AQ: Frequency inverter maintenance
1) In inverter regular inspection, we must cut off power before operation. Wait 4minutes (the bigger the longer, the maximum waiting time is 15 minutes) till the frequency inverter display panel LED indicator lights turn off, to make the main circuit DC filter capacitor fully discharged, and measure with a multimeter to confirm before proceeding.
2) Detach control board and main circuit from the frequency inverter, clean the inverter circuit board and internal IGBT modules, input and output chokes and other parts with brush and dust cleaner. Use cotton swab with alcohol or neutral chemical to clean PCB dirty place.
3) Check the inverter inner wire insulation has overheating traces, corrosion and discoloration or not, if found out, we should handle or replace it in time.
4) As the frequency inverter has vibration, temperature changes and other effects, screws maybe loose, we should tighten all screws.
5) Check input and output chokes, transformers, etc. is overheating, discoloration or smelly.
6) Check the intermediate circuit filter electrolytic capacitor safe valve is bulging out or not, and the outer surface has cracks, leakage, swelling and so on. Generally, the inverter filter capacitor life cycle of about five years, the inspection intervals is one year. The capacity of the capacitor can be measured by digital capacitance measurement, when the capacity drops to 80% rated capacity or less, it should be replaced.
7) Check the cooling fan operation is in good condition or not. The cooling fan lifetime is limited by bearings, we should replace the cooling fan or bearings in 2-3 years. If there are abnormal sounds and vibration, we need to replace in time.
8) Check the frequency inverter insulation resistance is in the normal range or not (all terminals with ground terminals). Note, do not use the megger to measure the circuit board, otherwise it will damage the circuit board electronic components.
9) Disconnect the inverter R, S, T terminals with power supply, and U, V, W terminals with motor cable, measure the insulation resistance between each phase conductor and each phase conductor with the protective ground terminals with the megger, to see if it’s in normal value or not, generally its higher than 1MΩ.
10) After inspection, we should use frequency inverter drive the motor with no load for a few minutes, and check the motor rotation direction.
