What is Star Delta Starter?
A star delta starter is a type of electrical device that is used to start three-phase induction motors. It works by initially connecting the motor to the power supply through a star-shaped configuration, which reduces the amount of current flowing through the motor. This helps to reduce the starting torque and current required to get the motor up to speed.
Once the motor has reached a certain speed, typically around 80% of its full load speed, the star delta starter will switch the connection to a delta configuration. This allows the motor to run at its full load and full power.
The main component of a star delta starter is a TPDP switch, which stands for triple pole double throw switch. This switch is responsible for changing the connection of the stator winding from a star configuration to a delta configuration.
Working of Star delta Starter:
- The starter is installed between the power supply and the three-phase induction motor.
- When the starter is turned on, the TPDP switch is placed in the "START" position.
- In the "START" position, the stator windings of the motor are connected in a star configuration.
- When the motor is energized, it begins to rotate at a reduced speed due to the reduced voltage and current flowing through the stator windings.
- As the motor reaches a certain speed, typically around 80% of its full load speed, the TPDP switch is automatically switched to the "RUN" position.
- In the "RUN" position, the stator windings are connected in a delta configuration. This allows the motor to operate at full load and full power.
- Once the motor is up to speed and running in the delta configuration, the TPDP switch can be left in the "RUN" position until it is time to shut the motor off.
Overall, the main advantage of using a star delta starter is that it allows you to start a three-phase induction motor with reduced starting current and torque, which helps to protect the motor and power supply from damage.
Advantages:
- Inexpensive: Star delta starters are generally less expensive than other types of reduced voltage starters, such as auto-transformer starters or part winding starters.
- No heat is produced: Because a star delta starter does not use a tap-changing device, it does not generate any heat during operation. This increases the efficiency of the starter and helps to reduce energy consumption.
- Reduced starting current: One of the main advantages of a star delta starter is that it reduces the starting current of the motor to about 1/3 of the current required for direct-on-line (DOL) starting. This helps to protect the motor and power supply from damage and reduces the electrical load on the system.
- High torque per ampere of line current: A star delta starter allows the motor to develop a high level of starting torque while still drawing a relatively low amount of current from the power supply. This can be beneficial in applications where a high level of torque is required to get the motor up to speed, but the electrical system has limited capacity.
Disadvantages:
- Reduced starting torque: Because the stator windings are connected in a star configuration during the starting phase, the starting torque of the motor is reduced to about 1/3 of its full load torque. This can be a disadvantage in applications where a high level of starting torque is required to get the motor up to speed.
- Limited compatibility: A star delta starter is only suitable for certain types of motors, specifically three-phase induction motors. It is not suitable for use with other types of motors, such as DC motors or synchronous motors.
- Risk of stalling: If the motor is heavily loaded and there is not enough torque to accelerate it to the required speed before the TPDP switch switches to the delta position, the motor may stall. This can cause damage to the motor and the starter.
Applications:
Star delta starters are commonly used in a variety of industrial and commercial applications, including:
- Centrifugal compressors: Because these types of compressors require a high level of torque to get up to speed, a star delta starter can be used to reduce the starting current and protect the motor and power supply from damage.
- Conveyor systems: In conveyor systems, a star delta starter can be used to reduce the starting current of the motor and protect it from damage when starting under heavy load.
- Pump systems: In pump systems, a star delta starter can be used to reduce the starting current of the motor and protect it from damage when starting under heavy load.
Why Star Delta Starter Preferred in Induction Motor?
When an induction motor is started directly with a full voltage supply, it can draw a very high starting current from the power supply. This high starting current can cause problems such as voltage drops in the power supply and tripped circuit breakers. The star-delta starter is a type of starting method used to reduce the starting current of an induction motor.
In the star-delta starter, the stator windings of the motor are initially connected in a star configuration. This causes the voltage applied to each winding to be reduced by a factor of 0.577. As a result, the starting current drawn from the power supply is also reduced by a factor of 0.577. This reduction in starting current helps to mitigate issues such as voltage drops and tripped circuit breakers.
After the motor has reached a certain speed, the stator windings are switched to a delta configuration, allowing the motor to operate at its full voltage and power rating. The star-delta starter is a useful method for starting large induction motors, as it allows the motor to be started smoothly and without causing problems in the power supply.