Could distance from VFD to pump cause problems?
Could distance from VFD to pump cause problems?
(OP)
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?
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?





RE: Could distance from VFD to pump cause problems?
RE: Could distance from VFD to pump cause problems?
Thanks
RE: Could distance from VFD to pump cause problems?
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Could distance from VFD to pump cause problems?
Steve
RE: Could distance from VFD to pump cause problems?
Submersible motors can last 20 to 30 years when installed correctly, and running on smooth sinusoidal AC voltage, as with an across the line starter. Of course motor manufacturers don't like this so, they are always going to suggest a Drive.
This is a case where you don't need Drives. Four of the five pumps run at full speed all the time anyway. Which means the drives are costing you extra energy, and reducing the life of the motors. The one pump that does use a PID loop, could easily be controlled by other means like, dare I say it, a simple control valve.
I would solve the problem by removing the Drives. As someone on this forum keeps reminding us, "you can't solve the problem by using the same kind of thinking that caused the problem in the first place".
Of course in some states they give you cash incentives to install Drives, which creates the kinds of problems you are having now, and usually doesn't save any energy. Even in a different situation where a Drive might be able to save some energy, there is no way to do the math which shows the effect of short life of the motors and other equipment. A Drive would have to save a LOT of energy to be able to justify replacing the motors so frequently, not to mention frequent replacing of the Drives themselves, when otherwise all the equipment should last decades without the least bit of maintenance.
RE: Could distance from VFD to pump cause problems?
Yes, you probably need to install motor reactors.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Could distance from VFD to pump cause problems?
I was so interested in answering his question that I didn't pay much attention to his initial statements. That being said it is most likely an incorrect application of the VFD that caused the problem. I recommend that you read the following application guide for VFDs. http://www.nema.org/stds/acadjustable.cfm#download
This guide will NOT apply exactly if you have a submersible pump motor since this is not a standard NEMA motor configuration however the general principles apply. If you have a submersible pump motor then follow the recommendations of the motor manufacturer (not the drive manufacturer, which is probably written for NEMA motors).
You can get some information on VFDs and submersible pump applications at http:
Constant pressure control may not be the best control algorithm to accomplish your objectives. If you look at the Gould's Aquavar VFD control they have an algorithm which varies the pressure with the flow so that there is always sufficient pressure to meet demand without providing excess pressure which wastes energy.
RE: Could distance from VFD to pump cause problems?
RE: Could distance from VFD to pump cause problems?
You can see what the loss is for typical line reactors at http://www
The drop in voltage and increase in amperage does not affect the power consumption by the motor unless the voltage goes outside the typical rated limits for motors. The increase in power can be measured by the loss in the filter/line reactor which can be measured by I2Z or I*DELTAV*SQRT3.
RE: Could distance from VFD to pump cause problems?
Thanks for the link Gepman. If I am reading it right, it shows about 40 watts loss for each reactor on about a 20 HP load, and the losses increase as the FLA increases. Just something else that should be added back into energy use calculations. There is also a little less than 1% loss on an active harmonic filter as discussed in a previous thread. Every time you add a filter, you are losing something. These numbers may seem insignificant but, when there is only a few percent difference in power consumption between a drive and no drive, they become very significant.
However, a percent or two extra power consumption by a filter or reactor, is much less significant than the motor and or Drive, not lasting as long as an Across The Line Starter, and a motor running on smooth sinusoidal AC power.
RE: Could distance from VFD to pump cause problems?
1. Reflected wave modeling techniques for PWM AC motor drives, By Skibinski, G.; Kerkman, R.; Leggate, D.; Pankau, J.; Schlegel, D. This paper appears in: Applied Power Electronics Conference and Exposition, 1998. APEC '98. Conference Proceedings 1998., Thirteenth Annual,Page(s): 1021 - 1029 vol.2, 15-19 Feb 1998
Volume: 2 Issue
2. Cable characteristics and their influence on motor over-voltages
By Skibinski, G.; Leggate, D.; Kerkman, R.
