The main manifestations of motor energy consumption
The energy consumption of electric motors mainly manifests in the following aspects:
One is the low load rate of the motor. Due to improper selection of electric motors, excessive surplus or changes in production processes, the actual working load of electric motors is much lower than the rated load. Electric motors that account for approximately 30% to 40% of installed capacity operate at 30% to 50% of rated load, resulting in low operating efficiency.
The second is that the power supply voltage is asymmetric or too low. Due to the imbalance of single-phase loads in the three-phase four wire low-voltage power supply system, the three-phase voltage of the motor is asymmetric, causing the motor to generate negative sequence torque, increasing the three-phase voltage asymmetry of the motor, causing the motor to generate negative sequence torque, and increasing the losses during motor operation. In addition, the long-term low voltage of the power grid causes the current of the motor to be higher during normal operation, resulting in increased losses. The greater the asymmetry of the three-phase voltage, the lower the voltage, and the greater the losses.
Thirdly, old and outdated (obsolete) motors are still in use. These motors use E-class insulation, have a large volume, poor starting performance, and low efficiency. Although it has undergone years of renovation, there are still many places in use.
The fourth issue is poor maintenance management. Some units fail to maintain and repair motors and equipment as required, allowing them to operate for a long time, resulting in increasing losses.
Therefore, it is worth studying which energy-saving plan to choose based on these energy consumption performances.
There are roughly six energy-saving solutions for motors:
1. Choose energy-saving motors. Compared with ordinary motors, high-efficiency motors have optimized the overall design, selected high-quality copper windings and silicon steel sheets, reduced various losses, reduced losses by 20%~30%, and increased efficiency by 2%~7%; The investment payback period is generally 1-2 years, sometimes several months. Compared to J02 series motors, high-efficiency motors have increased efficiency by 0.413%. Therefore, it is imperative to replace old electric motors with high-efficiency ones.
2. Properly selecting the capacity of the electric motor to achieve energy savings. The country has made the following regulations for the three operating areas of three-phase asynchronous motors: the economic operating area is between 70% and 100% load rate; A load rate between 40% and 70% is the general operating zone; A load rate below 40% is considered a non economic operating zone. Improper selection of motor capacity will undoubtedly result in wastage of electrical energy. Therefore, using appropriate electric motors to improve power factor and load rate can reduce power loss and save energy.
3. Replace the original slot wedge with a magnetic slot wedge. Magnetic slot wedges mainly reduce the no-load iron loss in asynchronous motors, and the additional no-load iron loss is generated in the stator and rotor cores by the harmonic magnetic flux caused by the cogging effect in the motor. The high-frequency additional iron loss induced by the stator and rotor inside the iron core is called pulse vibration loss. In addition, the stator and rotor teeth are sometimes aligned and sometimes offset, causing changes in the magnetic flux of the tooth clusters on the tooth surface, which can induce eddy currents in the tooth surface layer and generate surface losses. Pulse vibration loss and surface loss are collectively referred to as high-frequency additional losses, which account for 70% to 90% of the motor's stray losses. The other 10% to 30% is called load additional losses, which are generated by leakage flux. Although the use of magnetic slot wedges can reduce the starting torque by 10% to 20%, the iron loss of motors using magnetic slot wedges can be reduced by 60k compared to motors using ordinary slot wedges, and they are very suitable for motor modification for no-load or light load starting.
4. Adopting Y/△ automatic conversion device. To solve the problem of energy waste when the equipment is under light load, Y/△ automatic conversion device can be used to achieve energy-saving without replacing the motor. Because the voltage obtained by different load connections in a three-phase AC power grid is different, the energy absorbed from the grid is also different.
5. Reactive power compensation for power factor of electric motors. The main purpose of reactive power compensation is to improve power factor and reduce power loss. The power factor is equal to the ratio of active power to apparent power. Generally, a low power factor can 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.
6. Liquid speed regulation of wound motor. The liquid resistance speed regulation technology is developed based on the traditional product liquid resistance starter. The purpose of achieving stepless speed regulation is still to adjust the resistance by changing the distance between the electrode plates. This makes it have good starting performance at the same time. When it is powered on for a long time, it brings about heating and warming problems. Due to the unique structure and reasonable heat exchange system, its working temperature is limited to a reasonable temperature. The liquid resistance speed regulation technology for wound motors has been rapidly promoted due to its advantages of reliable operation, easy installation, large energy-saving range, easy maintenance, and low investment. For some wound motors that do not require high speed regulation accuracy, wide speed regulation range, and infrequent speed regulation, such as large and medium-sized wound asynchronous motors for fans, pumps, and other equipment, the use of liquid speed regulation has a significant effect.
