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In article <1262@island.uu.net> rich@island.uu.net (Rich Fanning) asks:

>Do the utility meters on the average house measure true watts or only
>current?

True watt-hours.


>I have always assumed they measured watts, but when I think of it now, why
>shouldn't the utility charge by the amp? It seems as if the utility
>charging for "amp-hours", rather than for watt-hours, would be in THEIR best
>interest.

Why?  A watt is only the rate of energy usage and the utility is in the
energy business.  Watt-hours are energy.


>Utilities provide financial incentives for raising the power factor of the
>load of industrial companies.  

Not really -- they provide financial penalties for not drawing energy at a
high power factor.


>I have always assumed that the industries get charged for "amp-hours".
>
>Do household and industrial customers get metered differently in this regard?

Industrial and commercial customers large enough or with significant
reactive loads get metered on three bases:  One meter measures the energy
usage, just like it does for a residence.  Another meter measures average
power factor and the demand (peak usage usually averaged over a 15minute
period).  Both of these numbers are then used to correct (i.e., increase)
the base rate to determine the final bill.

Rationale:

Drawing power at low power factors means that the feeder losses are higher
for the same energy delivery (lower transmission efficiency) and that the
both the feeders and transformers have to be larger.

Having high peak demands means that the load is variable -- the utility must
size its equipment to provide the maximum demand (a capital expense), but
the equipment is under-utilized.  Consider three customers, one having
10,000w of load connected all of the time, another having 30,000w connected
for an eigth-hour shift each day, the third having an electric furnace
drawing 300,000w for one 48-minute period each day.  All use the same
energy -- should they pay the same for service?

Residential demand is more steady and predictable, and the power factor is
close to unity.  More important, all customers are the same, so the rates
can be well based on the cost to supply the energy.

Rich
-- 
Hitting baseballs and writing software are two professions where you can
become a millionare with a 75% performance failure rate.
							 rsd@sei.cmu.edu
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