Anyone use VFD designed cable in water wells?

[SteveWag]

I have done the design work required for municipal drinking water wells for a about 30 years now. The trend, lately, is to use a VFD to power the well pump. I have always used steel conduit from the controller to the well head and the driller/installer has used individual wires down the well, connecting to the flying motor leads with waterproof connectors. These wires are secured, with some slack, to the drop pipe with Scotch #88 tape at about 15-foot intervals. The slack allows for some drop pipe lengthening. I also install a pressure transmitter just above the pump in order to determine the depth of water in the well, at least the depth of pump submergence. On very deep wells I have seen some VFD noise on the 4-20 mA signal of the pressure transmitter. The signal cable is installed alone in a steel conduit from the well-head to the controls. As this cable is only near to the VFD wiring in the well, I have to assume that that is the source.
So, has anyone used VFD designed cable inside a well? How would the deep end be sealed? Often the pump has 4-foot flying leads and is under 200-300 feet of water. Any comments or thoughts?
Thanks
Steve

 

[KllrWolf]

I do not know how many our customers do order special cable for VFD operation of our motors, as they only tell us anything after something has gone wrong. However, we do recommend filters on the output of a VFD to protect the motor. Depending on the filter you use, it could also reduce or eliminate any harmonic interference (noise). The side benefit is it not causing interference with your instruments.

As a side note, please only use a VFD when it is necessary. I hate explaining to customers that their use of a VFD is why their motors that easily work for 10+ years direct-on-line are now failing much sooner (even just using a good filter can get the life span back where it belongs). Water filled motors are different than other motors, and those difference are a major pain once VFDs are added.

 

[SteveWag]

I have always use load filters, sometime dv/dt (sine wave) if the distance is long. We have seen motors installed over ten years working just fine.
Our hydro guy insists on ramping the flow up and down, on starting and stopping, for about 30 min, sometimes 60 min.. I usually set the VFD up to start and run at 30 Hz min, usually about 45 Hz , zero flow, and then ramp to the desired flow. I have found that a VFD is the best way to get this ramping of flow.
Steve

 

[KllrWolf]

Just as a reminder, make sure to get the speed on the motor up to the minimum speed as quickly as possible to keep from damaging the bearings and water flowing past the motor for cooling purpose. Also make sure you allow a rest period between shutting down and starting. A VFD ramped start still produces a lot of heat when starting the motor.