Electric motor
An electric motor is an electric machine that converts electrical energy into circular motion. While a generator is an electrical machine that converts circular motion into electrical energy. Before the invention of the electric motor, steam engines and internal combustion engines were used to achieve circular motion. The electric motor has not yet replaced the mentioned machines completely, but because of ecology and politics, it could be said that it is only a matter of time. Electric motors are divided into the following types:
The noticeable development of electric motors began in the 19th century. Historically, the first significant application was achieved by the direct current electric motor, since the control of the direct current electric motor is simpler than the alternating current electric motor. Currently, the most widely used electric motors in industry are induction motors invented by Nikola Tesla, and the one in question was patented at the end of the 19th century. Due to development in the field of motor control technology, motors with permanent magnets are increasingly used in modern systems. One of the advantages of permanent magnet motors is a better power-to-weight ratio.
TECHNICAL CHARACTERISTICS
The type of electric motor for its application is selected based on its technical characteristics and economic value on the market. Due to the development of technology, the price of motor manufacturing and the price of motor control components changes, which over time leads to a change in the selection of the type of electric motor for a specific application. The basic technical characteristics of the electric motor are:
| Name | Measurement unit | Example |
| Voltage | volt [V] | Washing machine: 230V ac 1pElectrical bicycle: 48V dc |
| Power | wat [W] | Washing machine: 270-426 WElectrical bicycle: 250-1250WRimac Nevera: front motors 2x 220 kW, rear motors 2×450 kWŠkoda 15T ForCity tram: 16 x 46.6kW |
| Torque | [Nm] | Washing machine: 0.3 – 1.5 NmElectrical bicycle: 35 – 85 NmRimac Nevera: front motor each 270 Nm, rear motor each 900 Nm |
| Efficiency | percentage[%] | Washing machine: 70-80%Induction motor IE4: 62-97% |
| Motor control | Torque: carSpeed: tramPosition: CNC machineProduction measurement: conveyor in the production line of a factory | |
| Speed | revolution per minute [rpm] | Washing machine: 3400-14000 rpmInduction motor: <3000 rpmPC cooling fan: 300 – 1800 rpm |
In today’s world where energy efficiency is an important topic, the efficiency of the asynchronous motor that is currently most commonly used is classified. This classification is carried out on the basis of the standard “HRN IEC 60034-30 Rotating electrical machines – Part 30-1: Efficiency classes of line operated AC motors (IE code)”. Through the Official Journal of the European Union, the class of engine efficiency that should be incorporated into new systems is prescribed. The acceptable efficiency of an electric motor depends on its power. The Official Journal of the European Union puts different requirements if a variable speed drive is used compared to the fixed speed motors that are currently more commonly used.
APPLICATION
Regarding the application of the electric motor, it is not difficult to list in which systems it is found. Currently, the most popular systems in the media that have an electric motor are electric cars, electric scooters, bicycles, commonly known as personal means of transportation. The mentioned systems started to develop with the development of the battery because they depend on the energy from it. Modern applications in which a battery is used for power supply often require the motor to be as light as possible. For example electric bicycles and drones use because of this requirement brushless electric motors. Electrification of existing cars that were primarily produced with an internal combustion engine did not take off. In the case of bicycles, you can see on the roads a representative sample of classic bicycles with an added electrical motor.
In the early days of the development of electric motors, public transport vehicles (trams and trains) that did not need batteries for power supply, because they were powered via lines, first began to be developed.
Servo motors have the possibility of precise and fast positioning and are used in various CNC machines (for processing metal, wood, plastic, etc.) and 3D printers. They can be designed to be powered by direct current or alternating current. An essential characteristic of a servo motor is how much weight it can lift at a distance from its axis (e.g. a servo with a power of 5 kg/cm can lift a load of 5 kg that is 1 cm away from its axis).
CONTROL
The most common application of electric motors in industry is in the mode of operation where the motor operates at a static operating point (e.g. constant rotation speed). For such a mode of operation, it is necessary to select a good motor speed and, if necessary, a reduction drive. At lower powers, motors in such applications are direct on line starting. Motors with higher power when starting direct on line have a problem with a large starting current. The solution to the starting current problem is solved by a star/delta starters or a newer solution with a soft starter.
Motors that do not operate at a static operating point are driven by power electronics devices that change voltage, frequency and current. Such devices are called variable frequency drive (VFD) or just drive. With dynamic control of electric motors, it is necessary to choose whether we want to control with or without feedback loop. Feedback control is a type of control when a process value is measured and based on it determines whether one of the input values (voltage, frequency or current) to the electric motor should be increased or decreased.
PLC devices are used for complex electric motor control algorithms. Complex control algorithms can be based on feedback loop from the system, which tells how to control the motor. Each additional sensor makes the system more expensive and adds an element that has the potential to fail. If a certain process unit is not measured, the system does not have a sensor for it. This is called senseless control, and the unit in question is approximated or timed.
LIFE SPAN
As with any other machine, the lifespan of an electric motor largely depends on the conditions in which it works (humidity, temperature, corrosion, etc.), hours of operation and the quality of the electricity it is supplied with. When any engine component wears beyond the point when it is not economically worthwhile to repair or replace the worn part, the economic life of the motor ends. Depending on the size and power of the motor, the limit of economic life is different. As an example, the wear of the bearings can end the economic life of the smaller motors.
As the operating temperature rises above the nominal one for which the motor is designed, the life span of the winding insulation decreases. This can lead to the mistaken belief that buying new motors designed for higher temperatures will increase the life of the motor. This is not always true, as new motors designed with higher temperature winding insulation may actually be operating at higher internal motor temperatures.
With motors of high power or motors that are made for a special application, it is useful to think about a motor monitoring system. Such a system enables predictive maintenance of the motor, extends the life of the motor and reduces unexpected breakdowns. The electric motor monitoring system uses sensors to collect information about the state of the motor (e.g. vibrations on the shaft, voltage, current, electromagnetic field in the air gap, etc.) and on the basis of this, reports alarms and provides information on which maintenance can be planned.
The electric motor is a machine without which today’s industry is unimaginable. The optimization and reduction of labor force in the industry shows the trend of increasing the number of electric motors in the future. The trend of using electric motors in personal transport was brought to the world stage by the auto industry. While in public transport, the electric motor through rail transport has long been a recognized solution. In the big metropolises of Europe, in the last couple of years, electric bicycles and scooters have exponentially increased their share in the transportation of the population.