A variable speed motor is a kind of motor whose speed can change with the changing load demand. It normally achieves this by manipulating the frequency or voltage of the input current via a frequency converter. It offers improved energy efficiency and reduces energy consumption by 20% to 40%.
Definition
A variable-speed motor is a type of electric motor that can change its speed according to the requirement. Unlike other fixed-speed motors, the variable-speed motor controls the frequency or voltage of the input current. In 2023, the global variable-speed motor market size was around $15 billion and was expected to grow by about 9% annually in 2028.
Devices with variable-speed motors save energy between 30% and 50%. This adjustment, especially in the industrial sector, will avoid equipment overload and reduce waste of energy. After installing a variable speed motor at one factory, the energy efficiency ratio of its air conditioner system went up 20%, which reduced the consumption of electricity by 20%.
A water treatment plant, with the installation of a variable-speed motor system, was able to save over 10% in electricity costs annually. The frequency of maintenance was reduced by 25%.
After the introduction of the variable-speed motor, production efficiency increased by 15%, while the failure rate was reduced by 10%. The variable speed of the motor allows fine adjustment, which reduces product loss and defects, hence greatly improving product quality.
Variable-speed motors help control the pump station’s speed in the oil and gas industry, reducing energy consumption by an average of 12%. Such measures will not only cut down the costs of operations but also serve environmental protection.
One power company shaved 20 percent off its system maintenance costs while extending equipment life up to 15 percent after applying variable-speed motors. Variable-speed motors have this effect since they decrease the rate of motor starts and stops, thus reducing mechanical wear.
The initial investment in a standard variable-speed motor system is usually 30% to 50% higher than the traditional motors. An investment in a variable-speed motor generally pays back in the form of energy savings and reduced maintenance costs within 1 to 2 years.
Annual power generation in the scenario of variable speed motors utilized in wind turbines of the sector of wind energy has risen from 8 to 12%. The primary factor is variation of wind speed, as the former can be set according to the dynamic condition of winds. Therefore power generation efficiency goes higher using this variable speed motor.
The motors that are generally used in the HVAC systems are variable speed in nature. A variable-speed motor used in the air conditioning system in a large office building cut down the power consumed by 15%, reduced the response time of the temperature control system by 20%, and trimmed noise by 10%.
Working Principle
The variable speed motor applies the principle of the change of the frequency or the change of the supply voltage. Within an industrial field, the converter may alter the frequency within 5Hz and 60Hz, which is similar to the variation of the motor’s speed between 300rpm and 3600rpm.
A variable speed motor can shift the frequency of supply power from a standard 50Hz or 60Hz to a higher or lower frequency. For some wind turbine systems, an input frequency within the range of 40Hz and 80Hz is adjusted by the frequency converter.
For the variable speed motor, it may regulate the motor voltage itself in extreme load fluctuations within a production line. In some cases, transformers can reduce the range of variation in the load by 10% to 15% as the voltage adjusts.
A closed-loop control system would be able to monitor the real-time speed of the motor, load temperature, and a host of operating parameters. Real-time data being monitored can also be used as a basis for automatically adjusting an operating state by the motor—for instance, the motor speed during some automated production lines.
In the chemical industry, variable-speed motors in some mixing equipment have been used in adjusting speed to suit the various materials and mixing requirements. This application consumes less energy and saves more than 20% of energy in the process of mixing and minimizes waste in production.
All motors, cooperating with sensors, PLC control systems, and other units in an integrated smart factory, provide real-time data regarding production. Therefore, the system of intelligent control can control the speed of all motors according to the schedule of production, which makes it effective in production processes.
Such systems do contain variable-speed motors that control speed in real-time so that such air conditioning units can save around 30% to 40% of energy with comfort requirements as well.
The variable speed motors are far more efficient in their work compared to the fixed-speed ones. Variable speed motors even change their speeds, and in most cases, automatically vary as a response to changing loads. The equipment stability of working will increase by 20%, while cutting downtime to about 30% if variable-speed motors are applied within the automated production lines.
The energy-intensive industries such as oil, gas, power, chemicals, and water treatment are the primary demanders of variable-speed motors. For instance, in those aforementioned industries that adopted variable-speed motors, reduced their average consumption of energy by 12% to 18%, and their maintenance cost over the lifecycle had already been decreased to around 15% to 20%.
