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HV at very LOW freq. Tesla Coil
From: Jim Lux[SMTP:jimlux-at-earthlink-dot-net]
Sent: Tuesday, September 23, 1997 6:45 PM
To: Tesla List
Subject: Re: HV at very LOW freq. Tesla Coil
The system to which you refer is almost certainly what is known as a
"resonance transformer" originally developed by Charlton at the GE labs in
Schenectady. It was part of a 1 MEV xray system and consisted of 125 thin
pancake coils stacked up with the xray beam line down the center. These
coils were resonated at 180 Hz by parallel capacitors, and coupled to a
primary winding at the bottom, excited by a frequency tripler system that
took 3 phase power at 60 Hz that made 180 Hz. For the whole transformer,
the secondary L is about 15,000 H and C is about 50 pF.
The entire contraption was inside a steel tank some 3 ft in diamter and 4
ft long pressurized with Freon at 60 psi. Typically, this thing consumed
anywhere from 15 to 30 kVA at a power of 2 to 12 kW (obviously, the power
factor wasn't all that great)
To loosely quote from my reference: Craggs & Meek, "High Voltage Laboratory
Technique", pages 93 through 101
The advantages of the resonant transformer system are:
1) The absence of the iron core saves the space which would normally be
required for insulation between the windings and the core.
2) The waveform in the circuit is always sinusoidal and the oissilatory
current in the ht winding is so large, ie. 55 mA rms at 1,000 kV peak, that
the rated half wave full load current of 3 mA (of the x ray tube) doesn't
produce any measurable difference between useful and inverse voltages.
3) The slow build up of coltage overa few cycles after switching on
prevents the production of unduly large voltage surges.
4) The careful design of the coil stack and it's subdivison into so many
units, the spacing between which is carefully controlled, gives a very
uniform voltage gradient along the stack.
Craggs & Meek also talk about Tesla coils (i.e. resonant lines with an open
circuit at one end) in the next section. They give a taxonomy of various
excitation configurations and secondary configurations, including some data
on systems by Breit and Tuve, etc. (That's the 5MV coil running in a tank
of oil)