The energy consumption of motors is mainly reflected in the following aspects:
1. The motor load rate is low. Due to improper motor selection, excessive surplus or changes in production process, the actual working load of the motor is far less than the rated load. The motors that account for about 30%~40% of the installed capacity operate at 30%~50% of the rated load, and the operating efficiency is too low.
2. The power supply voltage is asymmetric or the voltage is too low. Due to the imbalance of the single-phase load of the three-phase four-wire low-voltage power supply system, the three-phase voltage of the motor is asymmetric, the motor generates negative sequence torque, and the loss of the motor during operation is increased. In addition, the grid voltage is low for a long time, which makes the current of the motor in normal operation larger, so the loss increases. The greater the asymmetry of the three-phase voltage and the lower the voltage, the greater the loss.
3. old and obsolete (obsolete) motors are still in use. These motors use E-class insulation, are large in size, have poor starting performance and low efficiency. Although they have undergone years of transformation, they are still used in many places.
4. Poor maintenance management. Some units fail to perform maintenance on motors and equipment as required and allow them to run for a long time, resulting in increasing losses.
There are roughly seven motor energy-saving schemes.
Choose energy-saving motors. Compared with ordinary motors, high-efficiency motors optimize the overall design, use high-quality copper windings and silicon steel sheets, reduce various losses, reduce losses by 20%~30%, and increase efficiency by 2%~7%; the investment recovery period is generally 1~2 years, and some are several months. In comparison, high-efficiency motors are 0.413% more efficient than J02 series motors. Therefore, it is imperative to replace old motors with high-efficiency motors.
Appropriately select motor capacity to achieve energy saving. The country has made the following regulations for the three operating areas of three-phase asynchronous motors: the load rate between 70%~100% is the economic operating area; the load rate between 40%~70% is the general operating area; the load rate below 40% is the non-economic operating area. Improper selection of motor capacity will undoubtedly cause a waste of electric energy. Therefore, using a suitable motor to improve the power factor and load rate can reduce power loss and save electric energy.
Magnetic slot wedges are used to replace the original slot wedges. Magnetic slot wedges mainly reduce the no-load iron loss in asynchronous motors. The no-load additional iron loss is generated in the stator and rotor cores by the harmonic magnetic flux caused by the slot effect in the motor. The high-frequency additional iron loss induced by the stator and rotor in the core is called pulsation loss. In addition, the stator and rotor teeth are sometimes aligned and sometimes staggered, and the magnetic flux of the tooth surface and tooth cluster changes, which can induce eddy currents in the tooth surface line layer and produce surface losses. Pulsation loss and surface loss are collectively called high-frequency additional loss, which accounts for 70%~90% of the stray loss of the motor. The other 10%~30% is called load additional loss, which is generated by leakage flux. Although the use of magnetic slot wedges will reduce the starting torque by 10%~20%, the iron loss of the motor using magnetic slot wedges can be reduced by 60k compared with the motor using ordinary slot wedges, and it is very suitable for the transformation of motors with no-load or light-load starting.
Y/△ automatic conversion device is used. In order to solve the problem of wasting electric energy when the equipment is lightly loaded, without replacing the motor, a Y/△ automatic conversion device can be used to achieve the purpose of saving electricity. Because in the three-phase AC power grid, the voltage obtained by different load connections is different, and the energy absorbed from the power grid is also different.
Power factor reactive compensation of the motor. Improving the power factor and reducing power loss are the main purposes of reactive compensation. The power factor is equal to the ratio of active power to apparent power. Usually, a low power factor will cause excessive current. For a given load, when the supply voltage is constant, the lower the power factor, the greater the current. Therefore, the power factor should be as high as possible to save energy.
Variable frequency speed regulation. Most fan and pump loads are selected based on the full-load working requirements. In actual applications, they are not in full-load working state most of the time. Since it is difficult to adjust the speed of AC motors, windshields, return valves or start-stop times are often used to adjust the air volume or flow. At the same time, it is difficult for large motors to start and stop frequently under power frequency conditions, and the power shock is large, which will inevitably cause power loss and current shock during start-up and shutdown. Using a frequency converter to directly control fan and pump loads is the most scientific control method. When the motor runs at 80% of the rated speed, the energy saving efficiency is close to 40%. At the same time, closed-loop constant voltage control can also be achieved, and the energy saving efficiency will be further improved. Since the frequency converter can achieve soft stop and soft start of large motors, it avoids voltage shock at start-up, reduces motor failure rate, and prolongs service life. At the same time, it also reduces the capacity requirements and reactive power loss of the power grid.
Liquid speed regulation of wound motors. Liquid resistance speed regulation technology is developed on the basis of traditional products, liquid resistance starters. The purpose of stepless speed regulation is still achieved by changing the distance between the pole plates to adjust the size of the resistance. This makes it have good starting performance at the same time. It is powered on for a long time, which brings about the problem of heating and temperature rise. Due to the unique structure and reasonable heat exchange system, its operating temperature is limited to a reasonable temperature. The liquid resistance speed control technology for wound-rotor motors has been rapidly promoted due to its advantages of reliable operation, easy installation, large energy saving, easy maintenance and low investment. It is effective in controlling the speed of wound-rotor motors that do not require high speed control accuracy, a narrow speed control range, and infrequent speed control, such as large and medium-sized wound-rotor asynchronous motors in equipment such as fans and water pumps.