Structure
A variable-speed motor consists of a stator, rotor, bearings, frequency converter, controller, and other cooling devices. The stator and rotor are the central parts of the motor, producing and transmitting electromagnetic force. The key component of the variable-speed motor is the frequency converter, controlling the speed of the motor by varying the input current frequency. Upon receiving the feedback from sensors in terms of motor efficiency, the controller changes the output of a frequency converter.
The stator is the fixed component of the variable-speed motor and consists of an iron core with windings. The magnetic field developed by the stator of a permanent magnet synchronous motor forces the rotor using the AC power fed from the frequency converter. Usually, the windings of the stator are configured in star and delta forms. Permanent magnet motors have relatively high efficiency; in fact, most have efficiency higher than 95%. Induction motors have about 90% efficiency.
The rotor is a part of a variable-speed motor that rotates and usually is produced from copper, aluminum, or steel. Large, high-power variable-speed motors are used for heavy machinery and equipment in the field of power generation, and its rotor can weigh hundreds of kilograms. Other devices, mostly fans and tools with smaller dimensions, use mostly small variable-speed motors, which are characterized by their rotors usually weighing several dozens of kilograms.
One of the most vital elements of the variable-speed motor includes a frequency converter. Industrial usages normally involve power ranges varying from 1 kW to even hundreds of kilowatts. However, the overloads, short circuits, or overheating associated with motors are avoided in modern devices with frequency converters along with adjustment abilities in terms of frequency.
The controller is the “brain” of the variable-speed motor system. Advanced variable-speed motor control systems allow for real-time regulation of the motor speed during load changes. This means that the motor will operate at the maximum efficiency point in all conditions. Intelligent control systems can also interface with other automation devices to constitute an integrated industrial automation system.
The cooling system in a variable-speed motor generally consists of air cooling or water cooling. The size and type of cooling system depend upon the power. In high-power variable-speed motors, the forced air cooling system is usually provided, while in extreme cases, a water cooling system is required. For a high-power motor, an appropriate cooling system may reduce the operating temperature of the motor by as much as 5°C to 10°C.
The structure of a variable speed motor also features some sensors. Basic sensors include temperature sensors, speed sensors, and current sensors. In some variable-speed motor systems, the current input is adjusted on the basis of feedback from the temperature sensors, preventing overheating.
For a variable speed motor, high-energy loss during transmission could be minimized if high-efficiency insulation materials were used. Most variable speed motors have 5%-10% more efficiency, being made up of high-performance materials.
Some new variable-speed motors now use modular designs that offer highly beneficial advantages of a lower maintenance cost and longer life for the equipment. In general, variable-speed motors that are furnished with modular designs will have 20%-30% lower maintenance costs than the traditional design.
Advantages
In some industrial applications, fans and pumps driven by variable-speed motors will consume 20% to 40% less energy than fixed-speed motors.
This allowed a company, by installing variable-speed motors in an automated production line, to achieve a reduction of equipment failure rate by 25% while increasing the life of the service of the machine by 15%.
Variable speed motors in a water treatment plant allow systems to automatically adjust their pump speed on the basis of the flow of water, therefore increasing pump energy efficiency by 18%.
Variable-speed motors, with high-precision control systems, can make micro adjustments to speed, allowing precise control of the process. In chemical production, variable-speed motors ensure that the stirring rate remains within a precisely set range, optimizing reaction efficiency.
Traditional motors have a high starting current, but variable-speed motors vary the current through frequency converters to start smoothly, thus avoiding the power fluctuations caused by high starting currents. The starting current of systems using variable-speed motors is usually 60%-70% lower than that of traditional motors.
In some HVAC systems, the noise of the HVAC system using a variable-speed motor has been reduced by 10% to 15%. This is a big plus in environments such as an office building and commercial space with hospitals where high noise is prohibited. The maintenance frequency of variable-speed motors is about 20% less frequent than traditional motors.
Variable-speed motors are quite easily integrated with PLC, SCADA, and other automation control systems that will continually update the operating state of the motor based upon real-time sensor data.
