Losses in Synchronous Motors: Types and Methods to Minimise
Unlike other motors, synchronous motors experience some losses such as electrical losses, magnetic losses, mechanical losses, and stray load losses. Understanding its losses and minimising them is crucial in optimising the performance of the synchronous motor.
Synchronous motors are known for their efficiency and precision in various industrial applications. However, like other electrical motors, synchronous motors are not immune to energy losses. Understanding these losses and adapting methods to minimise them is crucial for maximising their efficiency and reliability.
In this blog, we will explore the different types of losses in synchronous motors, their causes, and the methods that can be implemented to reduce them.
What is a Synchronous Motor?
A synchronous motor is an AC motor that operates at a constant speed synchronised with the frequency of supply. Unlike induction motors, its rotor rotates in perfect alignment with the stator’s magnetic field. It eliminates the slip and ensures efficient and precise operation. This feature makes synchronous motors ideal for applications requiring steady speeds and accurate control.
The construction of a synchronous motor consists of stator and rotor. Stator is the stationary part of the synchronous motor, consists of windings and generates a rotating magnetic field for the rotor. Rotor is the rotating part of the synchronous motor, equipped with the permanent magnet and rotates along with the stator’s magnetic field.
Watch the YouTube Video by "Sabins Civil Engineering" to learn about the working of synchronous motors.
The working principle of a synchronous motor involves the stator producing a rotating magnetic field when AC power is supplied to its windings. The rotor interacts with the rotating magnetic field of the stator and rotates. When the rotor achieves synchronous speed, it locks with the stator’s magnetic field and maintains a constant rotational speed equal to the supply frequency.
Key advantages of synchronous motors include constant speed under varying loads, high efficiency, and the ability to correct power factors makes them valuable in applications like pumps, compressors, and industrial power factor correction.
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What is a Synchronous Motor? | Construction, Working Principles and Applications
Types of Losses in Synchronous Motor
Synchronous motors are widely used for their efficiency and precise speed regulation. Understanding its losses is crucial in optimising performance and minimising inefficiencies. The losses in synchronous motors can be categorised as follows:
- Electrical Losses
Electrical losses occur in the winding of the synchronous motor due to its resistance in the conductor. Stator copper loss is the major component of this loss and is caused by the flow of current through the stator winding. This loss is proportional to the square of the current.
On the other hand, rotor copper loss arises in wound rotor synchronous motors due to the resistance of the rotor windings. Permanent magnet synchronous motors (PMSMs) eliminate rotor copper losses as they do not have rotor windings.
- Magnetic Losses
Magnetic losses are known as core losses and occur in the iron ore due to an alternating magnetic field. Hysteresis losses are the major reason behind these losses and are caused by the magnetic flux behind the magnetizing force in the core material.
On the other hand, eddy current losses are another type of magnetic loss generated by circulating currents induced in the core material.
- Mechanical Losses
Mechanical losses in synchronous motors are associated with the physical movements of components of synchronous motors. Friction losses occur due to the resistance between moving parts such as bearings and shafts.
However, windage losses are another form of mechanical loss caused by the air resistance encountered with the rotor. Employing streamlined rotor designs helps in minimising windage losses, and contributes to the overall efficiency of synchronous motors.
- Stray Losses
Stray losses are relatively small and unpredictable losses. It arises due to irregularities in the magnetic circuit, manufacturing imperfections, or harmonic currents. These losses are challenging to quantity as they account for a small percentage of energy loss in the synchronous motor. Even though minor, reducing stray losses helps to enhance the synchronous motor’s performance.
Methods to Minimise Losses in Synchronous Motors
Synchronous motors experience various types of losses, including electrical, magnetic, mechanical, and stray losses. Here are proper techniques to minimise these losses to enhance motor efficiency and longevity:
- Minimising Electrical Losses
Electrical losses are primarily caused by the resistance in the stator and rotor windings. These losses can be minimised by using high-quality conductors such as copper which has low resistance.
Further, optimising coil design reduces resistance, while an efficient cooling mechanism helps in maintaining a lower operating temperature as resistance increases with heat.
- Minimising Magnetic Losses
Magnetic losses or core losses are caused by the hysteresis or Eddy current in the core of the synchronous motor. These losses can be minimised by using high-grade core materials such as silicon steel, which exhibits low hysteresis loss.
Laminating the core reduces the Eddy current by restricting its flow, while an optimised magnetic circuit design minimises flux leakage and core saturation. Operating synchronous motors at appropriate frequencies helps in controlling these losses.
- Minimising Mechanical Losses
Mechanical losses include losses caused by friction and air resistance and can be reduced through several measures. Using high-quality precision bearings with regular lubrication minimises friction.
Streamlined rotor design reduces air turbulence and creates a dynamic performance to ensure that the rotor operates without unnecessary mechanical stress. Regular maintenance of mechanical components further prevents excessive wear and tear and reduces mechanical losses.
- Minimising Stray Losses
Stray losses arise from unpredictable errors such as harmonics and leakage currents, which can be addressed through design and mitigation techniques.
Reducing harmonics with proper winding configuration and the use of filters help reduce stray losses. Optimising synchronous motor design by minimising non-uniform air gaps also contributes to reducing stray losses.
Conclusion
Understanding and minimising losses in synchronous motors is critical for improving their efficiency and sustainability. By addressing electrical losses, magnetic losses, mechanical losses, and stray load losses through innovative design, material improvements, and operational strategies, industries can achieve significant energy savings and enhanced motor performance. Adopting these practices not only improves cost-effectiveness but also aligns with global energy conservation goals.
Synchronous motors, with their precision and reliability, will continue to play a pivotal role in industrial applications, and minimising losses ensures they do so efficiently and sustainably.
