Specific cases in the maintenance of the hottest f

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Specific cases in frequency converter maintenance

a recent repair of a Mitsubishi AK frequency converter was brought to us by a novice maintenance technician. A module of the machine was originally broken. After replacing the module, the novice wanted to measure whether the drive was normal and unplugged the trigger line of the module. As a result, it tripped as soon as it was powered on. After inspection, it was found that another module was burned! He couldn't understand why for a long time! It turns out that there may be a small amount of voltage at the trigger end of the IGBT module after the trigger line is unplugged. At this time, the module is in a semi conducting state, and it will burn out due to a short circuit as soon as it is powered on. GTR module does not have this feature, so it can be tested like this

an Anchuan 616gkw frequency converter is seriously damaged. It was originally a fast fuse (there is a fast fuse in each of the three phases). The electrician may be inexperienced and did not check whether there is a problem with the module. If the fast fuse cannot be found at the moment, he replaced it with a copper wire. After starting up, it makes a loud noise, the two modules burst, the absorption circuit is broken, and the driving board cannot be repaired. Replacing the board causes great losses! According to our experience, if the fast fuse is broken, most modules have problems, but if the module is broken, the fast fuse does not necessarily break! We have seen copper wire replace fast melting many times

we found that someone often grounded the a.5kw "n" line when replacing Mitsubishi a.5kw frequency converter with a.5kw! The frequency converter makes a loud noise as soon as it is powered on! The frequency converter is severely damaged. In 2016, the domestic market sales of 3 yuan materials reached 54300 tons! On the one hand, the "n" line of a.5kw is similar to the ground wire of a.5kw frequency converter! Some electricians connect the ground wire without seeing clearly; Some electricians mistakenly believe that the "n" line is the ground wire! Please be careful with the wiring of Mitsubishi Inverter users

many people call to ask how to measure the current of the module with the same appearance. In fact, it is very simple. As long as you use a capacitance meter to measure the capacitance of the module G-E or C-E junction, the capacitance of the module with a large current is also large! Pay attention to the comparison among modules of the same type

an electrician said that when testing the frequency converter, he found that the output voltage of the frequency converter was more than 1000 volts (input 380V), and asked whether it was the fault of the frequency converter? Will the motor burn? He still doesn't understand that the frequency converter will only reduce the voltage, not the voltage!! It turned out that he used a digital multimeter to measure. Because the output voltage of the frequency converter is a high-frequency carrier, the measurement of ordinary digital meters without anti-interference is very inaccurate here

some careless maintenance engineers did not remove the short connector when wiring the auxiliary power supply (R1, T1) of Mitsubishi A540 frequency converter. As a result, they did not understand the reason after burning the frequency converter. It turned out that when the short connector was not removed, the internal R and R1, t and T1 of the frequency converter were connected together. The electrician thought that there was no difference between the two lines from R and T, so he connected r to S1 and t to R1, resulting in a phase to phase short circuit. Because R and R1 The connection between T and T1 passes through the middle layer of the power board. As a result, the power board is burned and exploded into two layers! Generally, it is not necessary to connect the auxiliary power supply (R1, T1)

some novices in maintenance do not know how to use false negative color, structure and feel to realize load at the same time when repairing the frequency converter. Once the drive is faulty and the module is burned, they say that the quality of the module is poor! The dummy load is to use a resistance of hundreds of ohms (electric light cannon can also be used), which is connected in series on the main circuit. If there is a fast melting, remove it and install the resistance; If there is no fast melting, it can be disconnected anywhere on the main circuit and connected with this resistor in series! This resistance plays a current limiting role. When the module has a short circuit, it will not burn the module. After starting the machine, measure the output of the frequency converter to be normal, and then remove the false load.

many factories supply power by generators. When the generator has a fault, the output of high-voltage electricity often burns out the frequency converter and electronic instruments! We have often seen this kind of situation. A wire drawing factory in Zhejiang broke down more than 20 30kW frequency converters at one time, and stopped production for more than ten days, causing heavy losses. The factory has done a lot of protection methods in the generator, but the effect is not obvious! Later, we thought of a passive protection method, which is to add a varistor (821k for 380V and 220v471k for 220V) to the air switch at the input end of the frequency converter or instrument, so that when there is high voltage, the varistor will be short circuited, the air switch will trip, and the frequency converter will be protected. The failure rate of the frequency converter will be greatly reduced, and the varistor is very cheap. This method can be said to spend a small amount of money to do great things

there is no strict requirement on the wattage of the varistor in parallel (three-phase delta connection method). If the input current of d/a ------- digital quantity conversion is large, the varistor selected is relatively large (or several in parallel)! When the varistor acts, it is completely short circuited! At this time, your air switch is also required to be of good quality and fast response! The protection current should not be too large! Of course, the place to connect is the output end of the air switch

some customers said that there was a problem with varistors. He asked that there were varistors at the input end of some frequency converters, which should also have a protective effect! However, according to the actual situation of the frequency converter we have repaired, the existence of these problems makes China's plastic machinery industry unable to meet the level of foreign plastic machinery as soon as possible. Those who are slightly injured only burn the copper wire of the circuit board, and those who are seriously injured burn the rectifier module, switching power supply, CPU board, capacitor. The cause of serious injury may be that when the varistor is short circuited and explodes, its metal fragments are everywhere

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