Engineer story sharing(3)

At the industrial control site, we have seen high-power inverters. This one-piece high-power, large-sized, heavy-weight products are assembled by one and one component of the workers, and then subjected to rigorous testing of performance, and finally allowed to leave the factory.
Speaking of high-power inverter assembly, when I first entered the company, I also participated in assembly testing to familiarize myself with the production process. I remember that just a few months after I entered the company, I helped a master assemble a power of 100KW on the production line. The warehouse staff had already issued all the materials needed for product assembly (here only in the hardware part). The most used part of the impression is a screw with a different size: hexagonal, large flat, pill cross, self-tapping... and so on. It is not an easy task to properly lock and lock one screw of these specifications into place. First of all, you must be able to identify the size of these screws, and then familiarize yourself with the installation position of one of them. Finally, after 2 people confirm, you can use the weight tool to lock and mark it. First, confirm that the work has been completed. Second, Facilitate future maintenance identification.
The assembly started was quite smooth. After all, I used to get the wrench and screw it over, which is not so strange to the screw specifications. Half assembled, the master went home to take time off, and without the master, the assembly stopped. First, I am afraid that I am a newcomer who is prone to problems. Second, the product itself lacks a driver board, and the schedule is not as strict as the card.
The master told me repeatedly before leaving the company that I should not assemble it myself, but asked me to re-confirm the parts (especially the screws) issued by the warehouse whether the quantity is the same as the amount specified in the assembly standard book. If it is small, it can be recorded first.
The next day, the master came to the company and continued to assemble. It took half a day for the hardware to be assembled. Everything went smoothly!
After testing the main circuit in the next step, the static power-on test is started and the test is normal! Finally, I want to carry the load dynamic test. I didn't expect to hear a loud noise soon after power-on, and the three-phase output was instantly out of balance!
The master is also puzzled! After the power failure, check step by step to confirm that one module of the three-phase output is burnt out. In desperation, only disassemble to find the reason. How to install it, how to remove it, when the inverter module leaks out, it is clear that a module has burst, the color of the whistling is very obvious, and the module can be moved by hand fluctuation. According to the truth, the module cannot be moved. The module is fastened in place by four screws. Look carefully at the screw itself, no problem, no crack, no use of the wrong specifications. Just wonder! Screw in again with a new screw and find that it cannot be tightened. It turns out that the heat sink has a slip phenomenon. It shouldn't be! It was good to confirm at the beginning!
The final analysis may be a bit of a problem with the heat sink hole tapping. In desperation, only the heat sink is replaced and reassembled!
From then on, make sure that all important parts are tightened before the screw holes are installed.
Sometimes some problems can't be prevented, only strict checks and careful inspection. Avoid problems again!
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