Power Factor correction 2

[Tvandermescht]

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.

 

[ykee]

.96 PF does not require further correction.

 

[dpc]

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.

 

[itsmoked]

Welcome to Eng-Tips Tvandermescht.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

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.

 

[dpc]

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.

 

[majesus]

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.

 

[stevenal]

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.

 

[Tvandermescht]

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.

 

[waross]

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

 

[dpc]

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.

 

[waross]

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

 

[slavag]

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