The emergence and development of variable frequency speed control (VFD) has brought about a revolutionary change in the speed control methods of asynchronous motors. With the innovation and improvement of speed control technology in recent decades, it has not only promoted the automation of industrial production but also brought considerable economic benefits to enterprises. VFD technology is increasingly widely used in China's cement industry. It is applied to many aspects of the production process that require speed regulation, such as rotary kilns, coolers, feeding and batching systems, process fans, and water pumps. Based on our company's experience during the construction and trial production phases, we have summarized some observations for reference and correction by our peers. 1. VFD Selection Based on the current market, VFDs, like other products, have many brands and types. General-purpose VFDs generally adopt a given closed-loop control method, resulting in a relatively slow dynamic response speed. Engineering-grade VFDs, on the other hand, have internal detection systems with automatic compensation and automatic limiting mechanisms, maintaining good torque characteristics even when the equipment is running at low speeds, achieving true closed-loop control. Engineering-grade frequency converters typically offer three control options: 1) Open-loop control (same as general-purpose type); 2) With slip compensation, automatically compensating for sudden load drops; 3) Installed/cabinet-mounted type, with power ranging from 45 to 200 kW, requiring additional circuitry and a fixed housing, resulting in a larger size and more space requirements. Users should choose the appropriate type based on the power of the controlled motor and the site installation conditions. In terms of voltage ratings, there are 1AC 230V; 3AC 208V-230V, 380V-460V, 500V-575V, and 660V-690V levels; and multi-pulse (1 pulse or 18 pulse) 3300V and 6000V. Users should make the correct selection based on their requirements and load characteristics. In terms of frequency conversion range and control accuracy requirements, frequency converters include FC (frequency control), with a speed range of 1:25; VC (vector control), with a speed range of 1:100 to 1:1000; and SC (servo control), with a speed range of 1:4000 to 1:10000. Currently, VC is generally preferred in cement production lines due to its good reputation. Considering the above requirements, users can make the correct choice based on the specific production site conditions. 2. Installation and Commissioning of Frequency Converters In cement production, on-site installation of production equipment for local control is not advisable because cement production lines generate significant dust, and speed-regulating machinery is mostly installed outdoors or underground. The environment is harsher than in other industries. As a relatively precise instrument, the production site is often unattended and the environment is poor, which is detrimental to the equipment. Therefore, in cement production lines, frequency converters should be installed in the electrical control room. According to the frequency converter product manual, the cable length connecting the frequency converter to the motor should not exceed 50m; if a shielded cable is used, the maximum length should not exceed 25m. This necessitates considering the distance between the frequency converter and the controlled motor. The primary method to solve this problem is to insert a suitable current-rated outgoing reactor in series on lines exceeding 50m. Some frequency converters already have this reactor in series, and the connection cable between the frequency converter and the motor can be up to 300m long. Properly setting and debugging the frequency converter parameters is a fundamental guarantee for the normal operation of the equipment. Many problems encountered on-site are often due to parameter settings issues, unrelated to the equipment itself. Therefore, setting parameters correctly and appropriately is crucial. 1) Setting basic parameters: Basic parameters include the rated power, voltage, current, speed, and frequency listed on the motor nameplate. 2) Setting other parameters according to production process requirements: Frequency converters typically have dozens or even hundreds of settable parameters. In practical applications, most factory settings can be used, with only a few special settings required to meet production requirements. For example, in areas requiring heavy-load starting, a starting boost parameter must be set. This can be achieved by setting an additional voltage boost within the range of 0-250% of the motor's rated current to increase the starting current and ensure smooth equipment startup. 3. Precautions for Using Frequency Converters Taking a fan load as an example. First, check whether the starting torque of the selected fan motor meets the requirements. Currently, many high-power frequency converters are used in cement plants in China, and dampers are generally installed at the fan inlet. When the frequency converter starts, the dampers are initially closed, and after the frequency converter starts, all dampers are opened. If the input or output dampers are removed, one of the fans in cooling chambers four, five, six, and seven will stop during operation. The stopped fan will maintain a certain speed and run in reverse due to the high positive pressure inside the cooling chamber. When the frequency converter restarts, sometimes it cannot start due to excessive resistance torque. If the over-torque capacity was considered when selecting the motor capacity, or if a fan actuator valve was installed, the fan will start normally. Secondly, for mechanical equipment driven by frequency converters with higher power, a larger starting torque is required during startup, especially for fan-type loads with longer startup times. To protect the frequency converter from overcurrent, the startup time is set to be longer than 200 seconds. If a speed encoder is not selected on the motor... If the inverter cannot establish a complete speed closed loop at 6Hz during startup, the motor may stall. Due to the limited overload capacity of the main circuit semiconductor devices, the inverter's overload capacity is only 150% or 120% for one minute. Compared to a standard asynchronous motor (overload capacity around 200%), the inverter's overload capacity is smaller, and the allowable overload time is also very short. The overload capacity of the asynchronous motor cannot be fully utilized. Therefore, for high-power inverters, a speed encoder must be selected when the set speed exceeds the rated torque. In conclusion, inverters bring many conveniences and benefits to the cement industry, and their application will become increasingly widespread. Fully and rationally utilizing their performance will bring about a substantial revolution in the cement industry.