Suppliers of frequency converter supporting equipment remind you that before powering on the frequency converter, you should first check the temperature and humidity of the surrounding environment. If the temperature is too high, it will cause the frequency converter to overheat and give an alarm. In severe cases, it will directly cause damage to the power components of the frequency converter and short circuits in the circuit; Excessive humidity in the air can cause a direct short circuit inside the frequency converter. When the frequency converter is running, attention should be paid to whether its cooling system is normal, such as whether the air duct exhaust is smooth and whether the fan has abnormal sound. Generally, frequency converters with higher protection levels, such as those above IP20, can be installed directly in an open manner, while those below IP20 should be installed in a cabinet. Therefore, the heat dissipation effect of the frequency converter cabinet will directly affect its normal operation.
In the daily maintenance of the frequency converter, it is also necessary to follow the regulations. If a fault is found and the frequency converter trips, do not immediately turn on the frequency converter for repair, because even if the frequency converter is not in operation or the power supply has been cut off, there may still be voltage on the power input line, DC terminal, and motor terminal of the frequency converter due to the presence of capacitors. After disconnecting the switch, it is necessary to wait for a few minutes for the internal capacitors of the frequency converter to discharge before starting to work. When the frequency converter trips and stops, immediately use an insulation resistance meter to test the insulation of the motor driven by the frequency converter, in order to determine whether the motor is faulty. This method is very dangerous and can easily cause the frequency converter to burn out. Therefore, before disconnecting the cable between the motor and the frequency converter, insulation testing must not be performed on the motor, nor on the cable already connected to the frequency converter.
In daily use, a reasonable maintenance cycle and system should be developed based on the actual usage environment and load characteristics of the frequency converter. After each usage cycle, the frequency converter should be disassembled, inspected, measured, and comprehensively maintained once to detect and deal with potential faults in the early stages. Each frequency converter needs to be cleaned and maintained once every quarter. During maintenance, the dust and dirt inside the frequency converter and the air duct should be removed, and the surface of the frequency converter should be wiped clean; The surface of the frequency converter should be kept clean and shiny; During maintenance, carefully inspect the frequency converter to see if there are any heating or discoloration areas inside, if there are any cracks in the braking resistor, if there is any expansion, leakage, or protruding explosion-proof holes in the electrolytic capacitor, if there are any abnormalities in the PCB, and if there are any heating or yellowing areas. After maintenance, the parameters and wiring of the frequency converter should be restored. After power on, the frequency converter with the motor should be started and operated at a low frequency of 3Hz for about 1 minute to ensure normal operation of the frequency converter.
1、 Before powering on the frequency converter
The temperature and humidity of the surrounding environment should be checked first. Excessive temperature can cause the inverter to overheat and trigger an alarm. In severe cases, it can directly lead to damage to the power components of the inverter and short circuits in the circuit; Excessive humidity in the air can cause a direct short circuit inside the frequency converter. When the frequency converter is running, attention should be paid to whether its cooling system is in operation, such as whether the air duct exhaust is smooth and whether the fan has abnormal sound. Generally, frequency converters with higher protection levels, such as those above IP20, can be installed directly open, while those below IP20 should be installed in cabinets. Therefore, the heat dissipation effect of the frequency converter cabinet will directly affect the normal operation of the frequency converter. The exhaust system of the frequency converter, such as whether the fan rotates smoothly, and whether there is dust and blockage at the air inlet, are all important aspects that cannot be ignored in our daily inspections. Whether the electric motor reactor, transformer, etc. are overheated and have any odor; Are there any abnormal noises from the frequency converter and motor; Whether the current display on the frequency converter panel is too large or the current change amplitude is too large, and whether the output UVW three-phase voltage and current are balanced.
2、 Regular maintenance
Regularly remove dust and check if the fan inlet is blocked, and clean the cooling air duct and internal dust of the air filter every month.
Regular inspection should be conducted once a year: check whether screws, bolts, and plugs are loose, and whether there is a short circuit in the ground and phase to phase resistance of the input and output reactors. Normally, it should be greater than tens of megaohms. Whether there is corrosion on the conductor and insulator, and if so, wipe them clean with alcohol in a timely manner. Measure the stability of the voltage output of each circuit in the switch power supply, such as 5V, 12V, 15V, 24V, etc. Whether there are ignition marks on the contacts of the contactor, and if it is serious, replace it with a new contactor of the same model or larger than the original capacity; Confirm the correctness of the control voltage and conduct a sequential protection action test; Confirm that there are no abnormalities in the protection display circuit; Confirm the balance of the output voltage of the frequency converter when operating independently.
