Star-delta starters are commonly used in industrial applications to reduce the starting current and torque of three-phase induction motors. They employ a specific wiring configuration to transition the motor from a star-connected winding arrangement to a delta-connected arrangement during the starting process. Here’s how star-delta starters work and their wiring functions:
### 1. Starting Process:
1. **Star Connection:**
– Initially, the motor windings are connected in a star configuration (Y), where each phase winding is connected to a common point (neutral or star point) and to one of the supply phases.
– In the star configuration, the voltage across each winding is reduced by a factor of √3 compared to the line voltage, resulting in lower starting current and torque.
2. **Transition to Delta Connection:**
– After a predetermined time delay (typically a few seconds), the motor windings are switched to a delta configuration (Δ), where each winding is connected directly between two supply phases.
– Transitioning to the delta configuration increases the voltage across each winding to the full line voltage, resulting in higher torque and acceleration.
### 2. Wiring Functions:
1. **Main Contactor (Star Contactor):**
– The main contactor initially connects the motor windings in a star configuration during the starting process.
– It is typically a three-pole contactor, with each pole connecting one phase of the motor to the supply.
2. **Timer (Time Delay Relay):**
– A timer or time delay relay controls the duration of the star connection before transitioning to the delta connection.
– The timer is adjustable and set to a predetermined time delay based on motor characteristics and starting requirements.
3. **Delta Contactor:**
– The delta contactor is activated after the time delay set by the timer, switching the motor windings from star to delta configuration.
– It is typically a three-pole contactor, similar to the main contactor, but configured to connect the motor windings in a delta arrangement.
4. **Interlocking Mechanism:**
– Interlocking mechanisms ensure that the main contactor is de-energized before the delta contactor is energized, preventing simultaneous closure of both contactors.
– This prevents short circuits and ensures proper sequencing of the star-delta starting process.
### 3. Control Circuit:
1. **Start/Stop Push Buttons:**
– Start and stop push buttons are used to initiate and terminate the motor starting sequence.
– Pressing the start button energizes the main contactor, initiating the star connection, while pressing the stop button de-energizes the contactors, stopping the motor.
2. **Control Relay (Auxiliary Relay):**
– A control relay or auxiliary relay provides control logic and interlocking functions for the star-delta starting sequence.
– It coordinates the operation of the main and delta contactors, ensuring proper sequencing and safety.
### Benefits of Star-Delta Starters:
1. **Reduced Starting Current:**
– Star-delta starters reduce the inrush current during motor starting, minimizing voltage dips and stress on electrical components.
2. **Smooth Starting:**
– The gradual transition from star to delta connection results in smooth acceleration and reduced mechanical shock on the motor and driven equipment.
3. **Energy Efficiency:**
– By reducing starting current and torque, star-delta starters improve energy efficiency and lower operating costs.
4. **Extended Motor Life:**
– Gentle starting reduces mechanical wear and extends the lifespan of the motor and associated equipment.
Star-delta starters are widely used in applications where smooth starting and reduced starting current are essential, such as in pumps, fans, compressors, and conveyor systems. Their simple yet effective wiring functions make them a popular choice for controlling three-phase induction motors in industrial environments.
Several manufacturers offer star-delta starters, providing a range of options in terms of features, specifications, and applications. Here are some popular manufacturers known for their star-delta starters:
1. **Siemens:**
– Siemens offers a wide range of motor starters and control devices, including star-delta starters.
– Their star-delta starters feature robust construction, reliable performance, and advanced control options.
2. **ABB (ASEA Brown Boveri):**
– ABB manufactures a variety of industrial automation products, including motor starters and control solutions.
– Their star-delta starters are known for their quality, efficiency, and compatibility with a range of motor types and applications.
3. **Schneider Electric:**
– Schneider Electric provides comprehensive solutions for industrial automation, including motor control and protection devices.
– Their star-delta starters combine advanced technology with user-friendly design, making them suitable for various industrial applications.
4. **Mitsubishi Electric:**
– Mitsubishi Electric offers a diverse range of motor control products, including starters, drives, and controllers.
– Their star-delta starters are designed for reliability, efficiency, and ease of installation and operation.
5. **Eaton:**
– Eaton manufactures a wide array of electrical products and solutions for industrial applications.
– Their star-delta starters are built to meet stringent quality standards and offer features such as overload protection and motor monitoring.
6. **TECO Electric & Machinery:**
– TECO is a leading manufacturer of electric motors, drives, and control systems.
– Their star-delta starters are known for their durability, performance, and compatibility with TECO motors and equipment.
7. **Rockwell Automation:**
– Rockwell Automation specializes in industrial automation and control solutions.
– Their star-delta starters are part of a comprehensive range of motor control products designed to meet the needs of various industries.
These manufacturers offer a variety of star-delta starters with different voltage and current ratings, enclosure types, control options, and additional features to suit diverse industrial requirements. Customers can choose from these reputable brands based on their specific application needs, budget, and preferences.