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1 Transformers > 1.42 WELDING TRANSFORMERS

1.42 WELDING TRANSFORMERS

Figure 1.59 shows a schematic diagram of a welding transformer having thin primary windings with a large number of turns. On the other hand, the secondary has more area of cross-section and less number of turns ensuring less voltage and very high current in the secondary. One 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 tip of the electrode and the gap between the two pieces is filled.

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Figure 1.59 Welding Transformer

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Figure 1.60 Volt-ampere Characteristic of a Welding Transformer

The winding used for the welding transformer is highly reactive. Otherwise, a separate reactor may be added in series with the secondary winding.

Figure 1.60 shows the volt-ampere characteristic of a welding transformer.

1.42.1 Reactors Used with Welding Transformers

To control the arc, various reactors are used with welding transformers. Some methods to control the arc are given below:

  1. Tapped reactor: With the help of taps on the reactor, the output current is regulated. This has limite number of current settings shown in Figure 1.61.
  2. Moving coil reactor: Figure 1.62 shows a moving coil reactor in which the reactive distance between primary and secondary is adjusted. The current becomes less if the distance between the coils is large.

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    Figure 1.61 Tapped Reactor

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    Figure 1.62 Moving Coil Reactor

  3. Moving shunt reactor: Figure 1.63 shows a moving shunt reactor 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.
  4. Continuously variable reactor: Figure 1.64 shows a continuously variable reactor 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.
  5. Saturable reactor: Figure 1.65 shows a saturable reactor. To adjust the reactance of the reactor, the required DC excitation is obtained from a DC controlled transducer. Reactor approaches saturation if the DC excitation current is more. Therefore, changes of current are obtained due to the change of reactance.

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Figure 1.63 Moving Shunt Reactor

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Figure 1.64 Continuously Variable Reactor

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Figure 1.65 Saturable Reactor

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