Direct-current arc welder

Claim 2

A direct-current arc welder comprising a main transformer provided with one set of Primary windings connected to a threephase AC power source and two sets of three-phase secondary windings having a phase difference of 60* from each other, an interphase transformer connected between neutral points of said two sets of secondary windings and provided with a center tap, a group of controlled rectifier elements each having its anode side connected to one terminal of said each secondary winding, means to connect the cathode side of said each controlled rectifier to one end of a welding circuit including an electrode and a parent metal, means to connect said center tap of said interphase transformer to the other end of said welding circuit, a reactor incorporated into said welding circuit, a controlling device for controlling the conduction angle of said controlled rectifier elements thereby to adjust the electric power supplied to said welding circuit, and non-controlled rectifier elements each connected across the anode and cathode of each one of said group of controlled rectifier elements through a current-limiting element , said controlled rectifier elements and said noncontrolled rectifier elements being connected in the same direction, said current-limiting element being of such a value that the DC power necessary to maintain the arc is supplied to said welding circuit mainly through said controlled rectifier elements, while the DC power required to regenerate the arc after extinction is supplied to said welding circuit through said noncontrolled rectifier elements.

Claim 3

In a direct-current arc welding apparatus having a transformer including a primary winding and at least one secondary winding comprising two sets of three-phase secondary windings having a phase difference of 60* from each other, an interphase transformer connected between neutral points of said two sets of secondary windings, and provided with a center tap, said center tap being connected to a parent metal , said primary winding being connected to a three-phase AC power source, controlled rectifier elements each anode of which being connected to said secondary winding of said transformer and the cathodes of which are connected to a welding circuit which includes a welding electrode and said parent metal, means, connected to each of said controlled rectifier elements, for controlling the conduction cycle thereof, to thereby adjust the amount of power being supplied through said controlled rectifier elements to said welding circuit, the improvement comprising: first means for effecting the supply of DC power to said welding circuit necessary for maintaining an arc through said controlled rectifier elements; second means for effecting the supply of DC power necessary to generate the arc after extinction; and a reactive element connected between said welding electrode and said first and second means; wherein said first means comprises a current-limiting circuit having predetermined characteristics and wherein said second means comprises non-controlled rectifier elements, each connected in series with said current-limiting element, said respective series connection of said current limiting element and said non-controlled rectifier elements being connected in parallel across the anodes and cathodes of said respective controlled rectifier elements.

Claim 4

In a direct-current arc welding apparatus having a transformer including a primary winding and at least one secondary winding comprising two sets of three-phase secondary windings having a phase difference of 60* from each other, an interphase transformer connected between neutral points of said two sets of secondary windings, and provided with a center tap, said center tap being connected to a parent metal , said primary winding being connected to a three-phase AC power source, controlled rectifier elements each anode of which being connected to said secondary winding of said transformer and the cathodes of which are connected to a welding circuit which includes a welding electrode and said parent metal, means, connected to each of said controlled rectifier elements, for controlling the conduction cycle thereof, to thereby adjust the amount of power being supplied through said controlled rectifier elements to said welding circuit, the improvement comprising: first means for effecting the supply of DC power to said welding circuit necessary for maintaining an arc through said controlled rectifier elements; second means for effecting the supply of DC power necessary to generate the arc after extinction; and a reactive element connected between said welding electrode and said first and second means; wherein said first means comprises a current-limiting circuit having predetermined characteristics and wherein said second means comprises non-controlled rectifier elements, each connected in series with said current-limiting element, said respective series connection of said current limiting element and said non-controlled rectifier elements being connected in parallel across the anodes and cathodes of said respective controlled rectifier elements.