04-10-2014, 02:22 PM
Abstracts: This project uses a system to start a 3 phase motor at 440 volt AC mains supply 50 Hz with a set of 12 volt DC relays in star mode first and then to delta mode by an electronically adjustable timer. A set of relays are used to shift the motor connections from star to delta with a time delay. The project is supplied with six LEDs instead of a 3 phase motor i.e., two LEDs representing each phase winding of the motor. The interlocking arrangement of the relay coils and the electronic timer are all wired in low voltage DC of 12 volt fed from an inbuilt DC power supply for safe handling of the starter during the study. It still retains its application for a 3 phase motor starting with single phasing prevention also. During star operation the lamps would glow dim indicating the supply voltage across the coils are 440/root of (3). In delta condition after the timer operates the lamps would glow with full intensity indicating full supply voltage of 440volts. The timer comprises of a micro controller AT89S52 the output of which is fed to a relay for changing the mains supply from 3 phase star to delta through Op-amp circuit which convert square wave to sine wave to drive relay. The project also has the provision of single phasing protection since 3 phase motors get burnt if any one phase goes missing during running. The output to the lamps shall be completely cut-off in the event of any phase failure.