130kW Coil -- Oh No!
From: Chuck Curran [SMTP:ccurran-at-execpc-dot-com]
Sent: Tuesday, February 03, 1998 6:47 PM
To: Tesla List
Subject: Re: 130kW Coil -- Oh No!
Your progress to date has been impressive and very interesting! I really
hope that some of this might be on video and made available to those who
can't make the trip to visit your test site first hand. I have just started
wondering about a source for you that can provide a good flak jacket, sounds
like those porcelain fragments must have caught your attention. Best of
luck on your testing as it continues and I hope El Nino stays out to sea.
>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!
>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.