Automatic Star / Delta

Automatic Star / Delta

Automatic Star / Delta: Before we move on to the power and control circuit of the Star Delta Starter let’s look at the basic principle. The basic principle of the Star Delta Starter is that the motor must be rotated

connected to the star when it is started, and after a while, the bend will be converted to delta winding after the motor has achieved sufficient speed. The advantage of this is that when the motors rotate when they have connected the voltage in each phase is = (line voltage / 1.7332)

Details about magnetic contactors.

Suppose a 415-volt motor needs to be started by a delta starter. In that case, the voltage at the star connection at each stage of rotation when the motor is started will be 415 / 1.732 be.

After the motor has reached a certain amount of speed (about 90% of the rated speed) and some voltage is induced to turn it, then the turn will be switched to the delta. And the motor will run in delta-island connection.

The motors that the Star Delta Starter needs to start have six terminals available, the other starter has three numbers motor terminals but the Star Delta Starter requires 6 terminals because rotating connections have to be made once in Star Mode and Delta Mode for the rest.

Both the star and delta connections are available inside the Star Delta Starter, only changing during its operation. Why number 6. Terminals required.

Applications of Star Delta Starter

We know that the main purpose of the Star Delta Starter is to start a three-step induction motor in the Star connection while running on the Delta connection. Note that the Star Delta Starter can only be used for low to medium voltage and light starting torque induction motors.

In the case of direct online (DOL) start, the receipt flow in the motor is reduced by about 33% and the starting torque is reduced by about 25-30%. Thus, the Star Delta Starter can only be used for light loads when starting the motor.

Otherwise, the heavy load motor will not start due to low torque which will have to accelerate the motor at rated speed while converting to delta connection.

Reverse and Forward Control Diagram

Let’s look at the power circuit diagram of a star-delta starter.

Advantages

1. Cheap
2. No heat is generated, or the device needs to be used by changing the tap, so efficiency is increased.
3. Reduce the flow to 1/3 of the current starting directly from online.
4. Create high torque in amperes of current per line.

Disadvantages

1. Starting torque also decreases by one-third as the starter reduces the starting current to one-third of the rated current [line voltage also decreases by 57% (1 / to3)]
2. It requires six top or terminal motors (delta connected)
3. For del delta connection, the supply voltage must be equal to the rated motor voltage.
4. If the motor does not reach at least 90% of its rated speed during star switching (from star to delta), the current peak may be as high as the direct and line starter (DOL),so it may cause harmful effects on the contacts of the contacts, so it Will not be reliable.
5. Required Required (Application or Load) Torque More than 50% of three phase induction motor torque if we cannot use Star Delta Starter