difference of 0.9lagging and 0.95lagging for a 500MW generator

[QBplanner]

Hi All:
I am not sure my last post got through or not so I write it again.
I would like to know that will it be a big jump on the cost if we require a 500MW generator has a 0.9lagging power factor instead of 0.95lagging one? Will the improved the cooling system or field winding /rotor winding cost a lot?
Thanks!

 

[rcw retired EE]

The generator, windings, rotor, etc all have to be able to carrry 5.5% more current at the same temperature rise.

I would expect a 5-10% increae in price unless it is a "standard" design with additional coolers. (500MVA = Standard?? not likely.)

 

[QBplanner]

Thanks a lot!

Do you know which parts of machine design (In detail) should be modified in order to extend the power factor from 0.95 to 0.9. I know mainly will be rotor and field winding but just have no idea how much additional work will be involved.

 

[waross]

A generator set may be rated in MW but the alternator by itself will be rated in MVA.
500 MW @ 0.95 PF = 526.3 MVA
500 MW @ 0.9 PF = 555.6 MVA
All other things being equal, 555.6/526.3 = 1.0556, or about 5.56% more copper and iron.
Or more air circulation to remove the extra heat.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[rmw]

Does the nameplate on your generator rate the generator at 0.95 PF? I'd be surprised if it does unless it was special built. Generators are usually rated for a wider PF variation thatn .05 PF in my experience. I normally see as high as 0.85 for the design limits.

rmw

 

[QBplanner]

Thanks for rcwilson ,waross and rmw 's response.
I agree for thermal units 0.85 lagging can be reached very often.

But for hydro units as big as 500MW real power output, you will seldom see any machine rated beyond 0.9 lagging.
If as Rcwilson said, a 5-10% cost increase for a 500MW machine is not a small amount of saving.

I am in North America, NERC or FERC only provides Guidelines (0.9 lagging/0.95leading at gen's terminal) but no standard for new generator interconnection requirements.

Therefore, sometimes when we require customer generator match the 0.9lagging. there are always disputes about why you need a 0.9 lagging PF.

Then my question is always the reversed one from the generator owner. what problem do you have to meet 0.9lagging from 0.95lagging.

Because from system point of view , it is hard to justify if 0.9 lagging is really needed. However, I can not change my company's standard which were set up by some people who only knows copying NERC/FERC 's.
That is why I started tis issue and try to learn what the problems are for Gen owners/designers if pf has to be extended to 0.9 lagging. Then maybe I can contribute something in order to modify our standard to 0.95lagging/leading at Point of Interconnection.

Anyway, many thanks to all of you. I am looking forward to getting more suggestions or helps.

 

[edison123]

Lower pf will require more rotor copper resulting in overall size increase (with accompanied cost of all components) and higher exciter rating. Having worked on 40 hydro generator rewinds up to 130 MW, I have never seen a pf higher than 0.9. May be as you say, a 500 MW is a very special unit and only OEM's could tell you the cost factor.

* Women are like the police. They can have all the evidence in the world and yet they still want a confession - Chris Rock *