How is a star-delta motor starter used in induction motors?
1 Answer
A star-delta motor starter is a common method used to start three-phase induction motors. It allows the motor to start with reduced current, minimizing stress on the motor windings during the starting process. The basic idea behind the star-delta starter is to initially connect the motor in a "star" configuration for starting and then switch it to a "delta" configuration for normal running. Let's go through the steps of how a star-delta motor starter is used in induction motors:
Initial Configuration (Star):
Before starting the motor, the stator windings are connected in a "star" configuration, also known as a "Y" connection.
In the star configuration, each stator winding is connected to a common point, typically called the "star point" or "neutral point."
The star point is connected to one phase of the supply voltage, and the other three phases are connected to the respective stator windings.
Starting the Motor:
When the motor is initially started, it operates in the star configuration. The star connection results in a lower voltage across each stator winding compared to the line voltage, typically √3 times lower (where √3 is approximately 1.732).
As a result, the starting current is reduced to about one-third (√3 times) of what it would be in the delta configuration, easing the motor's starting process.
Running Configuration (Delta):
After a predetermined period (typically a few seconds) of starting the motor in the star configuration, the motor is switched to the delta configuration.
In the delta configuration, the stator windings are reconnected to form a "delta" or "triangle" connection.
The voltage across each winding in the delta configuration is now the same as the line voltage, which means the motor can operate at its rated voltage and speed.
Transition Switching:
The transition from the star configuration to the delta configuration is typically achieved using a special switching mechanism, such as a timer or a combination of contactors and control circuits.
The switch from star to delta is made after the motor has gained enough speed and can handle the higher current in the delta configuration.
The star-delta motor starter provides a smooth start for the induction motor, reducing the mechanical and electrical stress during starting. It is commonly used for larger motors where the high starting current could cause issues like voltage drop, excessive heating, and mechanical stresses. Once the motor is up to speed, the star-delta starter operates in the more efficient delta configuration for normal running conditions.
Initial Configuration (Star):
Before starting the motor, the stator windings are connected in a "star" configuration, also known as a "Y" connection.
In the star configuration, each stator winding is connected to a common point, typically called the "star point" or "neutral point."
The star point is connected to one phase of the supply voltage, and the other three phases are connected to the respective stator windings.
Starting the Motor:
When the motor is initially started, it operates in the star configuration. The star connection results in a lower voltage across each stator winding compared to the line voltage, typically √3 times lower (where √3 is approximately 1.732).
As a result, the starting current is reduced to about one-third (√3 times) of what it would be in the delta configuration, easing the motor's starting process.
Running Configuration (Delta):
After a predetermined period (typically a few seconds) of starting the motor in the star configuration, the motor is switched to the delta configuration.
In the delta configuration, the stator windings are reconnected to form a "delta" or "triangle" connection.
The voltage across each winding in the delta configuration is now the same as the line voltage, which means the motor can operate at its rated voltage and speed.
Transition Switching:
The transition from the star configuration to the delta configuration is typically achieved using a special switching mechanism, such as a timer or a combination of contactors and control circuits.
The switch from star to delta is made after the motor has gained enough speed and can handle the higher current in the delta configuration.
The star-delta motor starter provides a smooth start for the induction motor, reducing the mechanical and electrical stress during starting. It is commonly used for larger motors where the high starting current could cause issues like voltage drop, excessive heating, and mechanical stresses. Once the motor is up to speed, the star-delta starter operates in the more efficient delta configuration for normal running conditions.