VFD Failure on Generator Power

[drktmplr12]

I would be looking for two additional information factors, the drive manufacturer's consultation or instructions about running on generator power. It's possible the drive's trip settings can be relaxed for generator power. And the generator manufacturer's consultation or instructions about running straight into a 100% front end rectifier load. What problem that may cause that the manufacturer may know about (voltage regulation, distortion).

For example, if half of the load was straight running line connected three phase motors, they would provide some buffering or rotating line conditioning to mitigate the line effects of the big non linear rectifier load. Without that there was no buffering or line conditioning.

Are you assured the generator was always on and connected and it was the drive that tripped. Is it the sense that the drive tripped from detecting a distorted supply that itself caused.

I have consulting with SQD and generator manufacturer's to discuss the interactions from both sides. That is good advice.

I am under the impression the generators were always on the the drive tripped to protect itself from distortion that it caused or some process related condition that overloaded the motor.

 

[drktmplr12]

We only know what they are now, after the storm, correct?

honestly imo it is likely just a drive set-up issue exacerbated by the storm

That is the conclusion I've reached based on my research on the matter and discussion in this thread.

That being said, I have gleaned a lot of very useful information here and I very much appreciate everyone that participated. This is a wonderful community. Thank you.

The discussion doesn't have to end here, but I will be wrapping up my report today. If there are any major developments I will likely post an update.

 

[Besoeker]

So even going down the high harmonics track, why would the harmonics be greater during the storm and not now, running from the SAME generators without the storm in play? Or did I misinterpret something here?

Or did I miss something?
I walk about quite a lot. Usually, over 10 miles/16 klicks a day. I have to do it with that lovely fuzzy beast.
Sometimes that clears my head.

 

[Electric-Light]

Can you figure what was damaged on the drive (diodes, lgbt or MOVs?)

The dramatically lower TCD (I-THD) means the higher impedance of the generator is already rounding off the peaky waveform. The electrical industry always talk about true RMS and you're always monitoring this as the voltage but its not always of interest to the load.

A light bulb is responsive to Vrms but non-linear loads are not. The output of a modified square wave inverter with 140v flat area modulated to 120v rms makes the light bulb light light up as bright as a normal outlet. The DC link voltage is normally 170v or 340v, but with the funky waveform I talked about, it would drop to 140v or 280v which causes increases the duty cycle on the back end and increases the load on front-end diodes. That's a common symptom of flat topping which happens easily when rectifier loads like VFDs are fed from a high impedance source like a generator.

So you should actually grab the current, voltage, vpk, ipk on all phases along with the waveform over some time while on generator and on utility.

 

[drktmplr12]

Can you figure what was damaged on the drive (diodes, lgbt or MOVs?)

The dramatically lower TCD (I-THD) means the higher impedance of the generator is already rounding off the peaky waveform. The electrical industry always talk about true RMS and you're always monitoring this as the voltage but its not always of interest to the load.

A light bulb is responsive to Vrms but non-linear loads are not. The output of a modified square wave inverter with 140v flat area modulated to 120v rms makes the light bulb light light up as bright as a normal outlet. The DC link voltage is normally 170v or 340v, but with the funky waveform I talked about, it would drop to 140v or 280v which causes increases the duty cycle on the back end and increases the load on front-end diodes. That's a common symptom of flat topping which happens easily when rectifier loads like VFDs are fed from a high impedance source like a generator.

So you should actually grab the current, voltage, vpk, ipk on all phases along with the waveform over some time while on generator and on utility.

This is a good idea. We will consider this!

 

[Sahib]

first thing I would do - fit a DC link choke.

One obvious effect of harmonics is overheating. That may not lead to tripping of drive in the short run. Less obvious one is generator hunting due to harmonics. Generator hunting may cause drive to trip immediately or in the short run. But did OP note anything like that?

