(57) A striking circuit of the pilot arc for plasma arc torches (25), comprising a low
power impulse generator (27), suitable for striking the pilot arc between the cathode
(28) and auxiliary anode (29), which is positioned inside the torch body (25) and
kept separate from the direct current generator (20), which feeds both the pilot arc
and the main arc, until the arc has been permanently struck; the separation of the
part of the circuit in which the low power impulses are present is obtained by using
an insulated inductor (37), with a ferrite separation nucleus between the feeder (21)
and the torch body (25), and a discharger (41), situated in series with the impulse
generator (27), associated with an oscillator and an amplifier, so as to obtain, between
the high voltage outlet of the impulse generator (27) and the earth (31), high voltage
impulses, having a frequency of about 250 kHz. The electromagnetic emissions are thus
reduced during the functioning of the torch (25) and the whole system is more compact,
reliable and functional, with respect to the known art.
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