Starting a synchronous motor typically involves various methods depending on its size, application, and operational requirements. One common method for starting a synchronous motor is through the use of a squirrel cage induction motor, also known as an auxiliary motor. In this method, the synchronous motor is initially brought up to speed by the induction motor, which is connected mechanically to the synchronous motor’s shaft.
As the induction motor accelerates, it drives the synchronous motor rotor to synchronous speed.
A synchronous motor is self-starting under certain conditions due to its design and inherent characteristics. This self-starting ability primarily arises when the motor is connected to an electrical grid or system where the grid provides a rotating magnetic field.
When the synchronous motor is energized and connected to the AC power supply, it locks onto the frequency of the grid and starts rotating at synchronous speed, provided its field winding has been excited appropriately.
To start a synchronous generator, the process is somewhat similar to starting a synchronous motor.
The generator’s field winding must be excited initially to create a magnetic field within the rotor. Once the field winding is excited, the generator is typically driven by a prime mover such as a steam turbine, gas turbine, or diesel engine. The prime mover drives the generator shaft, rotating it at a speed close to synchronous speed.
As the generator shaft accelerates, it synchronizes with the grid frequency and voltage, allowing it to generate electricity at the desired frequency and voltage level.
When a synchronous motor is started, the field winding is initially unexcited or not energized.
This means there is no magnetic field present in the rotor, and therefore, the motor cannot start rotating on its own. To start the motor, the field winding must be energized first to establish a magnetic field. This can be achieved using a separate DC power source or an excitation system that provides the necessary DC voltage to the field winding.
Once the field winding is excited and a magnetic field is established, the synchronous motor can be brought up to speed through various starting methods, such as using an auxiliary motor or direct grid connection, depending on the application requirements.