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Re: oil dielectric
Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>" <davep-at-quik-dot-com>
> Hi Dave,
>> Having done some thermal design & studied transformer
>> design, I'd find that surprising. Oil, in a conventional
>> transformer functions in two ways:
>> Electrical Insulation
>> The thermal effect is by being heated by hot spots
>> (core eddy currents, coil resistance losses), then flowing,
>> by natural convection, or, less commonly, pumped
>> circulation, to a cooler spot where it can dump heat.
>> Sometimes the cool spot is aided by heat sinks ('fins').
>> cf any text on transformer design.
> Does this also apply to air core transformers with no ferromagnetic
No core heating. The rest applies.
> The coil resistance losses are minimal in a resonant coil.
I can't see why. Resonance implies high currents. Arcs
demonstrate high currents. Resistance losses are
utterly insensitive to frequency.
> From a practical standpoint, I've run my secondary for long
>periods of time
Air is an effective cooler. Or is this the oil filled one?
> and there is no noticeable heating in any part of the circuit.
What power levels?
Typical _Tesla_ transformers have large exposed areas
(as compared to a conventional transformer), so cool
themselves well.) And the power in the secondary is
a deal lower than that in the primary. cf the
> I say nervous because a sealed container, can, if heated,
> even by a fault, 'rapidly disassemble': Explode.
> Unlikely, probably, here, but possible. (Power
> transformers can and have exploded, when not vented.)
> You're talking the difference between an iron core transformer
>and an air core transformer in resonance.
I'm talking an assembly described by the builder as sealed.
> Further, the current flowing through the wires of an air core
>transformer is a milliamp or less.
perhaps THIS air core transformer.
> You can't heat the wires (hence the oil) without appreciable
Tesla coil systems involve high voltages and arcs/sparks.
arcs and sparks ignite things.
>>I like this coil so much I'm going to wind another one. This time
>>I'll use finer wire if I can get some.
> In general, fine wire increases losses, limiting power,
> and increases heating...
.and losses... limiting voltages...
> In general, this is correct. With this type of coil, it doesn't
> appear to be the case. The better the insulation of the coil,
>the higher the frequency I can reach.
Frequency is generally set by inductance. Finer, longer
wire tends to more inductance, lower frequency.
> The higher the frequency, the higher the voltage
I can't think why.
> (in general.) The higher the voltage, the lesser the current.
Until the arcs/streamers start.
> The lesser the current, the smaller the wire can be.
The larger the losses, the lower the efficiency.
> The smaller the wire, the higher the inductance
the lower the frequency.
> and voltage (for the same length of windings.)
More wire, means more inductance, or a smaller winding.
Smaller winding means lower voltages.
> The higher the voltage, the lesser the current, etc.
> And of course, the coil will be operated at resonance, so the
>impedance will be minimum.
Minimum impedance maximizes current...
> I don't see how covering a coil with oil can be a problem.
Oil is ignitable, notably by electric arc/spark.
The description was of oil 'in the center',
rather than 'covering'.
> If anything, it is a great help, and this is attested to by
>Tesla in several references.
Indeed. Tho he did not use it in the largest coils.
> (His book mentions the importance of oil covered secondaries.)
He wrote several.