Instantaneous Peak Demand Metering Survey

I am not aware of such at a domestic level, but at the manufacturing site we were metered on actual usage (15 minute windows), power factor (15 minute windows) and peak instantaneous power.

We were also charged a penalty for every instant that our instantaneous demand excceeded our forecast maximum usage. (We had to forecast our maximum usage and that was also billed as an "availability" charge, probably to make sure the value was realistic.)

It has a lot to do with the requirements of the power company maintaining enough "rolling capacity" to cope with the system loading.

I think we peaked at 3000A/phase one day at 3 phase 415 (phase to phase).

Our average usage was around 1250A/phase through the week, so the amount that our "excursion from normal usage" represented was significant in a local context since most houses would average 4A on one phase (25kWh per day)

JRaef, 25 years in metering and I have never known of a single case of billing based on instantaneous demand metering.

Firstly, demand is technically kWh/h. In other words, in the case of a 15 minute demand cycle the formula is kWh ÷ 1/4hr. With a simple bit of algebra this becomes kWh X 4 for the kWh value measured during the 15 minutes.

Again considering a 5 minute demand cycle, the result is kWh X 12, and so on.

For a 1 minute demand cycle the formula result becomes kWh X 60, and you can only imagine what the formula would become in the case of 'instantaneous'.

The point is, it is not practical to meter and bill from instantaneous demand.

The situations that come anywhere close to that description involve solutions to the problem of determining the transformer and supply requirements where high and very momentary bursts of demand occur, such as in x-ray and arc-welding. These type of situations are most often handled from one-time or interval (such as once a year) valuation measurements with highly specialized equipment, and then making a determination of equipment needs. The charges for demand are calculated and billed from a tariff formula rather than actually metered regularly.

Demand charges equivocate to the highway taxes built into fuel costs. They are designed to provide for the installation and maintenance of the supply equipment required by the load served. Heavier users pay a larger portion of the system maintenance costs. These provisions are calculated into the tariff charges, and in the case of a regulated utility they are clearly stated in the tariff.

I gave some effort to keeping this clear and concise but it still came out rather wordy, sorry. CJM

Most Utilitities all over the world charge normally some Fixed Charges at declared rates based upon your total connected load irrespective you use it; momenterily, regularly or even you do not connect during the whole billing month.

Keeping in view the diversity factor of your total connected load and the phenomenon of instantaneous peak demand created by few of the appliances, the utilities have readily charged you in one fashion or the other by levy of fixed charges.

My practical experience with two indipendent Utilities is that the Utilities practically limit the current of the feeder to the declared total connected load limit of the consumer by using sensitive over current relays, well than any instantaneous peak demand metering is meaningless all they want is that you should provide a more or less persistant load factor to their system.

The regular power demand of our systems normally runs at about 8, and peaks at about 12MW when all equipment are powered on. Normally at about 10 A.M. when power drawn starts to peak / breaches the 10MW level, ConEdison also starts levying heavy fines during those (10MW and beyond) periods. To avoid such heavy fines, we adapted cost saving measures to run generators and start co-generating power once we hit the 7MW level of our daily power demand.

I spent 30 years with an electric utility company, worked in three different states, and four different rate jurisdictions. I have had close contacts with many other people in the same line of work, and I have never ever been aware of metering that was based on truly INSTANTANEOUS peak demand. As CJMcGill already pointed out, the demand is based upon a window, usually 15 or 30 minutes and is derived by kWH per hour. Even under these circumstances the demand is integrated or averaged over the window. For example, if I had a demand window of 15 minutes and I had a demand of 10 MW for 7.5 minutes and 0 MW for 7.5 minutes, my demand would show up as 5 MW. Window splitting used to be a common practice for some industries that had short term, highly demand intensive loads, such as arc furnaces or transformer testing. You could wait 7.5 minutes into the window, turn on 10 MW of load, keep it on 7.5 minutes into the next window, and only be billed for 5 MW. The solution is to use a rolling 15 minute window that starts over every minute. In any case, I have never known of a truly instantaneous peak demand billing.