This projects implements an automatic induction motor starter using microcontroller which works same as that of DOL starter. The microcontroller continuously monitors the three phases of input supply for over voltage and single phasing conditions and accordingly switches the relays to switch the motor.
Induction motors are popular due to their low-cost, sturdy construction, fast pick-up, low maintenance expenditure and good efficiency. The DOL (direct-on-line) starters and star/delta starters used for starting and running of induction motors provide coarse type of protections against voltage fluctuations and single phasing. Induction motors are very sensitive to low voltage and single phasing during which they draw a heavy current and can burn out unless switched of within few seconds of occurrence of such conditions. This makes the requirement of a sensitive protective device essential to avoid burning of induction motors under such conditions. The circuit of an automatic starter, incorporating the important features given below, is described here. It is meant to be used in conjunction with a DOL starter. Automatic start on resumption of proper conditions Single phasing prevention 24-hour programmable off timer (on completion of actual runtime of the motor). An induction or asynchronous motor is a type of AC motor where power is supplied to the rotor by means of electromagnetic induction, rather than a commutator or slip rings as in other types of motor. These motors are widely used in industrial drives, particularly poly-phase induction motors, because they are rugged and have no brushes. Single-phase versions are used in small appliances. Their speed is determined by the frequency of the supply current, so they are most widely used in constant-speed
applications, although variable speed versions, using variable frequency drives are becoming more common. The most common type is the squirrel cage motor.