Variable-speed motors in wind and hydraulic power generation are able to read wind speed and hydraulic flow variations, adjusting the speed of the generator, raising annual power production by 8%-12%.
In some large industrial applications, variable-speed motors can balance the power system load by adjusting the load demand. In some manufacturing plants, after adopting variable-speed motors, a 15%-20% reduction in power load fluctuations was reported.
Applications
Variable-speed motors are very widely used in fan and pump equipment within the HVAC industry. With the same conditions, the systems using variable-speed motors within HVAC can achieve 30% energy saving along with higher reliability and comfort.
The water pumps need to adjust the flow according to the different water demands, but the traditional motors are usually running at a fixed speed and cannot adapt to this variation. With variable-speed motors, the water pumps can dynamically adjust their speed according to actual demand, and pumps driven by variable-speed motors consume 20% to 40% less energy than traditional equipment.
One challenge in the traditional wind turbines of the wind power system is to adapt to changes in wind speed. However, the variable-speed motors can run with real-time changes in the wind. In this aspect, variable-speed motors can increase power generation by 10% to 15%.
In irrigation systems, the traditional system relies on fixed-speed pumps to deliver water. Variable-speed motor-driven irrigation systems can dynamically vary pump speed depending on soil moisture, weather, and other variables. Agricultural irrigation systems with variable-speed motors reduce water and electricity costs by 15% to 25%.
Variable-speed motors are widely used in welding, painting, and assembly in the production of automobiles. For the production line, automated equipment driven by a variable-speed motor can increase the efficiency by more than 15% and reduce mechanical failures during production.
Some high-end power tools are fitted with variable-speed motors, which enable speed to vary from 500 to 3000 rpm. This feature increases the versatility and efficiency of the tool by great measure.
Brands such as Tesla have used highly efficient variable-speed motors in electric vehicle drive systems, achieving a maximum speed of 15,000 rpm, which enables fast acceleration and high efficiency in electric vehicles.
Variable-speed motors are flexible, and in this case, they provide speed control while being stable. Robots used in automated assembly processes use variable-speed motors to make sure that the movement of the arm is precisely controlled, hence making each action accurate.
Installation
The most critical part of variable-speed motors installation is the pre-installation preparations, which will guarantee hitch-free operation. However, in some industrial applications, the power rating might dictate the method of installation and choice of equipment. Motors with ratings above 50kW require special installation equipment and supports.
The direction in which the input and output lines of the motor go should be checked on installation. The shaft installation angle of some high-power motors is not allowed to be over 2 degrees.
It is essential to follow electrical regulations when connecting electrical wiring. It follows that electrical connections between each of the variable-speed motors must also conform to cables and terminal standards. Poor electrical connections would lead to damage in equipment or unstable operations and may even cause an accident in safety.
During the installation of a variable-speed motor, there should be adequate space for ventilation around the motor. High-power variable-speed motors can generate more than 1000W worth of heat during operation and may require additional forced air cooling or water cooling systems.
Some industrial robots with variable-speed motors require that the vibration levels be less than 0.5mm during installation to ensure the precision of the robotic arm. Noise reduction materials or vibration damping devices are usually used during installation, and the noise can be reduced by 5 to 10 decibels.
Grounding is another important consideration. In variable-speed motors, the casing should be suitably grounded such that its resistance is less than 1 ohm. This might involve provision for electromagnetic interference shielding if the working environment is vulnerable to such conditions.
Once installed, initial debugging or testing is required. First, check whether there are mistakes with the electrical connections of the motor and the control system, and then idle the test. In the process of an idle test, verify that the speed of the motor is in the prescribed range and does not generate any abnormal noise or vibration. In the debugging process, the parameters of the frequency converter should be set; some variable-speed motors must adjust the starting frequency between 50Hz to 60Hz.
After debugging, the load test should be performed to ensure that the motor load is within the safe range and does not exceed 110% of the rated load. During the test, in case of overheating or abnormal vibrations, the motor should be stopped for a check at once.
Long-term monitoring and maintenance are required after installation and debugging. Regular checks of the electrical connections, mechanical parts, and cooling systems of the motor should be done. Maintained variable-speed motors experience 30% to 40% fewer failures than non-maintained equipment.
