AUTOMATIC STAR DELTA STARTER

This equipment/appliance reduces starting current and starting torque. Automatic Star Delta Starter design normally consists of three contactors, an overload relay or circuit breaker, and a timer for setting the time in the Star position (starting position). For the Star Delta Starter, a motor must be in delta connected position during a normal run and the main purpose is to be able to use the starter. When the motor is at idle, it just is like the short-circuited transformer at secondary side because all the rotor bars are connected together to form a closed path. This will draw a large current flow through the rotor bars. So, when the motor is started, stator draws high current which is 8-10 times that of the rated current. Therefore, before starting the motor, it is necessary to reduce the voltage applied to the motor. In Star connection current is in different phases but line voltage is root three times that of the phase voltage. So, the voltage is reduced which results in reduction of current if motor is started in star connection. In Delta connection the voltage is same as that of phase voltage so full voltage is applied if we run the motor in delta connection. The Star/Delta Starter is generally obtained from three contactors, pneumatic timer, and a thermal overload relay or circuit breaker, for 3 phase motor at 440 volt AC main supply 50 Hz.