×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Power Factor correction
2

Power Factor correction

Power Factor correction

(OP)
We have a transformer 1600Amp with a bulk power factor correction. With a 12*60Kvar steps = 720Kvar
•    The systems run with a 0.7 without the caps.
•    The systems run with a 0.96 with the caps.
•    I have work it out that we need +_ 800Kvar.
To the point.
•    Can you change the 12Step controller to a 20Step controller to try to add extra caps?
•    Can you add two caps in parallel if the contactor can take the amps (If I do this I do not have to change the controller)?
•    Can you add an extra bank off caps in parallel on the bus bar system if you control it by the same controller?
•    Is it true if you do a correction of a third of your total load you cannot add a extra capacitor bank in parallel with you existing system.  

  

RE: Power Factor correction

.96 PF does not require further correction.

RE: Power Factor correction

Well, 0.96 used to be considered pretty good, but many utilities now penalize for anything below 0.97 (lagging or leading).  

If you can add more caps per step and stay within the contactors make/break ratings, that might be one option.

You will need to review any modifications with the equipment manufacturer.  

You could maybe just add a fixed cap bank and let the controller handle the additional correction, provided your load does not drop too far that you would be overcorrecting.  



 

RE: Power Factor correction

Quote (dpc):

Well, 0.96 used to be considered pretty good, but many utilities now penalize for anything below 0.97 (lagging or leading).
Really? I had not heard that yet, it's a bit distressing. Almost all of the charts provided by pfc cap manufacturers are based upon correction to .95pf. Looks like a re-work of those charts is in order.

RE: Power Factor correction

jraef,

In the Northwest, BPA rates to their retail utility customers has had the 0.97 penalty limit for a couple of years, although I'm not sure they are actually enforcing it.  As a consequence, these utilities are changing their tariffs to penalize below 0.97.

BPA also has a 12 month ratchet so that your penalty is based on the worst month out of the last 12.  (I think it's 12 months - might be 24).

So one bad month can cost you.     

RE: Power Factor correction

That's getting pretty severe.


Not trying to blame or defend anyone. Just the sign of the times with high copper prices... Trying to reduce cost everywheres I suppose.
 

RE: Power Factor correction

dpc,

I hate to term the BPA kVAr demand ratchet penalty a pf penalty, since pf to me means you are looking at concurrent values of kW and kVAr or an average over the same period. BPA actually looks at the peak kW hourly demand versus the peak heavy load hours hourly lagging kVAr demand. These peak values rarely occur during the same hour. Anything outside the 25% deadband is compared to similar values from the prior 11 months, with the maximum value determining the charge. And yes, they do charge it. A similar determination is made for light low hours leading kVArs. 25% deadband does work out to 97% pf if the two demands happen to occur during the same hour.

Since the the calcs are based on hourly demands, you can find yourself paying over 12 months for a single bad hour.  

RE: Power Factor correction

(OP)
DPC,

Can you help me on this Questions
Can you change the 12Step controller to a 20Step controller to try to add extra caps?
•    Can you add two caps in parallel if the contactor can take the amps (If I do this I do not have to change the controller)?
•    Can you add an extra bank off caps in parallel on the bus bar system if you control it by the same controller?
•    Is it true if you do a correction of a third of your total load you cannot add a extra capacitor bank in parallel with you existing system.  


 

RE: Power Factor correction

Our friends from India have indicated that they are penalized for any deviation, 99% leading or lagging will incur penalties.
I'll get to the original question tomorrow.  

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Power Factor correction

As far as adding more steps to the existing controller, you would need to talk with the manufacturer.  Unless it was designed to be expanded, adding additional stages may not be simple.  

As I've already mentioned, you can add more capacitors in parallel on the same bus.  You may not need automatic switching for all of the capacitors.  

And as I already mentioned, in theory you could add more capacitors to each step if the contactors are adequately rated, but this may not be practical.  

As to your last question, it makes no sense to me.   

RE: Power Factor correction

Can you change the 12Step controller to a 20Step controller to try to add extra caps?
I agree with dpc. Unless the manufacturer has designed the controller so that additional steps may be added, it is probably not feasible.

• Can you add two caps in parallel if the contactor can take the amps (If I do this I do not have to change the controller)?
You have to be aware of how the controller is connected and how it functions. If you add too much capacity at a particular step  the controller may see the power factor over corrected and immediately disconnect the extra capacitors. It will then see a low power factor and reconnect the capacitors. Not a good situation.

•    Is it true if you do a correction of a third of your total load you cannot add a extra capacitor bank in parallel with you existing system.  

There are a couple of things that you can do:
You can permanently add enough capacity to your transformers to offset the magnetizing current.
Measure the magnetizing current of your main transformer at no load. Connect enough VARs of capacity to the transformer to equal the magnetizing VARs.
Look at other major loads to see if any can have capacitors connected to switch with the load. Large motors are a good candidate.
Another possibility is to select 4 or 5 smaller motors for correction as a group. Use an auxilliary contact on each motor starter in series so that when all the motors in the group are running, a contactor switches in enough capacity to correct the motors.
The specifics depend on your individual loads, (lots of small motors, several medium motors, or 1 or 2 large motors).
You should be able to switch in capacitors with selected equipment and let the controller correct the balance of the VAR deficit.
 

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Power Factor correction

Dave and Bill.
Great!!!!
Unpossible add something.
Best Regards.
Slava

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources