Most induction motors are started directly on line, but when very large motors are started that way, they cause a disturbance of voltage on the supply lines due to large starting current surges.
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Star delta starter received the starting current is about 30 % of the starting current during direct on line start and the starting torque is reduced to about 25 % of the torque available at a D.O.L start.
Star Delta 3-phase Motor Automatic starter with Timer
From L1 The phase current flows to thermal overload contact through Fuse, then OFF Push button, On Push button Interlocking Contact 2, and then C3. This way, the circuit is completed, as a result;
star delta 3 phase motor automatic starter with timer writing rh pinterest com star delta starter wiring diagram 3 phase pdf 3 Phase Motor Wiring Connection
when you press the start button 2 contactors energise. One forms the star connection and the other switches the mains to the windings. A timer is started then too. After a few seconds the timer has timed out and the star contactor is de-energised and at that time the delta contactor energizes. The star contactor and delta contactor have interlock contacts wired in the control circuit that prevent both from energizing together. Below is a control circuit. This is called an open transition star delta starter. There is another circuit that is called a closed transition starter.
star delta diagram
A conventional star delta starter for starting a three phase star delta motor comprises three pole power contactors for supplying three phase power to star position and delta position, a timer control with a logic circuit for controlling AC power supply switching operation for star position and delta position and for adjusting a time delay of switching over from star connection to delta connection, an overload relay for
Most induction motors are started directly on line, but when very large motors are started that way, they cause a disturbance of voltage on the supply lines due to large starting current surges. To limit the starting current surge, large induction motors are started at reduced voltage and then have full supply voltage reconnected when they run up to near rotated speed. Two methods are used for reduction of starting voltage are star delta starting and auto transformer stating.
Theory of Star Delta Starter Method of Starting of Induction Motor
The Star Delta Starter is a very common type of starter and is used extensively as compared to the other type of starting methods of the induction motor. A star delta is used for a cage motor designed to run normally on the delta connected stator winding. The connection of a three-phase induction motor with a star delta starter is shown in the figure below.
Star Delta starter for a three-phase asynchronous motor
By connecting the armatures of the motor in star they are subjected to the line-to-neutral voltage (230V). By connecting them in a triangle they are subjected to the line-to-line voltage (400V); intuitively the current consumption and the torque will be lower for star connection.