Overbraking / High DC Bus Voltage Fault on Drive

[X49]

I have a 600V 250hp drive that sometimes trips on "Overbraking", when requested to run. This fault occurs when the DC bus voltage reaches 1174V. The same motor has caused this fault when connected to three different drives. Our other 250hp motor does not cause its drive to trip.

The drives have load reactors, and the motors are connected with individual conductors in conduit with a length of about 40-50 feet (not armored cable).

Is caused by reflected waves in the cables?
Could this be a problem with the motor itself and are any tests that could be done on the motor or cable to identify the problem?

 

[resqcapt19]

What type of load is the motor driving?

 

[X49]

The motor is driving a centrifugal pump.

 

[jraef]

Who's drive and what model?



"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[resqcapt19]

Is there a flow through the pump that results in an "over running" load on the motor?

 

[X49]

The drive is a Schneider Altivar 61.

The application is a booster pumping station, with a jockey pump and two larger 250hp pumps, all in parallel. The 250hp duty pump starts while the jockey is running. I wouldn't expect much flow though the duty pump upon startup, but I'm no expert on such things.

 

[Skogsgurra]

Forget about reflections and such esotheric phenomena.

My guess is that the pump's speed either overshoots/oscillates or that it brakes somewhere during operation. If it overshoots or brakes, the DC link will increase until you reach the tripping voltage somewhere close to 1200 V for a 600 V drive.

Try to make the retardation ramp longer and/or speed control less "crisp" i.e. slow it down.

If you are running scalar control (U/f), you probably don't have overshoot or oscillations. If you are running vector control in speed or frequency mode, you may have overshoot or oscillations.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[jraef]

"...sometimes trips on "Overbraking", when requested to run"

Immediately when requested to run, or after an amount of time WHILE it is running?

Is the other duty pump already running when this one is called to run?

Why I ask...

I have had more than one Pressure Boosting System pump drive issue that happened because the check valve from one pump that is supposed to prevent back-flow from the common header is not fully closed. When the system was Across-the-Line, nobody noticed because as soon as you energized the pump, any small amount of backspin was insignificant. But once VFDs are introduced, even a small amount of backspin can be problematic. When the VFD is energized and the ramp is long and starts at zero, the motor windings become excited by the low drive output, but are not producing very much torque at first. So the excitation allows the motor to regenerate, but the output torque of the motor at that low speed is too low to overcome the backspin, so the motor regenerates long enough to build up a feedback to the DC bus that trips the drive. If you cannot fix the back-flow, you can try starting the ramp at a minimum speed and go there immediately when you give the drive a run command, if it allows that in programming. You can also try a DC Injection Brake BEFORE accelerating, which some drives are capable of as well. I no longer remember enough about the Altivar drives to help you on that aspect though.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[Skogsgurra]

Yes, of course, Jeff!
Exactly that also happens in a ventilation system where several fans "fight" to push air through the same outlet. If one of them doesn't run, it spins backwards and then it needs to brake when started. With high DC link as a result.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.