VFD Malfunction

[SteveWag]

I was recently called to look at a problem at a well pump facility. Installed is an Eaton SVX9000, a TCI KMG Sine Wave Filter, 4400 feet of motor wire in buried PVC conduit and a 20 HP submersible well pump. The system has operated since 2008 without any problems. Four weeks ago it was found that the pump/VFD would not operate above about 48 hertz. That is, the drive could/would not operate at full speed either on remote or local (potentiometer). I verified that the remote input was 100%. I removed the load wiring from the VFD and operated it at 60 HZ both in remote and local. The current settings look OK, with no current limiting of speed. There is an identical unit, working, less the sine wave filter, about three feet away, with about 150 feet of motor supply wiring. I took the operator interface from that unit, inserted it into the malfunctioning VFD and downloaded the settings from the working unit with no luck. Anyone have any reason for the drive logic to limit the hertz output?
Thanks
Steve

 

[jraef]

Usually something like that is the result of a current limit, but you said that you checked that, right? Because usually how a VFD limits current is to override the speed command setting to reduce speed, which reduces the load and thus the current. It may also be called "stall prevention" something like that however, I'm no longer fluent in SVX9000 programming.

"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

 

[jraef]

Here, I looked it up for you...

620 Load drooping
Setting a proper value to the LoadDrooping parameter enables the load drooping.
This function causes the speed to decrease as the load torque increases. At rapid load
changes this gives a smoother torque response, when a part of the required power is
taken from the system inertia. This operation causes a constant, torque-dependent
steady-state error in speed response.

Emphasis added.


"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

 

[KllrWolf]

If you think the current is affecting the VFD operation, you can check everything after it - filter, cable, and motor. If it is the motor stalling out like jraef suggests, it might be something in the pump causing excessive drag. I would definitly do the basic checks like a megger on the motor and cable if you think the load might be part of the problem.

 

[jraef]

I meant to review that and his Post instead. I wanted to add this...

If this is on a pump and has been working fine for a long time but suddenly changes, it could be an indicator of a flow problem because flow = load in a pump. So if for example you have a pipe break or a severe leak, your flow is increasing and thus the load on the motor. The drive is responding to the added load by reducing the commanded speed. Up to 48Hz the motor load is within the drive's parameters, but above that it is overloading and if you have that feature enabled, the response is to drive the speed down artificially.

"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

 

[itsmoked]

That includes a valve that was partially closed, having been opened fully recently.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[burnt2x]

Is this pump operating alone? Or is it supplying a common header with other submersible pumps? I have experienced a similar problem; VFD cannot operate higher than 50Hz before. The equipment setup is: there are two identical submersible pumps feeding a common header. I tried measuring the flow on each line: pump1 discharge with the VFD in question, then the flow towards the reservoir tanks after the common header (using clamp-on ultrasonic flowmeter). Some flow was lost at the final delivery pipe to the reservoirs! The other pump was on standby but I took a flow reading on its discharge pipe and some flow was read out --> returning pumped water in the second submersible pump well--> a defective discharge check valve, (the discharge valve of pump2 was left open). Could this be what's wrong with your setup?

 

[SteveWag]

Thanks all. Nice and quick response. There are two wells supplying a long transmission line that ends a treatment plant. Each well is metered with a flow meter and the water entering the plant is metered. The flow numbers seem OK. Even the VFD/Well that is malfunctioning seems to be right on, flow wise, at the speed it’s operating at. I’ll measure motor current in all phases next time I visit, and keep everyone posted.
Thanks All
Steve