The operating principles of a 3-phase star-delta starter involve two main configurations: star (Y) and delta (∆). In the star configuration, the motor windings are connected in a configuration resembling the shape of a star, with each winding connected between a phase and a common point (neutral point). This configuration allows the motor to start with reduced voltage across each winding, thereby reducing the starting current and torque. Once the motor reaches a certain speed and stabilizes, the starter switches the windings to the delta configuration.
The principle of operation of a star-delta starter is to initially connect the motor windings in the star configuration during starting. In this mode, the voltage applied to each winding is reduced compared to the line voltage, resulting in lower starting current and torque. This reduces mechanical stress on the motor and minimizes voltage dips in the electrical supply. Once the motor reaches about 80% of its rated speed and stabilizes, the starter switches the windings to the delta configuration. In delta mode, the motor operates at full line voltage, providing higher torque and enabling efficient running of the motor at normal operating conditions.
The working principle of a Direct-On-Line (DOL) starter involves directly connecting the motor windings to the power supply during starting. This results in the motor receiving full line voltage from the start, causing a high inrush current and torque at the moment of starting. DOL starters are simple in design and suitable for small motors where the high starting current is acceptable and does not cause excessive mechanical stress or voltage drops in the supply network.
The working principle of a Wye Delta starter combines the star (wye) and delta configurations in two stages of starting. Initially, the motor windings are connected in the star configuration (wye) during starting, reducing the voltage applied to each winding and thereby reducing starting current and torque. Once the motor reaches a certain speed and stabilizes, the starter switches the windings to the delta configuration (∆), where the motor operates at full line voltage. This sequential switching helps in reducing mechanical stress during starting and ensures smooth acceleration of the motor.
A star-delta starter is used for 3-phase motors primarily to reduce the starting current and torque during motor startup. By initially connecting the motor windings in star configuration, the starter limits the voltage applied to each winding, which reduces the starting current to approximately one-third of what it would be with a Direct-On-Line (DOL) starter. This reduced starting current prevents excessive voltage dips in the electrical supply and minimizes mechanical stress on the motor and connected equipment. Star-delta starters are commonly used in applications where starting current limitations are critical, such as in large motors, conveyor systems, pumps, and compressors, ensuring efficient and reliable motor operation while extending the lifespan of electrical components.