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Re: 130kW Coil Update
From: Greg Leyh[SMTP:lod-at-pacbell-dot-net]
Sent: Friday, November 28, 1997 5:04 AM
To: Tesla List
Subject: 130kW Coil Update
All,
The construction efforts with the 4-axle crane went well, with
negligible loss of life or property. The structure became
surprisingly tall to all of us once it was assembled, and the
view from inside the top electrode is quite spectacular...
I can see my house, which is about 7 mi from the Navy Base!
Our schedule for operating the coil at full power has slipped by
a couple weeks, due to several factors:
WEATHER - El Nino has dealt us quite a bit of rain in the past
several weeks, making much of the outdoor work dificult, or
impossible. Normally, this time of the year is much drier.
And although the coil is designed to be outdoors for its entire life,
the final construction work for the equipment that goes inside of the
vault requires drier conditions.
Rotary Gap - The rotary gap armatures (4 total) appear to require
more than 15HP at 3000RPM, even with the aerodynamic shrouding in
place. The shrouding is designed to spoil the streamwise and
spanwise vortices that stem from the electrode tips, however the
shrouds themselves seem to have a bit of boundary layer friction.
Without the shrouding though, the spinning electrodes would have
developed about 160 ft-lb of shaft torque at 3000RPM, requiring
over 90HP of motive power!
Solution - bigger motor. We are currently modifying the lower
framework of the gap to accommodate a Westinghouse 30HP, 500VDC
electric motor. The anticipated load at this point is about
22HP, so the motor should have a comfortable operating margin.
I've also had to change over from a variable freq drive (for the
old 3PH 15HP induction motor) to an SCR phase controlled scheme
for the new motor. This also eliminates the microcontroller and
fragile CMOS circuitry present in the fancy VFD unit, which I have
worried incessantly about since the beginning. The coarser features
of the SCR's (1000V, 300A pucks x3PH) should prove to be far more
robust in this hostile EM environment. The rest of the control
circuitry is iron and copper, relay logic for the most part.
Everything else is going well, and the finished tower with top
electrode weighs in at 37.92 kHz. (I had calc'd 38kHz; lucky guess?)
More construction pix are on the way to Chip, further schedule
info forthcoming, as weather and rotary gap improve.
-GL