[SGVLUG] Calling the brightest of cal tech and other nerds!

[David Lawyer]

> > On Sat, Dec 23, 2006 at 12:51:02PM -0800, Michael Rubel wrote:
> > >There is a Caltech steam tunnel which runs under California Blvd., just 
> > >west of Wilson.  In addition to steam, it carries electrical power to the 
> > >campus from the physical plant building, which is near the gym.  I've seen 
> > >the conduits myself.  If I understand correctly, they have a generating 
> > >capacity of about 15 MW.  Not sure how much of that runs to campus, but 
> > >anything close to 15 MW would create quite a magnetic field.  :)
> > 
On ? at ?, ? wrote:
> > ...although, come to think of it, the net current should be zero if they 
> > form a circuit, hence no magnetic field... perhaps the leaks to ground on 
> > campus are significant.
> 
On Sat, Dec 23, 2006 at 01:40:53PM -0800, Dustin Laurence wrote:
> More significant would be that surely all that power would be delivered
> as 3-phase, isn't it?  3-phase should sum to zero current always, I
> think.  Perhaps that is what you meant and I just caught up.

If they use just a 3-conductor cable, then the 3 instantaneous
currents may not sum to zero if the system is grounded.  The sum of
the 3 currents in the cable plus the ground current should sum to
zero however.

So suppose the 3-phase input to Caltech first goes into a Y connected
transformer primary with the common point grounded.  Then since the
secondary will supply low voltage single phase (as well as 3 phase ??)
if the single phase loads are not the same there will be return
current via the ground.  Provided there is another ground at the
location of the power Co. supply transformer located perhaps a few
blocks away from Caltech.

I observed (a few years ago) the high magnetic fields extending W on
California starting at Wilson.  These fields extended for a few
blocks thru residential areas.

When I was measuring fields, I checked out a residence where someone I
knew lived next to a power Co. substation.  The magnetic field at his
front door was several times the supposed safe level.  And there were
no overhead wires so the field must have been coming from underground.
So there could be perhaps about 1000 public locations in Pasadena
(streets, sidewalks, etc) where the magnetic fields are too high.
Since there aren't laws regulating this, it's hard to fix the
problems.  Since the population of Pasadena is only 0.05% of national
population, there might be about 2 million locations in the US that need
correcting.  Even fixing these would still leave the problem of
magnetic fields from overhead power lines.  So it's such a huge
problem (but easy to fix --just remove some of the grounding) that I
decided not to get involved with it.

			David Lawyer