Energy is a vital material foundation for a nation, and the imbalance between energy supply and demand has become one of the main factors restricting my country's socialist economic construction. Regarding energy issues, the State Council has proposed the policy of "giving equal importance to conservation and development," relying on technological progress and making energy conservation a key technological and economic policy for solving energy problems. According to incomplete statistics, there are 15 million electric motors in the country's fan, pump, and compressor sectors, consuming 40-50% of the nation's total electricity generation. Most of these motors operate with low energy efficiency. Improving the energy efficiency of these motors by 10-15% could save over 30 billion kW of electricity annually. According to the thermal power design code SDJ-79, the air volume margin for forced draft and induced draft fans of coal-fired boilers should be 5% and 5%-10%, respectively, and the air pressure margin should be 10% and 10%-15%, respectively. It's difficult to calculate pipeline resistance and consider various problems that may occur during long-term operation during the design process. Typically, the maximum airflow and pressure margin of the system are used as the basis for selection. However, the models and series of fans are limited, and when a suitable fan model cannot be selected, an acceptable margin of 20-30% is often used. Therefore, when these fans are running, the airflow requirements of the production process can only be met by adjusting the opening of dampers or duct baffles. Both fans and pumps have square torque characteristics. When a pump is running, the flow rate is adjusted by the opening of valves to meet water supply requirements. The operating conditions are similar to those of fans. Adjusting the opening of dampers, duct baffles, or valves to regulate the fan airflow and pump flow rate is called throttling regulation. During throttling regulation, the inherent characteristics of the fan or pump remain unchanged; simply closing the opening of dampers, baffles, or valves artificially increases the pipeline resistance, thereby increasing pipeline system losses and hindering the energy-saving operation of fans and pumps. Speed ​​control devices are used to change the speed of fans and pumps, thereby altering the fan airflow and pump flow rate to meet the needs of the production process. This adjustment method is called fan and pump speed control. Operating fans and pumps with speed control results in the lowest energy consumption and highest overall efficiency. There are various speed control methods for AC motors, but frequency conversion speed control is the most efficient and optimal solution. It can achieve stepless speed regulation of fans and pumps and can easily form closed-loop control systems to achieve constant pressure or constant flow control. I. The energy-saving principle of frequency conversion speed control for fans and pumps: As shown in the diagram, the characteristic curves of centrifugal fan and pump (air pressure H - airflow Q) are: n1 - represents the characteristics of the fan and pump running at rated speed; n2 - represents the characteristics of the fan and pump running at reduced speed (n2); R1 - represents the resistance characteristics when the fan and pump pipeline resistance is at its lowest; R2 - represents the resistance characteristics when the fan and pump pipeline resistance increases to a certain value. When the fan and water pump operate on the characteristic curve R1, the operating point is A, with flow rate and pressure of Q1 and H1 respectively. The power required by the fan and water pump at this point is proportional to the product of H1 and Q1, i.e., proportional to the area of ​​AH1OQ1. Due to process requirements necessitating a reduction in airflow to Q2, the operating point of the fan and water pump is actually shifted to point B on R2 by increasing the pipe network resistance. This increases the air pressure (water pressure) to H2. The power required by the fan and water pump at this point is proportional to the area of ​​H2Q2, i.e., proportional to the area of ​​BH2OQ2. Clearly, the power required by the fan and water pump has increased. While this control method is simple, it consumes a lot of power and is not energy-efficient, trading high operating costs for a simple control method. If frequency conversion speed regulation is adopted, the speed of the fan and water pump decreases from n1 to n2. At this time, the working point moves from point A to point C. The flow rate is still Q2, and the pressure decreases from H1 to H3. At this time, the power required by the fan (water pump) after frequency conversion speed regulation is proportional to the product of H3 and Q2, that is, proportional to the area of ​​CH3OQ2. As can be seen from the figure, the power reduction is obvious. II. Calculation of energy saving of fan and water source : As mentioned above, the change in fan and water pump flow rate is an effective measure to save electricity. According to the provisions of GB12497 on the economic operation management of motors, there is the following calculation formula. The relationship between the motor input power P1V and the flow rate Q corresponding to the flow rate adjustment by baffle is: P1V≈[0.45+0.55（Q/QN）2]P1e (1) Where: P1e——motor input power (kW) at rated flow rate. QN——Rated flow rate III. Application example: A cement plant's vertical kiln centrifugal fan is 245KW, with a 4-pole motor and an actual air volume of 0.6~0.7. It is planned to be converted to a frequency converter drive. Estimate the power saving rate and investment payback period. Take Q/QN=0.65, from equation (2) from equation (1) P1V=〔0.45+0.55（0.65）2〕245 =0.6428×245=157（KW） When the air volume is adjusted by the damper, the required shaft power of the fan is 157kW. When the air volume is adjusted by the frequency converter speed controller, the power saving rate relative to the air volume adjustment by the damper is 0.6. Annual power saving, calculated based on 300 days per year. 24 × 306 × 157 × 60% = 678240 kWh ≈ 678,000 kWh Annual electricity savings (electricity price 0.40 yuan/kWh) 0.4 × 678240 = 270,000 yuan Investment recovery period: Investment recovery period = Total equipment investment (yuan) ÷ Annual electricity savings (yuan) = 18 ÷ 27 = 0.67 (years) = 8 (months) Therefore, it can be determined that after the vertical kiln centrifugal fan of the cement plant adopts frequency converter drive, the annual electricity saving is 678,000 kWh, the annual electricity cost saving is 270,000 yuan, and the investment recovery period is 8 months, which is a considerable technical and economic benefit. The cement plant ordered one frequency converter speed control cabinet, equipped with one Senlan BT40S250kW frequency converter, as well as circuit breakers, fuses, meters, indicator lights, etc., worth 180,000 yuan. After being put into operation, the frequency converter was adjusted to around 35Hz to meet the air volume requirements of the kiln. At this time, the motor current was about 210A, the frequency converter output voltage was 298V, and the actual output power was P=√3 IVCOφ4=3×210×298×0.9≈97.5kW, which basically matches the theoretical calculation value of 157×0.6=94.2kW. The above analysis shows that the use of frequency converters for speed regulation of the fans and pumps significantly reduces energy consumption. Furthermore, the reduced mechanical speed decreases wear and tear, extends service life, and provides considerable indirect economic benefits.