While choosing an industrial drive motor, load type, power requirements, speed requirements, and the operating environment should be considered. The kind of load is big, and it often operates for an especially long time; therefore, a high-efficiency motor-IE3 or IE4-is recommended, which saves 15% to 20% in energy consumption. You need to choose a suitable motor according to the temperature, humidity, and protection level of the working environment.
Determining Torque
Consider a conveyor system where the conveyor belt is 10 meters in length, a load of 500 kilograms is placed, and the working speed is 2 meters per second. The torque required from the motor is calculated to be about 8 newton-meters.
In any such manufacturing line system, say, a motor is supposed to drive a workpiece with an aggregate weight of 2 tons. The velocity or operating speed is considered 60 meters/minute. At this point in such condition, the working load should be maximum with capacity; hence, at least 15 Newton-meters of torque the motor will need to provide in order for smooth working of the entire system.
By changing the conveyor belt design to a variable-speed system, the motor efficiency could be increased by approximately fourfold. A pump system is required to pump 1000 liters per hour at a working pressure of 10 bar (1000 kPa). The motor torque demand varies with the pump’s efficiency and the fluid frictional losses. If the flow rate is reduced by 50%, the motor torque demand will increase by 30% in return.
For example, in a general mechanical production workshop, its motor power requirement ranges between 5 kW and 50 kW. It can be shown from research that to save electricity consumption using high-efficiency motors saves 15% to 20%. Assuming a factory consumes 50,000 kWh of electricity every year, changing to high-efficiency motors saves 8,000 to 10,000 yuan per year. In addition, some cranes may require 25 Newton-meters of starting torque while their smooth operation only needs 10 Newton-meters of torque.
In extremely high-temperature environments, such as above 40°C, the power output of the motor may decrease by 10% to 15%. If a motor operates under excessive torque load during its long-term use, its lifespan could be reduced by about 30%.
Assuming this electric motor has an initial investment of 50,000 yuan and it is expected that with the energy optimization, it will save 15% of the operational cost over a 10-year period of time, plus another reduced maintenance cost, the total ROI would be close to 25%.
Suppose the maintenance cost of a motor per year is 5,000 yuan. Poor selection of a motor’s torque could lead to a maintenance cost of over 10,000 yuan. It is estimated from a large amount of data analysis that the maintenance cost occupies 10% to 15% of the motor’s purchase cost.
Determining Speed
In the packaging production line, the required is to drive a 1-meter drum size with a speed of 60 RPM. Now, if any company’s conveyor system requires a transport speed of 60 meters/minute and the total weight of the goods to be conveyed is 500 kilograms, the required motor speed should be 3000 RPM.
Assume that some precision machine tool possesses a work table area of 500 square mm with the need to manage the speed of the motor within 3000 RPM, as well as flow rate and a certain working pressure such as pump operation at 50 L/ second under 5-bar pressure conditions. If the design of the pump system calls for 3000 RPM of the motor to maintain given flow rate and pressure, at an increased load on the pump due to variation in flow and pressure, then the motor shall have to correct the speed accordingly.
Now, assume that the cycle in a production line is 2 hours and at one stage the motor should reach 5000 RPM in 30 seconds while at another stage it should hold 1000 RPM. Then, one should select a motor capable of stepless regulation for flexibility in the production process.
Assume the motor’s power demand is 5 kW. If the speed is too high during operation, the motor could overheat. Data shows that when operating at lower speeds, the motor’s efficiency improves by 10% to 15%.
If the motor operates at 6000 RPM, the motor life could be only 3 years with 2500 operating hours per year, while if the operating speed is reduced to 4000 RPM, the motor’s life can extend to about 5 years.
The motor of high-temperature furnaces should work in a specific environment of temperature. Moreover, the rotation speed is not higher than 1500 RPM. Assume that the equipment load is 2 tons, and the temperature in the operating environmental reaches 100 ℃. Choosing a high-speed motor might cause overheating. When the working environment of the motor is relatively humid, choosing a low-speed motor can effectively reduce the abrasion of the device.
This will lead to a very uneven load on motors whose speed will increase by 15%, assuming the design for 50Hz and the actual power supply frequency is 60Hz.
Analyzing the Operating Environment
In mining, humidity often exceeds 80%, with exposure to dust and high temperatures. In an environment with temperatures up to 45°C, the motor’s efficiency may decrease by 10%. If no protective measures are taken, the motor’s temperature may exceed 90°C.
In food processing, strict hygiene requirements are needed: the motor surface is to be made of stainless steel, while the operating temperature should not exceed 40°C. In a chemical factory production line, the motor housing must be made of corrosion-resistant materials with a service life about 25% longer than conventional motors.
Above 4000 meters above sea level, the cooling efficiency of the motor decreases, and the power must be reduced by 15% to 20%. The selection of a motor with a good cooling system can also be operated normally.
A certain steel mill, the blast furnace fan driven by the motor, the vibration frequency is 500 revolutions per minute, the motor must choose a high vibration resistance, the bearing must use rolling bearings.
