Vacuum and air melting coils and power supply differences

Dear All,
Are the vacuum melting coil design and power supply parameters are different than air melting systems ?
Briefly I would place melting crucible with its coil under vacuum chamber
10^-2mbar, power supply is a 10 khz 20 kw inductotherm.
The guy from inductotherm told me that it will not work, because power supply and coil design of vacuum melting systems are different than air melting systems. so i need to change everything
Can someone have a comment to do on this subject. what is the difference ? what should be done to make it works under vacuum ?
Thanks
Pierre
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One big difference between vacuum and airmelt is the voltage. If you use an airmelt power supply for "vacuum" you will get arcing or corona formation. You need a lower voltage for "vacuum" and better coil insulation. Cooling can also be more important since there is very little convection in vacuum melting.
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Thanks for information,
I saw some vacuum melting coil working at 250 to 400 V from ALD which is similar to air melt coil voltage.
In this case may be the voltage will be suitable with correct insulation. Do you have knowledge about the materials for coil insulation.
I will try to learn more about the corona formation what is it shortly ?
Regards Pierre

an
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The power supply is lower voltage (higher amps) and has insulation wrapped around the coil windings before the refractory. Alan Black San Martin Casting & Foundry www.sanmartin.com

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