Whether we like it or not, almost everything we use in everyday life comes from some sort of factory. From food and water to clothes, everything is manufactured or processed. And wherever things are produced, there is a production line running continuously, 24 hours a day, 365 days a year. And every single production line in the world needs motors to keep it in motion and fans to cool it.
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This also applies to the water industry. Wherever you have a water supply, there are electric motors driving the pumps. Any industry you can think of needs motors. As a result, there are an estimated 300 million industrial electric motor-driven systems in the world.
If we could improve the efficiency of each of these motors by only a few percent, it would save a huge amount of energy. Synchronous reluctance motors offer the kind of big savings we’re looking for but it took many years of development to get this far. Let’s take a look at 5 things to know about synchronous reluctance motors.
In business terms, SynRM technology can save a lot of electricity and therefore money per year. In environmental terms, it can also lead to a significant reduction in CO2 emissions.
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ABB’s IE5 SynRM motor and drive packages are optimised to create a perfect match, delivering the highest efficiency levels available on the market.
And because they run cooler, SynRM motors are more reliable, last longer and require less maintenance compared to other motor types, with no compromise on performance.
§ Market overview
§ Key characteristics
§ “Confrontation” between synchronous and asynchronous electric motors
§ Electric motor or generator selection
§ Electric motor malfunctions
The use of natural resources is inconceivable without the transformation of some kinds of energy into others. Devices performing mechanical movements for such energy transformation are referred to as energy-converting machinery. For example, a heat machine may be used to convert thermal energy released during fuel combustion into mechanical energy. The same term is used for devices that convert energy with the certain parameters into energy of the same kind but with the different parameters. Thus, a hydraulic machine is one that serves to convert mechanical energy of a translational liquid flow into mechanical energy transmitted through a rotating shaft.
A significant proportion of energy stored in nature in the form of chemical energy, nuclear energy, kinetic energy of rivers and seas, wind energy and solar radiation energy is converted into electrical energy in the modern world. The practicability of such a conversion is due to the fact that electrical energy can be transmitted over long distances, distributed among consumers and converted back into mechanical, thermal or chemical energy at low cost.
Machines that convert mechanical energy into electrical energy or vice versa are called electrical machines.
An electrical machine designed to convert mechanical energy into electrical energy is referred to as a "generator". An electrical machine designed for a reverse conversion is called an "engine". Electrical machines are reversible. Any electrical machine can perform electromechanical conversion in two permissible directions. If mechanical energy is transmitted to the moving part of an electrical machine, it operates as an electrical power generator. If electrical energy is delivered to the machine, its moving part performs mechanical work.
An electrical machine is an electromagnetic system that consists of interconnected magnetic and electric circuits. The magnetic circuit includes stationary and movable magnetic cores made of magnetic material and a non-magnetic air gap separating them from each other. Electric circuits in the form of two or more windings can move relative to each other together with the magnetic cores on which they are located.
Electromechanical energy conversion in electrical machines is based on the phenomenon of electromagnetic induction. Electrical machines operating based on the law of electromagnetic induction are referred to as inductive machines.
Along with inductive electrical machines, there are so-called capacitive electric machines, in which the electromechanical energy conversion is based on the phenomenon of electrostatic induction and is associated with a periodic variation of the electric field in a capacitor with relatively moving electrodes. However, such machines cannot compete with inductive machines in terms of their weight, size and cost parameters and are not used in the field of industrial electromechanical energy conversion.
§ Market overview
The global AC motor market is segmented based on type and application. The market is divided into synchronous motors and asynchronous motors by type. An AC motor typically consists of two main parts: a static stator with coils that receive alternating current to generate a rotating magnetic field and a rotating rotor with windings. The development of energy-efficient systems to alleviate raising concerns over energy consumption and carbon dioxide emissions is expected to encourage the global AC motor market. Companies focus on research activities to provide eco-friendly solutions to their technologies and processes as the world population grows, environmental issues worsen, and energy shortage appears.
The global asynchronous motor market is expected to grow by 5% a year in the period from to . It is expected to exceed USD 20.167 billion by as compared with USD 14.42 billion in . Asynchronous motors are divided into home, industrial, commercial, transportation, and others by application. Several factors such as the growing demand for affordable energy-efficient motors and the growth in production and industrial sectors in developing countries are encouraging the asynchronous motor market[1].
Three-phase asynchronous motors are used in many industrial fields, including pumps, compressors, conveyors, air blowers, and fans. Due to their high efficiency and reliability, these motors are used in heavy industries, including steel casting, cement production, and mining. Fans, pumps, and air compressors are often driven by asynchronous motors in heating, ventilation, and air conditioning (HVAC) systems. These motors maintain reliable operation and minimum noise levels over a wide range of operating temperatures.
