Star Delta starters, also known as Wye-Delta starters, are a type of motor starting method used in three-phase induction motors. These starters are employed to reduce the starting current and torque during the initial startup of the motor. The transition from star to delta connection occurs after the motor has reached a certain speed. Let's break down the key aspects of Star Delta starters:
Basic Configuration:
Motor Connections:
Star (Wye) Connection: At the start, the motor windings are connected in a star configuration, reducing the voltage applied to each winding.
Delta Connection: After a certain period, the motor connections are switched to a delta configuration for normal running conditions.
Control Circuit:
Star Delta starters have a control circuit that includes contactors, a timer, and relays.
The control circuit sequences the switching between star and delta configurations.
Operating Sequence:
Starting (Star) Sequence:
The motor is initially started in star configuration.
During the star sequence, the voltage across each winding is reduced to 1/√3 times the line voltage (approximately 58% of the full voltage).
This reduces the starting current and torque, minimizing stress on the motor and the power supply.
Transition Period:
After a preset time or when the motor reaches a certain speed, the control circuit transitions to the delta configuration.
Running (Delta) Sequence:
The motor continues to run in the more efficient delta configuration.
The voltage across each winding is now at the full line voltage.
Advantages:
Reduced Starting Current:
Star Delta starters help minimize the initial inrush current during motor startup, reducing stress on the power supply.
Smooth Acceleration:
The transition from star to delta provides a smoother acceleration, avoiding sudden torque peaks.
Efficient Running:
After the transition, the motor operates in the more efficient delta configuration, providing full voltage to each winding.
Application:
Star Delta starters are commonly used for large induction motors where the high starting current could lead to voltage drops and disturbances in the power supply.
These starters are often applied in industries such as manufacturing, mining, and water pumping, where the starting requirements of the motor are critical.
Notes:
The transition from star to delta can be controlled by either a timer or by monitoring the motor speed.
The choice of using a Star Delta starter depends on the specific motor characteristics, the load requirements, and the available power supply.
Always follow local electrical codes and standards when installing or configuring motor starters.
Star Delta starters are a practical solution for managing the challenges associated with starting large three-phase induction motors, providing a balance between reduced starting current and efficient running.