[BC] AC Voltage Drop

[Ron Nott]

You may be surprised to learn that power plants are exempt from the National 
Electric Code.  The Arizona Public Service Co. plant known as Four Corners 
(2,000+ MW) was constructed between 1961 and 1970 (5 units) and some of the 
slovenly wiring within it would amaze and scare you.  It was good when new, 
but over the years electricians do insane things.  Much of the wiring is in 
tunnels below the plant which have filled with water from boiler condenser 
leaks, etc.  When necessary, we used a large pump to get most of the water 
out after which the electricians had to go into them while circuits carrying 
4160 volts were still energized (not me!  I was the engineer looking down 
into the manhole).

Another factor is that the ultimate loads of the plant (from 300 to 500 
miles away, e.g. Las Vegas & Phoenix) are not purely resistive.  So the 
lines have SWR which is referred to in VARs and megaVARs (volt-amperes 
reactive).  Because the distant loads are mostly inductive due to 
transformers and motors, huge capacitor banks are located in the switchyard 
to compensate for this.  Their values can be remotely varied from the 
control room for minimum VARs to the alternators.  Back in the 80s, the cap 
bank for the 500 KV line going to Las Vegas failed and many caps burned up. 
The light from this was so intense it caused actual pain to our eyes.

Finally, voltage regulators such as the buck-boost type can cause all kinds 
of distortion to the wave form.  This can reflect back down the line for 
miles resulting in all manner of junk power on the lines.
ron
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----- Original Message ----- 
From: <RichardBJohnson at comcast.net>

>
> Utility companies don’t care about any codes including local codes. That’s 
> why they can use 12.5 kV feeds using insulators designed for the original 
> 2300 V around-town distribution. When my service was “upgraded” from a 60 
> A 4-fuse service to a 200A CB box, the drop from the pole was not changed. 
> It remains #8 phosphor bronze, which gets hot when my clothes drier runs. 
> The utility company refuses to change it claiming everything is 
> “temporary,” and will be redone in a year to two. The word, “temporary” is 
> used by utility companies as a license to do anything they want. Do a 
> Google search for “Unitil” and see what I mean.
>
> Any three-phase feed to your facility needs to be a closed delta or closed 
> wye. The wye is useful because you don’t need to make your own 120 V using 
> dry-type transformers. Delta is nice because it provides good balance. 
> However, you need to use a transformer to generate 120/240, which puts 
> your entire LV panel on one incoming leg.