The asynchronous motor market is expected to be dominated by the Asia Pacific Region (including: China, Japan, South Korea, India, Australia, ASEAN and rest of the world).
The demand for asynchronous motors has increased due to a rapid growth in the number of manufacturing and industrial facilities. Asynchronous motors are used in fans, air blowers, machine tools, compressors, pumps, conveyors, bulldozers, etc. Asynchronous motors are essential for the stable and reliable operation of the growing number of railways, subways, high-speed trains, etc. Asynchronous motors are used for various processes in the agricultural sector. Elevators and escalators are in high demand due to rapid urbanization, which has also driven up the demand for asynchronous motors.
Considering current trends in energy efficiency, the most commonly used type of motor today is the asynchronous motor (AM), although AMs have already reached the limit of their design and technological improvement. Further improvement of the efficiency of these motors is possible only by extensive methods: using more copper and steel and installing a copper squirrel-cage rotor. The main disadvantage of such solutions is the increase in the size of the motor and its cost. Moreover, the use of a copper squirrel-cage rotor results in a significant complication and increase in the cost of production technology due to the high melting point of copper.
Regarding the Russian market scale, approximately 1.17 million electric motors were produced in Russia in . For comparison, the production volume was 1.24 million units a year earlier. Thus, a drop of 5.4% was recorded. This is evidenced by statistics from BusinesStat published on June 7, [2].
In , Russia produced about 1.45 million electric motors by estimate. A year later, the production volume fell by 6.5% to 1.36 million units. In , a growth by 2.8% to 1.39 million units was recorded. In , another decline followed: approximately 1.24 million electric motors were produced which represents a 11.1% drop year-on-year.
§ Key characteristics
A synchronous machine is an alternating current machine in which the rotor speed is equal to the speed of rotation of the magnetic field in its working gap. A synchronous machine can be used as a fixed-frequency voltage generator (turbine generator, hydraulic generator or diesel generator) in which a steam or gas turbine or a diesel engine is used as the prime mover. A synchronous machine is often used as a motor with a constant speed of the rotor driving large fans, compressors, centrifugal pumps, DC generators, etc. In addition, a synchronous machine is used as a compensator to increase the power factor of the power supply network and to regulate its reactive component of power.
An asynchronous machine is an electromechanical converter in which the occurrence of torque on the rotor shaft is possible only at different rotation speeds of the magnetic field and the rotor. There are single-, two-, three- and multi-phase asynchronous machines. Three-phase asynchronous machines with a squirrel-cage rotor make up the bulk of the world's fleet of electrical machines due to their high-technology, reliability, low cost and long service life[3].
Over the last 50 years, the design and production technology of asynchronous electric motors have been worked-out and optimized so well that any further improvements or enhancements to their electrical parameters, even with the use of modern computer software, no longer allow us to expect a noticeable reduction in such a large gap between them and modern synchronous electric motors in terms of specific power characteristics.
Let's consider the major differences between synchronous and asynchronous electric motors, as well as their advantages and disadvantages.
1. Asynchronous electric motor operating principle
The main structural components of an asynchronous machine are stator and rotor (Fig. 1.1)
*Stator / Rotor
Asynchronous machines are most widely used as engines. This is the main engine used in the industrial and agricultural sectors, as well as in everyday life. Several million asynchronous motors of unified series with the power from 0.06 up to 400 kW are produced in our country every year.
Electrical engineering facilities manufacture asynchronous motors with a wide range of power. The maximum power of asynchronous motors is several tens of megawatts. Indicator systems use asynchronous motors with a power from fractions of a watt to hundreds of watts. The speed of a general-purpose motor ranges from 500 to 3,000 rpm.
80% of all electric motors produced in the industrial sector are asynchronous due to the numerous advantages of this type of drive. Such drive is[4]:
· reliable;
· inexpensive to manufacture;
· easy to maintain;
· does not require high operating costs;
· easily controllable by a frequency converter
However, when choosing an electric motor, its disadvantages should be considered, such as:
· limitation of the number of revolutions by the mains frequency (at a 3-phase mains frequency of 50 Hz, the maximum speed is 3,000 rpm);
· dependence of torque on line voltage;
· high starting current;
· starting torque is less than the maximum torque.
