Fig. Use of welding transformer |
Welding transformer is a transformer having thin primary winding
with large number of turns. While the secondary is having more area of
cross-section and with less number of turns. This ensures very high
current and less voltage in the secondary.
One end of the secondary is connected to welding electrode and
another end is connected to the pieces to be welded. Due to the contact
resistance between the electrode and pieces to be welded, when a very
high current flows, I2R heat is produced. This heat is very
large. Due to this heat, a tip of the electrode melts and fills the gap
between the two pieces.
A winding used for the welding transformer is highly reactive or a
separate reactor may be added in series with the secondary winding.
1.1 V-I Characteristics
Volt ampere characteristics for a welding transformer is as shown in the Fig. 2.
Fig. 2 Volt ampere characteristics for a welding transformer |
1.2 Reactors used with with Welding Transformer
The welding transformer can be used with various reactors for control of arc. The various methods of such control are :
i) Tapped Reactor : In this, output current is regulated by taps on the reactor. This has limited number of current settings.
Fig. 3 Tapped reactor |
ii) Moving Coil Reactor :
In this method, the relative distance between primary and the secondary is adjusted.
When the distance between the coils is large the current obtained is less.
Fig. 4 Moving coil reactor |
iii) Magnetic Shunt Reactor : In this method, position of central
magnetic shunt can be adjusted. This adjusts the shunted flux and hence
output current gets changed.
Fig. 5 Magnetic shunt reactor |
iv) Continuously Variable Reactor : The height of the reactor is
continuously varied in this method. Greater the core insertion greater
is the reactance and less is the output current.
Fig. 6 continuously variable reactor |
v) Saturable Reactor :
The reactance of the reactor is adjusted by changing the value of
d.c. excitation obtained from d.c. controlled transducer. More the d.c.
currents, reactor approaches to saturation. This changes the reactance
of reactor and hence changing the current.
Fig. 7 Saturation reactor |
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