Asynchronous motors are widely used in industry and home appliances, accounting for more than 70% of the global motor market. Their working principle is to generate torque through the difference in magnetic field between the stator and the rotor. Usually, the speed is 1%-6% different from the rated value, and the efficiency can reach more than 90%.
Definition
In the global electric motor market, asynchronous motors account for over 70% of the market share. The motors used in household air conditioners typically have a power of around 500W, while some large industrial machinery motors can reach up to 2000kW in power.
The speed of an asynchronous motor usually varies by 1%-6% from the rated value.
Modern high-efficiency asynchronous motors have an energy efficiency rating of IE3, which is about 12% higher than traditional motors. If a 10-year usage cycle is considered, using high-efficiency motors can save around 20% in electricity costs.
About 80% of industrial electric motors worldwide are asynchronous motors. A large steel plant uses asynchronous motors with a power of 5000kW, capable of running continuously for 24 hours, with a service life of up to 20 years.
Asynchronous motors account for more than 90% of the motors used in global household appliances. After switching to asynchronous motors, appliance manufacturers reduced production costs by 15%-20%.
For example, in a chemical plant, the asynchronous motors used need maintenance approximately every 1000 hours of operation, and the regular maintenance costs account for about 5%-10% of the total equipment operating cost.
Asynchronous motors controlled by frequency converters can improve energy efficiency by over 15%. After introducing frequency converters into an automated production line, the total energy consumption of the production line was reduced by 12%, and production efficiency increased by 10%.
80% of smart asynchronous motors can predict failures in advance.
The global market size for asynchronous motors has reached $12 billion and is expected to reach $15 billion by 2026. The annual production of electric motors in China has surpassed 500 million units.
All newly produced asynchronous motors must meet the IE3 energy efficiency requirements, and in some regions, they are even required to meet IE4 standards.
Working Principle
Over 75% of electric motors globally are asynchronous motors.
Depending on the type of motor and working conditions, slip usually ranges from 1% to 6%. For an asynchronous motor with a rated speed of 1500 rpm, if the slip is 5%, the speed will drop to approximately 1425 rpm.
In 2018, the market share of asynchronous motors reached 70%. The motors used in ordinary household air conditioners typically have a power of around 200W to 300W.
Water pumps commonly use asynchronous motors with power ranging from 5kW to 100kW. Approximately 80% of motors in global water pump systems are asynchronous motors, and these devices have a service life of about 15 years.
The efficiency of modern asynchronous motors is typically above 90%, meaning 90% of electrical energy is converted into mechanical energy, with the remaining 10% converted into heat. After adopting high-efficiency asynchronous motors, a large manufacturing company saved around $200,000 in energy costs annually.
In heavy industry, asynchronous motors can even reach a power of 10,000kW. A steel plant uses asynchronous motors with a power of 5000kW and runs over 5000 hours each year.
The average lifespan of an asynchronous motor is typically 15 to 20 years. If high-quality materials and processes are selected during the design, the lifespan can be extended to over 30 years. An asynchronous motor used in a petrochemical enterprise has been running for over 25 years and still maintains high efficiency and stable performance. The annual maintenance cost for this motor is less than 3% of the equipment cost.
In wind turbines, the use of asynchronous motors exceeds 60%, with their average annual performance improvement being about 15%.
A large factory reduced its energy costs by about 18% and improved production efficiency by 12% by using frequency converters in its production line.
Structure
There exist mainly three parts of the structure of an asynchronous motor: stator, rotor, and the external components.
For a 5kW industrial asynchronous motor, the quality of the material of the stator core ensures energy efficiency rating. Use of silicon steel sheets can result in 10%-15% reduction in energy losses in the stators.
Approximately 80% of asynchronous motors globally use squirrel-cage rotors. For example, the cost of a squirrel-cage rotor for a 2.2kW small motor is 30%-40% lower than that of a wound rotor.
The asynchronous motors with copper rotors increase their efficiency by some 5%-10%. In the case of large systems, for instance, water pumping systems, it is about roughly 8% better energy efficiency compared to that of an asynchronous motor with aluminum rotor.
