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From the perspective of energy conservation and environmental protection, high-efficiency and energy-saving motors are the current international development trend. The United States, Canada, and Europe have successively promulgated relevant regulations. The CEMEP standard formulated by Europe divides efficiency into three levels: eff1 (highest), eff2, and eff3 (lowest) based on the running time of the motor, which will be implemented step by step from 2003 to 2006. The latest IEC60034-30 standard divides motor efficiency into four levels: IE1 (corresponding to eff2), IE2 (corresponding to eff1), IE3, and IE4 (the highest). Our country promises to implement IE2 and above standards from July 1, 2011.
At present, my country’s industrial energy consumption accounts for about 70% of the total energy consumption, of which motor energy consumption accounts for about 60% to 70% of the industrial energy consumption. Adding non-industrial motor energy consumption, the actual energy consumption of the motor accounts for about 50% of the total energy consumption. Above, however, the application proportion of high-efficiency and energy-saving motors is currently low. According to a sample survey of 198 motors from key domestic enterprises by the National Small and Medium-sized Motor Quality Supervision and Inspection Center, only 8% of them are high-efficiency and energy-saving motors that have reached level 2 or above, which has caused a huge waste of resources for the entire society.
Some organizations have calculated that if the efficiency of all electric motors is increased by 5%, 76.5 billion kilowatt hours of electricity can be saved throughout the year. This number is close to the annual power generation of the Three Gorges in 2008. Therefore, the energy-saving motor industry has a large development space and strong demand. In terms of policy, the National Standardization Administration issued the mandatory standard “GB18613-2012 Energy Efficiency Limit Values and Energy Efficiency Levels of Small and Medium-sized Three-Phase Asynchronous Motors” in 2012.
Energy-saving measures for high-efficiency motors
Motor energy saving is a systematic project that involves the entire life cycle of the motor, from motor design and manufacturing to motor selection, operation, adjustment, maintenance, and scrapping. The effect of energy-saving measures must be considered from the entire life cycle of the motor. Domestic Externally, we mainly consider improving efficiency from the following aspects.
The design of energy-saving motors refers to the use of modern design methods such as optimized design technology, new material technology, control technology, integration technology, and test and detection technology to reduce the power loss of the motor, improve the efficiency of the motor, and design an efficient motor.
While the motor converts electrical energy into mechanical energy, it also loses a part of its energy. Typical AC motor losses can generally be divided into three parts: fixed loss, variable loss, and stray loss. Variable losses vary with load and include stator resistance losses (copper losses), rotor resistance losses, and brush resistance losses; fixed losses have nothing to do with load and include iron core losses and mechanical losses. Iron loss is composed of hysteresis loss and eddy current loss, which is proportional to the square of the voltage, and hysteresis loss is also inversely proportional to frequency; other stray losses are mechanical losses and other losses, including friction losses of bearings and fans and rotors. etc. Windage losses due to rotation.
Characteristics of high-efficiency motors
Save energy and reduce long-term operating costs. It is very suitable for use in textiles, fans, water pumps, and compressors. The purchase cost of the motor can be recovered by saving electricity in one year;
Start directly or use a frequency converter to adjust the speed, and the asynchronous motor can be fully replaced;
The rare earth permanent magnet high-efficiency energy-saving motor itself can save more than 15℅ of electric energy than ordinary motors;
The power factor of the motor is close to 1, which improves the quality factor of the power grid without adding a power factor compensator;
The motor current is small, saving power transmission and distribution capacity and extending the overall operating life of the system;
Energy-saving budget: Taking a 55-kilowatt motor as an example, a high-efficiency motor saves 15% more energy than an ordinary motor. The electricity cost is calculated at 0.5 yuan per kilowatt hour. The cost of replacing the motor can be recovered by saving electricity within one year of using an energy-saving motor.
Advantages of high-efficiency motors
Direct start, full replacement of the asynchronous motor.
