[R-390] Voltage Reduction Scheme

[mikea]

On Sun, Feb 20, 2011 at 07:03:44PM -0600, Tisha Hayes wrote:
> Quote: "The addition of an external bucking transformer comes to mind as a
> wise thing with the power companies pushing line voltages up into the near
> 130VAC range to keep from replacing all that wire to carry the load."
> 
> You will see in the immediate future, electrical utilities being pressured
> to optimize their systems and to place their tap-changers on an active
> control system for voltage reduction. Many of the utilities that I am
> working with today are trying to actively manage their voltage distribution
> schemes. The thought once was to figure out the maximum sag that would be
> present on a distribution line and to set the substation tap changers to a
> semi-fixed position to avoid a brownout condition. Now the emphasis is on
> finer control of distribution voltages so you will see less of a min/max
> change in line voltages.

With hybrid or battery-only vehicles becoming more common, loads from
charging them are now beginning to be examined by utilities, and they
don't like what they see. There's an article on p. 23 of the latest ECN
(http://www.ecnmag.com/) titled "Challenges of charging plug-in hybrid
electric vehicles" that is worth reading. The author says that every
vehicle being charged at Level-2 specs adds a load equivalent to 1 to 3
houses for the duration of the charge. That's going to heat up a pole pig
PDQ.

> The same thing is true of capacitor banks to manage reactive power. Many
> were on a TOD (time of day) setting, now they are being moved to active
> control tied into the power factor at the distribution substation.
> Transmission and generation facilities want the distribution (your local
> electric utility) to fit into a narrower range of power-factor values with
> penalties if it is too far off.

I've seen the effects of our local powerco changing transformer taps and/or
doing power-factor correction changes during the day. That was a major
reason for our getting a 100 KW UPS for our datacenter at work. Before
the UPS, every little glitch would knock the mainframe and some number of
servers right down. After the UPS, I get an E-mail message when the powerco
decides to do the nasty, but things stay up.

> I have been involved in a few analyses of distribution system losses. In
> some cases they can be as high as 8-12%. For a utility to reduce it down to
> 4-6% can save them millions of dollars in a year. Moving to active control
> ends up being something that has a ROI (return on investment) of 2-3 years.
> That also goes back to feeder monitoring so when they do need to make line
> change-outs on the distribution system they are working on circuits with the
> greatest % of losses and the utility can see the greatest bang for the buck.

Car charging is going to make for some really interesting copper losses. 

All of this, of course, will make for interesting voltage excursions at the
wall socket if it isn't kept well under control. Maybe a 3TF7 or other
voltage regulator will turn out to be useful. ;=)

-- 
Mike Andrews, W5EGO
mikea at mikea.ath.cx
Tired old sysadmin