Power factor correction 1

[HamidEle]

The calculated capacitor to be needed to improve PF is 60kvar. But the closest standard size is 50Kvar. the next size is 75kvar. I am thniking of adding some heaters in the pump house to help improve the P.F. Is it workable solution? Is there any other alternative? We don't want to spend money on an automatic capacitor or a custom designed one, which is more expensive. I appreciate any inputs.

 

[wareagle]

Almost all of you charge is for energizing an unloaded transformer. IF the utility would agree, you might check into using a single phase 13.2 kv 25 kva transformer for
small load and disconnect the 5000 kva transformer or move it to where it can be used more efficiently.

 

[HamidEle]

But the customer will like to keep the transformer in service just in case the other major loads could be on one day.

 

[jghrist]

Remember that,when the 5MVA transformer is unloaded, the exciting current is 1.2%, which is almost purly inductive. That's why there is 65 kVars in the system, which will lead to lower Power factor of 0.20.

The no-load losses will make the power factor fairly high on the 25 kV side. See thread238-192000. If you try to compensate for magnetizing current with capacitors on the low side, you will end up with a leading load power factor. This could cause high voltage problems. How much of a power factor penalty are you talking about on a 5-15 kVA load? Probably less than the cost of your no-load losses that you don't seem to worry about.

 

[HamidEle]

The power factor will probably be 0.20. If we measure the no-load KVA. This will be almost pure KVARs.

 

[dpc]

This thread is an infinite loop. I think we're wasting our time....

 

[sslobodan]

You got the formula to calculate capacitor banks needed to calculate capacitor banks, now You should consider one more thing. You should ask the power company to rectify and calculate your Power factor after transformer (what is an normal issue), that is in case that transformer is not in your property (they will not accept it than).

If it is, I believe that smaller transformer station would show as a cost effective solution. Remember that beside your load power spent you should pay for currents of magnetization and power factor correction equipment for some 120 - 160 KVar the cost of such capacitors (and what if you need to connect more p. load and rectify power factor for that also in future) and that might show up as a costly long time solution. If I was your boss we would have serious talk about engineering principles in planing and projecting.
What you should know is:
1. Who is the owner of that transformer (why would you pay for power company reactive power loses)
2. What is your load.
3. What is your expected load in near future

In case you have big transformer in your property you should consider selling it and buying transformer of smaller power, I believe that counting on current cost of transformers you would not lose anything in its initial cost. Buy small power transformer that will cover your near future consumption, and consider purchasing one more in future that is able to work in parallel operation with this one. Create long term development project that would include more transformer fields with or without parallel operation. If you don't do that your costs will rise over time and costs for buying new capacitor banks for rectifying power factor before transformer load reaches over 70% will be so costly that my boss would fire the person that suggested buying such big transformer at first (5 days ago he wanted to cut from my salary difference between p-factor correction from 0.87 to 0.95 instead 0.93, I was calculating because junior engineer gave me wrong data and it was just talk and no capacitor banks were ordered).

 

[burnt2x]

Hamid,

I understand that the problem is the customer! aha! Why does the customer disagree taking out the 5MVA loaded at 1% of its rating! You don't have to worry about penalties if your transformer is sized to your needs - and that's the solution. You don't get charged for low PF, you don't have to buy capacitors, and most of all, your voltages don't spike!

Convince the customer to just de-activate the 5MVA, don't pull it out but install a 50kVA, 25kV primary(if line-line, or 13.8 kV if line-neutral loading).

My two cents!

 

[waross]

This reminds me of a customer wanting advice on a power factor penalty of 90% (Penaly, not PF). It was a similar situation. A large unloaded transformer. The solution in that case was to de-energize the transformer.
In this case I would suggest adding enough capacity between the 5MVA xfrmr and the 50KVA xfrmr to equal the exciting KVARs of both transformers.
Don't correct to unity, just correct enough to eliminate the penalty charges. If standard sizes don't get you in the window, calculate the penalties payable for the smaller size and contact the utility for their policy on slightly leading power factors.
Then decide what size to go with.
respectfully