KVA and KW Needed for servicing panel and pumps

[Buck4202]

Have a question I am hoping so one can explain how to approach:

I need the transformer size and generator size for the equipment listed below?

Bldg 1 TF 12470/480 ____ kVA
1000 Amp Service, full building on generator
60HP Fire Pump
1HP Jockey Pump

+ Bldg 2: TF 12470/480 ____ kVA
400 Amp Service, full building on generator
No Fire Pump

Diesel Generator ____ KW to serve both buildings?

 

[tom baker]

A 1000 amp service does not mean you have 1000 amps of load.
Typically you would use a recording power meter and use for 30 days.
You could also do a load calc
These is not a fill in the blank answer for your question

 

[Buck4202]

Transformers should be sized for max load and generator should be sized for the max load

 

[sgtsparky]

At a minimum you would need the size of the building and the occupancy the required lighting load will be part of the calculation but I agree with the others the size is based on the load.

 

[Buck4202]

This is a hypothetical question…the transformers need to be sized off the service panel and pumps. The generator is sized based off the size of the transformers

 

[Buck4202]

A 1000 amp service does not mean you have 1000 amps of load.
Typically you would use a recording power meter and use for 30 days.
You could also do a load calc
These is not a fill in the blank answer for your question

This is hypothetical, so if this is for a new building there is no way to gather meter data.

 

[Carultch]

Have a question I am hoping so one can explain how to approach:

I need the transformer size and generator size for the equipment listed below?

Bldg 1 TF 12470/480 ____ kVA
1000 Amp Service, full building on generator
60HP Fire Pump
1HP Jockey Pump

+ Bldg 2: TF 12470/480 ____ kVA
400 Amp Service, full building on generator
No Fire Pump

Diesel Generator ____ KW to serve both buildings?

1. The 12470V values are "out of the picture", until you care about details on the medium-voltage circuit. Any amps on the secondary side, will correspond to the 277/480V output voltage of the transformers

2. HP is the mechanical power of the pumps and their motors. The NEC has a reference table that cross-references motor HP ratings to corresponding amp ratings (FLC for full load current, or "full load code").

3. In general, KVA relates to Amps as such: KVA=sqrt(3)/1000 * Amps * Volts phase-to-phase, assuming all phases are balanced.

4. Without knowing the details of the loads served by the services, you would get a very conservative result for the ratings of the transformers and generator, by only using the information you provided. The load calculation that determined the service Amp ratings would likely be used instead, which enumerates the total KVA. Otherwise, you would account for unnecessary safety factors, or errors from rounding to the nearest standard size breaker, neither of which applies to sizing the transformers and generator.

 

[topgone]

Have a question I am hoping so one can explain how to approach:

I need the transformer size and generator size for the equipment listed below?

Bldg 1 TF 12470/480 ____ kVA
1000 Amp Service, full building on generator
60HP Fire Pump
1HP Jockey Pump

+ Bldg 2: TF 12470/480 ____ kVA
400 Amp Service, full building on generator
No Fire Pump

Diesel Generator ____ KW to serve both buildings?

Let's do a rough estimate:
bldg 1:
Main Fire Pump 60 HP = 60 kVA
Jockey pump 1 HP = 1 kVA
Total = 61 kVA X 1.3 ~ 75 kVA
bldg 2:
400 A CB = 400 X 0.8 = 320 A
kVA = 480 X 1,732 X 320 = 266 kVA
Transformer = 1.3 X 266 = 345 kVA ~ 500 kVA
Total kVA = 575, choose 500 kVA
Your generator size depends on whether you have a big motor in the buildings (loads that require high starting kVA).
The normal thing is that the transformer size could be used to size your generator if no high current is required during starting.

 

[Carultch]

Let's do a rough estimate:
bldg 1:
Main Fire Pump 60 HP = 60 kVA
Jockey pump 1 HP = 1 kVA
Total = 61 kVA X 1.3 ~ 75 kVA
bldg 2:
400 A CB = 400 X 0.8 = 320 A
kVA = 480 X 1,732 X 320 = 266 kVA
Transformer = 1.3 X 266 = 345 kVA ~ 500 kVA
Total kVA = 575, choose 500 kVA
Your generator size depends on whether you have a big motor in the buildings (loads that require high starting kVA).
The normal thing is that the transformer size could be used to size your generator if no high current is required during starting.

Where does 1.3 come from?
Also, I know it's a rough estimate, but is it realistic to approximate KVA directly from the number of horsepower? That means the combined power factor and efficiency multiply together to be about 75%.

 

[topgone]

Where does 1.3 come from?
Also, I know it's a rough estimate, but is it realistic to approximate KVA directly from the number of horsepower? That means the combined power factor and efficiency multiply together to be about 75%.

The rule of thumb I use is to assume 1 HP = 1 kVA. You can have yours (a different PF and efficiency assumption).
1.3 served me well in allowing a factor to cater to future loads. That said, it is my idea of how to do a rough estimate when data are incomplete and there is a period given to me to crank out a figure. Never failed me though.