Because the air on the platform contains 20% salt, the protection level of the motor should achieve IP68, and the housing material should be salt-resistant. The uniqueness of the marine environment means the motor needs to be deeply cleaned and maintained at least twice a year.
If there is a bigger amplitude between day and night or in northern areas where temperature drops to lower than -30°C, then motors suitable for the low temperature must be selected or it’s necessary to install more heating devices.
While applied to coal mines and some industrial work places with the appearance of some inflammable gases explosion proof motors should be chosen. A Frequency Variable Speed Drive Electric Motors need to be used while using in fields related to wind and similar energy sources.
Precision machinery driven by motors used in the production of electronic products should be operated within a temperature and humidity-controlled environment; the fluctuation in temperature should fall within the range of ±1°C and humidity within ±5%.
Installation Space
For some automatic production lines, installation space is only 600×600mm. In a warehouse logistics system where the height is up to 2 meters and the width is up to 1 meter, compact design for bearings and housing must be used for low-height motors in the narrow spaces of the motor installation.
In a manufacturing factory, there are several production lines, and each production line requires two motors to drive different types of machinery. The total area for the production lines is 50 square meters, and the motor mounting positions are very compact.
Assuming that the workshop’s air conditioning system operates 10 hours per day, the power of the motor is selected as 3 kW. A DC motor or a frequency-controlled motor is usually selected.
In workshops with large vibrations created by motor-driven equipment, the motor selected should have good resistance to such vibrations, while in housing design strong noise isolation is to be provided.
In larger manufacturing plants, or for greater extension possibilities, or where frequent changes are needed, it is sometimes advantageous to select one or more flexible, modular motors that can operate under variable conditions. Considering some high-risk industrial environments, for ensuring the service life of the motor, it’s relevant to select well-ventilation and easy places for installation locations.
Assume the motor will work with the gearbox, its size 600mm*600mm. It also requires the same size and axial layout for the motor.
Suppose the motor is to be part of an automated robotic arm, and the total size of the robot is 1.5 meters by 1.5 meters. A compact motor will fit perfectly with the design of the robot and allow it to have maximum flexibility and precision.
Efficiency Class
If a 15 kW motor‘s efficiency is improved from 80% to 90%, the saving in annual electricity cost will be more than 5000 yuan, which may be tens of thousands of yuan for some large factories.
The IEC60034-30-1 standard classifies the motor’s efficiency from IE1 (low efficiency) to IE4 (ultra-high efficiency). Suppose an IE2-level motor on a production line operates 10 hours a day and consumes 40,000 kWh of electricity per year. An IE4-level motor, under the same operating conditions, would consume only 32,000 kWh, saving about 20% of electricity.
Energy efficiency is of greater importance to industrial facilities, which have to operate on a 24/7 schedule. It was estimated that if the efficiency of one motor in a steel mill increases by 1%, it would save more than 100,000 yuan per year for its electricity cost.
For a motor rated at 22 kW, its operational efficiency can reach over 95% when operating under an 80% load. But with a 40% load, its efficiency can drop to as low as 85%.
The efficiency of the motor of a wind turbine generally needs to be higher than 98%. Assuming a 7.5 kW motor, a 5% increase in efficiency could save about 2000 yuan in annual electricity costs. If this motor’s purchase cost is 10,000 yuan, after five years of operation, the savings in electricity costs would approach half the motor’s cost.
High-efficiency motors reduce equipment maintenance costs. Prolonging a motor’s life from 5 years to 7 years will greatly increase the overall return on investment.
Some developed countries provide a 10% subsidy toward the purchase of motors on the condition that the motor chosen is at least IE3 efficient. In some industrial environments with low load or intermittent usage, the choice of a high-efficiency motor could lower the return on investment.
Usage Frequency
In the production lines, if a motor has to work for 300 hours a week, then its durability requirement is much higher compared to a motor that works only 40 hours a week. The selection of the motor has to be done considering higher intensity of work and frequent start-stop cycles.
For example, in a motorcar manufacturing plant, a specific production line can run for more than 8000 hours annually. The standard of motor manufacturers states that a standard motor has a life of 10,000 hours.
Some automated warehouse systems require that the motor run more than 16 hours a day, exceeding 4000 hours a year. Market research said that high-frequency motors use 1 or 2 years less compared to low-frequency used ones.
Motors that run over 600 hours per month typically require lubrication and cleaning every 3 months. Motors with frequent operation may require inspections and maintenance at shorter intervals. In many high-frequency operational factories, the maintenance cost of the motor often accounts for more than 10% of the total operating cost.
Some high-precision processing equipment requires motors with frequency controllers if they run more than 2000 hours per year. For example, in some high-speed CNC machines, the motor may start and stop more than 20 times a day. Using a motor with a frequency controller can improve stability and durability.
Some enterprises have found that in high-frequency operation, upgrading to the IE3-level efficient motor can save 10% to 20% of the electricity cost. For a production line running 6000 hours per year with a 15 kW motor, electricity savings could exceed 5000 yuan annually.
Statistic data revealed that the failure rate of a standard motor was 30% higher than in a normal temperature environment. Motors at high usage frequency should choose waterproof and dustproof features.
