From rLab

Plans for developing a 25Kw+ induction furnace

Looking at a 3-phase powered system using IGBTs supplied by Tom, they're rated 600A@600V which would theoretically allow a power of around 300Kw but we can't pull anything like in practice. They power supply for the building would be limited to about 40A per phase which would result in a total power of around 30Kw, allowing for 5Kw of losses then that would give us something around 25Kw of usable power.

Have to find out from the IGBTs what their switching frequency range is but it seems that most common units in this power range operate in the range of 30-100KHz. The units from Tom come with some driver circuitry, we'll have to asses what that is and what it's ratings are.

A typical crucible might be 80mm diameter and about 150mm long, Assuming a 10mm copper pipe secondary with a 2mm turn spacing that would yield something around 12 turns, which would give a coil inductance of around 7uH. At frequencies of 30kHz and 100kHz that would result in load capacitance of 4uF and 0.36uF respectively. Assuming we wanted to target something around mid-range on that, let's say 2uF as the load capacitor.

That would get something around 5 Ohm as the characteristic impedance, the IGBT drive stage will be doing 340V approx so 25Kw would give a current of 74A on the primary for an impedance of around 3.2Ohm so we'll actually need a step UP transformer to get good matching!

Typical IGBTs of this class seem to require around 10mJ on the gate for each cycle, so at a maximum of 100kHz, that would result in a dissipation of 1Kw in driving the gate of each IGBT. The forward voltage drop on the IGBT when fully saturated seems to be around 0.9V at the currents we need, so that would result in an additional 70W or so in conduction for each of the IGBTs. That would be around 1070W dissipated in each IGBT, for a total of around 4.3Kw, which fits nicely with the prediction above.

Parts needed

Part Spec Source
Mains plug 5-pole 63A round pin ??
Mains cable 5-core 63A ??
Rectifier 3-phase 63A ??
DC Smoothing cap 10,000uF 450V ??
Current sensors ?? ??
Switching modules 600V 600A IGBT Tom
Matching transformer ?? ??
Resonant Capacitor ?uF conduction-cooled ??
Drive coil 10mm copper pipe ??
Cooling radiator Car type Tom
Cooling fan 12V car type ??
Coolant pump ?? ??