Square wave power supply for arc welding

DETAILED DESCRIPTION It is therefore an object of the invention to provide an A.
C.
constant potential power source which can be matched with a constant speed wire feeder in a submerged arc welding process.
Another object of the invention is to provide an A.
C.
power source which performs well in deep groove submerged are welding applications involving heavy-section ferrous metals.
A further object of the invention is to provide a method and apparatus for holding a constant voltage at the weld output terminals no matter what current the arc demands.
In a specific embodiment of the present invention, the main power transformer converts the primary 480 volt single-phase input power to a secondary open circuit voltage of 92 volts at 60 Hz and provides various control, synchronizing and auxiliary voltages for the system printed circuit board and accessory loads.
Four thyristors and a memory core inductor are controlled in such a manner as to provide essentially square wave current.
The square wave is adjustable in amplitude with very rapid zero crossings.
The transition time is in the range of 80 to 150 microseconds which is many times faster than sine wave reversal time.
The thyristor bridge is controlled in a firing sequence so as to prevent free wheeling of the square wave inductor at polarity reversals of the voltage supply.
The inductor is capable of storing vast amounts of energy in the form of flu, integrated from applied voltage-seconds.
The thyristor firings are timed to deliver this energy into the arc, inducing voltage equal to the instantaneous voltage of the utility supply at that point in time, even though the average arc voltage may be considerably lower.
It is this ability to generate high re-striking voltages with a basically low voltage regulated source that permits running constant potential mode submerged are welding with alternating current.
Two regulating subsystems operate together to control the output: 1.
A voltage control loop monitors the arc voltage at the terminals or from remote sensing leads to produce a signal which is processed and sent to the voltage regulator for comparison with the reference signal as set by the welding operator