Power System

Cycle average...

Normally 30 minutes for metering.

That is what your utility has elected to use for a time base.

See [for instance]:

http://engineeringarticle.blogspot.co.il/2011/12/calculation-of-electrical-maximum.html

I do not know what circumstance may apply in your local area.

Round here, the Grid operator normally changes (if necessary) the number and type of generators needed to meet the expected load every 15 minutes.

Thus by experience and custom and practice, I think they may consider that those consumers who go over the maximum they have promised for over 15 minutes should be charged for complicating the already difficult load prediction and economic operation decisions needed to "dispatch" the generators.

Believe it or not, we got in trouble for reducing load too quickly.

An emergency situation and we killed all power to a plant. 13MW of load just vanished causing the grid to speed up. It just shows how fine the balancing act is with supply and demand when you consider the entire UK grid sped up.

http://www.dynamicdemand.co.uk/grid.htm

At this moment in time we are running at 50.01Hz

There are some interesting demand management strategies that can be done by monitoring grid frequency, and shedding non-essential loads when the frequency falls. For instance, simple circuit boards can monitor line frequency and shut off loads such as water heaters or even air conditioning. Some slight staggering is desirable to keep from energizing/deenergizing too many items all at once.

"Demand Management" is just one more reason we should be expanding the number and location of pumped storage facilities?

There might well be some good opportunities for that, especially in mountainous topography.

Not within 25 miles of the city of Ely, there isn't! The land is as flat as the proverbial pancake.

Supposedly the State of Kansas has been compared to a typical pancake, and in terms of relative size comes out even flatter.

<...the State of Kansas...> Very little of it is less than 6ft/1m above sea level.

I couldn't agree more, they help keep a steady base load from the big stations.

No doubt that will annoy the tree huggers.

Should not annoy the tree huggers - where else will they put the random power from solar and wind until it is dark or windless? Also an excuse for higher tariffs and may be good for water birds and salmon.

The tree huggers get upset because wind farms chop up birds and turbines mince fish.

I got in to quite an argument with a vegan about her boots, I shouldn't be wearing leather. The argument ended when I went in to the manufacturing of her plastic boots.
It must be very hard and very expensive being green

Somebody rolled some dice once upon a time.

It varies by utility. Here in the US it can be anywhere from 15 to 30 minutes.

They had to pick a demand window length; instantaneous is too short, the system would immediately respond to every motor being started or transformer being energized. So 15 minutes was basically picked as the SHORTEST time frame from which to chose because system demand would potentially affect equipment heating, and 30 minutes is basically the longest time in which it WOULDN'T. But every utility selects their equipment based on different criteria as per a cost-benefit analysis, so their demand window is based on that.

RESPECTED SIR,

Thank you for explaining the concept.

Excuse me sir i am confused that for a window lengh of

30 minutes. if if there is a load 400kw for 20 minutes and

300 kw for 30 minutes my MD IS 300KW , can my generator

of 300kw will stand to support 400 kw load.

As i know MD decides capacity of generator.

It is not really a matter of generators. At the distribution level of supply, transformers and cables are more tolerant of overload than generators, but 15 to 30 minutes becomes significant.

Generators on large national systems generally have no overload capacity - they run at baseload.

A limited number of generators run at part load to cover sudden trip-off of large generators or to fine control frequency. If a large station e.g. 2000 MW trips, then a fall of frequency naturally reduces load.

In addition, underfrequency may trigger voltage reductions or shedding of loads to bring load and generation into balance.

The capacity of large (say >10 MW) generators to increase output quickly is limited - about 90 to 100% load in 10 seconds is practical. The energy storage (mechanical inertia) in electric power systems is limited - 1% sudden generation loss (or load increase) from 100% causes 1% frequency drop in 10 seconds (and onward) unless corrective action occurs.

Despite the fact that every Tom, Dick, Harry (and Magdumshirish) expects to be able to turn on or off his light, shower or air conditioner whenever he likes, power systems manage to cope - management like maximum demand penalties on large users or reduced charge per kW if a consumer agrees he can be cut off as a load shed are part of the process.

A simple telephone call to the utility supplier will answer that one.

You have to look back at the history and design of demand meters, as well as the rate structures (tariffs) that customers are billed on. When first developed in the late 1800's, a demand meter readout looked like an analog swept needle meter with two pointers, the driven one and the follower. The follower was simply pushed along by the driver needle, always indicated the highest reading of the driver, and was reset to the current reading by the meter reader.

In those early days the driver needle was moved by an analog meter movement known as a "Hot Wire Ammeter", basically a piece of wire whose length changed due to the amount of current passing through it. The amount of time necessary for the meter movement to achieve the correct average steady state reading (because of the high thermal lag) was chosen as 15 minutes.

As time went on induction disk meters evolved, along with whole bunch of clever electromechanical contrivances to ensure that the readings on the newer meters were still backwards compatible with the installed base of older ones, a situation that still exists today.

Whatever the technology, you must check with your supplier to know exactly what and how you are being metered for; especially the width of the sliding window and whether it is peak or average during that window.