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Anonymous Poster

Capacitor Banks on Generators Needed or Not

11/20/2010 2:00 PM

Hello,

I just need to ask why we are not obliged to add capacitor banks for power factor correction to the main distribution boards when they are fed only by generators (No Normal Source (Transformer) is feeding it), and on the other hand, when we add the normal source (by transformer) to the emergency supply (generator) and link then via the automatic transfer switch, we will need to add capacitor banks to the Main Distribution Board.

Thank you a lot.
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Tornado
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#1

Re: Capacitor Banks on Generators Needed or not

11/20/2010 2:15 PM

When running on the generators, presumably you are not billing yourself for adverse power factor.

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energygod
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#2

Re: Capacitor Banks on Generators Needed or Not

11/21/2010 12:46 AM

Whoever thought Tornado's answer was OFF-TOPIC should not be voting- they don't have a clue what they are saying or reading.

Poster-

You are NOT "required" to use the capacitor banks when connected to "outside" power sources- you can spend as much as you want to spend for your service, and the utility company will be thrilled. The ONLY reason that you install and operate the capacitor banks is to correct the power factor of your installation.

When you are running from your generator, you stand the risk of "frying" the generator (if the load is high enough and your power factor is low enough). Generators are rated for either kVA output or for kW output (based on the "standard" 80% power factor at the feed. Your utility probably charges you for a power factor lower than 85% to 90% (typical values). IF you are trying to run a 475 kW load with a 70% power factor from a 500 kW generator, you will be overloading the generator. Simplistically, 475 kW at 75% power factor = 633.3 kVA, 500 kW at 80% pf = 625 kVA generator capacity.

By the way, you ARE still "charging yourself" for poor power factor (sorry Tornado) without the capacitor bank in place because you are requiring the generator to produce more kVA than you actually need, which is costing you operating fuel costs. For your benefit, re-wire the system to feed the distribution system AND the capacitor bank AFTER the transfer switch between the generator and the utility. Then you will get the best of both worlds ALL the time.

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Aseer
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#3
In reply to #2

Re: Capacitor Banks on Generators Needed or Not

11/21/2010 11:38 AM

Very good answer anergygod and well explained.

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perry
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#6
In reply to #2

Re: Capacitor Banks on Generators Needed or Not

11/23/2010 12:10 AM

energygod; i thought operating fuel cost were based on KW, engine prime power, KVA will over heat the generator windings? perry
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energygod
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#7
In reply to #6

Re: Capacitor Banks on Generators Needed or Not

11/23/2010 6:19 AM

kVA is actual generator output (true power).

kW is kVA times power factor (apparent power).

Generator fuel use is dependent on efficiency of prime mover AND load (true power).

If true power load exceeds capacity of generator, overheating of windings is a possibility. In no circumstance will it be a "good" thing.

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Tornado
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#4

Re: Capacitor Banks on Generators Needed or Not

11/21/2010 2:24 PM

I agree also with the fuller explanation. With low PF the extra current (I2R loss) entails a minor amount of added fuel consumption. Correcting the PF will help with some other issues, but only a little with energy efficiency per se. One problem lately is that residential PF correction is being scammed as an energy efficiency measure, which is only minutely true.

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norton850
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#5

Re: Capacitor Banks on Generators Needed or Not

11/21/2010 10:49 PM

You should be careful with capacitor banks on gensets, if you go into a leading PF there can be voltage regulation problems.
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Anonymous Poster #1
#8

Re: Capacitor Banks on Generators Needed or Not

08/15/2011 9:35 AM

Poor power factor represents additional current in the system - current that doesn't deliver any power to the load.
This additional current will result in additional loss of energy (I2R losses) in any conductors - and power transmission systems require a lot of conductors.

There is of course I2R loss in the windings of the generator - so the generator will overheat if the power factor is too far out. Quadrature-phase currents can also contribute to the generator vibrating.

Depending on jurisdiction, you can in many cases ignore power factor so long as the total current does not overload the system.
But you will always end up paying for it.
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dhayanandhan
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#9
In reply to #8

Re: Capacitor Banks on Generators Needed or Not

02/28/2013 4:14 AM

The poor Power Factor, in addition to more I^2 x R losses, the EXCITATION CURRENT for the Alternator also will increase, causing strain on DC EXCITATION SYSTEM, may reach SATURATION STAGE and cause problem.

DHAYANANDHAN.S
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dhayanandhan
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#10

Re: Capacitor Banks on Generators Needed or Not

02/28/2013 4:18 AM

Dear Friend,

Adding Capacitor to the MCC will safe guard the Cable also, and when Transformer Power is connected, the same Capacitors will take care.

DHAYANANDHAN.S
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Anonymous Poster (1); Aseer (1); dhayanandhan (2); energygod (2); norton850 (1); perry (1); Tornado (2)

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