Due to the wide variety characteristics of the induction motor, it plays the premier role in the industrial sector. Some of those are self starting, rugged construction, high efficiency, good power factor and ease of control, etc. Squirrel cage types of induction motors are mostly used widely than the other types.
When the motor is at idle, it just look like a short circuited transformer at secondary side because all the rotor bars are connected together to form a closed path. This will turn a large current flow through the rotor bars. So when the motor is started, the stator draws the high current which is 8-10 times that of the motor rated current. Before staring the motor, it is necessary reduce the voltage applied to the motor.
The project is designed to provide low voltage start to induction motors. This is achieved by using star to delta conversion. Star / Delta starters are probably the most common reduced voltage starters in the 50Hz industrial motor world. Star delta is used in an attempt to reduce the start current applied to the motor then after sometime full load current is applied to the motor. Since in star connection current is the same in different phases while line voltage is the root three times the phase voltage. So the voltage is reduced (results to reduce current) if motor is started as star. And also in delta connection the voltage is the same as that of phase voltage so full voltage is applied if we run the motor as delta connection. The Star / Delta starter is generally obtained from three contractors; electromechanical timer and a thermal overload for operating a 3 phase motor at 440 volt at ac mains supply 50 Hz. The interlocking arrangement of all the contactor coils is traditionally wired in 440 volt AC.
The project is designed 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 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 lamps instead of a 3 phase motor i.e., two lamps representing each phase winding of the motor.
Automatic Star Delta Starter Using Relays for Induction Motor Automatic Star Delta Motor starter
