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130kW Coil -- Oh No!
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From: Thornton, Russ #CSR2000 [SMTP:ThorntoR-at-rc.pafb.af.mil]
Sent: Tuesday, February 03, 1998 7:04 AM
To: 'Tesla List'
Subject: RE: 130kW Coil -- Oh No!
Hi Greg,
Sounds like positive progress is being made. May I make a, perhaps
naive, suggestion on the rotary gap. Would it be possible to take the
stationary and moving electrodes and place each in separate molds then
filled with a material like Lucite. Then machined down so that they are
essentially just cylinders and when rotated against each other will,
aerodynamically, appear like two flat disks. I am ignoring the
centrifugal forces and heat effects for simplicity but it was just a
thought. What do you think?
PS My trip to SF keeps slipping. Now looks to be in March. Hope to see
this coil in action.
Russ Thornton
CSR 2040,
Building 989, Rm. A1-N20
Phone: (407) 494-6430
Email: thorntor-at-rc.pafb.af.mil
>----------
>From: Tesla List[SMTP:tesla-at-pupman-dot-com]
>Sent: Tuesday, February 03, 1998 12:22 AM
>To: 'Tesla List'
>Subject: 130kW Coil -- Oh No!
>
>
>----------
>From: Greg Leyh [SMTP:lod-at-pacbell-dot-net]
>Sent: Sunday, February 01, 1998 4:47 PM
>To: Tesla List
>Subject: 130kW Coil -- Oh No!
>
>Hi All,
>
>The final development and testing efforts of the coil during the
>last few weeks have brought considerable progress, and a few setbacks
>as well. Most of the major problems so far have had to do with the
>dynamics of the rotary gap system.
>
>The latest setback on the rotary gap system has to do with
>the sharp pulsations of air pressure exerted on the stationary
>electrode holders by the quickly moving rotating electrodes. As the
>moving electrode passes the stationary one (at 420 km/h with a
>clearance of 0.9mm), the shock wave tends to hammer the stationary
>electrode supports, which are supported by an array of large porcelain
>insulators. These shockwaves are strong enough even at half speed
>that hearing protection is required anywhere near the gap.
>Although the porcelain insulators are quite massive, they appear to
>be susceptable to vibrational fatigue, and during power tests
>last Friday one of these insulators failed completely, resulting in
>a rather impressive spray of porcelain shards, ejected out of the
>vault through the access door. T. Leonard was far enough away, and
>I was behind my favorite steel plate, so no one caught any action.
>
>On a positive note -- at the time of the insulator failure, the coil
>was generating 22 ft long discharges into the air from the top sphere,
>with the mains at one-fourth of full power! Electrically speaking
>at least, the coil appears to be doing quite well.
>I finally got the Fluke ScopeMeter to work with the coil energized,
>and grabbed some waveforms just before the rotary exploded.
>The measured waveforms on the charging reactor and HV circuitry
>have come out fairly close to the projected values from PSPICE,
>with the exception that PSPICE predicted more ringing on the diode
>stacks at the end of the charging cycle than was actually observed
>with the HV scope probe. (those pesky ideal components)
>
>* The charging reactor waveforms indicate that the coil is _not_
>in fact drawing 2.5 times the normal amount of power (as the 60Hz
>CT's on the mains indicate). The current waveform measured on the
>charging reactor is a haversine 4.8A tall by 3msec long. PSPICE
>predicted a haversine 4.6A tall by 2.4msec long. With a HVDC of
>12,700V and a rep rate of 200PPS, this gives a power usage of 32kW,
>where the CT's on the mains say 120A per 400V leg!
>
>Does anyone have experience with standard 5A FS panel meters and
>300:5 CT's? How sensitive are they to non-sinusoidal waveforms?
>
>Also, we were able to bring the primary voltage to 55kV in the
>single-shot mode (~1PPS), at which point the top sphere issues
>7' to 8' streamers, and the RF current at the base of the coil
>is 60A pk.
>
>Our plan for the electrode support insulators involves replacing
>all 8 of the porcelain posts with 3.5" x 6" x 27" solid slabs of G-10.
>The material is already in hand; however the machining efforts,
>modifications to the rotary gap frame and testing will probably
>set our schedule back another two weeks.
>
>I'll report on our progress again when the G-10 is installed.
>
>
>-GL
>
>
>