The "12th Five-Year Plan for Energy Conservation and Emission Reduction" recently issued by the State clearly outlines the requirements for industrial energy conservation. It addresses the fact that during the 11th Five-Year Plan period, the added value of the tertiary industry accounted for a lower-than-expected proportion of GDP, while the proportion of heavy industry in total industrial output rose from 68.1% to 70.9%. High-energy-consuming and high-emission industries grew too rapidly, and structural energy conservation targets were not achieved. Therefore, it is imperative to strengthen the management of industrial energy consumption.
The 12th Five-Year Plan policy promoted the development of frequency converters
Since its development, frequency converter technology has achieved significant energy-saving effects in many production processes. The National Twelfth Five-Year Plan for Energy Conservation and Emission Reduction requires the implementation of energy-saving renovation projects, with motor system energy conservation being one of the main projects. This plan mandates energy-saving renovations to motor systems, including variable frequency speed control, permanent magnet speed control, and reactive power compensation, to optimize system operation and control and improve overall system efficiency. The plan proposes that by 2015, the operating efficiency of motor systems should be 2-3 percentage points higher than in 2010, achieving an energy-saving capacity of 80 billion kilowatt-hours during the Twelfth Five-Year Plan period.
Therefore, since the 12th Five-Year Plan, energy conservation and environmental protection have been the core of my country's industrial economic development. While pointing the way for the sustainable development of my country's industry, they have also effectively driven the sustainable development of my country's frequency converter industry, enabling the industry to continuously expand its market share and become an important cornerstone of my country's industrial economic development with its strong development momentum.
Variable frequency drive (VFD) energy saving is mainly used in situations where it is necessary to change the characteristics of the drive machinery by varying the speed of the AC motor to meet production process requirements. It is frequently used in fans and water pumps. When a motor can only operate at its rated speed, its drive machinery can only operate at a certain rated speed.
When production processes require adjustments to process parameters, the flow rate can only be forcibly changed by increasing (or decreasing) the system resistance. The motor, however, always operates at its rated condition, resulting in wasted energy. Traditional speed control methods for equipment such as fans and pumps involve adjusting the opening of outlet (or inlet) baffles and valves to regulate air and water flow. Besides wasting energy, this increases system accessories and the probability of system failure. When using variable frequency speed control, if the required flow rate decreases, the pump or fan speed can be reduced to meet the requirement.
In summary, frequency converters primarily achieve energy savings through two methods: power factor compensation and soft starting. Regarding power factor compensation, reactive power increases line losses and equipment heat generation. Furthermore, a lower power factor leads to a decrease in the active power of the grid, resulting in significant reactive energy consumption in the lines, low equipment efficiency, and substantial waste. By using a variable frequency drive (VFD), the internal filter capacitors of the VFD reduce reactive power losses and increase the active power of the grid.
In terms of energy saving through soft starting, hard starting of motors can severely impact the power grid and place excessive demands on grid capacity. The large current and vibrations generated during startup can cause significant damage to baffles and valves, severely impacting the lifespan of equipment and pipelines. However, utilizing the soft-start function of a frequency converter allows the starting current to begin from zero, reducing the impact on the power grid and the demand on power supply capacity, extending the lifespan of equipment and valves, and thus saving on equipment maintenance costs.
However, it's important to note that the use of frequency converters should avoid the problem of underpowered inverters. This issue arose because the operating conditions at the time of design and production limited resources, leading to the use of inverters with power ratings lower than the motor's rated power in many areas to save costs. However, with technological advancements and changes in production processes, this underpowered inverter problem inevitably re-emerges, causing it to malfunction.
Therefore, during the trial period of the frequency converter, to prevent problems from occurring, testing and adjustments should be carried out in advance. Furthermore, after 6 to 10 years of normal use, the frequency converter is prone to entering a period of high failure rate, frequently experiencing component burnout, failure, and frequent activation of protection functions, seriously affecting its normal operation.
10 principles for selecting energy-saving frequency inverters
Meanwhile, when selecting frequency converters for speed regulation or energy saving, the following 10 principles should be followed as a prerequisite for deciding on a solution. Local electricity prices are higher, resulting in greater economic benefits for the same amount of electricity saved; this is also a factor that must be considered.
1) There are certain conditions for frequency converters to save energy. Under the condition that the use is not affected, by appropriately changing the operating parameters, the power consumed by unreasonable operating parameters can be saved, and the operation can be transformed from normal operation to economical operation.
2) To save energy, the frequency must be reduced. The greater the reduction, the more electricity is saved. In principle, without reducing the frequency, the inverter cannot save electricity.
3) It is related to the motor load rate. When the load rate is between 10% and 90%, the energy saving rate is at most about 8% to 10%, and the energy saving rate is higher when the load rate is lower. However, the reactive power saving rate is about 40% to 50%, which is not included in the electricity bill.
4) It is related to the rationality of the original operating parameters. For example, it is related to the adjustable values of pressure, flow rate, speed, etc. A larger adjustable value results in a higher energy saving rate, and vice versa.
5) This is related to the original adjustment method. Adjusting operating parameters using inlet or outlet valves is uneconomical. Switching to frequency converter speed control is much more economical and reasonable. Using frequency converter speed control can save 20%–30% more electricity than manually adjusting operating parameters with valves.
6) This is related to the original speed control method. For example, the original speed control using a slip-ring motor was inefficient, especially at medium and low speeds where the efficiency was below 50%, making it very uneconomical. Switching to frequency converter speed control saved this energy. Currently, slip-ring motors are still widely used in light industry, textiles, papermaking, printing and dyeing, plastics, and rubber industries. Therefore, using frequency converters to achieve energy saving and technological transformation is an urgent task.
7) It depends on the operating mode of the motor. For example, the energy savings are different for continuous operation, short-term operation, and intermittent operation.
8) It is related to the length of time the motor is running. For example, if the motor is run for 24 hours a day or 365 days a year, the energy savings will be greater, and vice versa.
9) It is related to the power of the motor itself. Under the same energy-saving rate, the larger the power, the greater the energy saving value and the greater the economic benefits, even if the energy saving rate is relatively lower than that of a smaller power motor, the actual benefits are greater.
10) It is related to the importance of the production process equipment in this unit. First, select equipment with high power consumption, high product cost, and whose current speed regulation method is not economical and reasonable, and modify it. After replacing it with frequency converter, there will be immediate and twice the result with half the effort.
