Abstract: An arc welding and arc plasma cutting machine having a dc high-voltage generator is provided. The dc high-voltage generator includes a first dc power source, a second dc power source, an one-way rectifier, and a voltage clamping circuit. The first dc power source applies a dc voltage through the one-way rectifier across an electrode and a work piece. The second dc power source is connected across the first dc power source and superimposes a dc voltage on the power produced by the first dc power source for developing an arc discharge across the electrode and the work piece. The voltage clamping circuit connected in parallel to the one-way rectifier to restrict a high-voltage applied to the one-way rectifier below a given level for protecting the one-way rectifier from breakage due to application of the high-voltage.

Abstract: In an arc welding machine and a plasma cutting machine, by connecting the output of a second DC power supply unit to a circuit fed by a first power supply unit, a DC high voltage from the second DC power supply unit is applied, during start, across an electrode and a base metal which are not in contact with each other, so that radiation noise can be reduced considerably and leakage of high frequency power from an extension cable can be eliminated to attain steady arc start.

Abstract: In an arc welding machine and a plasma cutting machine, by connecting the output of a second DC power supply unit to a circuit fed by a first power supply unit, a DC high voltage from the second DC power supply unit is applied, during start, across an electrode and a base metal which are not in contact with each other, so that radiation noise can be reduced considerably and leakage of high frequency power from an extension cable can be eliminated to attain steady arc start.

Abstract: An activated sludge treatment method of waste water which comprises (a) the step of micronizing as far as possible the sludge in the waste water containing the BOD component to a degree not to have the cells of the microorganisms therein broken or destroyed and adsorbing the BOD component to the micronized sludge, and (b) the step of oxidizing the BOD component adsorbed to the sludge by blowing in an oxygen-containing gas and flocculating the sludge. By this method, the treatment of waste water is accomplished with a shortened residence time of the waste water in an installation for the treatment and with the production of excess sludge in a considerably reduced amount.