Jump to content

Pf Correction At The Motor Load To Reduce Losses


energyguy

Recommended Posts

Good Afternoon - I am an energy manager at a large company - not an engineer. However, I have been told by our engineers that applying power factor correction capacitance at the individual motor loads can reduce electrical distribution losses. I think it comes from reducing line losses and other losses in the system. I also read the power factor link on the L M Photonics site which, in part reads as follows:

 

"The magnetizing current and the leakage reactance can be considered passenger components of current that will not affect the power drawn by the motor, but will contribute to the power dissipated in the supply and distribution system. Take for example a motor with a current draw of 100 Amps and a power factor of 0.75 The resistive component of the current is 75 Amps and this is what the KWh meter measures. The higher current will result in an increase in the distribution losses of (100 x 100) /(75 x 75) = 1.777 or a 78% increase in the supply losses.

In the interest of reducing the losses in the distribution system, power factor correction is added to neutralize a portion of the magnetizing current of the motor. Typically, the corrected power factor will be 0.92 - 0.95 Some power retailers offer incentives for operating with a power factor of better than 0.9, while others penalize consumers with a poor power factor. There are many ways that this is metered, but the net result is that in order to reduce wasted energy in the distribution system, the consumer will be encouraged to apply power factor correction."

 

However I also read in the posts that PF correction does nothing to reduce kWh consumption. I am a little confused. It seems as though from the section above that PF correction at the individual loads would help mitigate some losses in my facility's electrical distribution system and that should show up at the meter. What am I missing here? Please help!

Link to comment
Share on other sites

Hello energyguy

 

Welcome to the forum.

 

Yes, you are correct. If you apply power factor correction to the individual loads, there will be a reduction in losses in the supply up to the point of connection of the power factor correction.

There will be no reduction in the energy consumed by the load or circuits downstream of the connection of the power factor correction.

If you apply bulk power factor correction at the point of supply, there will be no KWHr saving, however, if you connect the power factor to each individual motor, then there will be a reduction in the losses in the cables to those motors, so there will be a saving in KWHrs. This should be a very small amount relative to the total power consumed, and if it is indeed significant, then the size of the cables should be addressed as there is to much voltage drop and associated losses.

In many countries, the regulations require for a maximum voltage drop of less than 5% on any circuit, and in order to reduce the voltage drop during start, many installations are closer to 2% worst case than 5%, so the savings could well be in the order of less than 1% of the energy consumed which is vastly different from the 20 - 40% claimed by some.

 

Best regards,

Link to comment
Share on other sites

Hello energyguy

 

Welcome to the forum.

 

Yes, you are correct. If you apply power factor correction to the individual loads, there will be a reduction in losses in the supply up to the point of connection of the power factor correction.

There will be no reduction in the energy consumed by the load or circuits downstream of the connection of the power factor correction.

If you apply bulk power factor correction at the point of supply, there will be no KWHr saving, however, if you connect the power factor to each individual motor, then there will be a reduction in the losses in the cables to those motors, so there will be a saving in KWHrs. This should be a very small amount relative to the total power consumed, and if it is indeed significant, then the size of the cables should be addressed as there is to much voltage drop and associated losses.

In many countries, the regulations require for a maximum voltage drop of less than 5% on any circuit, and in order to reduce the voltage drop during start, many installations are closer to 2% worst case than 5%, so the savings could well be in the order of less than 1% of the energy consumed which is vastly different from the 20 - 40% claimed by some.

 

Best regards,

 

 

 

Thank you very much for your quick reply and for welcoming me to the forum. It seems the more I click around the site the more incredibly relevant and detailed information I find. It's fantastic.

 

From what two of my three in-house electrical engineers tell me, they believe that distribution losses compounding (I may not be using the exact nomenclature) across the distribution system caused by reactive power can be greater than "classroom theory". They believe that by applying capacitors at the individual loads you can see potential savings for those loads from 2% to 6% or even a smidgeon higher in some limited instances (certainly no where near 20% or more which you mentioned that some claim). Are these guys totally off their rockers? BTW - My third engineer disagrees completely and says there will be zero savings from installing PF capacitors at the loads.

 

 

Link to comment
Share on other sites

Hello energyguy

If your power factor is low, then you can save a reasonable amount of the distribution losses, however to save as much as 6% wuld suggest to me that there is an expectation that the distribution losses are greater than 10%.

If that is the case, then you have a serious problem with undersized cables!!

It is possible that even greater savings would be achieved by correctly sizing the cables in the first place.

If you have 10% voltage drop, then the motors will draw more work current than they should and this will increase the copper losses in the motors and possibly compromise there performance and reliability.

 

I would be concerned about the potential to save as much as 6%, as this implies other problems than just bad power factor.

 

Best regards,

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...