Demand Vs Load?

[grounded7]

Hi,

During my time at university, we used the terms demand and load interchangeably. However currently I am using a software that displays, the results of a load flow anaylsis, different numerical values for Demands (in kW, kVAR, kVA) and Loads (kVAR and kW) on a feeder . I am confused as to what these number actually represent and how they differ from one another.

Additionally, can someone share their thoughts about the term 'average Amps and average Volts' and how do you think they might be calculated?

Many thanks.

 

[jghrist]

The definition of "Demands" vs "Loads" should be defined somewhere in the software documentation. Demands are usually an average over some period, like "15 minute demand" or "30 minute demand" if they were from metering. They could also be "thermal demand", meaning that instead of an integrated average, they represent the load that would heat an element the same as a constant current of the recorded value in same time interval. "Load" could be anything, from being synonymous with Demand to an instantaneous value.

Average Amps and average Volts would be the average rms value over some period of time. I recently looked at a manual for a meter (Cutler-Hammer PX4000) that calculates rms values over a 200 ms period. The "average" of these 200 ms rms values is recorded for each interval. Intervals can be 5 minutes, one hour, or one week.

 

[bacon4life]

They might refer to the number you enter as the load versus the simulated load that includes including system losses and any changes to power due to off nominal voltage for constant current and constant impedance loads.

 

[grounded7]

Thanks for the explanation guys.

jghirst, my first instincts were that 'demand' could be the load over a certain period of time or maybe during that specific time when the analysis was run.

I looked around in the technical reference and the index for the software but couldn't find any proper statement that states the difference or the definition of demands. I thought it might be some generic terminology that experienced people in this field use, that they haven't stated it anywhere in the software documentation.

I am just a bit worried because I have to comment on some results and I can't really say what they are unless I get to the gist of it.

 

[pwrtran]

Add to jghrist post - load sometimes refers to the connected kVA, it could be transformers, could be lighting fixtures or welding machines, but it may not be the actual power consumptions. However, demand is the actual power drawn from the supply by those connected kVA loads, it might be recorded as 15 minutes rolling average, or might be instantaneous peak demand. That is my understanding.