Carefully carry out daily maintenance and repair work on the frequency converter, mainly including:
1. Regularly dust the frequency converter, with a focus on the rectifier cabinet, inverter cabinet, and control cabinet. If necessary, the circuit boards inside the rectifier module, inverter module, and control cabinet can be removed for dust removal. Whether the lower air inlet and upper air outlet of the frequency converter have accumulated dust or are blocked due to excessive dust accumulation. The frequency converter requires a large amount of ventilation for its own heat dissipation, so after running for a certain period of time, the surface dust accumulation is very serious, and regular cleaning and dust removal are necessary.
2. Open the front and rear doors of the frequency converter, carefully inspect the AC and DC busbars for deformation, corrosion, and oxidation, check for loose screws at the busbar connections, check for loose screws at each installation fixing point, and check for aging, cracking, or deformation of the insulation sheets or columns used for fixing. If any, replace and re tighten them in a timely manner. Correct and reinstall the deformed busbars.
3. After dust removal on circuit boards, busbars, etc., necessary anti-corrosion treatment should be carried out, insulation paint should be applied, and busbars with partial discharge or arcing should have their burrs removed before treatment. For insulation boards that have experienced insulation breakdown, the damaged parts must be removed, and insulation boards of the corresponding insulation level should be used to isolate them near the damage. The insulation should be tightened, tested, and deemed qualified before they can be put into use.
4. Check if the fans in the rectifier cabinet and inverter cabinet are running and rotating normally. When stopping, rotate them by hand to observe if the bearings are stuck or making noise. If necessary, replace or repair the bearings.
5. Conduct a comprehensive inspection of the input, rectification and inversion, and DC input fast melting, and replace them promptly if burned out.
6. The capacitors in the intermediate DC circuit should be checked for leakage, expansion, bubbling, or deformation of the casing, and whether the safety valve is broken. If conditions permit, the capacitance, leakage current, and withstand voltage of the capacitors can be tested. Capacitors that do not meet the requirements should be replaced. For new capacitors or capacitors that have not been used for a long time, they must be passivated before replacement. The service life of filter capacitors is generally 5 years. For capacitors that have been used for more than 5 years and have significantly deviated from the detection standards in terms of capacitance, leakage current, withstand voltage, etc., partial or complete replacement should be carried out as appropriate.
7. Perform electrical testing on the diodes and GTOs in the rectifier and inverter sections, measure their forward and reverse resistance values, and carefully record them in a pre prepared table to check whether the resistance values between each pole are normal and whether the consistency of devices of the same model is good. Replace them if necessary.
8. Inspect the main contactors and other auxiliary contactors inside the A1 and A2 incoming cabinets, carefully observe whether the dynamic and static contacts of each contactor have arcing, burrs, surface oxidation, and unevenness. If such problems are found, replace the corresponding dynamic and static contacts to ensure safe and reliable contact.
9. Carefully inspect the terminal block for aging, looseness, hidden faults such as short circuits, secure connections of all connecting wires, damaged wire skins, and secure plug connections of all circuit boards. Whether the connection of the main power line is reliable, whether there is heating or oxidation at the connection, and whether the grounding is good.
10. Is there any abnormal noise, vibration, or burnt smell in the reactor.
In addition, if conditions permit, the filtered DC waveform, inverter output waveform, and input power harmonic components can be measured.
3、 Replacement of spare parts
A frequency converter is composed of various components, some of which may gradually decrease in performance and age after long-term operation, which is also the main reason for the failure of the frequency converter. In order to ensure the long-term normal operation of the equipment, the following components should be replaced regularly:
1. Cooling fan
The power module of a frequency converter is a device that generates severe heat, and the heat generated by its continuous operation must be discharged in a timely manner. The lifespan of a typical fan is approximately 10kh to 40km. According to the continuous operation of the frequency converter, the fan needs to be replaced every 2-3 years. There are two types of direct cooling fans: two wire and three wire. One wire of the two wire fan is the positive wire, and the other wire is the negative wire. When replacing, do not connect it incorrectly; In addition to the positive and negative poles, there is also a detection line for the three wire fan. Be careful when replacing it, otherwise it may cause the frequency converter to overheat and sound an alarm. AC fans are generally divided into 220V and 380V, so do not mistake the voltage level when replacing them.
2. Filter capacitor
Intermediate DC circuit filtering capacitor: also known as electrolytic capacitor, its main function is to smooth DC voltage and absorb low-frequency harmonics in DC. The heat generated by its continuous operation, combined with the heat generated by the frequency converter itself, will accelerate the drying of its electrolyte, directly affecting its capacity. Under normal circumstances, the service life of capacitors is about 5 years. It is recommended to regularly check the capacitance once a year. Generally, if the capacitance decreases by more than 20%, a new filter capacitor should be replaced.