Power factor tips

Discussion in 'General Electronics Chat' started by inwo, Dec 19, 2013.

  1. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
    2,435
    315
    We have a city waste water treatment plant in our tiny city, paying a large penalty for a pf of 59%.

    Plant was federal project with all the overkill redundancy and intrinsically safe sensor circuitry.

    Only 6 years old. Most all motor load is on vfds.

    Most everything works well. I've been called a dozen times or so for repairs.

    Where would I start looking for the low hanging fruit?
    My knowledge predates vfds.
    My meter doesn't do harmonics. thd

    Will I need to update my equipment to even get a sense of what's going on?

    My wife is in charge of another building in town. Library. After obtaining a grant for an updated AC system, she was taking heat for utility bill. 83% in her building. Only two suspects there. Compressor load and lighting.

    I believe the city should look into the treatment plant first.
    Is my assumption of vfds having good pf wrong?
     
    Last edited: Dec 19, 2013
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,571
    2,382
    VFD's can be the culprits, the service supplier here will bring in a team to assess and record the P.F. and recommend suitable Capacitor correction.
    Max.
     
    inwo likes this.
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,073
    3,856
    Call the supplier of the vfds. They will likely have a simple, safe, standardized solution for you.
     
    inwo likes this.
  4. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
    2,435
    315
    That was my first suggestion to the city.:confused:

    Back in the day, I worked for a contractor when pf correction was just becoming popular. We just had the power company give us the recommendations. Just as you suggest.

    My wife, and city, claims they (power company) have no interest in helping.:(
    Their suggestion is to call a contractor.
    I am an electrical contractor (licensed in the state), but have no recent knowledge when vfds are in the mix.

    The city doesn't understand the savings potential. I don't have the confidence or experience to guaranty results.

    Can you explain in general terms how the vfds with capacitor input power supply busses lead to poor pf?

    Understand the effect on thd but not how this relates to pf problem.

    I asked if penalty was for distortion and was told it is specifically for pf.
     
  5. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
    2,435
    315
    I'll give it a shot.
     
  6. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
    2,435
    315
    What about a meter suggestion to localize the problem?
    All I have is an amprobe acd-30p.
    http://content.amprobe.com/DataSheets/ACD30P.pdf

    Without thd.:(

    I remember a job a while back. My fluke was reading over 600vac upstream 50' from a small 10hp vfd. (480 volt system)

    Special meter or filtering must be required.

    As general practice, I use input reactors on my jobs.
    Haven't checked yet, but don't remember seeing them on this job.
     
  7. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    Options

    Read the technical press

    http://www.waset.org/journals/waset/v78/v78-344.pdf

    Get a specialist contractor in

    http://www.sml.ltd.uk/power_factor_correction.html

    Do it yourself - work it out from the texbook

    http://books.google.co.uk/books?id=...factor correction in pumping stations&f=false

    One suggestion, however, most pumping stations have some redundancy so you can take measurements / experiment on some plant that is offline for maintenance.

    Look also at the type of motor. If you have the old slow moving type spreader bars in the treatment system their motors can be inefficient.

    Is there any UV treatment involved? The UV generator probably has an opposite phase PF to the motors.
     
  8. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,073
    3,856
    The problem may not be the big VFDs. Look for lightly loaded induction motors in air handling or pumps - especially if the are running under no load conditions. The post above says waste plants rotate demand through different sections. If so, do any pump motors or blowers continue to run with no load?

    See this document from ABB claiming that FVDs prevent the need for PF.

    here
    Especially the note in the last paragraph.
     
  9. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
    2,435
    315
    Again, this is why I'm puzzled. All except two motors are are on vfds now.
    I've been under the assumption that one advantage of vfds is better pf.

    I guess I'll start with those.
     
    Last edited: Dec 20, 2013
  10. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
    2,435
    315
    Can you explain or link?
    My understanding contradicts.
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,571
    2,382
    I phoned a couple of contacts I have who are engineers that are with the service provider, and they say it is not so much P.F. that is a problem but Electrical noise from VFD's.
    In the past I have usually used 3ph chokes either just on the motor side and in some case input and output.
    Max.
     
    inwo likes this.
  12. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,073
    3,856
    inwo likes this.
  13. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
    2,435
    315
    That's what my research led me to believe.

    The pf problem then, still eludes me, as the cities cost penalty is for pf not harmonics. Unless I've been given false information.

    As in previous post. I also use input reactors. Just as "good practice". Output reactors are specialized and only required on long runs, I believe.

    ps.
    Your contacts didn't hint that they monitor and penalize for noise did they?
     
    Last edited: Dec 20, 2013
  14. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
    2,435
    315
    A lot to digest.
    Mostly things I've found in my searches.

    An explanation for poor pf on vfd systems doesn't jump out.

    Think I will concentrate on the non-vfd loads first as I don't have proper equipment for the others.
     
  15. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,073
    3,856
    That is the best plan from my point of view.
     
    inwo likes this.
  16. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,571
    2,382
    No they don't.
    Max.
     
    inwo likes this.
  17. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    Excellent article and worth the full read. Pat attention to the comments about lightly loading, as this applies to transformers as we'll. I'd get out the single line drawings to map out a strategy. Request your annual usage data from the utility as they likely have hour by hour usage with pf. Compare that with plant loading.
     
Loading...