Saturday, 2 February 2013


The project is designed to check the sequence of the 3 phase supply. It is very important to know the phase sequence particularly for 3 phase motors. For example, if the 3 phase motor is used for pumping action, any phase reversal accidentally resulting in wrong sequence could force the motor run in the wrong direction. This could result in dry run of the motor to develop permanent fault.

In this project direct 3-phase AC supply 50Hz is fed through voltage drop arrangement duly stabilized by zener diodes to a logic circuit comprising of NAND gates and OR gates to detect the proper sequence of RYB by series of pulses of fixed duration. In the event of changing the sequence from RYB to say YBR, the combination of NAND and OR gates develops an output with a missing pulse during the fixed time duration. This pulse is used in triggering a monostable 555 timer. Thus, while the sequence is not there the triggering to the timer is missed which is indicated by an LED driven from the output of the 555 timer. DC requirement of the circuit is powered from a step down transformer along with a bridge rectifier and filter capacitor.

Further this project can be enhanced by providing an inbuilt digital sequence checker comprising of LEDs in a circle to indicate wrong sequence by glowing of LEDs in anti-clockwise direction. The LEDs can be driven from a programmable microcontroller.

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