Main transformer and reactor coil are Class-H insulated by US DuPont Nomex(R) Paper and Japaness HITACHIChemical insulating varnish with high insulation strength, high temperature resistance and dust tightness. Main circuit with SCHNEIDER AC contactor, featuring off-load current pull-in, fully enclosed structure, high stability and reliability. Main circuit with Swiss LEM current transformer, featuring high temperature resistance, anti-interference, monitoring the current output from the interphase of balancing reactor, which protects the main transformer effectively. The protection against short circuit of control cable prevents damage to the PCB caused by internal short of control cable, short between control cable and the workpiece or the output cable. Anti-interference of high frequency, which prevents damage to the PCB caused by high frequency and voltage generated by the working argon/arc welder around the SAW machine. Protection Class-IP21S, featuring physical insulation between main circuit and control circuit, which prevents the control circuit from being interfered by the main circuit, the whole structure has excellent moisture resistance, anti-dipping and dust tightness.