Key Points on Motor Controllers and Starters

Purpose of Motor Controllers

• Automation Engineers: Write logic programs for PLCs and DCS systems.
• Function: Control process variables, manipulate valves, set control loop modes, start/stop motors.
• Voltages: Digital outputs typically use 24V DC or 120V AC.
• Three-Phase Motor Control: Requires a motor controller for 480V AC motors.

Types of Motor Controllers

• Definition: Devices that prevent motors from energizing until activated.
• Components: Circuit disconnecting means, contactor/motor actuator, circuit/motor overload protection.
• Also Known As: Motor starters.

Motor Controllers by Starting Method

1. Full Voltage, Non-Reversing (FVNR):

   • Allows full line voltage to pass to the motor.
   • Motor operates in a single direction.
   • Known as "across the line" controllers.

2. Full Voltage Reversing:

   • Operates motor in both forward and reverse.
   • Achieved with two contactors.
   • Phase reversal causes opposite motor rotation.
   • Incorporates safeguards to prevent simultaneous contactor activation.

3. Reduced Voltage Starting:

   • Limits starting current for large motors.
   • Methods:
     • Auto-transformer
     • Star-delta
     • Soft starter

4. Multi-Speed Controllers:

   • Control motors at varying speeds.
   • Methods:
     • Variable Speed Drive (VSD)
     • 2-speed control

Types of Motor Starters

1. Manual Motor Actuation:

   • Operator switches motor on/off.
   • Safety restrictions limit use to ≤10 horsepower motors.

2. Magnetic Motor Starters:

   • Common single-speed starters.
   • Activated by PLC, pushbutton, or selector switch.
   • Used with FVNR and full voltage reversing controllers.

3. Auto-Transformer Motor Starters:

   • Used in reduced voltage starting for large motors.
   • Utilizes transformers to reduce initial voltage.

4. Star-Delta Starter:

   • Similar to auto-transformer starting.
   • Uses three contactors to manage voltage configuration.

5. Soft Starters:

   • Uses solid-state electronics to control startup voltage/current.
   • Gradually increases voltage during startup.

6. Variable Frequency Drives (VFD):

   • Similar to soft starters but allows speed variation.
   • Regulates both voltage and frequency.
   • Reduces startup current.

Conclusion

• Various Techniques: Cater to different applications.
• Safety and Efficiency: Ensure controlled motor starting.
• Further Learning: PLC programming resources available on RealPars.com.