1. Before powering on the frequency converter
First, check the ambient temperature and humidity. Excessive temperature can cause the inverter to overheat and alarm, and in severe cases, directly damage the inverter's power components and cause short circuits. Excessive humidity can cause internal short circuits within the inverter. During inverter operation, check the cooling system for proper functioning, such as whether the exhaust duct is unobstructed and whether the fan makes any abnormal noises. Inverters with higher protection ratings, such as IP20 and above, can generally be installed in an open environment. Inverters with IP20 or below should generally be cabinet-mounted. Therefore, the cooling effect of the inverter cabinet directly affects the normal operation of the inverter. The inverter's exhaust system, such as whether the fan rotates smoothly and whether there is dust or blockage at the air inlet, are areas that cannot be ignored in daily inspections. Also check whether the motor, reactor, and transformer are overheating or have any unusual odors; whether the inverter and motor make any abnormal noises; whether the current display on the inverter panel is too high or the current fluctuation is too large; and whether the output three-phase voltage and current are balanced.
2. Regular maintenance
Regularly check for dust inlets to ensure they are not blocked, and clean the air filter, cooling ducts, and internal dust monthly.
Regular inspections should be conducted annually: Check for loose screws, bolts, and connectors; check for short circuits in the input/output reactors' resistance to ground and between phases (normal resistance should be greater than tens of megohms); check for corrosion in conductors and insulators, and clean them immediately with alcohol if necessary; measure the stability of the output voltages of each circuit in the switching power supply, such as 5V, 12V, 15V, and 24V; check for arcing marks on the contactor contacts, and replace severely damaged contactors with new ones of the same model or larger capacity; confirm the correctness of the control voltage and perform sequential protection operation tests; confirm that there are no abnormalities in the protection display circuit; and confirm the balance of the output voltage when the frequency converter is running alone.
Perform routine maintenance and repair work on the frequency converter diligently. This mainly includes:
(1) Regularly clean the inverter, focusing on the rectifier cabinet, inverter cabinet, and control cabinet. If necessary, remove the circuit boards from the rectifier module, inverter module, and control cabinet for dust removal. Check whether the lower air inlet and upper air outlet of the inverter are covered with dust or blocked due to excessive dust accumulation. Because the inverter itself requires a large amount of ventilation for heat dissipation, the surface of the inverter will accumulate a lot of dust after a certain period of operation, and it must be cleaned and dusted regularly.
(2) Open the front door of the inverter and disassemble the rear door. Carefully check whether the AC and DC busbars are deformed, corroded, or oxidized, whether the screws at the busbar connection are loose, whether the screws at each installation and fixing point are loose, and whether the insulating sheets or insulating columns used for fixing are aged, cracked, or deformed. If so, they should be replaced in time and tightened again. Busbars that have been deformed must be corrected and reinstalled.
(3) After dust removal from circuit boards, busbars, etc., necessary anti-corrosion treatment shall be carried out and insulating varnish shall be applied. For busbars that have partial discharge or arcing, the burrs shall be removed before further treatment. For insulating boards that have broken down, the damaged parts shall be removed, and the area around the damage shall be isolated with an insulating board of the corresponding insulation class. The insulation shall be tightened and tested, and the board shall be put into use only after it is deemed to be qualified.
(4) Check whether the fans in the rectifier cabinet and inverter cabinet are running and rotating normally. When the machine is stopped, rotate it by hand to observe whether the bearing is stuck or making noise. Replace the bearing or repair it if necessary.
(5) Conduct a comprehensive inspection of the input, rectification and inverter, and DC input fast fuses, and replace them promptly if any are found to be burnt out.
(6) Check whether the capacitors in the intermediate DC circuit are leaking, whether the casing is bulging, bubbling, or deformed, and whether the safety valve is broken. If possible, test the capacitance, leakage current, and withstand voltage. Replace any capacitors that do not meet the requirements. For new capacitors or capacitors that have been idle for a long time, passivation treatment must be performed before replacement. The service life of filter capacitors is generally 5 years. For those that have been used for more than 5 years and whose capacitance, leakage current, withstand voltage, and other indicators deviate significantly from the test standards, they should be partially or completely replaced as appropriate.
(7) Use a multimeter to perform electrical tests on the diodes and GTOs of the rectifier and inverter sections, measure their forward and reverse resistance values, and carefully record them in a pre-prepared table to see if the resistance between each electrode is normal and whether the consistency of the same model of device is good. Replace if necessary.
(8) Inspect the main contactors and other auxiliary contactors in the A1 and A2 incoming line cabinets. Carefully observe whether there is arcing, burrs, surface oxidation, or unevenness in the moving and stationary contacts of each contactor. If such problems are found, the corresponding moving and stationary contacts should be replaced to ensure that the contact is safe and reliable.
(9) Carefully check the terminal blocks for aging or loosening, for any hidden short circuits, for the secure connections of all wires, for any damage to the wire sheaths, and for the secure connections of all circuit board connectors. Check the reliability of the main power supply connections, for any signs of overheating or oxidation at the connections, and for proper grounding.
(10) Check whether the reactor has any abnormal noise, vibration or burnt smell.
In addition, if conditions permit, the filtered DC waveform, inverter output waveform, and input power supply harmonic components can be measured.
3. Spare parts replacement
Inverters consist of various components, some of which gradually degrade in performance and age after prolonged use. This is a major cause of inverter failure. To ensure the long-term normal operation of the equipment, the following components should be replaced periodically:
(1) Cooling fan
The power module of the frequency converter is the component that generates the most heat. The heat generated by its continuous operation must be dissipated in a timely manner. The lifespan of a typical fan is approximately 10-40 hours. Based on continuous operation of the frequency converter, the fan should be replaced every 2-3 years. Direct cooling fans come in two-wire and three-wire versions. For two-wire fans, one wire is positive and the other is negative; do not connect them incorrectly during replacement. Three-wire fans have a detection wire in addition to the positive and negative wires; be extremely careful during replacement, otherwise it will trigger an overheating alarm on the frequency converter. AC fans are generally available in 220V and 380V versions; do not mix up the voltage ratings when replacing them.
(2) Filter capacitor
Intermediate DC circuit filter capacitor: Also known as an 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, accelerates the drying of its electrolyte, directly affecting its capacitance. Under normal circumstances, the capacitor's lifespan is about 5 years. It is recommended to check the capacitor's capacitance annually; generally, if its capacitance decreases by more than 20%, it should be replaced with a new filter capacitor.
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