Importance

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Abstract

A plasma-arc power supply apparatus includes a main electrode terminal, a nozzle electrode terminal and a workpiece terminal which are respectively coupled to a main electrode, a nozzle electrode and a workpiece of a plasma-arc apparatus. A DC power supply has its first output terminal coupled to the main electrode terminal, and a second output terminal. A pilot arc path is coupled between the second output terminal and the nozzle electrode terminal. A switch is connected in the pilot arc path. A plasma-arc path is coupled between the second output terminal and the workpiece terminal. A current detector has its first input coupled to the plasma-arc path, has its second input coupled to the pilot arc path, and produce a detection signal corresponding to the values of pilot arc and plasma-arc currents in the pilot arc and and plasma-arc paths, respectively. When the pilot arc current is flowing, a control unit closes the switch and controls current from the DC power supply in accordance with the difference between detection signal and a predetermined pilot arc reference signal, and when the plasma-arc current is flowing, the control unit opens the switch and controls current from the DC power supply in accordance with the difference between the detection signal and a predetermined plasma-arc signal.

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First Claim