Can I calculate connected load from utility bill?

[dft97]

Hello,
I am in the initial stages of applying for a service upgrade for one of our facilities. I have the utility bills for the past 2 years, and I have the average PF and Demand values for each billing period.
Example:
The last biling period has:
PF 86.46
Demand 204.52 KW

We are looking at adding more equipment to this facility. It currently has a 200A service, and we are looking to upgrade to a 400A. I am being asked to provide the Connected load and the expected demand. Can I estimate this from the utility bill, and add the load values from the specs of the new machines we are adding?

This is my first project of this type, forgive the simplicity of the question.

Thanks

 

[mosesnbklyn]

Yes, find the maximum demand for the last 12 months and add your estimated demand. One issue w/ utility demand readings are that they are an average over the billing period. I would ask the utility if they have the peak demand history from the meter.

You could also do a brief load study during peak conditions (winter or summer depending on HVAC loads).

 

[dft97]

Thank you mosesnbklyn.

I have the peak demand over the last 2 years, 273.04 KW
Now if I know that my new machine is 3 phase, 600 V, 72A (peak), then I would I know that the demand of my machine would be:

P = 1.73 * 600V * 72A
= 74.7 KW

And my new peak demand would be: 74.7 + 273 = 347KW?
At this demand, would a 600V 400A service be adequate?
Average PF over the last 2 years was 90.54.

Thanks

 

[X49]

First of all, your power caluation for the new load would be 74.7 kVA, not kW. Make things more simple by doing all of your calcuations in amps.

Assuming a power factor of 0.9, your peak demand from the last two years would have been about 303kVA. This equals 292 amps on your 200A service! I'm surprised your main overcurrent device did not trip. Are you sure your numbers are accurate? If so, your service should be upgraded whether you add loads or not.

Adding your new load of 72A will result in an expected peak demand of 364A (assuming 90% power factor for the new load).

A 400A service can accomodate a 320A load continuously, or up to a 400A load temporarily. I would assume that since you had no problem with 292A on your 200A service, that most of the load is not continuous. I would expect a 400A service to be fine, but you will not have much spare capacity for future loads.

 

[VTer]

@x49- Actually I would argue that by adding the load in amps you are complicating everything. Add your load in kVA please.

273.04kW/0.85pf(assumed) = 321kVA peak recorded
+
Sqrt(3)*0.6*72 = 75kVA
321+75= 396kVA - Assuming machine is always working this is your “worst case/peak” scenario demand load, not your connected. For your connected load you have to add all the individual loads in your building. The demand is lower because not all of your connected loads are energized/working all at the same time.

Anyways I would add 25% to the total demand for future expansion. This all gives you 495kVA.
At 600V service this gives you 495/(sqrt(3)*0.6) = 476A which comes out to a 600A, 80% rated CB. I would personally go with the 600A service based on the numbers you provided.




"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic — and this we know it is, for certain — then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". – Nikola Tesla

 

[dft97]

Thanks all of you for your help today. Coming from a controls background I never really had to worry about anything above the disconnect. Now I do.