2. Synchronous electric motor operating principle
The design of the stator of a synchronous machine, also called an armature, is practically the same as one of the stator of an asynchronous machine. The main difference of a synchronous machine is the design of the rotor (inductor) which intrinsically represents a salient-pole or non-salient-pole electromagnet (Fig. 2.1, a, b). The winding of the electromagnet is fed from an external DC power source through slip rings and brushes. A permanent magnet can be used as an inductor in a synchronous machine.
A salient-pole rotor (Fig. 2.1, a) is usually used in machines with four or more pairs of poles. In this case, the excitation winding is made in the form of rectangular cross-section cylindrical coils placed on the pole cores and secured with pole pieces. The rotor, pole cores and pole pieces are made of sheet steel. Two-pole and four-pole high-power machines operating at a rotor speed of 1,500 and 3,000 rpm are usually manufactured with a non-salient-pole rotor (Fig. 2.1, b). The use of a salient-pole rotor in them is impossible because it does not ensure the necessary mechanical strength of fastening of the poles and the excitation winding. The excitation winding in such a machine is placed in the slots of the rotor core made of massive forged steel, and is secured in them with non-magnetic metal wedges. In synchronous motors with a salient-pole rotor, bars of the squirrel cage made of a material with increased specific resistance (brass, etc.) are placed in the pole pieces. This cage serves as a starting winding. The same squirrel cage made of copper bars is used in some synchronous generators. It is called a damping or damper winding, since it ensures rapid damping of rotor oscillations that occur in some operating modes of a synchronous machine. Currently, synchronous motors are often made without a starting winding, but with massive poles. Eddy currents arise in these poles during starting, they interact with the rotating magnetic field and thus produce a starting torque. Non-salient-pole machines are also made without a damper winding which function is fulfilled by eddy currents flowing in closed loops in a massive rotor[5].
Although asynchronous motors are considered more reliable and affordable, their synchronous "fellows" have some advantages and are widely used in various industries. The distinctive characteristics of a synchronous electric motor include[6]:
· Operation at a high power factor.
· High efficiency compared to an asynchronous machine with the same power.
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· Maintaining output capacity even when the line voltage drops.
· Constant rotation speed regardless of the mechanical load on the shaft (within permissible ranges)
Synchronous motors have also some disadvantages:
· Quite a complex design making their production more expensive.
· The need for a DC source (exciter or rectifier).
· Difficulty of starting.
· The need to correct the angular speed of rotation by changing the frequency of the supply voltage.
However, using synchronous motors is preferable in some cases:
· To improve the power factor.
· In long-term process flows where there is no need for frequent starts and stops.
Thus, the “pros” of electric motors of this type significantly outweigh the “cons”, that is why they are currently in high demand.
§ Electric motor or generator selection
Ultimately, the choice between a synchronous and asynchronous electric motor depends on specific requirements and operating conditions. It largely relies on the total power of all connected equipment and its subsequent operating conditions.
Therefore, when choosing a generator model, the following aspects shall be considered[7]:
· Quality of electric current. Synchronous models provide higher quality of generated electric current, while the output voltage remains in the same amplitude, which is certainly highly appreciated. However, it should be understood that at the moment of starting of some household appliances, the short-term load increases significantly and sometimes exceeds the nominal power many times. Synchronous installations tolerate such peak loads very poorly, therefore they require a more careful selection of power with regard to the necessary power reserve. On the contrary, asynchronous models easily tolerate short-term increased overloads, but generate electric energy of lower quality.
· Scope of use. The fact that asynchronous generators cannot boast of high quality of the generated electric energy does not prevent them from being successfully used as an emergency power source in summer cottages, country houses, at construction sites, and are ideal for connecting various tools. But if the equipment sensitive to the quality of electric energy is planned to be used, then it is permitted to connect only synchronous generators in this case.
· Price. Asynchronous motors are more affordable as compared to synchronous ones.
· Ease of maintenance. Asynchronous generators are easier to maintain and less sensitive to short circuits.
When choosing an electric motor, the following criteria should be guided by[8]:
· type of electrical current supplied to the equipment;
· electric motor power;
· operating mode;
· climatic conditions and other external factors.
Synchronous electric motors are the optimal solution for equipment with constant operating speed: DC generators, compressors, pumps, etc.
Asynchronous electric motors meet the requirements of various industrial applications:
· Multi-speed asynchronous drives are produced for elevators and other equipment requiring the stepped variation of speed.
· When operating winches and metalworking machines, electric motors with an electromagnetic braking system are used. This is conditioned by the need to stop the drive and fix the shaft during power interruptions or outages.
· In processes with pulsating loads or during intermittent duties, asynchronous electric motors with high-slip parameters can be used.
At present, direct current electric motors are not applied as often as they used to be. They have been practically superseded by asynchronous motors with a squirrel-cage rotor.
