With the separation of power generation and grid connection, and increasingly fierce competition for grid connection, how to reduce power generation costs, improve the competitiveness of power generation enterprises in grid connection bidding, strengthen internal management, and tap energy conservation potential are major issues that power plants must seriously study. Using high-voltage frequency converters to technically upgrade high-energy-consuming electrical equipment in power plants can not only reduce plant power consumption, reduce coal consumption for power supply, and increase grid-connected power consumption, bringing direct economic benefits, but also improve the safety and reliability of units and reduce unit failures. 1. Variable Frequency Speed ​​Regulation Energy-Saving Principle According to the principles of fluid mechanics, for a fan driven by a squirrel-cage induction motor, the shaft power P is related to the air volume Q and air pressure H. It can be seen that the air volume Q is directly proportional to the motor speed N, while the required shaft power P is directly proportional to the cube of the speed. Therefore, when 80% of the rated air volume is needed, by adjusting the motor speed to 80% of the rated speed, i.e., adjusting the frequency to 40Hz, the required power will be 51.2 times the original. Figure 1 shows the relationship between shaft power P, air volume Q, and air pressure H. The energy-saving effect of variable frequency speed control is analyzed from the fan's operating curve. When the required air volume decreases from Q1 to Q2, if a regulating damper is used, the pipe network resistance will increase, the pipe network characteristic curve will shift upward, and the system's operating point will change from point A to a new operating point B. The required shaft power P2 is proportional to the area H2 × Q2. If speed control is used, the fan speed decreases from n1 to n2, and its pipe network characteristics do not change, but the fan's characteristic curve will shift downward, thus its operating point will shift from point A to point c. At this time, the required shaft power P3 is proportional to the area HB × Q2. Theoretically, the saved shaft power Delt(P) is proportional to the area H2HBCB. Considering the efficiency decrease after deceleration and the additional losses of the speed control device, statistical analysis based on practice shows that fans can save approximately 30% to 60% energy through speed control. 2. Significance of the Project Upgrade Our plant's No. 3 generator set has a capacity of 125 MW. The No. 3 boiler's blower has two units arranged on both sides. Currently, airflow adjustment is achieved manually by adjusting dampers, without considering energy conservation. In actual operation, during winter at full load, the damper opening is typically between 40% and 50% (average 45%), and during summer, it is typically between 60% and 70% (average 63%), with operating current between 76 and 80A. This results in considerable energy waste due to damper throttling, with a potential for 35% to 55% energy savings. Therefore, implementing energy conservation and consumption reduction measures is of great significance. Furthermore, the No. 3 boiler blower motor capacity is too large. The design institute selected an 800kW model, but for some reason, it was changed to 1000kW during equipment procurement. Furthermore, Unit #3 operates at a long-term load of around 110MW, resulting in excessive excess capacity in the blower motor, making upgrades essential. Therefore, after extensive investigation and evaluation, our factory decided to undertake this project. Last year, we purchased two sets of high-voltage frequency converters (model zINvERT-6H1000/06YA) from Guangzhou Zhiguang Company. These were put into operation in January of this year during a minor overhaul of Unit #3, with excellent operational results. 3. Actual Energy Saving Effect After Frequency Conversion Upgrade After more than two months of operation, the energy-saving effect is significant, with a substantial decrease in plant power consumption and reduced coal consumption. To determine the exact amount of energy saved, our production technology department organized tests on February 28, 2006, under both power frequency and frequency conversion conditions. During the test, the boiler operating reference conditions were basically the same. Energy consumption comparison tests were conducted at loads of 125 MW, 113 MW, 100 MW, and 90 MW. To reduce the error caused by the test, four measurements were taken under each load condition, and the average value was taken. The instrument used for the test was a DK-45C three-phase multi-functional field calibrator (accuracy: 0.1 class). The test data are shown in the attached table. 3.1 Data Analysis From the comparison table of measured power of the blower under variable frequency operation and measured power under power frequency operation, it can be seen that when the unit load is 125 MW, the average power of the blower on side A under variable frequency operation is 552.825 kW, and the average power of the blower on side A under power frequency operation is 744.66 kW. Therefore, the average energy saving value is the difference between the power under power frequency and variable frequency operation, which is 191835 kW. Similarly, the energy saving value on side B is 209.115 kW. Therefore, the average energy saving value of the blowers on both sides A and B under the condition of unit load of 125MW is 200.475 kW, and the energy saving effect is 26.83%. Similarly, the average energy savings at loads of 113MW, 100MW, and 90MW are 225.678 kW, 255838 kW, and 296.925 kW, respectively, with corresponding average energy savings rates of 34.48%, 35.70%, and 43.04%. 3.2 Energy Saving Calculation Based on an annual operating time of 7200 hours, and according to the load curve, it is assumed that the operating probability is 5% at 90MW, 15% at 125MW, 55% at 113MW, and 25% at 100MW. Direct Economic Benefit Analysis: 1) Based on the above conditions, the average electricity saving per wind turbine under the above operating conditions at both power frequency and variable frequency is ΔW = 200.475 × 7200 × 15% + 225.678 × 7200 × 55% + 255.838 × 7.200 × 25% + 296.925 × 7200 × 5% = 216,513 + 893,692.8 + 460,508.4 + 106,893 = 1677,606.8 kW•h 2) Increased revenue from grid connection = annual savings × grid connection price (Note: The grid connection price for our plant's No. 3 unit is 0.36,248 yuan/kW•h = 1677,606.8 kW•h × 0.36,248 yuan/kW•h = 608 0.9891 yuan = 608,100 yuan. From the test results, the energy-saving effect of the frequency converter is quite significant. Under the same boiler operating reference conditions, when the load range of Unit #3 is 90 MW to 125 MW, the average energy saving effect of a single frequency converter is between 200.475 and 296.925 kW, with an average energy saving rate fluctuation range of 26.83% to 43.04%. Oxygen content has a certain impact on the energy-saving effect. Under the premise of meeting the boiler's standby air volume, the lower the oxygen content, the greater the energy-saving effect, but the increase is not significant. Therefore, the actual energy-saving effect during operation will be slightly higher than that during the test, but the difference is not large. Atmospheric pressure and vacuum also have a certain impact on the energy-saving effect. During the test, the average atmospheric pressure was 100.9 kPa, and the air density was higher than in summer. Therefore, the output of the blower during normal operation was higher than that during the test, and the actual energy-saving effect was lower than that during the test. During the test, the vacuum was -96 kPa, while in summer the operating vacuum was -91 kPa. At kPa, with the same load, the boiler output increases, but the energy-saving effect of the blower decreases. Due to climatic reasons, the actual energy-saving effect is slightly lower than that under test conditions. Because of the use of variable frequency speed control, the blower often operates at low speeds, thus greatly reducing impeller wear, blower vibration, and bearing wear. This extends the blower's overhaul cycle and saves maintenance costs and time. Simultaneously, since the damper does not need to be adjusted during operation, the damage to the equipment caused by the vibration phenomenon that easily occurs when adjusting the damper is avoided. The variable frequency speed control system can act as a soft starter, thus avoiding the impact on the motor during direct starting. 4. Conclusion High-voltage variable frequency devices have significant energy-saving effects, especially at low loads. After adopting variable frequency speed control, soft starting of the motor is achieved, extending motor life. Full opening of the blower damper also reduces duct vibration and wear. The excellent energy-saving effect will be increasingly applied in power systems, possessing significant practical value and playing an important role in building a resource-saving society.