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Capacitor Placement in Distribution System

Capacitor Placement in Distribution System

Capacitor Placement in Distribution System

I have been working for capacitor placemnet in our 12.47 kV distribution system for power factor correction.  3 substations that are feeding from a 115 kV radial  transmission line have really power factor. Each substation have kVAR demand around 5000 kVAR.  To correct substation power factor to 96/97, i at least need 2000 kVAR Capacitor bank in each substation during peak. I was wondering wheather i should go for different distribuiton line capaciotrs banks or single capbank at substation.

Most of the distribution feeders are underground. And laod factor is 50-60%.

I would appreciate your suggestions.


RE: Capacitor Placement in Distribution System

This link discusses some of the different types available.

Some things to consider:
You mention that most of the feeders are underground, does that mean you will need padmounted capacitors rather than pole mounted banks?  

Is voltage drop on long feeders a consideration?  Sometimes capacitors are placed approximately 2/3rds of the way down a feeder to create a more uniform voltage profile.  In general, line losses will be reduced the closer to the loads the capacitors are.  Capacitors also increase the system capacity upstream of the location.

Will the capacitors be switched? Daily, weekday/weekend, seasonally or never?  Is switching 1 large substation bank ok, or will you need multiple smaller sections.  Capacitors on the feeders can cause high voltage problems during light load periods, and correcting to leading pf can aggravate harmonic issues.

RE: Capacitor Placement in Distribution System

I would install fixed capacitors on overhead lines sized to compensate for the minimum reactive load on the line.  This will reduce line losses.  It may be economical to install switched capacitors on the lines as well, particulary if the lines are heavily loaded.  This would require some study.  It may also be economical to install fixed or switched capacitors on the underground lines, but these will be more expensive.

The 2/3 rule of thumb mentioned by bacon4life should be adequate for the fixed capacitors if the load is relatively uniformly distributed along the line.  The loss reduction is not very sensitive to location.

RE: Capacitor Placement in Distribution System

LaliGuras: I'm surprised that all of your feeders have such poor power factors.  Since you mentioned 'underground', then I am assuming that this is NOT due to inductive losses on long feeders.

Therefore, the low power factor must be due to customers with low power factors.  

Doesn't your utility 'punish' industrial customers via billing penalties for bad power factors (such as charging for kVA rather than kW, etc)?

Sometimes, the best place to correct for loads with bad power factors is right at the loads themselves.

RE: Capacitor Placement in Distribution System

TinFoil, you are right. Must of these feeders are less than 5 miles in length and feeds industrial and commercial loads with low power factors. We have already started to panalyzing them. The urgency of correcting power factors is  our power purchaching contract with our power supplier. we are supposed to maintain at least 96%.

Correcting power factors at load level, in my case, requires lage numbers of Underground capacitor bank with controllers which is expensive than correcting in substation.

I was just wondering wheather any body has gone through this kind of situation, and which one they believe is better option.

Thank you all for your time.


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