In the boiler fan system of a thermal power plant, the forced draft fan provides the oxygen required for combustion, while the induced draft fan maintains a suitable negative pressure in the furnace. The required oxygen quantity varies depending on the steam pressure. In fans using motors running at full speed at industrial frequency, oxygen quantity and negative pressure are controlled by adjusting the position of the duct damper or by regulating the speed through a hydraulic coupling. However, adjusting the duct damper results in significant energy consumption due to the pressure difference before and after it. Hydraulic couplings, which use liquid as the intermediate medium for force transmission, suffer from low transmission efficiency, require extensive maintenance, are prone to vibration, and are difficult to modify. Variable frequency drive (VFD) technology is the mainstream of modern electric drive technology. Its superior speed regulation performance and significant energy-saving effect can improve the operating conditions of existing equipment, enhance system safety and reliability, increase equipment utilization, and extend equipment lifespan. The Power Company of Qishuyan Locomotive & Rolling Stock Plant, a subsidiary of China South Locomotive & Rolling Stock Corporation (CSR), successfully upgraded the forced draft fans and induced draft fans of a thermal power plant boiler using ABB's ACS600 frequency converters. The original operating style was preserved, and the project was completed with low investment cost, minimal modification work, and a short construction period. After the upgrade, operators could master the new operating methods within one hour after simple on-site training. Moreover, the new operating methods are more intuitive and convenient than the original control panel method. 1. Energy-Saving Principle of Variable Frequency Fans According to fluid mechanics principles, the air volume Q (m/s) is directly proportional to the fan speed, the air pressure H (ks/cm) is directly proportional to the square of the fan speed, and the motor shaft power is directly proportional to the cube of the fan speed. The relationship between the motor shaft power P (kW) and Q and H is: P = Q·H/10². [b][align=center]For more details, please click: Application of AC Frequency Converters in Thermal Boiler Fans[/align][/b]