The rare earth permanent magnet high-efficiency energy-saving motor itself can save more than 3% of electric energy than ordinary motors.
The power factor of the motor is generally higher than 0.90, which improves the quality factor of the power grid without adding a power factor compensator.
The motor current is small, saving power transmission and distribution capacity and extending the overall operating life of the system.
Adding a driver can realize soft start, soft stop, and step-less speed regulation, further improving the power-saving effect.
Five major losses for motors
Stator Losses
The main means to reduce the I^2R loss of the motor stator. The most commonly used methods in practice are:
Increase the cross-sectional area of the stator slot. Under the same stator outer diameter, increasing the cross-sectional area of the stator slot will reduce the magnetic circuit area and increase the magnetic density of the teeth;
Increase the stator slot full rate, which is more effective for low-voltage small motors. Applying optimal winding and insulation dimensions and a large conductor cross-sectional area can increase the stator slot full rate;
Minimize the length of the stator winding end. The stator winding end loss accounts for 1/4 to 1/2 of the total winding loss. Reducing the winding end length can improve motor efficiency. Experiments show that the end length is reduced by 20% and the loss is reduced by 10%.
Rotor losses
The I^2R loss of the motor rotor is mainly related to the rotor current and rotor resistance. The corresponding energy-saving methods mainly include:
Reduce the rotor current, which can be considered from two aspects: increasing the voltage and motor power factors;
Increase the cross-sectional area of the rotor slot;
Reduce the resistance of the rotor winding, such as using thick wires and low-resistance materials. This is more meaningful for small motors because small motors generally have cast aluminum rotors. If a cast copper rotor is used, the total loss of the motor can be reduced by 10% ~15%, but today’s cast copper rotors require high manufacturing temperatures. The technology has not yet been popularized, and its costs are 15% to 20% higher than those of cast aluminum rotors.
Iron Loss
The following measures can reduce motor iron loss:
Reduce the magnetic density and increase the length of the iron core to reduce the magnetic flux density, but the amount of iron used in the motor will increase;
Reduce the thickness of the iron chips to reduce the loss of induced current. For example, using cold-rolled silicon steel sheets instead of hot-rolled silicon steel sheets can reduce the thickness of the silicon steel sheets, but thin iron chips will increase the number of iron chips and the manufacturing cost of the motor;
Use cold-rolled silicon steel sheets with good magnetic permeability to reduce hysteresis loss;
Use high-performance iron chip insulation coating;
Heat treatment and manufacturing technology. The residual stress after processing the iron sheet will seriously affect the loss of the motor. When processing silicon steel sheets, the cutting direction and punching shear stress have a greater impact on the loss of the iron core. Cutting along the rolling direction of the silicon steel sheets and performing heat treatment on the silicon steel punched sheets can reduce the loss by 10% to 20%.
Stray Losses
Today’s understanding of motor stray losses is still in the research stage. Some of the main methods to reduce stray losses are:
Use heat treatment and finishing to reduce short circuits on the rotor surface;
Insulation treatment on the inner surface of the rotor slot;
Reduce harmonics by improving the stator winding design;
Improve the rotor slot design and cooperation to reduce harmonics, increase stator and rotor tooth slots, design the rotor slot shape into inclined slots, and use series-connected sinusoidal windings, scattered windings, and short-distance windings to reduce high-order harmonics greatly; Using magnetic slot mud or magnetic slot wedges to replace the traditional insulating slot wedges and filling the slots of the motor stator core with magnetic slot mud is an effective method to reduce additional stray losses.
Wind Friction Loss
It deserves people’s due attention, it accounts for about 25% of the total loss of the motor. Friction losses are mainly caused by bearings and seals, which the following measures can reduce:
Reduce the size of the shaft as much as possible, but it must meet the requirements of output torque and rotor dynamics;
Use high-efficiency bearings;
Use efficient lubrication systems and lubricants;
Adopt advanced sealing technology.
