decreased flow resistance means a greater air flow and a greater load on the motor.
• Possibly a change in the air exhaust section (you don't describe this but I presume it may be to a dust collector system).

I read your posts to say the fan and drive are run at speeds that do vary from time to time. So, with a large fan the inertia is significant and changing or attempting to change the speed too quickly can cause a temporary overload. Your parameters for acceleration time may have been marginal and now are a little too short because of unseen changes in the load.

Do these times when it trips occur when there has been a very brief power loss? If so, the drive could be coming back on line to a spinning load. This requires that the parameters allow it to "catch" a spinning load. I doubt that this is the case, but all possibilities can be looked at.

--JMM

Sir,the motor is maintained at nearly 50% during its run without any significant change.We have our own power plant and the voltage fluctuations are very negligible.

Hello,

I was just using that as an example. A motor running intentionally slow will have a lower impedance than normal speed. If that same motor is then run at increased voltage to obtain the necessary torque at that lower speed, then these two factors compound to create a much higher current than anticipated. The example was a pump motor that I witnessed and not your described specific item.