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Do Power factor correction capacitors reduce Energy bill?


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#1 chaterpilar

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Posted 02 November 2005 - 09:56 AM

Assuming a system of 10 MVA load 380 VAC (3 phase) is running at 0.83 pf and it is improved to 0.93 by adding power factor correction capacitors.

Will there be any reduction in KWh, in other words will the monthly energy bill reduce?

PF increment might make the energy use....but bill may remain the same....

thanks for your replies....

#2 marke

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Posted 02 November 2005 - 06:12 PM

Hello chaterpilar

This has been discussed elswhere on this forum, but to summarise:

  • The addition of power factor correction will not alter the current into a motor.
  • The addition of power factor correction will noat alter the power drawn by a motor.
  • The addition of power factor correction will reduce the inductive current drawn from the supply on the supply side of the capacitors. Down stream of the capacitors, the current does not change.
  • The reduction in inductive current drawn will reduce the overall current and thereby reduce copper losses upstream of the capacitors.

      If the capacitors are applied at the main board close to the supply metering, there will be no improvment in KW.
      If the capacitors are installed at each motor, there will be a reduction in copper loss between the metering point and the motors. This should not be significant, and if it is, then the cable have been undersized!

      Best regards,

#3 chaterpilar

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Posted 03 November 2005 - 03:56 AM

Thanks Marke for your prompt reply...so in effect it does not reduce the energy bill

chaterpilar

#4 jraef

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Posted 03 November 2005 - 04:05 AM

It does not affect the energy consumption portion of the "bill", but if the utility charges extra in penalties for having poor power factor, it may reduce the amount of the bill in terms of net monies.
"He's not dead, he's just pinin' for the fjords!"

#5 marke

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Posted 03 November 2005 - 04:15 AM

If you apply bulk correction at the point of supply or your main board, there will be no KWHr reduction, but as Jraef says, you will get a reduction in the KVA max demand penalty or pf penalty if one is charged.

If the correction is applied at each individual motor, you may see a small improvement, but it will be very small. If it is significant, you have a problem with undersized cables!!

Best regards,

#6 subhash

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Posted 01 October 2006 - 05:06 PM

Hallo Dears,
I would like to add my experience I conducted trial on 40 hp motor by connecting
15 Kvar at load side on out put of delta contactor for Y/d starter and measured power at Main
incomer found that @ 10 % energy saving with additional capacitor.Now i planned to go for
other motors also is this reduce my plant KWH at present my plant PF is unity with APFC
and fixed Kvar at central place on main PCC.
Pl suggest
Subhash

#7 marke

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Posted 01 October 2006 - 05:44 PM

Hello subhash

How did you measure the power used?

Best regards,

#8 subhash

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Posted 14 October 2006 - 07:29 PM

QUOTE(marke @ Oct 1 2006, 11:14 PM) View Post

Hello subhash

How did you measure the power used?

Best regards,


Dear Marke
Sorry that delay in reply
To measure power consumption with and without capacitor
I used power analyser ( digital Kwh Meter ) at input supply of same feeder
Regards
Subhash


#9 marke

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Posted 14 October 2006 - 08:07 PM

Hello Subhash

I am surprised that you would see a 10% reduction in KWs used by adding the capacitor and suspect that there is some reason other than the correction of the power factor that is making this change.
  1. 15 KVAR for a 40HP motor seems like a lot of correction to me, I would have expected a value of around 7.5KVAR should be sufficient. Do you know the pf before and after the correction was applied?
  2. Can you be sure that the load on the motor is identical in both tests? was there any possible change in motor shaft load?
  3. What is the voltage drop between the point where the capacitor was added and the point where the KW was measured?

