interpreting Utility meter data and calculating amps

[Electric-Light]

So a more broad academic question is what is the "best" interval to measure peak power?

Why do you need to know? That's the answer to the best interval to use.
Sizing transformer or generator overload capability? or billing?

Duke in Indiana is 30 minutes.
SDG&E uses 15 minutes.

Solar panel people takes demand forgranted, but demand is expensive. They always want to get paid for kWh at top notch price, but not owe any demand. I think demand charge is good. If homes were assessed demand charge, people will think twice about how much things they use at once and nobody will have a 200A service.

For 20kW and higher demand:
https://www.sdge.com/sites/default/files/regulatory/ALTOUSecondary-01-01-15.pdf
$140/mo base charge, 15 minute demand
$24/kW +$10/kW peak-time
+kWh usage.

They consider peak as 11AM to 6PM weekdays in summer and 5PM to 8PM in winter.
So essentially, for businesses, the peak will occur in 11AM to 6PM in the summer, so demand is $34/kW, based on highest 15 minute average.

If the maximum peak of 100kW is observed at 8PM, but maximum during 11AM to 6PM for the bill period was 80kW
The charge is $24 x 100 + $10 x 80 = $3,200. A 240v 200 amp service maxed out for 20 minutes in summer on a demand plan can be expected to ring up at $1,632 in demand charge (48kW x $24/kw + $10/kW peaktime)

If the interval is too long you could/will be getting readings lower than peak, but too short and you could start picking up inrush values and such. Does something like a fluke 1735 logger have adjustable parameters for power calculation interval?

Call the PoCo. The smart meter may already have what you need available for view on their website and let you view it over the web. If you elect to use a power analyzer, you still need to set it according to the rate schedule anyways and it may not have the ability to do Time of Use.

From a heating standpoint there is normally not much value in going to less than 2 minutes for sizing measurements as you are near momentary times (then you need to make PQ measurements). You might consider a 2-5 minute interval for a severe bump load (a sawmill blade comes to mind). This gets closer to the classic thermal demand where you had an exponential response (a fast response rise to the 90% point). You could even opt for a thermal or induction type demand if equipment is over-heating and the normal 15-30 minute demand looks within equipment capacity.

Pacific Gas & Electric tariff says that if the customer load is intermittent or fluctuates wildly, they have the discretion to use billing demand calculation at 5 minutes. So, if you have a very abrupt load that pulls 250kw for 2 minutes, that could get you tagged for 100kW demand.

 

[electrofelon]

Why do you need to know? That's the answer to the best interval to use.
Sizing transformer or generator overload capability? or billing?

For sizing the electrical service equipment.

 

[Electric-Light]

For sizing the electrical service equipment.

The highest demand observed (most likely 15 min avg) on that table is about 150kW. Using 0.8PF(as generally used for generators) , 187kVA seems reasonable.

 

[Phil Corso]

Electrofelon...

Normally, to size a transformer, one needs to know its 8-hr demand!

You already know the monthly kW-hr and kVAr-hr consumption (although the total days, hence hrs, vary)! Thus, I suggest you determine the kVA required using a root-mean square (RMS) calculation!

Regards, Phil Corso