Types of electric motors: Classification, operation and industrial applications

Introduction

Types of electric motors represent one of the most far-reaching innovations in modern engineering, efficiently converting electrical energy into mechanical energy through the interaction of magnetic fields generated in their main components: the stator and the rotor. This basic principle, based on fundamental laws of electromagnetism, has enabled their application in a wide variety of sectors, from industrial automation to transportation and renewable energy systems.

The design and selection of an electric motor not only involves understanding its operating principles, but also evaluating key factors such as required power, torque, energy efficiency and specific environmental conditions. These aspects are essential to ensure optimum performance and long service life, positioning electric motors as key players in the development of sustainable and efficient technologies.

This article seeks to serve as a bridge between fundamental concepts and their practical application, providing engineers and technicians with the tools necessary to design, select and maintain electric motors that meet the specific needs of each system. It is hoped to foster a deeper understanding that will inspire further research and development in this essential field for modern industry.

What is an electric motor and its components

Electric motors are fundamental devices in industry and everyday life, designed to convert electrical energy into mechanical rotational energy through the action of magnetic fields generated in their coils. They are rotating electrical machines composed of a stator and a rotor. They are used in countless sectors such as industrial, commercial and private installations.

Some electric motors are reversible in that they can convert mechanical energy into electrical energy by functioning as generators or dynamos. Electric traction motors used in locomotives or hybrid cars often perform both tasks, if properly designed.

Main components of electric motors

• Coil: It is a fundamental element in the operation of an electric motor, consisting of a set of conductors wound around a ferromagnetic core. When an electric current is applied, a magnetic field is generated that interacts with the rotor and the stator, inducing the rotary motion.
• Rotor: It is the rotating component of the motor, located inside the stator. It may consist of permanent magnets or an iron core with windings. Its movement is a consequence of the interaction between the magnetic field generated by the stator and the rotor itself.
• Stator: It is the fixed part of the motor and is composed of coils arranged on a laminated magnetic core. Its main function is to generate a static or rotating magnetic field when fed with electric current, which induces the movement of the rotor.
• Bearings: These are mechanical elements designed to reduce friction between the rotor and the stator, allowing smooth and efficient movement. They can be ball or roller bearings, selected according to the axial and radial load to be supported by the motor shaft. Their proper maintenance is critical for the durability and performance of the system.
• Shaft: The shaft is the mechanical component responsible for transmitting the torque generated by the rotor to the external drive system. Its design must consider factors such as mechanical resistance, rigidity and capacity to support dynamic loads. It can be solid or tubular, depending on the operational requirements of the motor.

Auxiliary components

• Housing: The housing protects the internal components of the motor against contaminants, mechanical impacts and adverse environmental conditions. It also contributes to the thermal dissipation and safe mounting of the motor in its specific application.
• Ventilation and cooling systems: These are necessary to dissipate the heat generated by the electrical and mechanical losses of the motor. They may include fans, dissipation fins or liquid cooling systems in high power applications.
• Control and power components: Electric motors require control and power systems to manage their starting, speed and torque. These include variable frequency drives, contactors and overload protection systems.

Electric motors combine these elements to optimize their performance and efficiency in various industrial applications. The following image shows an illustration of an electric motor with some of these components:

Classification and operation of electric motors

Below is a description of the main types of motors and an in-depth look at the operation of direct current (DC) motors.

Engine classification

Their classification depends on the type of current they operate with, which determines their design and specific applications.

There are three main types of electric motors:

• Direct Current Motor (DC): Operates exclusively with direct current.
• Alternating Current Motor (AC): Operates only with alternating current.
• Universal Motor: Can operate with alternating current as well as direct current.

Before controlling a motor, it is essential to understand its principle of operation and the reasons why it is chosen for specific tasks. The motor’s ability to perform a particular job and its efficiency are key factors in its selection.

Direct current motors (DC)

The DC motor is widely known as a “mechanical workhorse” because of its versatility and ease of controlling both speed and direction of rotation. This makes it an excellent choice for equipment requiring precision, such as winches, cranes, missile launchers and elevators.