The asynchronous motors with rolling bearings have a life span of about 30% longer compared to those with sliding bearings. The life of an industrial motor that runs for over 4000 hours yearly and with rolling bearings is normally about 20 years while those with sliding bearings have only about 10 years.
The asynchronous motor with a cast iron housing weighs approximately 50 kg, while for the motor with an aluminum alloy housing, it is lighter by about 20%.
A cooling fan system can lower the operational temperature of the motor by 10°C to 20°C. After adding a cooling system to some high-power motors, their overload capacity increased by 15%-20%.
Advantages
Asynchronous motors hold a share of up to 70% in the market; besides, the unit price of low-power motors usually accounts for less than $300.
A routine maintenance cycle for a standard 3kW industrial asynchronous motor lasts from 1 to 2 years. The mean time between failures at the equipment level using asynchronous motors is about 3000 hours, thus 20% higher than that using other types of motors.
In relatively stable load conditions, a state-of-the-art high-efficiency asynchronous motor can have an efficiency of more than 95%. In the replacement of motors installed in the production process, the high-efficiency asynchronous motors provided annual savings of about 15% in energy costs to the large manufacturing company. At this rate, it could pay back the replacement cost of motors within 5 years.
Asynchronous motors result in an operational efficiency enhancement of about 12%-15% in water pump systems compared to conventional systems.
Asynchronous motors can operate up to 15 to 20 years. Generally, for each asynchronous motor produced by a household appliance factory, major failures of the motor do not appear within 5 years. Three times the average service life of equipment using asynchronous motors is its investment.
The starting current of the asynchronous motor is usually 5 to 7 times the rated current. Using an asynchronous motor, the peak starting current is only 6 times the rated current, whereas in a DC motor, the peak current can reach 10 times the rated current.
For equipment such as pumping stations and conveyor belts, which needs to run for 24 hours, asynchronous motors can operate for more than 30,000 hours without being stopped. In contrast, other types of motors can only be operated continuously for about 10,000 hours.
In addition to direct starting, there are several other methods for starting an asynchronous motor. Among them include reduced voltage starting, star-delta starting, and soft starting.
A power company used asynchronous motors to drive fans in high-temperature applications. They were able to achieve 24 hours of continuous operation. The temperature range for asynchronous motors can be between -40°C and +60°C.
Asynchronous motors used in air conditioning systems have achieved 10%-20% higher energy efficiency compared to similar DC motor systems.
Applications
Sales in asynchronous motors comprise more than 70% of the sales in the world’s electric motors. For example, in several electronic products manufacturing plants, with a yearly production capacity of 100,000 units, some 500 asynchronous motors are put to work just to guarantee smooth and stable production.
About 90% of all washing machines that were produced used an asynchronous motor as the powering motor. Common house washing machine – asynchronous engine has from 0.2 to 0.6kW power and lives around 10 years on average.
About 60% of the world’s agricultural water pumps use asynchronous motors. In one large farm in China, 50 5kW asynchronous motors were set up in the irrigation system, saving about 20% of energy consumption compared to fuel pumps.
About 80% of the world’s offshore drilling platforms use asynchronous motors; about 40% of the world’s wind turbines use asynchronous motors; and about 25% of the world’s electric vehicles use asynchronous motors as their power source.
More than 80% of mining enterprises in the world adopt asynchronous motors as main driving equipment.
About 70% of the steel enterprises in the world use asynchronous motors for driving. A steel plant consumes about 5 million kWh every year for motor energy, and asynchronous motors help this company save about 20% of the energy consumed.
About 65% of the hoisting equipment in construction around the world is using asynchronous motors. The maintenance cost of tower crane equipment with asynchronous motors is 20% lower than those using other kinds of motors.
About 80% of the food processing plants around the world are driving their production line equipment by asynchronous motors. For example, a certain food processing plant with an annual output of 500,000 tons is driving various equipment with about 200 asynchronous motors.
