KW usage

[rattus]

It is NOT the measure of the maximum power in a 15 minute (or whatever interval) period. It is really the energy drawn over the period divided by the time of that period so it is the average power over that period. The maximum power drawn would most likely be higher.

Can't argue that point Mivey. Now, how did they read the old demand meters which recorded the demand on a paper disc?

BTW, demand may be expressed in KW or KVA, right?

 

[Besoeker]

Bes, my aging mind recalls that demand is a measure of the maximum power drawn over a 15 minute period or something like that. Usage would be stated in KWH; demand would be stated in KW.

I agree.
I was just making the point that the bill from the POCO would be for energy use in kWh. Here, UK, we get billed for kWh plus a fixed standing charge.

As a complete off-topic comment, our supplier is the energy company, E.ON.
Like most large companies, it has a menu based telephone help service.
"If you have a query about your bill press 1....."
You usually get a very politely spoken recorded female voice directing you around the menu. For E.ON, my daughter is one of the two voices used.

 

[mivey]

Now, how did they read the old demand meters which recorded the demand on a paper disc?

Those meters measured the instantaneous demand. The vertical position (for a drum/strip or radial for a disc) showed the power flowing through the meter and the horizontal axis (for a drum/strip or transverse for a disc) showed the time intervals. To approximate the demand over an interval, the user had to look at the varying line drawn during the time interval and estimate a straight line that had approximately the same area under the curve.

BTW, demand may be expressed in KW or KVA, right?

Right. There is kvar demand as well. What we are really after is the kVA as that determines the size and cost of equipment and resources (kvar is good too in that resource costs for kW and kvar supply are different). A lot of times, the kW is measured and billed under an assumption of a not-to-exceed minimum power factor such that the charge for kW covers the kVA cost (and/or kvar depending on the allocation break-out).

The demand we get from most meters is the integrated demand over some time interval and is the average power during that interval. It uses the accumulated energy (scaled for time, of course) to fill an electronic register or move a mechanical needle or dial that is reset at the end of each interval. The moving needle had a peak arm (or peak dial reading for the dial types) that had to be manually reset and the electronic register has an asociated peak storage register that has to be reset as well.

Another interesting demand type is the thermal demand which measures the heating effect by using thermal elements which can heat and cool just like real equipment does (there is also an electronic version which simulates the thermal elements).