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Effect of Power Factor Correction in Fuel Consumption

04/21/2017 2:02 PM

Dear friends,

My name is mogtaba. I freshly graduated as an electrical engineer & now I am working in a mining co. The load is supplied by 2 KVA perkins diesel generator working at low power factor (0.67-0.72). I am wanted to connect power factor correction but unfortunately transmission lines and transformers are already connected & I can't take the advantage of reducing equipment's capacity due to economical reasons. I am interested in power factor correction because I want to reduce fuel consumption.
I am asking about the relationship between fuel consumption and power factor correction (KVA & KVAr reduction) or fuel consumption vs % loading ?
In the diesel generator manual fuel consumption and % loaded relationship is shown but I am confused if the % loaded is in KVA or in KW ?.
Does power factor correction reduce fuel consumption significantly (ex: >15% )if its corrected from 0.72 to 0.95.
Hope you can help :)

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#1

Re: Effect of Power Factor Correction in Fuel Consumption

04/21/2017 3:20 PM

The amount of power the engine supplies to the alternator (in hp) is closely related to the KW the alternator produces.

A low power factor means the current and voltage from the alternator are out of phase, so a portion of the current is not doing any useful work in the load. Only the portion of the current in phase with the voltage delivers power to the load.

Improving power factor would reduce the winding resistance losses in the alternator due to the excess current, but probably would not affect fuel consumption significantly.

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#2
In reply to #1

Re: Effect of Power Factor Correction in Fuel Consumption

04/21/2017 3:30 PM

Agreed. Slight, but not great, improvement in fuel consumption. One could compute the I2R losses owing to the excess current, and thereby estimate how much fuel is allocated to those losses compared to the load.

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#3

Re: Effect of Power Factor Correction in Fuel Consumption

04/21/2017 3:42 PM

The addition of capacitor banks for power correction will not reduce fuel usage significantly...The secret to fuel economy is to run the generator in it's sweet spot, which is generally 2/3 to 3/4 loaded....so the % loaded is the most important factor...

"What is the difference between kW and kVa?

The primary difference between kW (kilowatt) and kVA (kilovolt-ampere) is the power factor. kW is the unit of real power and kVA is a unit of apparent power (or real power plus re-active power). The power factor, unless it is defined and known, is therefore an approximate value (typically 0.8), and the kVA value will always be higher than the value for kW.

In relation to industrial and commercial generators, kW is most commonly used when referring to generators in the United States, and a few other countries that use 60 Hz, while the majority of the rest of the world typically uses kVa as the primary value when referencing generator sets.

To expand on it a bit more, the kW rating is essentially the resulting power output a generator can supply based on the horsepower of an engine. kW is figured by the horsepower rating of the engine times .746. For example if you have a 500 horsepower engine it has a kW rating of 373. The kilovolt-amperes (kVa) are the generator end capacity. Generator sets are usually shown with both ratings. To determine the kW and kVa ratio the formula below is used.

.8 (pf) x 625 (kVa) = 500 kW

What is a power factor?
The power factor (pf) is typically defined as the ratio between kilowatts (kW) and kilovolt amps (kVa) that is drawn from an electrical load, as was discussed in the question above in more detail. It is determined by the generators connected load. The pf on the nameplate of a generator relates the kVa to the kW rating (see formula above). Generators with higher power factors more efficiently transfer energy to the connected load, while generators with a lower power factor are not as efficient and result in increased power costs. The standard power factor for a three phase generator is .8. "

http://www.dieselserviceandsupply.com/Generator_Faq.aspx

http://www.dieselserviceandsupply.com/Power_Calculator.aspx#kvatokw

http://www.eng-tips.com/viewthread.cfm?qid=310797

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#4

Re: Effect of Power Factor Correction in Fuel Consumption

04/21/2017 5:22 PM

See, I told you starting your own thread, instead of asking questions on a 5 year old thread would get you some intelligent answers.

Make sure you respond to those that try and answer your question, nothing is more frustrating when answers are given and no one ever hears from the O.P. again.

By the way, welcome to CR4.

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#6
In reply to #4

Re: Effect of Power Factor Correction in Fuel Consumption

04/22/2017 1:48 AM

Hhhhhhhhh, Thx

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#5

Re: Effect of Power Factor Correction in Fuel Consumption

04/22/2017 1:44 AM

Okay, but electrical power is obtained from mechanical power & reactive power is reduced so some mechanical power is reduced which will reduce the prime mover consumption is reduced.

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#8
In reply to #5

Re: Effect of Power Factor Correction in Fuel Consumption

04/22/2017 4:00 AM

That doesn't make much sense.

As others have said, the only way fuel consumption is reduced is if power (not KVA) taken by the end users is reduced.

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#11
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Re: Effect of Power Factor Correction in Fuel Consumption

04/24/2017 9:13 AM

That argument reminds me of the Dirac Catastrophe, spiraling into the sun. Can't you simply make an engine run?

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#7

Re: Effect of Power Factor Correction in Fuel Consumption

04/22/2017 1:50 AM

Thx friends, good answers

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#9

Re: Effect of Power Factor Correction in Fuel Consumption

04/22/2017 11:55 PM

Dear Mogtaba elkhider,

The power factor improvement results in:

1. Reduction of Line Currnet, 2. Reduced ((I^2) x R) loss in the Windings. The resistance of the winding is so small and the difference in terms WATTS will be very small percentage when compared to the capacity of the generator.

You have referred that the generator is of 2 KVA and the present power factor is 0.67 to 0.72 say an average of 0.7. You have not indicated to what extent the PF is to be improved. Let us you want to improve PF to 0.95.

You know the Power = Sq.Root of 3 x v x I x Cos Alpha (angle) For PF 0.7 Cos angle is 45.57 Deg. For PF 0.95, Cos Angle is 18.19 Deg. This will work out to (0.736) X I (at pf 0.7) hence I^2 x R loss will reduce to ( (0.5429) times to that of the loss at 0.7 pf. which is very small fraction when compared to the full load.

Since you are a fresh graduate you can work out and compare yourself. The fuel saved will be very small fraction when compared to the total fuel consumption. But improving the power factor will reduce the heating effect on the winding. cable etc., which is good.

DHAYANANDHAN.S

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#10

Re: Effect of Power Factor Correction in Fuel Consumption

04/24/2017 7:01 AM

Er, power factor correction is about better matching the load to the supply so as to overcome cable sizing and heat dissipation issues...

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