Generator Power Factor

[mako]

Sirs,

Situation: 3 Phase Generator,11 KV,50 HZ is the only Power source we have and we have an 11KV Pri/480-277 Sec transformer.

Question: Since the Generator is of 80% P.F.,do we still need Capacitor Bank for Power Factor Correction? If we will not use Capacitor for Power Factor Correction, would the Generator be enough to correct the power factor of the system?Will there be a chance on our secondary side to have a P.F. lower than 80% which is lower than the Generator P.F.?

Thank you.

 

[charlie b]

Re: Generator Power Factor

The generator's rating in terms of power factor has nothing to do with whether you do, or do not need a capacitor bank. That "need," or the absence of a need, is determined by the load (in KW and in KVAR) and by your distribution system's capability.

What is the load you intend to supply with this generator / transformer?

By the way. It might be more polite to say, "Sirs and Mesdames." We have a significant number of women who actively participate in this Forum.

 

[mako]

Re: Generator Power Factor

Then, the Generator has nothing to do with Power Factor Correction on the load side of the transformer.
At the secondary of Transformer, our loads are computers, electronic communication cabinets, lighting with electronic ballasts, AHU , split-type ACUs, Kitchen Loads,Fluorescent lightings,and electric discharge lightings.Our Transformer is 1.5MVA.

 

[ron]

Re: Generator Power Factor

The power factor is load dependent and essentially doesn't care if you have a generator or connected to the utility grid. The power factor of the load consumed will be the same.

 

[mako]

Re: Generator Power Factor

Thank you.

 

[charlie b]

Re: Generator Power Factor

Originally posted by mako: Then, the Generator has nothing to do with Power Factor Correction on the load side of the transformer.

That is correct.

The loads that you list are mostly resistive. The ones that have an inductive portion are the motors (in the air conditioning units) and some of the lights (e.g., the fluorescent lights). But it is not possible for anyone to say whether or not you need power factor correction, without having one of two things. (1) If you have exact numbers (watts and VARS) for each and every load, you can add them up to get a complete picture of the load. (2) If this system is already in operation, then you can measure the KW and the KVAR.

But even if you knew these things, the choice of whether or not to use capacitor banks is still up to you. They will improve the power factor, but there is still the matter of how "improved" you need it to be. In other words, you have to decide what an acceptable power is factor for your purposes.

 

[coulter]

Re: Generator Power Factor

Mako -

The only times I have been concerned about the KVAR loading is:
1) If the power provider (utility) says the KVARS are excessive and they are going to charge a penalty, or;
2) If the generating system is getting close to full load.

The first doesn't apply to you, since you own the generator.

Someone else here (different thread) came up with some pretty good ratings definitions:

KW relates to the generator driver rating - how much horsepower can the engine put out.

KVA relates to the ability of the generator to reject heat.

As you know, a low power factor load draws more current for the same KW (real power) as a high pf load.

So, if you are getting close to the generator amp rating and you have a low pf, then VAR correction caps make sense. The VAR correction caps will lower the generator current, total KW will remain the same.

One of the things you discuss is loads with a high harmonic content. VAR correction caps won't help that.

If you do decide to add the caps, my normal inclination is to put them as close to the low pf loads as possible. This reduces the amps through the switchgear and transformers.

Caution: Some generator voltage regulators do not function well with a leading pf load. So, adding more VAR correction than necessary, or failing to switch off VAR correction when it is not needed can cause problems with the Voltage regulator.

carl

 

[ccjersey]

Re: Generator Power Factor

I would like other opinions on this, but I always consider the KW rating of a generator to be RELATED to the capacity of the prime mover required and of course the real power produced. Usually about 1.75-2.0 engine hp/kW ratio.

The kVA is the electrical capacity of the generator end.

So power factor of 80% is some sort of an industry standard for building/rating generator sets.

If load power factor is lower than rating then electrical limit is reached before engine limit, and if load power factor is higer than rating, then engine may not be able to support full electrical capacity.

 

[ccjersey]

Re: Generator Power Factor

How's that for thinking alike

 

[charlie b]

Re: Generator Power Factor

Originally posted by coulter: Someone else here (different thread) came up with some pretty good ratings definitions:
KW relates to the generator driver rating - how much horsepower can the engine put out.
KVA relates to the ability of the generator to reject heat.

I posted something along those lines some time back.

Originally posted by ccjersey:The kVA is the electrical capacity of the generator end.

I would accept this version, but only if you accept the notion that the "electrical capacity" is limited by the effects of high temperature on the insulation system. You may note, for example, that some of the larger transformers have more than one rating. Some have permanently installed fans, and their rating goes up while the fans are running. The fans help remove the heat, so you can get more KVA out of the transformer.

 

[ccjersey]

Re: Generator Power Factor

I agree! Electrical capacity is surely limited by temperature. The manufacturer can use a higher temperature rise and give a "standby" set a higher rating than if it were rated more conservatively and expected to run continuously and last a long time as in a cogeneration or CHP installation.

Guess the same goes for the engines too.