Star-delta starters are used in induction motors to reduce the starting current drawn from the power supply. When an induction motor starts, it initially draws a high current that can be several times higher than its rated current. This high starting current can cause voltage dips in the electrical supply system and may lead to overheating of motor windings and excessive mechanical stress on the motor shaft. By using a star-delta starter, the motor is first started in the star configuration, where each phase of the motor windings is connected in series with a resistor. This reduces the voltage applied to each winding and consequently reduces the starting current. Once the motor reaches a certain speed, typically around 80% of its rated speed, the starter switches the windings to the delta configuration, where they are connected directly to the power supply, allowing the motor to operate at full speed with reduced current draw.
Star-delta starters are preferred over direct-on-line (DOL) starters for starting induction motors because they provide a gentler starting method that reduces mechanical and electrical stress on the motor and the power supply. DOL starters connect the motor directly to the full voltage of the power supply during starting, causing a high inrush current that can disrupt the power grid and cause voltage drops. In contrast, star-delta starters reduce the starting current by starting the motor at reduced voltage in the star configuration before switching to full voltage in the delta configuration. This gradual starting method extends the life of the motor and reduces the likelihood of electrical disturbances in the supply system.
The use of star-delta starters in induction motors is detailed in documents such as PDFs to explain their operational benefits and implementation. PDFs may outline how star-delta starters help reduce starting current, minimize voltage dips in the power supply, and protect motors from excessive mechanical stress during startup. They typically provide diagrams, technical specifications, and operational procedures for installing and using star-delta starters effectively in various industrial and commercial applications.
The principal reason for using star-delta starters in induction motors is to limit the inrush current during startup. Induction motors draw significantly higher currents when starting up due to the initial rush of current needed to overcome inertia and bring the motor up to operating speed. This inrush current can be several times higher than the motor’s rated current, which can cause voltage drops in the electrical supply system and mechanical stress on the motor components. By using a star-delta starter, the motor starts in the star configuration with reduced voltage applied to each winding, resulting in lower starting current. Once the motor reaches a certain speed, the starter switches the windings to the delta configuration to operate at full voltage and full speed, but with significantly reduced current draw compared to a direct-on-line (DOL) starter. This method helps protect the motor and the electrical system from damage and ensures smoother operation during startup.