Abstract : This paper mainly introduces the application of variable frequency speed governor in belt conveyor, which provides a new control mode for belt conveyor. Keywords: variable frequency; belt conveyor; high power 1 Introduction With the construction and commissioning of large-scale modern mines across the country, the demand for high-capacity, long-distance, and intelligent belt conveyors has been increasing year by year. At present, high-power and intelligent belt conveyors are mainly imported, but imported belt conveyors are expensive, and the cost of operation and maintenance is also high. In order to replace imported equipment, the Electromechanical Plant of Jincheng Coal Industry Group has developed a telescopic belt conveyor for underground coal mines with controllable variable frequency soft start, controllable variable frequency speed regulation, hydraulic automatic tensioning, and centralized intelligent control functions. As a kind of electric driven friction transmission bulk material conveying machinery, it is mainly used for conveying raw coal in the roadway of fully mechanized coal mining faces. 2. Application Principle The application of frequency conversion soft starters in underground coal mines has always been a focus of attention in this industry. For belt conveyors, the following requirements should be met during startup: 1) Low starting current and short starting current impact time to extend motor life and reduce the impact of electromechanical starting current on the power grid, thereby minimizing its influence on other electrical equipment. 2) Minimize the starting impact on mechanical equipment during startup, thus extending the service life of key components such as the reducer and belt. 3) Achieve high-power balance. 4) Controllable startup process. Previously, soft starts for high-power belt conveyors in underground coal mines mostly adopted mechanical soft start technology. Due to the limitations of its application technology, it could not fully meet the above requirements. The explosion-proof and intrinsically safe AC frequency conversion control device developed in this project solves the contradiction between heat dissipation and underground explosion-proof requirements, thus achieving high-power frequency conversion soft start and meeting the above requirements. This equipment utilizes a high-power variable frequency soft starter for underground coal mines (with a starting frequency of 0.5～60Hz adjustable resolution ±0.01Hz at 3 × 400kW power). It is connected to a PLC microcomputer programmable automatic control system along with sensors for hydraulic automatic tensioning devices, misalignment, tearing, temperature, and speed protection devices, achieving highly intelligent control and protection. The variable frequency speed control soft starter changes the motor speed by altering the AC frequency, allowing the motor to start smoothly and reliably, gradually increasing its speed from 0 to the operating speed according to the system's set time, based on the input curve. This results in a smooth and reliable start, minimizing impact on the entire machine, extending the belt's lifespan, and reducing the belt's strength grade. The principle is shown in Figure 1. [align=center] Figure 1 Electrical Control System Diagram[/align] This project uses a PLC microcomputer programmable automatic control system to control the entire belt conveyor operation. Various feedback signals are centrally processed and commands are issued. Various controlled protection devices are uniformly commanded by this system. The design of the protection and monitoring devices focuses on protecting the belt while also considering the characteristics of underground operation. The program was developed by the Jincheng Coal Industry Group Leasing Station based on the usage of imported conveyor belts, overcoming their shortcomings, and is suitable for the technical characteristics of Chinese coal miners. Its main technical parameters are as follows: Belt width: 1400mm; Conveying capacity: 2500t/h; Laying length: 2000m; Inclination angle: -3°～+5°; Power supply voltage: 1140/660V; Storage belt length: 120m; Motor power: 3 × 400kW; Belt speed: 3.5m/s; Drive drum diameter: Ф1030mm; Unloading drum diameter: Ф900mm; Tail drum diameter: Ф630mm; Idling drum diameter: Ф1030mm; Roller spacing: Upper roller 1.5m; Lower roller 3m; Roller diameter: Ф159mm; Drive method: Variable frequency soft start; Belt tensioning method: Tensioning winch plus China University of Mining and Technology hydraulic automatic tensioning device . Application Achievements The equipment has been tested by authoritative departments and obtained the corresponding coal mine safety mark, explosion-proof certificate, and other market access permits. Industrial trials were conducted on the 3302 working face roadway of the Sihe Mine of Jincheng Coal Industry Group, achieving a maximum daily coal transport capacity of 29,000 tons and a maximum monthly coal transport capacity of 550,000 tons. The equipment exhibits a reasonable structure, scientifically selected parameters, and stable and reliable performance. The imported belt conveyor (excluding the belt) for the 2302 working face roadway at Sihe Mine costs 14.48 million yuan, while this equipment (excluding the belt) costs 8.83 million yuan. With comparable coal transport volumes, this equipment saves 5.65 million yuan in production costs. This equipment not only improves production efficiency and saves on production costs but also has broad application prospects. It can be used for transporting raw coal in mechanized coal mining faces, and the key technologies of this project can be used to modify similar belt conveyors. The high-power variable frequency soft-start device and PLC microcomputer programmable control program developed in this project can be commercially operated independently. Therefore, this equipment should be promoted in coal mine production.