Welding transformer working principle and application
Basic idea of welding transformer
A welding transformer is a step down transformer that has thin primary winding with a large number of turns and its secondary has more area of cross-section and less number of turns ensuring less voltage and very high current in the secondary. The welding transformer reduces the voltage from the source voltage to a lower voltage that is suitable for welding. Usually between 15 and 45 volts. The secondary current is quit high and it may be typically 200A to 600A, but it could be much higher. The secondary may have several taps for adjusting the secondary voltage to control the welding current. The taps are typically connected to a several high-current plug receptacles or to a high-current switch. One end of the secondary is connected to the welding electrode, whereas the other end of the secondary is connected to the welding electrode, whereas the other end is connected to the pieces to be welded .If any high current flows, heat is produced due to the contact resistance between the electrode and the pieces to be welded. The generated heat melts a trip of the electrode and the gap between the two pieces is filled. Figger shows a simple welding transformer.
The impedance of welding transformer may be higher than that of the impedance of a general purpose transformer. The impedance of welding transformer may play a role in the process of establishing an arc and controlling the current. Large welding transformers are most likely to be designed for three phase input. There are many smaller transformers that are designed for single phase input.
DC welding transformer
For welding with direct current (DC) a rectifier is connected to the secondary of the transformer. There may also be a filter choke or an inductor to smooth the DC current. the entire transformer and rectifier assembly may be called a welding power supply. The winding used for the welding transformer is highly reactive. Otherwise, a separate reactor may be added is series with the secondary winding.
ARC control of welding transformer
To control the Arc ,various reactors are used with welding transformers. Some methods to controls the arc are given below.
With the help of taps on the reactor, the output current is regulated. This has limited number of current settings.
Moving Coil reactor
A moving coil reactor is one in which the reactive distance between primary and secondary is adjusted. The current becomes less if the distance between the coils is large.
Moving shunt reactor
A moving shunt reactor is one in which the position of the central magnetic shunt can be adjusted. Change of the output current is obtained due to the adjustment of the shunted flux.
Continuously variable Reactor
A continuously variable reactor is one in which the height of the reactor is continuously varied. Greater reactance is obtained due to greater core insertion and hence the output current is less
To adjust the reactance of the reactor, the required DC saturation if the DC excitation current is more. Therefore, changes of current are obtained due to the change o reactance