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.
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
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.
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?
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
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
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.
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.
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!
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.
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.
