[R-390] Line Voltage Survey

[Bill Hawkins]

Worked at a blasting cap plant in the early sixties. The plant had
a 13.7 KV feed that was transformed to 440 V ungrounded delta. That
way a ground fault couldn't make something hot and cause an explosion.
Easy to see that you had a ground fault, too. Three low wattage
bulbs in a Y to ground controlled static build-up and indicated
a fault.

Things were spread out, as you might imagine. There are tables for
the distance separating buildings depending on the explosive, to
prevent propagation of an explosion in one building to others.

So the lab where government ordnance was developed and tested was
over 1500 feet from the feed point, and 400 feet from the last 440
to 110/220 transformer. I learned that the number for good line
regulation was one foot per volt. The voltage at the lab ran 100
to 130, which was not good for test equipment or environmental
chambers.

It fell to me as the junior engineer to do something about it. I
found that GR made a motor-driven Variac regulator that would do the
job, and designed a shed for it (keeping sparks away from powders)
and the feed lines to the lab. Somebody else decided that we couldn't
run 440 to the shed.

Voltage here in Bloomington, MN, now runs 120, was closer to 125
ten years ago. Higher voltage allows motors to draw less current
(less drop in the distribution system), but resistive lamps draw
more current - that's why power companies like CFLs.

The thing that messes up the wave shape is overloaded transformers
that saturate at the peaks.

Bill Hawkins


-----Original Message-----
From: Pete Lancashire
Sent: Monday, October 31, 2011 5:25 PM

there are also motor driven units. I have one of the little newer
Chinese ones. There are the older GR's, and the one I use to use about
20 years ago. I use to live i a rural area where at the end of the
line was a farm. I would get some pretty nasty voltage fluctuations
and the the sine wave shape was at times a memory. I had a servo motor
driven 30/30/30 AM Superior 3 ph'er ganged together plus a 100A  OneAC
filter transformer. When the farm was not doing anything voltage would
be up to
128V and the wave was pretty much a sine wave. Voltage would drop to
as low as 120V.

-pete