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Dust-the general term for fine impurities, although it seems extremely small, but it has the cohesion of "covering up soil into mountains", so it should not be taken lightly! In the maintenance of electrical equipment for many years, the author has dealt with various malfunctions caused by dust accumulation many times. Today I will make a summary for your colleagues to communicate.
1. In 2009, the author received and repaired a Zhongchen 37KW inverter. The fault was: the machine suddenly reported the "OUC" DC bus overvoltage fault code during operation. After testing the AC input terminal voltage and DC P and N terminal voltages are normal, the author will disassemble the machine for maintenance. After turning on the machine, the author found that the switch power supply + drive signal board and protective function board inside the machine were covered by a thick layer of dust, so compressed air was used to remove dust. After finishing the cleaning, the author turned on the power to test, and as a result, an unexpected scene occurred-the malfunction was actually healed! It seems that the fault phenomenon is caused by dust. After carefully reviewing the principle of the protection function circuit, the author made a rough judgment on the cause of the fault: the dust covering the protection function circuit board, under the action of long-term voltage, formed It is similar to a low-resistance resistor, so that it has a parallel relationship with the chip resistor of the comparison circuit that participates in monitoring the DC bus voltage condition, and then causes the voltage comparison to act!
2. In 2011, the author handled an intermittent tripping fault of a leakage circuit breaker in a coal washing plant. After some investigation, the author identified the suspected fault as a three-phase ZX7 series manual welding machine. After disassembling the machine, it was found that due to the lack of necessary cleaning and maintenance, a lot of coal dust and carbon powder had accumulated inside the welder. Between the side of the three-phase power input terminal and the metal shell of the welder, the accumulated coal dust gradually undergoes carbonization under the continuous action of voltage, which eventually leads to irregular discharge, which causes the leakage circuit breaker to operate!
3. In 2019, a FX3U series plc used in the workshop production line of a certain unit had a sudden "three no" failure phenomenon during use. Preliminarily judged on site that the internal switching power supply circuit was damaged. After disassembly and inspection, it was found that the cause of the damage of the switching power supply circuit at the bottom of the PLC was also caused by dust accumulation-the dust under the DC bus energy storage capacitor of the switching power supply caused a short circuit fault under the action of the voltage between the two pins! Then the front-end Fuse, NTC, rectifier bridge and other components of the line are damaged!