Operating principles

The basic principle of operation of the motors is through a magnetic effect transformed into mechanical energy by induction caused in the direction determined by the magnetic poles, which are induced by the energization of the coils.

The operation of the DC motor is based on the physical principle that a conductor carrying electric current, being immersed in a magnetic field perpendicular to the flux lines, tends to move in a direction also perpendicular to the flux lines. This interaction follows the right-hand rule: the orientation of the magnetic field, the current in the conductor and the direction of motion are related to each other.

The engine consists of two main components

• Field poles: They are stationary and generate the magnetic field.
• Armature: It is mobile and rotates within the magnetic field generated by the poles.

The armature contains windings connected to commutator segments, while the brushes transmit current to the armature through the commutator. As the armature rotates, changes in the direction of the electric flux generate a variable magnetic field that interacts with the stationary field. This interaction causes the armature to move continuously.

And whenever there is a displacement of one of the components, a force will arise that will restore the alignment, with the realization of a mechanical work whose necessary energy is provided by the source that supplies the electric current that generates the magnetic field. Therefore, by imposing a misalignment of two energized electromagnets, mechanical work is being done and there is a process of electromechanical energy conversion.

Initial limitations

If the magnetic fields of the armature and poles are perfectly aligned when the motor is started, there will not be sufficient force to initiate rotation. This problem is solved by adding multiple windings to the armature, which ensures that there is always a misaligned field capable of generating motion.

Counter Electromotive Force (CEMF)

When a DC motor is in operation, it simultaneously acts as a generator due to the movement of the armature within the magnetic field. This phenomenon induces a voltage known as counter electromotive force (CEMF), which opposes the voltage applied by the battery. The CEMF plays a crucial role in the control of the motor, limiting the current flowing through the armature, avoiding excessive consumption.

Without CEMF, the armature’s low internal resistance would allow excessive current flow, which could damage the motor or cause it to operate outside its safe limits. Although unavoidable, CEMF contributes to improving the motor’s energy efficiency by regulating its electrical consumption.

Loads and performance

DC motors are used to drive various mechanical equipment such as pumps, fans or circular saws. The load is the mechanical equipment that the motor must move and directly affects its performance:

Higher load increases power consumption due to higher mechanical energy demand. Motor speed, current consumption and efficiency are directly dependent on the load characteristics. To maximize motor performance and ensure efficient motor operation, it is essential to balance motor characteristics with the specific demands of the load.

Types of DC motors

• Series motors: The field is connected in series with the armature, they use few turns of thick wire to support all the current.
  • Advantage: Generate high torque from start-up.
  • Applications: Portable power tools, cranes, winches and automotive starting systems.
• Shunt motors: The field is connected in parallel to the armature, they offer a more constant speed under different loads.
• Compound motors: Combining characteristics of both series and shunt motor, they are versatile for applications requiring precise control under a variety of conditions.

Alternating current motors (AC)

AC motors are more common in modern electric vehicles due to their efficiency and lower maintenance requirements. They fall into two main categories:

Synchronous motors

A synchronous motor is a machine that transforms electrical energy into mechanical energy. The average normal operating speed is exactly proportional to the frequency of the system to which it is connected.

Types of synchronous motors

The synchronous motor is constructed with a set of AC polyphase distributed windings, called armature, which is usually located in the stator and connected to the AC supply system. The configuration of the opposing element, usually the rotor, determines the type of synchronous motor.

DC excited field wound motors on round or silent pole rotors, with power ratings from 200 to 100000 hp and higher, are the dominant industrial type. In the brushless synchronous motor, excitation (field current) is supplied through shaft-mounted rectifiers from an AC exciter.

In the slip-ring synchronous motor, excitation is supplied from a shaft-mounted exciter or a separate DC power supply.

Synchronous induction motors rated less than 5 hp, which are typically fed by adjustable speed inverters, are designed with a different reluctance in the air gap on the direct and quadrature shaft to develop reluctance torque.

• The rotational speed of the stator magnetic field is equal to that of the rotor.
• Offer high efficiency and performance.
• They include variants such as permanent magnet motors (PMSM), permanent magnet motors (PMSM), permanent magnet motors (PMSM) and permanent magnet motors (PMM).

