Smart questions
Smart answers
Smart people
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Member Login




Remember Me
Forgot Password?
Join Us!

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips now!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

Join Eng-Tips
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Donate Today!

Do you enjoy these
technical forums?
Donate Today! Click Here

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.
Jobs from Indeed

Link To This Forum!

Partner Button
Add Stickiness To Your Site By Linking To This Professionally Managed Technical Forum.
Just copy and paste the
code below into your site.

LaliGuras (Electrical)
10 Jan 06 9:24
I have been working for capacitor placemnet in our 12.47 kV distribution system for power factor correction.  3 substations that are feeding from a 115 kV radial  transmission line have really power factor. Each substation have kVAR demand around 5000 kVAR.  To correct substation power factor to 96/97, i at least need 2000 kVAR Capacitor bank in each substation during peak. I was wondering wheather i should go for different distribuiton line capaciotrs banks or single capbank at substation.

Most of the distribution feeders are underground. And laod factor is 50-60%.

I would appreciate your suggestions.

Lali
bacon4life (Electrical)
13 Jan 06 13:36
This link discusses some of the different types available.
http://www.nepsi.com/pros_cons.htm

Some things to consider:
You mention that most of the feeders are underground, does that mean you will need padmounted capacitors rather than pole mounted banks?  

Is voltage drop on long feeders a consideration?  Sometimes capacitors are placed approximately 2/3rds of the way down a feeder to create a more uniform voltage profile.  In general, line losses will be reduced the closer to the loads the capacitors are.  Capacitors also increase the system capacity upstream of the location.

Will the capacitors be switched? Daily, weekday/weekend, seasonally or never?  Is switching 1 large substation bank ok, or will you need multiple smaller sections.  Capacitors on the feeders can cause high voltage problems during light load periods, and correcting to leading pf can aggravate harmonic issues.



jghrist (Electrical)
13 Jan 06 17:13
I would install fixed capacitors on overhead lines sized to compensate for the minimum reactive load on the line.  This will reduce line losses.  It may be economical to install switched capacitors on the lines as well, particulary if the lines are heavily loaded.  This would require some study.  It may also be economical to install fixed or switched capacitors on the underground lines, but these will be more expensive.

The 2/3 rule of thumb mentioned by bacon4life should be adequate for the fixed capacitors if the load is relatively uniformly distributed along the line.  The loss reduction is not very sensitive to location.
tinfoil (Electrical)
16 Jan 06 14:16
LaliGuras: I'm surprised that all of your feeders have such poor power factors.  Since you mentioned 'underground', then I am assuming that this is NOT due to inductive losses on long feeders.

Therefore, the low power factor must be due to customers with low power factors.  

Doesn't your utility 'punish' industrial customers via billing penalties for bad power factors (such as charging for kVA rather than kW, etc)?

Sometimes, the best place to correct for loads with bad power factors is right at the loads themselves.
LaliGuras (Electrical)
16 Jan 06 15:28
TinFoil, you are right. Must of these feeders are less than 5 miles in length and feeds industrial and commercial loads with low power factors. We have already started to panalyzing them. The urgency of correcting power factors is  our power purchaching contract with our power supplier. we are supposed to maintain at least 96%.

Correcting power factors at load level, in my case, requires lage numbers of Underground capacitor bank with controllers which is expensive than correcting in substation.

I was just wondering wheather any body has gone through this kind of situation, and which one they believe is better option.

Thank you all for your time.

LaliGuras

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close