发布时间：2024-02-12 来源：http://www.tongyuhengcheng.com/ 浏览量：
Ensure that any machine equipment in the motor control cabinet has a good grounding device, and use short and thick grounding connections to the common grounding address or copper bar of the grounding device. All control systems connected to frequency converters (such as a PLC) need to use short and thick transmission line grounding devices, just as they need to be grounded together. Generally, flat electrical conductors (such as metal wire mesh) are chosen due to their lower characteristic impedance at high frequencies.
Low voltage modules, solenoid valves, and AC contactors in the motor control cabinet should be maintained using circuit breakers; When the connection between the frequency converter and the motor exceeds 100m, and when the volume of the switching power supply provided by the frequency converter exceeds 600kw/a or the volume of the power supply system's switching power supply exceeds 10 times the volume of the frequency converter, it is proposed to increase the input output reactor.
Ensure that the AC contactor in the motor control cabinet has a magnetic blowing effect. The DC contactor uses an R-C suppressor, and the DC contactor uses a "gear" diode, which is installed in the winding resistor. It is also reasonable to choose a zinc oxide varistor suppressor.
If the machine equipment operates under conditions that are sensitive to noise, filters can be selected to reduce the impact of radiation sources. At the same time, in order to achieve better practical results, there should be good contact between the filter and the assembly board.
The motor cables should be separated from other variable frequency cables for wiring, with a smaller spacing of 500mm. At the same time, it is necessary to prevent the long-distance parallel wiring of motor cables and frequency conversion cables. If the frequency conversion cable and the host power cable are crossed, they should be crossed at a 90 ° angle as much as possible. At the same time, it is necessary to use suitable clips to fix the shielding layer of the motor cable and variable frequency cable onto the assembly board.
In order to better and reasonably suppress the coverage and transmission of radio waves, shielded twisted pair cables must be selected for the motor cables of the frequency converter. The conductivity of the shielded layer must be at least 1/10 of the conductivity of each phase of the transmission line core.
The motor control cabinet should each be equipped with a zero line busbar group and a protection zone busbar group (PE). The grounding device and PE conductive busbar must be connected to the load-bearing beam (copper bar to copper bar connection). They need to face the surrounding area directly at the cable cap. The additional grounding device bank also needs to be connected to the maintenance power circuit (grounding device bank) based on another cable line. Shielding the system bus is used to ensure reliable shielding and connection of each cable line. It completes large-scale metal to metal connections based on a load-bearing beam.
It is not allowed to install the actual operation panel equipped with a display screen near the power cables and machine equipment containing inductive coils, such as switch power cables, AC contactors, solenoid valves, magnetic induction line valves, transformers, etc., as they can form strong electromagnetic fields and endanger the measurement accuracy of instrument equipment.
The output power components (transformer, propulsion components, load output power switch power supply, etc.) and the control system (electromagnetic valve control part, program controller) must be assembled separately. However, it is not suitable for products that integrate output power components and control system design schemes. The plastic casings of variable frequency governors and filters should be connected to the electrical control cabinet with low resistors to reduce the impact of high-frequency instantaneous current. The ideal scenario is to assemble the control module onto a conductive, gray black metal material sheet, and assemble the metal onto a large metal material table surface.
When designing the motor control cabinet, attention should be paid to the regional standards of EMC, and different machinery and equipment should be planned as a whole in different regions. Each region has different regulations on the transmission and anti-interference level of environmental noise. Metal material shells are more practical in the region, or grounding devices and protective plates are used to isolate the cabinet body. Moreover, considering the calorific value, the air ducts of the motor control cabinet should be effectively designed, and the exhaust system should be smooth to prevent vortices and dust deposition in the cabinet at designated locations. The fan is generally installed near the ventilation opening, the supply fan is installed at the bottom, and the inlet fan is installed at the upper end of the box.
According to the waterproof level of the facilities inside the control box, it is necessary to consider the anti fouling and waterproof function of the control box. Generally, the facilities used are: central air conditioning, fans, heat exchangers, and anti cooling electric heaters. At the same time, different efficiency machines and equipment should be selected according to the number of boxes. Regarding the selection of fans, the key consideration is the normal operating temperature inside the cabinet and the higher working temperature outside the cabinet. Calculate a temperature difference, the ventilation speed of the fan, and estimate the gas volume inside the cabinet. After knowing three data information: temperature difference, ventilation speed, and gas volume, calculate the duration of gas replacement in the cabinet, and then calculate the specific ventilation speed based on the temperature difference. Then select the specific fan you want. Due to the general decrease in ambient temperature at night, condensation water may be generated and attached to the circuit board inside the cabinet. Therefore, corresponding anti cold electric heaters should be selected to ensure the ambient temperature inside the cabinet.
The main regulations for connecting frequency converters are that they should be assembled in the middle of the control box. The frequency converter should be assembled vertically, and the upper and lower parts should prevent large components that may obstruct the exhaust system and air supply; The distance between the upper and lower edges of the frequency converter, the distance between the top and bottom of the motor control cabinet, or the smaller distance between the baffle and the large components that must be installed and used, should all exceed 150mm; If a unique customer must remove the computer keyboard during use, the computer keyboard hole on the frequency converter control panel must be tightly sealed with adhesive tape or replaced with a fake control panel to prevent a large amount of smoke and dust from entering the internal structure of the frequency converter.
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