Asynchronous (induction) motors

• The magnetic field of the stator induces current in the rotor.
• Very reliable and low maintenance.
• Widely used for their robustness and low cost.

Innovation in design: efficiency and sustainability as priorities

The design of modern electric motors for electric vehicles is driven by two main objectives: maximizing energy efficiency and minimizing power losses. Engineers strive to improve power density and available torque while maintaining compact dimensions and reduced weight.

To achieve this, advanced materials and innovative manufacturing technologies are used to optimize performance, reduce friction and extend engine life. In addition, today’s designs incorporate sophisticated electronic control systems that ensure efficient energy management and rapid response to dynamic driving demands.

These innovations not only improve the range of electric vehicles, but also contribute to their overall reliability and sustainability, aligning with global emission reduction targets.

Advantages over internal combustion engines

Compared to internal combustion engines (ICE), electric motors offer significant advantages in terms of performance. One outstanding feature is their ability to deliver peak torque instantaneously, resulting in faster acceleration and greater responsiveness.

These qualities are especially valuable in urban environments, where constant stops and starts demand operational efficiency.

Flexibility in design: adaptability for optimum performance

The configuration of electric motors in vehicles varies according to design requirements. Some models use a single motor to drive an axle, while others use separate motors for each wheel.

The latter configuration enables all-wheel drive, improves maneuverability and optimizes vehicle stability. In addition, this flexibility in design facilitates a more balanced weight distribution, which has a positive impact on vehicle dynamics and overall performance.

Efficiency of electric motors

Motor efficiency is a measure of how effectively a motor converts electrical energy input into mechanical energy output to drive a load.

It is defined as the ratio of motor power output to power source input. The difference between input power and output power includes electrical and mechanical losses.

Higher horsepower ratings generally correspond to higher efficiencies. Small fractional horsepower motors tend to have low operating efficiency, while large integral horsepower motors are generally very efficient.

With a particular operating voltage and shaft load, the motor efficiency is fixed by design; it cannot be changed externally, while the power factor can be corrected externally.

Industrial applications of electric motors

Electric motors are fundamental in the automation and optimization of industrial processes, offering high energy efficiency and low maintenance. Their main applications in different sectors are presented below:

1. Manufacturing industry: In production lines, electric motors drive conveyors, presses, lathes and milling machines, ensuring precision and speed in the manufacture of parts.
2. Energy sector: They are used in electric generators, turbines and pumping systems in hydroelectric and thermal power plants, contributing to the generation and distribution of energy.
3. Automotive industry: From robots in assembly to traction systems in electric vehicles, electric motors enable greater efficiency and automation in production and mobility.
4. Mining and metallurgy: They are essential in conveyor belts, mills and industrial fans, optimizing the extraction, processing and refining of minerals and metals.
5. Petrochemical industry: They drive compressors, pumps and mixers in refineries and chemical plants, ensuring safe and efficient processes in the handling of hydrocarbons.
6. Food industry: They are used in processing, packaging and refrigeration equipment, ensuring quality control and compliance with sanitary regulations.
7. Water treatment and sanitation: Electric motors operate pumps and filtering systems in treatment plants, optimizing water distribution and purification.

In each application, motor selection depends on factors such as power, speed and energy efficiency, ensuring that it is tailored to the operational requirements of each industry.

Conclusion

Electric motors are essential for converting electrical energy into useful mechanical energy. In particular, DC motors excel in their ability to provide precise control over speed and direction, making them ideal for demanding industrial and commercial applications. Understanding their operating principles allows the most efficient type to be properly selected according to the specific needs of the job at hand.

References

1. https://insights.made-in-china.com/es/Electric-Motor-Selection-Guide_MTGAZiWdYJDp.html
2. https://tractian.com/es/blog/como-funcionan-los-motores-electricos
3. https://www.editores.com.ar/autor/alberto_farina/20200430_motores_electricos_trifasicos_seleccion_del_motor
4. Electric Motor Handbook – Wayne Beaty. James Kirtley.