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The main intention of this project is to provide protection for a single-phase pump motor by applying initial voltage gradually from low to high for obtaining soft start. The pump motor draws more current than its rated capacity during their starting condition which may lead to the damage of the windings of the motor. In order to avoid this problem, applied voltage is gradually increased from low to high so that the soft start of the pump motor is performed.
This project consists of two anti-parallel SCRs connected in series with an induction motor to the supply. The time to start the firing angle is heavily delayed by receiving delayed pulses from the operational amplifier. The op-amp operates in comparator mode that compares to zero voltage pulses to develop a sawtooth voltage which is further compared against a varying voltage by charging and discharging of a capacitor to develop delayed pulses for triggering the SCRs. A lamp is provided in this project in place of an induction motor for demonstration purpose.However a motor of 0.25 HP ( not supplied by us) can be used.
Furthermore, the project can be enhanced by using six SCRs: two connected back to back for each phase.