Why 3 Phase Synchronous Motor is Not Self Starting

Welcome to Electrical Live, your ultimate resource for all things electrical in the Home & Garden, Electronics, and Furniture Stores industries. In this article, we will delve deep into the world of 3 phase synchronous motors and understand why they are not self-starting. So, let's get started!

Understanding Synchronous Motors

Synchronous motors are a type of AC motor that operates based on the principles of electromagnetism. They are widely used in many industries due to their efficiency, reliability, and consistent speed control capabilities.

Unlike other AC motor types such as induction motors, synchronous motors require a separate starting mechanism to initiate their operation. This is because they do not possess the inherent ability to self-start. Let's explore the reasons behind this limitation.

The Key Factors

There are two primary reasons why 3 phase synchronous motors are not self-starting:

1. Lack of Starting Torque

Synchronous motors require an external source of torque during startup to overcome the initial static friction and rotational inertia. Unlike induction motors that generate starting torque due to the interaction between stator and rotor windings, synchronous motors lack these torque-producing mechanisms.

To address this, additional starting devices such as squirrel cage induction motors or synchronous condensers can be used to provide the necessary torque during the startup phase. These devices help the synchronous motor reach its synchronous speed, at which point it starts generating its own torque to maintain operation.

2. Dependence on External Excitation

Another crucial aspect of synchronous motors is their dependence on a direct current (DC) excitation source to create a rotating magnetic field. The stator windings of a synchronous motor are connected to the AC power supply, while the rotor windings are connected to a DC excitation source.

The magnetic field produced by the excitation source interacts with the rotating magnetic field of the stator, causing the rotor to follow the synchronous speed. Without this external excitation, the motor will not be able to maintain synchronization with the power supply and cannot self-start.

Starting Methods for Synchronous Motors

To overcome the self-starting limitation, various starting methods are employed for 3 phase synchronous motors. Let's explore some of the most commonly used techniques:

1. Pony Motor Method

In this method, a small induction motor, often referred to as a pony motor or an auxiliary motor, is connected to the same shaft as the synchronous motor. The pony motor is capable of self-starting and provides the initial torque required to bring the synchronous motor up to speed.

Once the synchronous motor reaches its synchronous speed, the auxiliary motor is disconnected, and the synchronous motor continues to operate independently. This method is commonly used in large industrial applications where synchronous motors are prevalent.

2. Electronic Motor Starter

With advancements in technology, electronic motor starters have become popular for starting synchronous motors. These starters provide the necessary torque during startup and ensure a smooth transition to synchronous operation.

Electronic motor starters employ electronic circuits to control the motor's speed, current, and voltage during the starting process. They offer various options for customization and can be easily integrated with modern control systems, making them an appealing choice for many industries.

3. Load Angle Control

Load angle control is another technique used to start synchronous motors. By manipulating the electrical load angle, which is the phase difference between the magnetic field produced by the stator and the rotor's magnetic field, the motor's starting performance can be improved.

Through appropriate load angle adjustments, the reactive power required to initiate rotation can be minimized, enabling the synchronous motor to start smoothly. This method is commonly employed in applications where precise control over the motor's speed and torque is crucial.

Conclusion

In conclusion, 3 phase synchronous motors are not self-starting due to the lack of starting torque and their dependence on external excitation. However, with the help of various starting methods such as the pony motor method, electronic motor starters, and load angle control, these motors can be effectively initiated into operation.

At Electrical Live, we hope this article has provided you with valuable insights into the functioning of 3 phase synchronous motors and why they require external starting mechanisms. Stay tuned for more informative content tailored to the needs of the Home & Garden, Electronics, and Furniture Stores industries. For any further queries or assistance, feel free to reach out to us!