The inverter should be installed inside the control cabinet, and the design of the control cabinet should pay attention to the following issues:
1. Wiring specification of inverter
The signal line and the power line must be separated: When using analog signals to remotely control the inverter, in order to reduce the interference of the analog signal to the inverter and other equipment, please separate the signal line of the inverter from the strong current circuit, and the distance should be greater than 30 cm. Even in the control cabinet, the same wiring specifications should be maintained, and the control loop between the signal and the frequency converter should not exceed 50 m at length.
The signal line and the power cable must be placed in different metal pipes or metal hoses respectively: if the signal line connecting the PLC and the inverter is not placed in the metal pipe, it is easy to be interfered by the inverter and external equipment; At the same time, because the inverter does not have a built-in reactor, the input and output power lines of the inverter will cause strong interference to the outside world. Therefore, the metal tube or metal hose where the signal line is located should extend to the control terminal of the converter to ensure that the signal line is completely separated from the power line.
Second, the operation of the inverter and the setting of related parameters
There are many setting parameters for the inverter, and each parameter has a certain range of options. In use, due to improper setting of individual parameters, the inverter cannot work normally.
Control mode: that is, speed control, rotation control, PID control or other ways. After the control mode is adopted, static or dynamic identification is required according to the control accuracy.
Minimum operating frequency: When the motor is running at low speed, the heat dissipation performance is very poor. If the motor runs at low speed for a long time, it will burn out. Also, at low speeds, the current in the cable increases, which also causes the cable to heat up.
Maximum operating frequency: The maximum frequency of the general inverter is 60Hz, and some even reach 400 Hz, and the high frequency will make the motor run at high speed. For ordinary motors, their bearings cannot exceed the rated speed for a long time.
Carrier frequency: The higher the carrier frequency setting, the higher the harmonic component, which is closely related to factors such as cable length, motor heating, cable heating, and inverter heating.
Frequency hopping: At a certain frequency point, resonance may occur, especially when the overall unit is relatively high; When controlling the compressor, avoid the surge point of the compressor.
3. Heat dissipation problems
The heat generation of the inverter is caused by internal losses. In the loss of each part of the inverter, the main circuit accounts for about 98%, and the control circuit accounts for 2%. In order to ensure the normal and reliable operation of the inverter, the inverter must be dissipated, and we usually use a fan to dissipate the heat.
The built-in fan of the inverter can take away the internal heat dissipation of the inverter box, if the fan cannot work normally, the inverter should be stopped immediately; The high-power inverter also needs to install a fan on the control cabinet, the air duct design of the control cabinet is reasonable, and all air inlets are equipped with dust nets, so that the exhaust air is smooth to avoid eddy current in the cabinet and dust accumulation in a fixed position; Select the matching fan according to the ventilation volume in the inverter manual, and pay attention to shockproof when installing the fan.
Fourth, the following points need to be paid attention to in terms of protection
1. Waterproof and anti-condensation: When placing the inverter on site, it should be noted that there are no leakage points such as pipe flanges above the inverter cabinet, and there is no splashing water near the inverter. In short, the protection level of the field cabinet should be above IP43.
2. Dustproof: All air inlets should be equipped with dust-proof nets to prevent flocculent debris from entering. The design of the dust filter should be removable for easy cleaning and maintenance. The grid of the dust filter should be determined according to the specific conditions of the site, and the joints around the dust filter and the control cabinet should be handled tightly.
3. Anti-corrosion gas: This situation is more common in the chemical industry. At this time, the inverter cabinet can be placed in the control room.
5. Electromagnetic interference
Due to the rectification and frequency conversion in the operation of the frequency converter, a large number of interfering electromagnetic waves will be generated around the frequency converter. These high-frequency electromagnetic waves have certain interference with nearby industrial computers and other instruments, and will produce high-order harmonics, which will enter the entire power supply network through the power supply circuit, thereby affecting other instruments and meters. When the power of the inverter is large, accounting for more than 25% of the whole system, anti-interference measures for controlling the power supply should be considered.
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