SCR Line Contactor in Welding Transformer
- The circuit diagram of SCR line contactor is shown in Figure. This circuit consists of two SCRs connected in the inverse parallel or back to back manner.
- This circuit is obtained by replacing the ignitron tubes by SCRs.
- Smaller ignitrons can be replaced by using a pair of water cooled SCR’s. The SCR line contactor circuit is similar to that of ignitron line contactor.
- Here the ignitron tubes are replaced by high capacity SCR’s, which are provided with water cooling arrangement. It is necessary for protection of SCR carrying very high current.
- Hence the current in the primary is exponentially decaying. The energy supplied by the capacitor to the load ( i.e. for welding) is given by, W = 1/2CV2
- This energy can be controlled to any desired value by control of voltage V on the capacitor.
- Energy storage welding is particularly important in welding of aluminum and similar other materials having low resistivity and high thermal conductivity.
The advantages of energy storage welding systems are that due to the use of energy storing elements like inductor or capacitor, the supply voltage fluctuations at the time of welding are reduced
- And these systems are ideally suited for welding of the low resistivity materials like aluminum as they need a large welding current.
- The disadvantages are that due to the use of high voltage capacitors or high current inductors, these systems are costly and bulky.