Best regards,

#10 subhash

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Posted 16 October 2006 - 06:57 PM

QUOTE(marke @ Oct 15 2006, 01:37 AM) View Post

Hello Subhash

I am surprised that you would see a 10% reduction in KWs used by adding the capacitor and suspect that there is some reason other than the correction of the power factor that is making this change.
  1. 15 KVAR for a 40HP motor seems like a lot of correction to me, I would have expected a value of around 7.5KVAR should be sufficient. Do you know the pf before and after the correction was applied?
  2. Can you be sure that the load on the motor is identical in both tests? was there any possible change in motor shaft load?
  3. What is the voltage drop between the point where the capacitor was added and the point where the KW was measured?
Best regards,


Hallo Mark
1. Motor Load was constant through out experiment for both with and without capacitor in circuit .
that same motor is connected with constant flow pump application.
2. Without capacitor power factor was : 0.80 and with capacitor power factor is : 0.95
3. Regarding voltage drop it is seems to be nil as where capacitor added and power measure is seprated
by Y/D starter contactor only.
4.Before correction feeder line current was - R-48.0A Y-48.0A B-49.0A / After correction Current is -R-40A Y- 40A B-41.0A

Regards

Subhash




#11 marke

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Posted 16 October 2006 - 07:33 PM

Hello Subhash

The plot thickens!!
If the power factor correction and the measurements were made at the same point, there should be no change in KW consumed. The capacitor does not alter the current into the motor, or the KW drawn by the motor unless the addition of the capacitor causes an increase in the voltage at the motor terminals. If the capacitor does cause an increase in voltage, then the current will fall, but the KW will remain the same.

The capacitor simply reduces the ractive current flowing from the supply and so it reduces the I2R losses in the supply.
I would have to question the accuracy of the meter used under varying power factor.

You could do a test with the meter and use a three phase resistive load (heaters) and make a measurement, then add capacitance to create a leading power factor and see what happens. The KW should not alter. If it does, then there is a problem with the meter.

It may also be a good idea to repeat the test that you have done a few times to ensure that the results are repeatable, just in case there was some variable that is unseen.

Best regards,

#12 subhash

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Posted 17 March 2007 - 09:07 PM

QUOTE(marke @ Oct 17 2006, 01:03 AM) View Post

Hello Subhash

The plot thickens!!
If the power factor correction and the measurements were made at the same point, there should be no change in KW consumed. The capacitor does not alter the current into the motor, or the KW drawn by the motor unless the addition of the capacitor causes an increase in the voltage at the motor terminals. If the capacitor does cause an increase in voltage, then the current will fall, but the KW will remain the same.

The capacitor simply reduces the ractive current flowing from the supply and so it reduces the I2R losses in the supply.
I would have to question the accuracy of the meter used under varying power factor.

You could do a test with the meter and use a three phase resistive load (heaters) and make a measurement, then add capacitance to create a leading power factor and see what happens. The KW should not alter. If it does, then there is a problem with the meter.

It may also be a good idea to repeat the test that you have done a few times to ensure that the results are repeatable, just in case there was some variable that is unseen.

Best regards,



#13 AB2005

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Posted 21 March 2007 - 05:47 AM

Hello Sabash

Some thing is missing here.
According to your spec, the input power before compensation is
P = V x I x Cosф x 1.73
25244 = 380 x 48 x 0.80 x 1.73
And after compensation
24981 = 380 x 40 x 0.95 x 1.73
Power reduction = 1%

You have some problem in your meter.


"Don't assume any thing, always check/ask and clear yourself".

#14 Prashant2748

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Posted 25 June 2010 - 11:50 AM

QUOTE (subhash @ Oct 17 2006, 12:27 AM) <{POST_SNAPBACK}>
Hallo Mark
1. Motor Load was constant through out experiment for both with and without capacitor in circuit .
that same motor is connected with constant flow pump application.
2. Without capacitor power factor was : 0.80 and with capacitor power factor is : 0.95
3. Regarding voltage drop it is seems to be nil as where capacitor added and power measure is seprated
by Y/D starter contactor only.
4.Before correction feeder line current was - R-48.0A Y-48.0A B-49.0A / After correction Current is -R-40A Y- 40A B-41.0A

Regards

Subhash

Hi subhash
you have done very good job, have you tried it on another motors
what is your experiance now?
is it really worth to connect the capacitors at motor ?




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