submersible well pump/vfd installation

[Atm]

Circuit length 289' from VFD to pump motor
5 hp deep well pump 480V 3phase
localized disconnect (less than 50' from well head)
VFD

Question: Is Flexible Motor Supply VFD cable the proper cabling for the above application? If so, how is the VFD cable normally terminated at or about the pump motor end/well head?

If VFD cable is not the best application, what is the best system?

 

[kwired]

VFD cable would probably be best for less EM interferences, but I have never seen it used on a submersible well application either. Usually either UF cable or PVC with THWN conductors.

 

[Cow]

I can tell you from experience, you need to consult the installation literature for the VFD you're using in regards to the motor cable length.

VFD cable is preferred or at least XHHW in conduit.

A line reactor and output filter is usually always recommended, if not required by the manufacturer.

 

[StarCat]

Termination of Motor Leads

Termination of Motor Leads

Circuit length 289' from VFD to pump motor
5 hp deep well pump 480V 3phase
localized disconnect (less than 50' from well head)
VFD

Question: Is Flexible Motor Supply VFD cable the proper cabling for the above application? If so, how is the VFD cable normally terminated at or about the pump motor end/well head?

If VFD cable is not the best application, what is the best system?

Every one I have ever worked on which are mostly farily shallow drops, you are dealing with a lead set coming off the pump motor that is generally of a length that gets you above the water level in the well. Then you generally make a splice that gets heat shrink put over it, and tie your cable to the discharge piping all the way up to ground level. From there its conduit to your well house. Never seen or worked on the real deep ones, but I'd guess its done very similar. I'd query the Application Engineers at the Pump Vendor for best practices. Of course I would think the motor and factory lead set must be rated for inverter duty. There is a lot of discussion of insulation types with respect to VFD load runs due to the frequencies involved. I would consider the wet environment to make this somewhat more important possibly.

 

[ptonsparky]

Standard well cable from the head down is all I’ve seen but as Kwire stated the distance from the VFD to head is a problem. Reading The Fine Manual will help.

The few times I’ve run across installations where the proper cable was used, there were no motor failures. Others that should have had it and ignored other suggestions in TFM suffered motor after motor failure. Unfortunately I didn’t understand why at the time.

 

[drktmplr12]

Circuit length 289' from VFD to pump motor
5 hp deep well pump 480V 3phase
localized disconnect (less than 50' from well head)
VFD

Question: Is Flexible Motor Supply VFD cable the proper cabling for the above application? If so, how is the VFD cable normally terminated at or about the pump motor end/well head?

If VFD cable is not the best application, what is the best system?

1. the cable for the submersible is going to be integral to the pump. how deep is the well and does the circuit length of 289' include the well depth?
2. normally VFD cable concentric grounds are bonded to the motor frame.
3. you would need a motor terminal box at the top of the well head to splice together the VFD cable with the integral pump cables.
4. be careful of what speed you operate the motor at. submersibles have a minimum speed required to cool properly. they depend on water flow for heat dissipation. the manufacturer can tell you what this speed is and the drive needs to be set to never go below that speed.
5. make sure the VFD is sized properly for the actual motor you intend to use. do not use NEC amps to size it. submersibles have unusually low power factors (~0.6)

 

[kwired]

1. the cable for the submersible is going to be integral to the pump. how deep is the well and does the circuit length of 289' include the well depth?
2. normally VFD cable concentric grounds are bonded to the motor frame.
3. you would need a motor terminal box at the top of the well head to splice together the VFD cable with the integral pump cables.
4. be careful of what speed you operate the motor at. submersibles have a minimum speed required to cool properly. they depend on water flow for heat dissipation. the manufacturer can tell you what this speed is and the drive needs to be set to never go below that speed.
5. make sure the VFD is sized properly for the actual motor you intend to use. do not use NEC amps to size it. submersibles have unusually low power factors (~0.6)

Usually only a few feet of conductor on the pump, you splice submersible pump cable with waterproof splicing method onto the motor leads and bring it whatever distance necessary to top of well casing and then connect to whatever you are supplying the well casing with in an area at top of well casing.

 

[Besoeker]

Every one I have ever worked on which are mostly farily shallow drops, you are dealing with a lead set coming off the pump motor that is generally of a length that gets you above the water level in the well. Then you generally make a splice that gets heat shrink put over it, and tie your cable to the discharge piping all the way up to ground level. From there its conduit to your well house. Never seen or worked on the real deep ones, but I'd guess its done very similar. I'd query the Application Engineers at the Pump Vendor for best practices. Of course I would think the motor and factory lead set must be rated for inverter duty. There is a lot of discussion of insulation types with respect to VFD load runs due to the frequencies involved. I would consider the wet environment to make this somewhat more important possibly.

Those I have dealt with came with a cable attached to the motor and long enough to be made off in an IP66 terminal box on the wall of the shaft. From there to the starter was done in XPLE steel wire armoured cable.
Don't know if this helps.

 

[Dzboyce]

Are you asking these questions to design the system or are you actually installing this system?

is the VFD being supplied by the pump distributor? They will sell a vfd that has been specifically programmed for a submersible pump motor. A sub motor has a minimum running speed of 30 hz because of the Kingsburg thrust bearing. It is usually programmed to attain 30 hz within 1/2 second. You can buy a general purpose VFD, but you have to know how to program it correctly.

No submersible motor manufacturer will warranty a 460v, 3 phase motor without installation of an output filter. For the distance between your VFD and the motor, you should be using a DV/DT filter.

The pumpinstaller, if it is not you, will use a prepackaged waterproof splice kit to attach the submersible pump wire to the motor leads. I have never used anything other than submersible pump wire inside of well casing. It is made specifically for that purpose. I purchase it in 1000 ft rolls from the pump distributor, NOT an electrical supply house.

For the portion of wiring between the VFD, and the well head, it will be recommended that you use XHHW wire rather than THWN, and use steel conduit rather than PVC. That being said, I have only ever used THWN in pvc conduit in 1,000+ installations, and have never had a failure. I have seen other installation where THWN has failed though. You should review JRAEF’s comments on this in other threads.

 

[Dzboyce]

Though I have always used THHN wire previously, I plan on using XHHW wire in the future. This is because of JRAEF’s recommendations. I’ve probably learned more about VFDs on this forum than all the classes I’ve attended.

 

[Jraef]

You can use the standard submersible pump cable that comes with / for the pump, in fact you must because it usually must integrate with a seal on the pump. Once above the highest possible water line you can transition, but most people just do it in a j-box at the well head. There isn't a lot to worry about with regard to EMI/RFI issues on the submesible cables. So from the VFD to that j-box, use either steel conduit with XHHW or use VFD cable if using PVC conduit.

The other previous warnings are all valid, I'll also add that you want to make sure the ESP (Electric Submersible Pump) mfr has OK'd the use of a VFD on their pump and if so, do they have any specific requirements, such as a dv/dt filter or even a sine wave filter on the output of the VFD. For that kind of distance it would be difficult to justify the added cost of a sine wave filter, but the ESP's have custom made motors, so they may require it.

 

[Atm]

Thank You for your help