Sizing a breaker 1.0 or 0.8 Power Factor?

[Percy Hoff]

I hope someone can help mewith this please. We recently built a 40Kw single phase generator set to backupa house. We used a 65Kw, 3-phase re-connectable alternator, connected it to doubledelta 120/240 volts. The rating sticker was marked as follows: 40Kw, 40Kva, 1.0Phase, 240 Volts, 1.0 Power Factor 167 Amps. We installed a 200 Amp CircuitBreaker.

The electrical inspector disagreed with the above. He stated that seeing thegenerator's original plate was marked at 50Kva, 0.8 power factor, the generatorcould NOT be rated at 1.0 power factor and therefore instructed that thebreaker be changed to reflect 40Kw Single phase, 240 volts at 0.8 power factor,which calculates to 208 Amps, so we were instructed to install a 225A CircuitBreaker. Is he correct or out to lunch?

 

[templdl]

I hope someone can help mewith this please. We recently built a 40Kw single phase generator set to backupa house. We used a 65Kw, 3-phase re-connectable alternator, connected it to doubledelta 120/240 volts. The rating sticker was marked as follows: 40Kw, 40Kva, 1.0Phase, 240 Volts, 1.0 Power Factor 167 Amps. We installed a 200 Amp CircuitBreaker.

The electrical inspector disagreed with the above. He stated that seeing thegenerator's original plate was marked at 50Kva, 0.8 power factor, the generatorcould NOT be rated at 1.0 power factor and therefore instructed that thebreaker be changed to reflect 40Kw Single phase, 240 volts at 0.8 power factor,which calculates to 208 Amps, so we were instructed to install a 225A CircuitBreaker. Is he correct or out to lunch?

Since no one has replied to you post yet I'll start it out this way.

What is the breakers supposed to be protecting anyway? How did you size the conductor or on what basis did you size the conductor?
It is a common misconception that a breaker protects the genset as most gensets do not have the capability to trip a breaker which is sized based upon the generating ampacity anyway if yu look at the breasker's TC curve.
The way I look at it the pf only has to do with the generator's ability to produce power. You should have sized the conductor based upon the the capacity of the genset. Is it based upon a 1 or .80pf? Either way I doubt if the cable size would be any different unless you were unlucky enough to fall between two wire sizes. Then size the breaker to protect the wire.
But I'm not familiar with the requirements in Canada regarding licensing for the installation of electrical systems. Since it appears as though you are not a licensed electrician that is of a concern to me.

 

[Birken Vogt]

No matter how I parse your numbers I cannot come up with an interpretation that makes sense to me. So I am going to have to ask you to clarify.

Is this a generator set package machine originally 3Ø that you converted to 1Ø? Or did you take an engine and alternator and put them together? What was the voltage and winding configuration of the original rating?

The rating sticker you mention in the first paragraph; who made it? You or the manufacturer?

Got a picture of the plate?

 

[kwired]

I hope someone can help mewith this please. We recently built a 40Kw single phase generator set to backupa house. We used a 65Kw, 3-phase re-connectable alternator, connected it to doubledelta 120/240 volts. The rating sticker was marked as follows: 40Kw, 40Kva, 1.0Phase, 240 Volts, 1.0 Power Factor 167 Amps. We installed a 200 Amp CircuitBreaker.

The electrical inspector disagreed with the above. He stated that seeing thegenerator's original plate was marked at 50Kva, 0.8 power factor, the generatorcould NOT be rated at 1.0 power factor and therefore instructed that thebreaker be changed to reflect 40Kw Single phase, 240 volts at 0.8 power factor,which calculates to 208 Amps, so we were instructed to install a 225A CircuitBreaker. Is he correct or out to lunch?

First thing is he is insisting you raise the overcurrent protection setting - I don't see why setting it lower then it can potentially be is a problem (as a general rule anyway)

Second thing - I don't see how you are getting 40kVA. I think the capacity across just one phase would be about 37.5 kVA, and at 1.0 power factor that would be about 156 amps.


Throwing power factor into generators starts to get confusing as it is not quite the same as it is for dealing with motors. The generator has a kW rating, and a power factor of less then 1.0 means the kVA will be lower instead of higher kW. Motors is the opposite, kW is always lower then kVA.

So if the original nameplate was 50 kVA @ .8 power factor, then (if I am right above on the 37.5 kW rating) I think the kVA rating across just one phase would be about 28.8kVA @ .8 power factor.

One error he has is saying it should be xx kW @ .xx power factor. If you have a power factor other then unity, then he needs to supplement it with kVA not kW, because watts is watts, but volt amps can have reactive current as a component.

 

[kingpb]

If you want to know what the generator rating is, you have to look at the manufacturer's reactive capability curve. I think all your questions will be answered.