The function of SCR contactor in resistance welding machine is

The function of SCR contactor in resistance welding machine is

Right Answer is:

To connect the large power supply to welding by closing a small switch

SOLUTION

SCR contractors are electronic control devices designed to handle large amounts of current. SCRs are triggered or turned on by pulses supplied by the timing or sequencing circuits of the welder. The SCRs are usually cooled by circulating water. 

During the welding process, a large amount of current is required for short periods of time. Silicon-controlled rectifiers (SCRs) are commonly used to control the starting and stopping of the large currents associated with electric welders. The current rating of these devices must be very high, sometimes in the range of 1000 to 100,000 amperes, and the power distribution equipment must be able to handle these high currents. 

The two main functions of SCR is in phase control mode with transformers and in converter configuration.

The common SCR phase-controlled machines are three-phase machines in either constant current or constant voltage modes. Because of electronic control of output characteristics, automatic line voltage compensation is easily achieved; this allows the machine to set the precise welding power, independent from the variations of input power. An SCR can also serve as a secondary contactor that allows the welding current to flow only when the control allows the SCRs to conduct. This is a very useful feature in spot welding and tack welding operations, in which rapid cycle operation is required. An SCR contactor does not provide electrical isolation; this requires that a circuit breaker or similar device would be provided for electrical safety.

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