Siemens Star Delta Starter ASD 6.3-10A 10 HP 7.5kw 3TE72910AW74

Star Delta Starter and its Uses

Star Delta Starters are widely used in the starting of 3 phase induction motors. The induction motor is connected through a star connection in Star Delta starting.  After the desired speed is reached, the motor is connected through a delta connection. A Star Delta Starter comprises of Triple Pole Double Throw switch. This switch is responsible for changing the stator winding from star to the delta. It also consists of contactors (main, star and delta), time relay 1 No., three-pole thermal overcurrent release 1 No, automatic cut-outs or fuse elements for the main circuit 3 Nos. and an automatic cut-out or fuse element for the control circuit 1 No.

Working Principle

Star Delta Starter works on the principle of reduced voltage starting method. The reduction in voltage is achieved by the physical configuration of the motor windings. As the motor windings are connected in star configuration during the starting phase, voltage across each winding is reduced. This results in torque reduction by a factor of 3. After some time, the windings are changed to delta configuration and the induction motor starts running normally. Star Delta starters have become most common for reduced voltage starting. They help in reducing the starting current applied to the motor. 

For the manufacture of Star Delta Starters, their contactors, one-timer, and one thermal overload are used. The size of the contactors is smaller than Direct On-Line Starters. Two contactors that are closed during are the main contactor and the delta contactor. Star contactor is the third contactor which is responsible for carrying star current when the motor is connected in a star configuration. 

Power Circuit of Star Delta Starter 

The power circuit gets power supply from the main circuit breaker. The reference source voltage is connected to the primary terminal of the motor by the main contactor. During the run, both the main contactor and star contactor are closed initially. After some time, when the star contactor is opened, the delta contactor is closed. The contactor controls are built into the starter. 

Control Circuit of Star Delta Starter 

The control circuit is used to provide two interrupting contacts for the motor shutdown. The OFF button can break the control circuit and motor when required. The thermal overload can automatically open the STOP control circuit on the detection of motor overload current by the thermal overload relay. This protects the motor from burning due to excessive load.  

Advantages of Star Delta Starter

• Simple operation.
• Cheaper than other reduced voltage methods.
• Torque generation and the overall performance are good.
• It is capable of drawing 2 times start current of the full load ampere of the induction motor connected.

Disadvantages of Star Delta Starter

• Cannot generate a very high starting torque.
• 2 sets of cables are required from starter to motor.
• In delta configuration, 6 terminal motors are needed.
• It can cause transient sparks. 

Uses 

• Widely used for low to medium voltage and light starting torque motors.
• It is used for motors that are not heavily loaded during the start and have long acceleration period. 
• For fans.
• For blowers.
• For pumps.