24 Single-Phase, Split-Phase, Two-Capacitor, Three-Phase, and AC Servomotors

AC motors are the backbone of numerous electrical systems, providing the motive force for a wide range of applications. This reading material aims to provide a comprehensive overview of various types of AC motors, including single-phase induction motors, split-phase motors with capacitors, two-capacitor induction motors, three-phase motors, and AC servomotors, along with their torque-speed characteristics.

Single-Phase Induction Motors:

• Single-phase induction motors are commonly used in household appliances, small machinery, and tools.
• They operate on a single-phase AC power supply and typically feature a starting winding and a main winding.
• Single-phase motors require additional starting mechanisms such as capacitors or shaded poles to generate a rotating magnetic field and achieve starting torque.

Split-Phase Motors with Capacitor and Centrifugal Switch:

• Split-phase motors with capacitors are a type of single-phase motor commonly used in applications where moderate starting torque is required.
• These motors feature a centrifugal switch that disconnects the starting winding once the motor reaches a certain speed.
• Capacitors are used to create a phase shift between the starting and main windings, enabling the motor to produce sufficient starting torque.

Two-Capacitor Induction Motors:

• Two-capacitor induction motors are another type of single-phase motor that utilizes two capacitors for starting and running operations.
• They offer improved starting torque and efficiency compared to split-phase motors with a single capacitor.
• Two-capacitor motors are suitable for applications such as air conditioning units, pumps, and compressors where high starting torque is required.

Three-Phase Motors:

• Three-phase induction motors are widely used in industrial and commercial applications due to their efficiency, reliability, and robustness.
• They operate on a three-phase AC power supply and do not require additional starting mechanisms.
• Three-phase motors offer higher power output, smoother operation, and better speed control compared to single-phase motors.

AC Servomotors:

• AC servomotors are precision motors used in automation, robotics, CNC machines, and other high-performance applications.
• They offer precise speed and position control, high dynamic response, and low inertia.
• AC servomotors are typically operated in closed-loop control systems, where feedback signals are used to adjust motor speed and position.

Figure 1: Construction of a Standard Servo Motor https://www.orientalmotor.com/servo-motors/technology/servo-motor-overview.html [6]

AC Servomotor Torque-Speed Curve:

• The torque-speed curve of an AC servomotor illustrates the relationship between torque output and rotational speed.
• AC servomotors typically exhibit a flat torque curve at low speeds, indicating high torque capability even at low speeds.
• As speed increases, the torque output decreases linearly, allowing for precise control over a wide range of speeds.

Understanding the characteristics and applications of various types of AC motors is essential for engineers, technicians, and designers working with electrical systems. By familiarizing themselves with single-phase, split-phase, two-capacitor, three-phase, and AC servomotors, professionals can select, operate, and maintain motors effectively to meet the diverse needs of modern industry and technology.

For further detail, please see the video lecture below:

References:

[1] “Single-Phase Induction Motors,” All About Circuits. [Online]. Available: https://www.allaboutcircuits.com/textbook/alternating-current/chpt-13/single-phase-induction-motors/

[2] Skill-Lync, “Speed-Torque Characteristics of Frequency Control Method for Induction Motor in MATLAB,” [Online]. Available: https://skill-lync.com/student-projects/speed-torque-characteristics-of-frequency-control-method-for-induction-motor-in-matlab

[3] “Centrifugal Switch in Induction Motor,” Electrical4U. [Online]. Available: https://www.electrical4u.com/centrifugal-switch/

[4] “Three Phase Induction Motor – Torque-Speed Characteristics,” Tutorialspoint. [Online]. Available: https://www.tutorialspoint.com/three-phase-induction-motor-torque-speed-characteristics

[5] J. R. Hendershot and T. J. E. Miller, Permanent Magnet Motor Technology: Design and Applications. CRC Press, 2009. [Online]. Available: https://www.amazon.com/Permanent-Magnet-Motor-Technology-Applications/dp/1420064401

[6] Oriental Motor Company. (n.d.). Servo Motor Overview. Retrieved April 14, 2024, from https://www.orientalmotor.com/servo-motors/technology/servo-motor-overview.html