Our project aims to start a 3 phase induction motor with a soft or steady start. A 3 phase induction motor requires a high power to start since it directly attends its full speed. This leads to a high electrical mechanical jerking as well as generation of high electrical electric stress on induction motor windings. This may result in induction motor failure due to high stress/windings getting burnt/ override and other similar issues. The best way to avoid this is to start the induction motor smoothly and slowly/steadily gain speed till the motor reaches maximum speed. The project provides a soft steady start to induction motor based on SCR firing trigger through introducing a quite brief delay and then the delay is gradually reduced till zero voltage triggering is achieved. This leads to a low voltage start and then full voltage after gradual increases. So the motor starts smoothly and reaches its full speed steadily.

The project incorporates 6 anti-parallel SCR’s with 2 of them for every phase and the output obtained from these is then provided to a lamp set that is used to demonstrate as a 3 phase induction motor. The system capacitor charging and discharging is then connected to comparators that result in delaying of firing pulses at motor start and constantly reducing delay size until motor reaches its full speed. The output obtained from these comparators it then passed on to trigger the SCR through the opto-isolators.