Could distance from VFD to pump cause problems? 3

[powersoff]

Hello,

I have 5 well pumps ranging from 25HP-60HP. The 5 pumps are being fed from 5 VFD's. The closest VFD to a pump is 200 feet the farthest is 400 feet. The control of the pumps is from a pressure transducer the pumps try maintain a setpoint. Only 1 pump is on a PID, when called the other 4 run at 100% speed. The second pump will turn on if the PID pump runs at 100% speed for 1 minute and then 1 minute later pump #3 and so on until all 5 pumps are running. To shut off the reverse is true if PID pump falls below 95% speed for 1 minute it turns off pump 2 a minute later until all pumps off except PID pump.
There is also a low pressure cutout switch if PSI falls below 30 no pumps can run unless done manually.
Does anyone have any suggestions as to why 2 pumps have failed in the last month?

 

[ozmosis]

I would advise a dv/dt filter between the VFD and motor in this case, as already pointed out. Submersible motors often have lower class insulation and rely on the cooling effect of the water around the motor than the typical fan cooling. It is typical that dv/dt filters or sinus filters are fitted in this case.

 

[martinrelayer]

Also some companies have special VSD application motors, with higher insulation class (specially made).
Also VSD manuals have guide to include dV/dt filter when the the cable lenght is over a limit and the motor is over certain HP.
Some other special guides talks about symmetrical and shielded cables (shield that is the earth conductor) and local PE.
In the mill I work for we have for all VSD, special VSD application motors (w/more insulation).

 

[thewellguy]

Powersoff, what brand and size of motor are you talking about? Most of the submersible well pump motors of this size are not rebuildable. Also Martinrelayer is correct all sub motors have minimum flow requirements so that there is enough water flow past the motor. This can be reduced in some cases if a suction sleeve is placed over the motor when it is istalled. For example a 6" motor (at full speed) in a 10" hole requires 520 gpm flow rate while the same motor in a 7" hole reuires 150 gpm flow rate per Franklin O & M manual

 

[mconroy]

Hi, I am new to the group and found this site searching for info on drives and well pumps. I provide power quality and harmonics testing and am working on a site with two 60 hp submersible well pumps on 6-pulse VFD's. The client is having problems with fiber optic communication interfaces that keep locking up. The external communication interfaces are powered from the VFD's internal 24 VDC power supply. It appears that the lock-up happens when the input voltage THD exceeds 4-5%. My question is if anyone has seen similar problems with auxiliary equipment such as communications equipment? Is it common to use the drive’s internal DC power supply to operate other equipment?

As a separate comment, I have used a lot of harmonic canceling transformers including phase-shifting and zig-zag type. The phase shifting technique can work well if the loads are balanced by creating a 12-pulse load with about 12-15% current THD as compared to a 6-pulse load with 30-40% current THD. The challenge is finding balanced loads that are on the same power source and utility and meter. The predominate harmonics with a 6-pulse system are 5th and 7th and with a 12-pulse are 11th and 13th. Utility primaries seem to be particularly sensitive to resonance issues at the 5th and 7th harmonics. In my area (Nebraska and Iowa) the local utilities have adopted IEEE-519 into their rate tariffs and are now going after customers that are producing harmonic currents that exceed the standard. The new tariffs are creating problems for sites that use VFD’s as simple line reactors and drive isolation transformers will not meet the standard. We have had to use a passive harmonic filter made in Canada that will make a 6-pulse VFD meet the IEEE-519 standard. We have found the passive filters are lower cost than active filters and are more reliable. I suspect that utilities in other parts of the USA have or will be adopting the IEEE-519 into their tariffs to address the issues raised in this forum so be prepared for more challanges!

 

[itsmoked]

Interesting stuff mconroy.

And welcome to Eng-Tips!

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Valvecrazy]

Welcome Mconroy
Do you know how they decide on the amount of the rate tariffs?

 

[ozmosis]

mconroy
welcome to Eng-Tips.
It might be better if you create a new thread concerning your posting. It means that the original post by powersoff is not hijacked.
It is possible to redflag your own thread and put a comment in for the administrator, then re-post in a new thread. You then get full attention from other users on your specific question/points.
regards
ozmosis