The main disadvantage of DC motors is the capability of operation only with a DC source or an AC/DC converter. In modern industrial production, meeting this condition requires additional expenses. However, despite significant disadvantages, this type of motor is characterized by a high starting torque and stable operation at high overloads. Drives of this type are mostly used in metallurgy and machine tool building, and they are also installed on electric transport.
§ Electric motor malfunctions
Electric motors are commonly used in the industrial sector, they are becoming more and more technically sophisticated which can often complicate maintaining their operation at peak efficiency. It is important to remember that the causes of malfunctions of electric motors and drives are not limited to one field of specialization: they can be of both mechanical and electrical nature.
Only the essential knowledge makes the difference between expensive downtime and extended service life.
The most common malfunctions of electric motors are damage to winding insulation and wear of bearings which occur for many different reasons. Therefore, it is important to find a reliable supplier of sections and order high-quality windings.
Rem&Coil produces all types of sections, as well as stator winding bars for electric motors and alternating and direct current generators. It does not matter to us how long ago your electric motor was manufactured. Thanks to the ideal geometry, the section laying process will take 1-2 days. The excellence of materials is very important to the plant, therefore only high-quality copper of at least M1 grade according to GOST 859 is used, as well as insulation of heat resistance classes F, H, C from the leading global manufacturers.
Engineers from Saint Petersburg are ready to solve any problem of our customers. They independently upgrade and produce new equipment so that you get exactly what you need. They are ready to consult you on any issues related to stator windings.
Rem&Coil specialists are ready to come anywhere in the world to help solve your technical problem related to sections. We offer a free test sample of sections so that our customers can get to know Rem&Coil better and decide on cooperation.
It is worth remembering that the quality of the production depends not only on the technology, but also on the materials used. Therefore, the plant cooperates only with the best suppliers of wires and insulation. All production exceeds international quality standards and ensures reliable operation of electric motors for years to come. Tests in the laboratory of the Saint Petersburg Polytechnic University have shown that the service life of our sections is 75 years[9].
In conclusion, it is worth mentioning that for each area, different types of motors are used because different industries require specific characteristics and properties of electric drives. For example, asynchronous motors which are simple and reliable are used in the industrial sector, while synchronous motors are used in power generation and aviation as they provide high accuracy and efficiency.
Asynchronous motors are more commonly used in the industrial sector because they are simpler, more reliable and versatile. However, synchronous motors are also used in certain industries that require high speed accuracy and efficiency, such as power generation, industrial installations, and marine transport.
§ References
[1] https://exactitudeconsultancy.com/ru/blog//05/06/induction-motor-market-growth/
[2] https://www.tadviser.ru/index.php/%D0%A1%D1%82%D0%B0%D1%82%D1%8C%D1%8F:%D0%AD%D0%BB%D0%B5%D0%BA%D1%82%D1%80%D0%BE%D0%B4%D0%B2%D0%B8%D0%B3%D0%B0%D1%82%D0%B5%D0%BB%D0%B8_%28%D1%80%D1%8B%D0%BD%D0%BE%D0%BA_%D0%A0%D0%BE%D1%81%D1%81%D0%B8%D0%B8%29
[3]
N.I. Zadoya "ELECTRICAL MACHINES Part 2. Asynchronous AC machines. Synchronous AC machines". Study guide for bachelors in the field of study: "Electric Power Engineering and Electrical Engineering". Ministry of Education and Science of the Russian Federation. Rubtsovsk Industrial Institute (branch) of the Federal State Budgetary Educational Institution of Higher Professional Education "Altai State Technical University named after I.I. Polzunov”
[4]
https://www.szemo.ru/press-tsentr/article/stator-asinkhronnogo-dvigatelya-ustroystvo-i-printsip-raboty/
[5]
N.I. Zadoya "ELECTRICAL MACHINES Part 2. Asynchronous AC machines. Synchronous AC machines". Study guide for bachelors in the field of study: "Electric Power Engineering and Electrical Engineering". Ministry of Education and Science of the Russian Federation. Rubtsovsk Industrial Institute (branch) of the Federal State Budgetary Educational Institution of Higher Professional Education "Altai State Technical University named after I.I. Polzunov”
[6]
https://www.szemo.ru/press-tsentr/article/ustroystvo-i-printsip-deystviya-sinkhronnogo-dvigatelya/
[7]
https://dgu.expert/statii/chto-luchshe-sinhronnyj-ili-asinhronnyj-generator
[8]
https://tehprivod.su/poleznaya-informatsiya/vybor-elektrodvigatelya.html
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