 

[drktmplr12]

One obvious effect of harmonics is overheating. That may not lead to tripping of drive in the short run. Less obvious one is generator hunting due to harmonics. Generator hunting may cause drive to trip immediately or in the short run. But did OP note anything like that?

We did not observe generator hunting immediately or in the short run. In fact, the wells may be operated by generator without issue at this point.

Some of the intricacies of how the VFD interacts with the local PLC and the local PLC with the SCADA system give reason to believe that VFD failure was unlikely and operations was observing -something- different.
We are considering the possibility that the VFD didn't trip at all, and there were widespread issues with their communications system due to power outages and trees. I am going to recommend they take a look at how the well control logic interacts with plant SCADA and make sure it is hardened to behave appropriately during widespread power outage and intermittent communications.

 

[Besoeker]

We did not observe generator hunting immediately or in the short run. In fact, the wells may be operated by generator without issue at this point.

Some of the intricacies of how the VFD interacts with the local PLC and the local PLC with the SCADA system give reason to believe that VFD failure was unlikely and operations was observing -something- different.
We are considering the possibility that the VFD didn't trip at all, and there were widespread issues with their communications system due to power outages and trees. I am going to recommend they take a look at how the well control logic interacts with plant SCADA and make sure it is hardened to behave appropriately during widespread power outage and intermittent communications.

Yes, seems like you have an issue I'm sure we have all faced at times. Absence of or inaccurate information being reported back from site. I think what you are considering sounds like a good idea. I wish you well with it - no pun intended.

 

[Electric-Light]

What are you saying? Was the VFD ruined or just that it did something it shouldn't have?

Failed means rendered no longer usable.

 

[Besoeker]

What are you saying? Was the VFD ruined or just that it did something it shouldn't have?

Failed means rendered no longer usable.

Apparently it still is.

 

[drktmplr12]

What are you saying? Was the VFD ruined or just that it did something it shouldn't have?

Failed means rendered no longer usable.

There is a gap between engineers and O&M, their needs are often opposed. That being said, sometimes engineers and operators use the same words and they mean different things.

In this case the perception of operators is that the "well control system was failing" so that's what I called it. In their view, if the well isn't delivering flow to the plant, it is failing and "rendered no longer usable." Perhaps in the context of this discussion, failure is a misnomer since we are specifically looking at the VFD. I apologize for any confusion that may have caused.

Here is an interesting power point related to operations and engineers

 

[Electric-Light]

There is a gap between engineers and O&M, their needs are often opposed. That being said, sometimes engineers and operators use the same words and they mean different things.

In this case the perception of operators is that the "well control system was failing" so that's what I called it. In their view, if the well isn't delivering flow to the plant, it is failing and "rendered no longer usable." Perhaps in the context of this discussion, failure is a misnomer since we are specifically looking at the VFD. I apologize for any confusion that may have caused.

Here is an interesting power point related to operations and engineers

Your descriptions are still too vague. If it's a car, the software intervenes in the event of a fan failure or coolant loss to reduce the chance of engine damage. If it's a plane, protection, the hardware to sacrificed to keep the thrust as long as it isn't pushed to the point of catching on fire or disintegrating and shooting bits of engine into the cabin (even then still giving manual override). It's not always a hardware issue. it's often undesirable programming that causes to act erratically or unnecessarily shut down. You could have the same hardware but the coordination between sensors, user input, engine and transmission can make or break a car.

But I'm not too familiar on drive software. If the system doesn't keep a good event log or a plot, that's not desirable.

Now for something I am much more familiar with, LED ballasts are often exposed to outside of design parameters because engineers underestimated realistic conditions or they were cutting corners, or the integrator or the user applied it inappropriately. Some didn't have any fall back mechanism or chose to not implement it and it would burn out. Some turned off and turned back on after it cooled off enough and gets stuck in a loop and some dimmed down to prevent overheating and covertly dimmed down to avoid burning out while hiding integrator's design flaws.