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From: jgk@osc.COM (Joe Keane)
Newsgroups: sci.electronics
Subject: Re: Watt Hour Meters
Summary: Watch those KVARs...
Keywords: capacitor banks, reactive power
Message-ID: <1847@osc.COM>
Date: 12 Jan 90 21:11:45 GMT
References: <1990Jan11.015852.7031@phri.nyu.edu> <5606@ae.sei.cmu.edu> <1115@rsiatl.UUCP> <1458@umigw.MIAMI.EDU>
Reply-To: jgk@osc.COM (Joe Keane)
Distribution: usa
Organization: Object Sciences Corp., Menlo Park, CA
Lines: 35

My two cents...

Yes, a typical electronic power supply will often behave like a slightly
capacitive load.  A full-wave rectifier conducts twice a cycle, with peak
current a bit before the peak voltage.  Of course, you have to consider the
magnetizing inductance of the power transformer, plus those nasty harmonics.

A _good_ switching power supply looks like a resistive load, the resistance
slowly changing in response to changes in output current and input voltage.

Power factor generally isn't a big problem in residential areas.  The
utilities often have capacitor banks (switched or unswitched) on feeders, but
these are more for voltage regulation than balancing reactive power.  The
voltage on a line with a capacitor bank will be higher than one without, and
will have less voltage fluctuation.

For industrial loads it's a different story.  The utility charges for power
factor, so it's often in the customer's best interest to buy a capacitor bank.

Some industrial loads are notoriously badly behaved.  Think about a rock
crusher or an electric arc furnace.  The classic `bad' load is a strip-mining
shovel.  If the operator screws up and stalls the motor, it draws a ridiculous
amount of lagging KVARs and very little real power.  Plus it's usually in the
middle of nowhere, with no other loads around.  What to do?

In article <1990Jan11.015852.7031@phri.nyu.edu> Roy Smith writes:
>	Anybody know what the total average power factor on the power grid
>is?  I would imagine it must be massively lagging, what with motors and
>transformers being most of the load.  I can't think of any typical capacitive
>loads on the power grid.  

How about charging current?  A long transmission line is a sizable capacitor,
and you're charging it up to a couple hundred kilovolts 120 times per second.
This won't supply all the leading KVARs you need, but it definitely needs to
be taken into account.