A synchronous motor is a type of AC (Alternating Current) motor that operates based on the principle of magnetic synchronism. It is designed to rotate at a constant speed that is synchronized with the frequency of the AC power supply.
The working principle of a synchronous motor involves the interaction between the magnetic field produced by the stator and the magnetic field of the rotor. Let’s break down the process step by step:
- Stator: The stator of a synchronous motor consists of a stationary set of windings that are supplied with AC power. These windings are typically three-phase windings, producing a rotating magnetic field when energized.
- Rotor: The rotor is the rotating part of the synchronous motor. It contains either permanent magnets or electromagnets. In the case of electromagnets, the rotor windings are supplied with DC power to create a magnetic field.
- Magnetic Field Interaction: When the AC power is supplied to the stator windings, a rotating magnetic field is created around the stator. This rotating magnetic field induces a magnetic field in the rotor.
- Synchronization: The key characteristic of a synchronous motor is that the rotor rotates at the same frequency as the rotating magnetic field of the stator. This synchronization is achieved by adjusting the DC current supplied to the rotor windings.
- Locking: Once the rotor’s magnetic field is synchronized with the rotating magnetic field of the stator, the rotor locks into step with the stator field and starts rotating at the same speed. This locking mechanism is what gives synchronous motors their constant speed.
- Torque Generation: The torque in a synchronous motor is produced by the interaction between the stator’s rotating magnetic field and the rotor’s magnetic field. The rotor is pulled into alignment with the rotating magnetic field, resulting in the generation of torque.
It’s important to note that synchronous motors require a separate power source for the rotor field current, known as the excitation current. This excitation current creates the magnetic field in the rotor and is typically provided by a DC power source.
Synchronous motors are commonly used in applications that require constant speed, such as power generation, industrial machinery, and synchronous clocks. They offer high efficiency and precise speed control, making them suitable for various industrial and commercial applications.
Here are some common applications of synchronous motors:
- Electric clocks – The precise speed of synchronous motors makes them ideal for keeping time. Clock motors are low-power synchronous units.
- Process industry – Synchronous motors are used to drive large compressors, pumps, rolling mills, crushers, elevators etc. where constant speed operation is critical.
- Power factor correction – Synchronous condensers and synchronous motors provide reactive power and improve power factor in large electrical systems.
- Constant speed applications – Textile mills, paper machines, metal working machines, printing presses, etc. often require constant speed drives. Synchronous motors are used.
- High power applications – Large synchronous motors (several megawatts) are used for ball mills, pulverizers, industrial fans, blowers, and pumps requiring high power.
- Locomotive traction – Synchronous motors are emerging for all-electric and hybrid diesel-electric locomotives. They provide high starting torque and constant speed.
- Wind turbines – The generator in wind turbines often uses a synchronous motor principle to produce electricity at grid frequency regardless of wind speed.
- Embedded generators – Permanent magnet synchronous generators are often used in aircraft to produce electric power embedded in the engines.
- Low-speed high-torque applications – Synchronous reluctance motors and permanent magnet synchronous motors are well-suited for precise speed/position control.