×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • 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!
  • Students Click Here

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

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Power Factor
2

Power Factor

Power Factor

(OP)
Please explain why the utility power company limit at 0.9 PF for the Genset system co-gen producer.
Thanks

RE: Power Factor

So, what research have you done?  Have you asked the utility?  Do you understand power factor and what lower power factor does to the utility?  Give us some more information about what you know so we have some idea where to fill in around the edges; this site is not for us to your job for you.

RE: Power Factor

Too much foam, not enough beer smile

RE: Power Factor

(OP)
Excuse me, I mean 0.9 PF limit is maximum limit not minimum.
Thanks

RE: Power Factor

davidbeache's comments may be even more valid now.
I always believed that 0.95 or 1.0 was more than 0.9 and this is confusing me. I would expect 0.9 to be the minimum, not the maximum.
If you are involved with co-generation there must be someone in your organisation who understands power factor and can help you.
I enjoyed Zogzog's graphic description, but it may now be in doubt.
yours

RE: Power Factor

Speculation: since we are talking about GENERATION, this may be a LEADING power factor requirement, as the utilitiy may need VARs furnished in this locale.

Therefore, the smaller the (leading) power factor, the greater the reactive power being delivered by the cogen rather than the utility.

RE: Power Factor

I think a quote from the utility's interconnect agreement would go a long way in helping to understand the question - what specifically is the utility requiring?

RE: Power Factor

Hi everybody

Excuse me. I have a communication problem with the forum. I do not know why. any way,
To answer of your question particularly to Davidbeach, I do not have information regarding the utility contract. This question came to me a long while ago when a friend asked me why the utility limit the PF at .9 maximum. That all I knew. I did not have the good answer to him so so why I reapeat this question again hoping that you shoud give me the idea.
Thanks all
JPEELECTRICAL

RE: Power Factor

Hi jpeelectric
Please accept my apology for my previous flipant answer.
The utility charges a penalty when the power factor falls below 0.9 or 90%   
90% is the minimum, not the maximum.
If the power factor is poor they must transmit more current to deliver the same power.
A simple example would be two loads side by side, one at 100% power factor and the other at 50% power factor.
If they are both using the same amount of Kilowatt hours, the load with 50% power factor will be drawing twice as much current. That means that the transformers, switches, cables, and generators must be twice as large so as not to overheat.
However, the revenue from both loads is based on kilowatt hours, and is the same.
Because of the added costs of supplying bigger equipment to cope with the poor efficiency of a poor power factor, the utilities charge a penalty if the power factor is poor. The figure of 0.9 or 90% is common but by no means the only figure. Some states in India charge a penalty if the power factor drops to 99%.
The actual ammount of the penalties also is subject to variation.
respectfully

RE: Power Factor

It is true that utilities generally penalize low lagging pf loads. However, the original post indicates this is a generator. I like Tinfoil's answer above. Requiring the co- gen to produce leading vars to improve overall system efficiency makes good sense. In this case .9 leading may be better than unity.

RE: Power Factor

stevenal, a bit of a quibble, but for a generator the definitions of leading and lagging turn around and a generator that is producing vars has a lagging pf while a generator absorbing vars has a leading pf, just the opposite of the definition for a load.

RE: Power Factor

@DavidBeach

I agree with your def'ns in your 'quibble', but I used a 'load-centric' rather than 'generation-centric' viewpoint to make my point (which is why I took care to mention 'furnishing VAR's' to be clearer to all).  

After all, it's the utility's perspective that counts, since they are setting the rules.  At my utility, we treat embedded generation more like 'anti-loads', so that we can talk about leading, lagging, real, reactive, etc in only one set of terms to avoid confusion.  Maybe if we owned generation, we'd be more careful to match IEEE terminatology! ;)

RE: Power Factor

David,

Okay, thanks for the correction. If the utility requires the generator to produce lagging vars in relative to the real power being supplied, then the requirement may be made expressed as a maximum pf. A minimum reactive factor of .436 might be a better way to express the requirement, but power factor may be more widely understood.

RE: Power Factor

tinfoil, I'm not sure it is IEEE terminology.  It has been customary to define leading and lagging in terms of which direction the vars are going at the terminals of the item in question.  For loads lagging vars are in while leading vars are out.  For generators lagging vars are out at the terminals and leading vars are in.  That way a lagging load and a lagging generator work together.

I have found that there is a much better definition of leading and lagging that doesn't require knowing whether you are dealing with a load or a source - if watts and vars are flowing in the same direction, the circuit is lagging while if the vars and watts flow in opposite directions, the circuit is leading.  That works for loads and generators and does not require any distinction between the two.

I know there was a discussion a while back as to whether or not vars actually have direction.  Maybe they do, maybe they don't, but using the same definition for direction of power you can get a workable definition of direction for vars and that works well for this.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

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!


Resources