This paper appears in: Applied Power Electronics Conference and Exposition, 1997. APEC '97 Conference Proceedings 1997., Twelfth Annual
Page(s): 114 - 121 vol.1, 23-27 Feb 1997
Volume: 1 Issue
Currently, I’m waiting on more information from Southwire (www.southwire.com). They design a triplex conductor interlaced with grounding conductor system. From what I gather the peak voltage destroying the motor systems is due to twice the dc bus voltage times the impedance mismatch ratio of the motor and cable. There is nothing you can do about the motor impedance (short of inverter duty design motors), but the cable impedance can be altered (i.e. line reactors). Filtering does costs and will reduce the system performance. My preference is not to filter.
Good luck.
RE: Could distance from VFD to pump cause problems?
The peak voltage is very close to the theoretical limit and the motor had problems with insulation faults after only a few month's operation.
I think that reactors have been installed now. But have not done any measurements after that.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Could distance from VFD to pump cause problems?
Also per the manual Filters or Reactors: Required if (1) voltage is 380 or greater and (2) Drives uses igbt or bjt switches (rise-times , 2 msec) and (3) cable from the drive to the motor is more than 50 ft. A low pass filter is preferable. Filters or reactors should be selected in conjunction with the drive manf. and must be specifically designed for vfd operation.
RE: Could distance from VFD to pump cause problems?
The last post by powersoff mentioned "VFD would fault off.I had continuity between pump motor leads and ground(earth)"
The description of the VFD "fault off" tells me that there is a problem that the VFD is picking up. Nowhere have I seen that the motor has failed. All points mentioned so far are very valid but until we know more details from powersoff on what is the actual problem, a lot of what we say could be meaningless. It is quite possible the user has used screened cable and over such a long cable distance the screen creates a high capacitance and the VFD sees this as an over-current fault. Or, the stray capacitance due to a motor that is 400feet from it's ground point could cause the VFD to see this as a ground fault.
It is quite common that "faults" indicated by the VFD are seen by certain users as "failures" of products whereas a fault indicated by a VFD is an indication that whatever it is measuring (current, voltage, temperature...etc) has simply been measured outside the tolerance of the VFD. It doesn't always mean something had "failed".
So, powersoff, perhaps you'd like to expand further on the fault then these fine brains in VFD's and valves can provide more accurate tips before we end up saying get a bucket on a piece of rope and get your water up that way.
RE: Could distance from VFD to pump cause problems?
The wire is direct burial cable in pvc conduit to well head.
The VFD brand is Altivar.
Thanks
RE: Could distance from VFD to pump cause problems?
The brand name Altivar is I believe a Square D brand and although not my favorite, I have used hundreds without any problems when my clients want them. I, like others, prefer to use what we are most familiar with.
To summarize the above replies, your best solution is to determine if the fault is in the motor or the leads, remove the VFD's where you don't need them, follow the manufacturer's recommendations for the motor if it is a submerisble pump motor (you never have really said), and install some type of attenuation device for any VFD's that remain including load reactors. The motor leads should be rated probably at least 1000V, I usually use something like a Belden or Olflex VFD cable or at least XHHW-2. Shielded cable as ozmosis says can cause high capacitance problems.
Let us know what your resolution is.
RE: Could distance from VFD to pump cause problems?
RE: Could distance from VFD to pump cause problems?
Yours is an interesting concept but if you really want to design the system so that one component fails before the other (similar to a shear pin) then you need exact information on the dielectric capabilities, capacitance, etc. of both the motor and the conductors. This will probably be hard to get. Also powersoff may replace the submersible pump motor (now or later) with a better insulated unit later and then he wouldn't have to replace the cable or conductors.
If powersoff installs a load reactor it is probably a moot point since the cable insulation would not be as much of a factor.
My philosophy is to design the system so that no part fails. I have used the "shear pin" method a few times but it takes good engineering information to be certain that your shear pin will fail with an overload but not with a normal load. I don't believe that information is available in this case.
RE: Could distance from VFD to pump cause problems?
I am grateful to all who replied and am researching options.
RE: Could distance from VFD to pump cause problems?
RE: Could distance from VFD to pump cause problems?
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).
RE: Could distance from VFD to pump cause problems?
RE: Could distance from VFD to pump cause problems?
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!
RE: Could distance from VFD to pump cause problems?
And welcome to Eng-Tips!
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Could distance from VFD to pump cause problems?
Do you know how they decide on the amount of the rate tariffs?
RE: Could distance from VFD to pump cause problems?
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