Power Factor Correction

[VoltzElectric]

Does anyone recommend, or has anyone installed a capacitor bank for an industrial plant to help with Power Factor Correction? And if so, do you recommend doing a large capacitor bank coming into the plant, or go to a more machine by machine basis, and install a kvar type box/system at the machine?
I know looking into the capacitor banks, it gets expensive quick!

Ive read quite a few other forums and different websites, and have mixed reviews on systems.

Any comments would be appreciated!

 

[bob]

Does anyone recommend, or has anyone installed a capacitor bank for an industrial plant to help with Power Factor Correction? And if so, do you recommend doing a large capacitor bank coming into the plant, or go to a more machine by machine basis, and install a kvar type box/system at the machine?
I know looking into the capacitor banks, it gets expensive quick!

Ive read quite a few other forums and different websites, and have mixed reviews on systems.

Any comments would be appreciated!

I believe you have 3 options.
1. Install 1 large bank near the main. This may be less expensive.
2. Install cap on each motor. This will reduce losses in the motor circuits.
3. Combination of both.
I believe most on the forum will select #2.
Have you calculated the reduction in energy costs by installing the caps?
If so, what is the ROI?

 

[StephenSDH]

Number 1 rule is don't install capacitors for an ROI. Because you don't know what you are getting into. There are all kinds of headaches that come along with capacitors and in the end you probably will get your ROI, let alone break even. They overheat from harmonics, introduce ringing to your electrical system while switching, and will burn out contactors.

If the utility is forcing you to install capacitors then you might want to look at any large motors in your plant that run 24/7(or close to it). If you are forced to install them you might as well benefit from reducing I2R losses. If you don't have any large motor loads then the easiest place is right at your main gear. You will not save any money by reducing I2R losses (reduced KW) by putting them at the switchgear.

 

[zog]

Does anyone recommend, or has anyone installed a capacitor bank for an industrial plant to help with Power Factor Correction? And if so, do you recommend doing a large capacitor bank coming into the plant, or go to a more machine by machine basis, and install a kvar type box/system at the machine?
I know looking into the capacitor banks, it gets expensive quick!

Ive read quite a few other forums and different websites, and have mixed reviews on systems.

Any comments would be appreciated!

Yes I have, at several plants in Michigan in fact. Is the plant getting PF penalties? Another option not mentioned is an adjustable unit that changes with the amount of corretion needed, that is the best solution for many industrial plants.

I know of several companies in MI that specialze in designing, installing, and testing PF correction systems if you feel you need some help.

 

[USMC1302]

I worked with a high school that had an adjustable system around 15 years ago. Not sure how expensive the install was, but I can tell you the school was getting hammered in demand/penalties. Once the system went on-line the utility bill was cut by over 1/3(was averaging $26k/mo). I think they believe they got their money's worth.

 

[Jraef]

I am in the "Option #2" column for several reasons,

• #1, the entire system approach (referred to as Bulk Power Factor Correction Correction) leaves you vulnerable to a host of problems, the worst of which is interaction (resonance) with other capacitors in your plant, i.e. VFDs, UPS systems etc. EVERY Bulk PFC system I have encountered was at the heart of a host of issues with power quality and electronic devices, everything from strange actions by UPS systems to blown SCRs on soft starters. Once the Bulk PFC systems were removed, no more problems.
• Capacitors-at-Load (CAL) is what option #2 is referred to as. It provides only the amount of capacitance added to the system to offset the amount of inductance each motor adds to the system. By not having added kVARs when you don't need them, you all but eliminate the possibility of resonance.
• Having CAL also reduces the effects of switching caps in and out of the system, which is what the Automatic Bulk PFC systems do. Capacitor switching, besides being tough duty for contactors, is a big source of nasty transients. You can add filtering and protection against that, but if you do an Automatic system correctly, where you take all those extra steps, it ends up costing as much or more than CAL.
• Both the Bulk Correction and Automatic systems leave you vulnerable to a complete system breakdown. So if one cap pops in one of those systems, the whole thing usually must be taken off line. When that happens, you end up getting the penalties you were seeking to avoid. If you use CAL, a single cap failure is not a catastrophic event.

Good sources for caps:
Sprague was #1 for a long time (now owned by Eaton I think)
ABB, who bought the #2 supplier a few years ago (already forgot their name).
Aerovox
Myron Zucker
I've had some really bad luck with GE capacitors, I don't recommend then.

 

[Besoeker]

Any comments would be appreciated

Is the plant being penalised for poor factor? If not, it probably isn't worth puting in PFC.
The way I've seen it done in a few large plants is an automatic PFC bank at each motor control centre (MCC). This is sized to correct for the number and rating of motors fed from that particular MCC.
On a cautionary note, you should look at the quality of the supply. If the plant has a significant proportion of non-linear loading (typically VSDs), you may have to consider means of preventing this causing the capacitors to take excessive current.
What we usually do is fit a 3-phase reactor upstream of the capacitor. The reactor value is selected for resonance a little below 5th harmonic. But that isn't a job for the inexperienced.