Capacitor Bank Placement 2

[SMLD]

System:

115kV/13.8kV substation with two 22mVA self tapping xfmrs, four 800amp circuit breakers
feeding four 13.8kV wye distribution circuits, with 477mcm al conductors. Total peak load of
system is 13mW. The system has 7 capacitor banks, of various kVAR ratings, on time control.
System PF is .98 to .99.

Question:

Some large customers are having PF problems (ie .72) within their facilities. If we, as the utility,
correct their PF with a primary installed capacitor bank, will that throw off our system PF which
is indicated back at the sub? These customers are 1.3 miles from the sub.

Also, what is a “good rule of thumb” for locating capacitor banks within a system when you have
concluded the need for them?

Thanks

 

[peterb]

1. Any capacitors which you install will increase the total reactive kVAR supply & hence will show up at your substation.
2. One rule of thumb would be to install the capacitors as close to the low power factor load as possible. This relieves the system from supplying the needed VARs over the distribution feeders and/or transformers. This frees up system capacity to carry additional revenue-generating kilowatts.

Based on the above, it may be worthwhile to investigate the relocation of some the capacitor banks to the problem circuits. Most utilities would probably leave the correction of customer PF to the customer, depends on whether there is any economic penalty in the tariff structure for poor PF.

 

[stevenal]

Think of a capacitor as a generator of kVars that can be conveniently located. To avoid losses, locate the capacitor as close to the reactive load as possible. In the case of a radial distribution feeder, the optimum location is where half the kVars will flow in each direction along the feeder. I believe Cooper has software that helps in locating capacitors.

Installing primary capacitors will not help your customer with their pf. (unless the customer in question is primary metered with the meter location ahead of the capacitor. I'm not sure why a utility would want to do this, however.)Primary capacitors would help support customer voltage.

Yes, more capacitors will affect pf seen at the substation, which already looks good.

If customer wants to improve pf to avoid low pf charges, advise them to consider installing caps on their system.

 

[redtrumpet]

That 22 millivolt-ampere substation, with 13 milliwatt peak load, surely has to be the smallest capacity 115-13.8 kV sub in the world.

 

[electricpete]

It probably goes without saying... but the var flow is the main thing that determines voltage throughout your system. Vars flowing through Inductance create voltage drop.

So in addition of the goal of placing caps where the var demand is, you should try to place them where there may be problems with low voltage (maybe the same place).

Load-flow studies are the computer tool to examine voltage profile based on var loading, real power loading, switching configurattion etc.

 

[Run1on]

SMLD:

I can help you with your customers problem. As the others have discussed there are a lot of issues to installing a capacitor bank in any system especially one with nonlinear loads.

Run1on