I. Heat dissipation issues
The heat generated by a frequency converter is due to internal losses. Among the various losses in a frequency converter, the main circuit accounts for approximately 98%, while the control circuit accounts for 2%. To ensure the normal and reliable operation of the frequency converter, heat dissipation is essential, typically achieved using a fan. The internal fan of the frequency converter removes heat from the internal enclosure. If the fan malfunctions, the frequency converter should be stopped immediately. High-power frequency converters also require additional fans on the control cabinet . The air duct of the control cabinet must be designed reasonably, with dust filters installed at all air inlets, ensuring unobstructed exhaust and preventing the formation of eddies and dust accumulation in fixed locations within the cabinet. The appropriate fan should be selected based on the ventilation requirements specified in the frequency converter's instruction manual, and vibration prevention should be considered during fan installation.
II. Electromagnetic Interference Issues
I. During operation, frequency converters generate a lot of interfering electromagnetic waves due to rectification and frequency conversion. These high-frequency electromagnetic waves can interfere with nearby instruments and meters, and can also generate higher harmonics. These higher harmonics can enter the entire power supply network through the power supply circuit, thus affecting other instruments. If the power of the frequency converter is very large, accounting for more than 25% of the entire system, anti-interference measures for the control power supply need to be considered.
II. When there are high-frequency impact loads in the system, such as welding machines or electroplating power supplies, the frequency converter itself may trigger protection due to interference. In this case, the power quality of the entire system should be considered.
III. The following points should be noted regarding protection:
I. Waterproof and anti-condensation: If the frequency converter is placed on site, it is necessary to ensure that there are no pipe flanges or other leaks above the frequency converter cabinet, and that there is no water splashing near the frequency converter. In short, the protection level of the on-site cabinet should be above IP43.
II. Dust Control: All air inlets must be equipped with dust screens to prevent fibrous debris from entering. The dust screens should be designed to be removable for easy cleaning and maintenance. The mesh size of the dust screens should be determined based on the specific site conditions, and the joints between the dust screens and the control cabinet must be tightly sealed.
III. Resistance to corrosive gases: This is more common in the chemical industry, in which case the frequency converter cabinet can be placed in the control room.
IV. Inverter Wiring Specifications
Signal lines and power lines must be routed separately: When using analog signals to remotely control the frequency converter, to reduce interference from the frequency converter and other equipment, please route the signal lines controlling the frequency converter separately from the high-voltage circuits (main circuit and sequential control circuit). The distance should be at least 30cm. Even inside the control cabinet, this wiring standard must be maintained. The control loop between the signal line and the frequency converter must not exceed 50m.
Signal lines and power lines must be placed in separate metal conduits or flexible metal hoses: If the signal lines connecting the PLC and the frequency converter are not placed in metal conduits, they are easily interfered with by the frequency converter and external equipment; at the same time, since the frequency converter does not have a built-in reactor, the input and output power lines of the frequency converter will generate strong interference to the outside. Therefore, the metal conduit or flexible metal hose containing the signal lines must extend to the control terminals of the frequency converter to ensure that the signal lines and power lines are completely separated.
1) Analog control signal lines should use double-strand shielded cable with a wire specification of 0.75mm². When wiring, be sure to strip the cable as short as possible (about 5-7mm), and wrap the stripped shielding layer with insulating tape to prevent the shielding cable from contacting other equipment and introducing interference.
2) To improve the ease and reliability of wiring, it is recommended to use wire clamp terminals on signal lines.
V. Inverter Operation and Related Parameter Settings
Inverters have many setting parameters, each with a certain selection range. During use, it is common to encounter situations where the inverter cannot work properly due to improper setting of individual parameters.
Control method: This includes speed control, torque control, PID control, or other methods. After adopting a control method, static or dynamic identification is generally required depending on the control accuracy.
Minimum operating frequency: This refers to the minimum speed at which the motor can operate. When a motor runs at low speeds, its heat dissipation performance is very poor, and prolonged operation at low speeds can lead to motor burnout. Furthermore, at low speeds, the current in the cables also increases, causing the cables to overheat.
Maximum operating frequency: The maximum frequency of a typical frequency converter is 60Hz, and some even reach 400Hz. High frequency will cause the motor to run at high speed. For ordinary motors, the bearings cannot run at speeds exceeding the rated speed for a long time. Can the motor rotor withstand such centrifugal force?
Carrier frequency: The higher the carrier frequency is set, the greater the higher harmonic components will be. This is closely related to factors such as cable length, motor heating, cable heating, and inverter heating.
Motor parameters: The inverter sets the motor's power, current, voltage, speed, and maximum frequency in the parameters. These parameters can be obtained directly from the motor nameplate.
Frequency hopping: Resonance may occur at a certain frequency point, especially when the overall system is relatively high; when controlling the compressor, it is necessary to avoid the compressor's surge point.
Disclaimer: This article is a reprint. If it involves copyright issues, please contact us promptly for deletion (QQ: 2737591964 ) . We apologize for any inconvenience.
