抄録
The use of AC arc plasma heating involves a problem that the arc plasma is apt to be unstable at current zero. This paper describes the stability of the transferred type AC arc plasma with the arc current increased and the effect of superimposing a pulse current on an AC current only at each current zero point on the arc plasma stability. The argon arc plasma was generated in the air between the tungsten electrode in the plasma torch and the copper counter electrode. The distance between the two electrodes was 40mm. The AC power supply was single phase and the voltage was 180-330Vrms, the current, 100-500Arms, the frequency, 50Hz. The superimposed pulse current was 5-15A, the pulse voltage, 100V, the pulse rise/fall time, 2, μs, the pulse width, 300, μs. Main results are as follows. As the arc current increased (100→500A), the re-ignition voltage decreased (290→240V), and the required power supply voltage for the arc plasma to stabilize was decreased (330→270Vrms), and through the investigation it was guessed that the required voltage would not decrease so much even if the current increased more than 500A. The superimposing pulse current caused the required power supply voltage to decrease farther (270→180Vrms). As the arc current increased and a pulse current was superimposed at each current zero point, the temperature and the electric conductivity between electrodes at current zero point would increase and the transient recovery voltage between electrodes would rise rapidly. Therefore, the required energy for the arc plasma to re-ignite and stabilize would decrease and the required power supply voltage would decrease.
