Abstract: Based on the requirements of coal washing and beneficiation process, this paper proposes the selection principles and harmonic prevention measures for frequency converters; and analyzes them in conjunction with engineering examples. Keywords: coal preparation plant, frequency converter, harmonics, motor heating 1 Overview In recent years, in coal preparation plants mainly using heavy medium process, general frequency converters have been widely used due to their advantages of intelligence, digitalization, networking, and energy saving. They are mainly used for hydrocyclone inlet pressure regulation and liquid level control. With the increasing scale of the plant, the power of frequency converter equipment has also increased. During use, problems such as harmonic interference, frequency converter overload and motor heating often occur. This paper only addresses this problem and proposes selection principles and solutions in conjunction with engineering examples. [b]2 Design Selection Principles 2.1 Basic Parameter Selection[/b] (1) Rated Voltage: The rated operating voltage of the frequency converter should not be less than the rated voltage of the power supply, U≥U. At present, many coal mines in the coal industry still use the 660V voltage level, and newly built mines mostly use 380V. (2) Rated Current: Its rated output current should be greater than that of the load motor, I≥1. This is particularly important and cannot be simply selected based on the inverter capacity. (3) Inverter capacity: Its rated power should be greater than that of the load motor, i.e., P≥P. According to the load type of the motor, it is divided into light overload application and heavy overload application. For the feed pump of the coal preparation plant, it is generally selected according to heavy overload. Therefore, the inverter capacity should be one level larger than the motor capacity. (4) Load matching: The load torque characteristics are generally divided into three types: constant torque load, fan and pump type load and constant power load. The frequency conversion equipment of the coal preparation plant is mostly pump type load, so a frequency converter with u/f-const control mode should be selected. Generally, a general fan and pump type load frequency converter can meet the process requirements. (5) Communication requirements: If the frequency converter adopts the fieldbus control method, different bus interfaces should be selected according to the requirements of the control host, such as Profibus, DeviceNet, etc. 2.2 Accessory Selection (1) Filters: For low-power (110kW and below) frequency converters, the harmonic interference is relatively mild, and most frequency converter manufacturers have already addressed this within their frequency converter modules, so no additional filters are needed. For high-power frequency converter modules, filters are mandatory accessories, and generally, dedicated filters from the same brand are selected: including input filters and output filters. Input filters cannot be used for IT power supply systems; they are only used in TN and TT power supply systems. [b][align=center]For more details, please click: Application Design of Frequency Converters in Coal Preparation Plants[/align][/b]