PF Cap Install Question
PF Cap Install Question
(OP)
We have a double ended 480V substation with a normally open tie. I would like to install 300kVAR of PF correction capacitors for this substation. The question I have is to either install 300kVAR cap on one side of the sub and only use one circuit breaker or install 150kVAR on both sides and use two breakers. The disadvantage of 300kVAR on one side would be VARs flowing through two transformers to the other bus, but I do not see that as a big concern. The sub is fed from the same source and the two transformers are fed from the same 25kV bus. The utility metering is upstream of the 25kV bus as well. See attached diagrams for option 1 and 2. Any thoughts would be appreciated.
"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic — and this we know it is, for certain — then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". – Nikola Tesla






RE: PF Cap Install Question
Keep the caps as close to the reactive load as possible.
RE: PF Cap Install Question
If the 480V tie breaker is operated normally open, then you want to have half of the capacitors on each bus. Otherwise, there will be less reduction of current (or maybe an increase) through one transformer and no decrease in the other transformer (it will still carry all of the reactive load on that bus).
If the tie breaker is closed, then there is no difference in var flow between the two options.
RE: PF Cap Install Question
The load is split equally between the two sides, but I would like to maintain breaker space in the switchgear and only use one breaker if possible. This will also keep the cost down. This is why I like option 1.
I am also not concerned with the current flow through the transformers or VAR flow downstream of the utility meter. The load has significantly reduced over the years and the transformers have plenty of capacity. I am more interested in cost savings by increasing the PF seen by the utility meter. I just was not sure if there are any other technical or practical reasons why option 2 would be a better choice.
"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic — and this we know it is, for certain — then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". – Nikola Tesla
RE: PF Cap Install Question
RE: PF Cap Install Question
Regards
Marmite
RE: PF Cap Install Question
If you are just connecting 300 KVAR you may have over voltage issues on transformer one if you lose the load on transformer two.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: PF Cap Install Question
RE: PF Cap Install Question
RE: PF Cap Install Question
Marmite, I heard about this back to back switching and will definitely investigate this more if we peruse option 2.
Waross, This will be a fixed cap with manual switching via CB. My calculated voltage rise on 1500kVA xfmr was only 1.5% so this also will not be an issue.
David, 25kV option is not very practical for our system and not cost effective.
Lionel, thank you for your input. I have seen option 2 installed many times in the field so I was a little hesitant with option 1. I think for this case, option 1 will be less costly and also leave space in the switchgear for future loads. It will also provide better return on investment while achieving the same goal in improving the PF seen by the utility meter. Thank you all for your input.
"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic — and this we know it is, for certain — then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". – Nikola Tesla