Capacitor's Revisited

Reply

  #1  
Old 08-20-07, 01:28 PM
Member
Thread Starter
Join Date: Aug 2007
Posts: 1
Question Capacitor's Revisited

I have read some of the posts concerning companies that claim a X% of saving per month by using their devices. I am also aware that this has been argued in a "professional" forum and that using a KwH meter would not yield these savings. I am somewhat confused and hoped someone would clear this up for me. I am friends with a master electrician that is an engineer for Chrysler and he gave me some advice that I think is being "shot down", so to say, here. So this is the theoretical setup and the question. He said that if I add up all of the HP rating from all pumps/motors (sump, well, freezer/refridge compressors, etc...) and came up with a number (let's say 5hp) that I could go to an electrical supply house, tell them I need a capacitor for a 5hp (motor?) and then hook it up directly to a 30(50?) Amp 220 breaker off of my electrical box that it would yield me some savings. Is this true to some degree? Even if it is not 10%, would it yield any savings and keep the power pull more even/subsidized?

Thanks.. looking forward to some input.
 
Sponsored Links
  #2  
Old 08-20-07, 02:09 PM
Member
Join Date: Feb 2002
Location: port chester n y
Posts: 2,117
The capacitor would improve the "Power Factor" of your system, but would not reduce your power consumption. Let's presume you are operating at 80% Power Factor-- that would mean that 80% of the current -flow between your house and the utlity transformer is "power-current" and the other 20% "reactive-current". If the capacitor improved the Power-Factor to 90%, it would mean a 10% reduction in the "reactive- current" with no reduction in the "power-current" which the KWHR meter registers.

Lets say you mixed a a scotch & water so that 70% of the liquid is whiskey . If you mixed another drink with less water, the scotch is now 90% of the liquid, but the same quantity ($$$$)
 
  #3  
Old 08-20-07, 02:17 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,531
> it would yield me some savings. Is this true to some degree?

Yes, but the amount would be quite small -- single digit percent at best.

> would it yield any savings and keep the power pull more even/subsidized?

There are two types of power delivered to your home: real and reactive. Motors and other inductive loads consume both real and reactive power; lights and heaters use only real power. Capacitors are used to correct the ratio of real and reactive power (called power factor) by reducing the reactive power consumed. Adding too much capacitance over-corrects the power factor which adds just as much inefficiency.

Industrial and commercial customers pay for the reactive power they consume; residential customers do not. Therefore, reducing reactive consumption does not directly affect your bill at all. The only gain you may see is due to a slight increase in efficiency as a result of the corrected power factor. However, if you over-correct you will not see any gain. There are other complicating factors too. Most appliances already have start and run capacitors sized to match the motors, so adding more capacitance is a waste.

Your friend is absolutely right for industrial sites which have hundreds or thousands of motors all running 24/7, but it doesn't apply nearly as much to residential sites.
 
  #4  
Old 08-20-07, 07:35 PM
Rollie73's Avatar
Member
Join Date: Mar 2007
Location: Bras D'Or, Nova Scotia ,Canada
Posts: 173
I have worked in a few older industrial plants where they will use a large HP motor, keep it running while coupled to nothing , in order to correct their power factor by "using" up as much of this reacitve power as possible. Not transmitting this reactive power back on lines equals big savings for those guys.

Try explaining to an accountant how a 100 hp motor that is running while attached to nothing is actually saving them money!! LOL.
 
  #5  
Old 08-20-07, 08:44 PM
Member
Join Date: Dec 2006
Location: orange county
Posts: 285
Exclamation

Capacitors can literally expand and "blow up" kinda like a m-40 firecracker I suppose ,when not rated correctly in micro-farads and voltage to suit the need. They also do this sometimes when sized properly. Changed out a "bloated" one today on a A/C unit.
 
  #6  
Old 08-21-07, 09:46 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,531
> use a large HP motor, keep it running while coupled to nothing

The good old synchronous condenser. Very popular in factories throughout the '50s before capacitors were widely used from what I understand.

> Try explaining to an accountant how a 100 hp motor that is running
> while attached to nothing is actually saving them money!! LOL.

Now that's the tough job!
 
  #7  
Old 08-21-07, 03:17 PM
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,399
I once worked in a large manufacturing facility where we had synchronous motors on the air compressors. We ran a slightly leading power factor on these motors to help raise the overall lagging power factor of the plant.
 
  #8  
Old 08-21-07, 07:33 PM
Rollie73's Avatar
Member
Join Date: Mar 2007
Location: Bras D'Or, Nova Scotia ,Canada
Posts: 173
Yep the sychronous condensor.
This particular one was in a pulp and paper plant owned by Stora Enso, and the plant was built in the 60's. I worked on the construction of the new plant in the 90's and most everything was then changed to capacitor banks.
 
  #9  
Old 08-23-07, 08:48 AM
Member
Join Date: Feb 2002
Location: port chester n y
Posts: 2,117
Possibly the largest capacitor bank in the World was the one the New Haven RR connected to the electrifcation system at Woodmont Ct. , near New Haven. This was done at a time when 4500 HP electric locomotives were pulling mile-long freights. The traction-motors were "series" motors operating on A.C.. To minimize the inductive reactance, The New Haven operated on 25 cycles.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes