Precautions for the Daily Maintenance of Frequency Inverter

With the advancement of factory automation technology, frequency inverters have increasingly become important driving and control devices. Therefore, ensuring the reliable operation of frequency inverters has become a crucial topic in equipment maintenance and in reducing downtime due to failures. To ensure that the frequency inverter operates reliably and continuously, regular maintenance is key. The specific content of daily maintenance can be divided into the following aspects:

Recording Operational Data and Faults:

It is essential to record the operational data of the frequency inverter and the motor daily. This includes recording parameters such as the inverter's output frequency, output current, output voltage, internal DC voltage, and heat sink temperature. These parameters should be compared with reasonable data to identify potential faults early. If the inverter trips due to a fault, it is important to record the fault code and the operating conditions at the time of the trip to facilitate a detailed analysis of the cause of the fault.

Routine Inspection of the Frequency Inverter:

Conduct inspections every two weeks. Record the three-phase output voltage of the inverter during operation and compare the balance between them. Similarly, record the three-phase output current of the inverter and monitor their balance. Check and record the ambient temperature and the temperature of the heat sink. Additionally, observe the inverter for any abnormal vibrations, unusual noises, and ensure that the cooling fan is functioning properly.

Maintenance of the Frequency Inverter:

Each frequency inverter should undergo a thorough cleaning and maintenance once every quarter. Maintenance involves removing dust and debris from inside the inverter and its ventilation paths, and cleaning the inverter's surface to keep it clean and shiny. During maintenance, carefully inspect the inverter for any signs of overheating or discoloration, check for cracks in cement resistors, signs of swelling or leakage in electrolytic capacitors, and ensure no abnormal areas or burn marks on the PCB board. After completing the maintenance, restore the inverter’s parameters and wiring, and power it up. Run the motor at a low frequency of around 3Hz for about one minute to ensure that the inverter is functioning normally.

Overhaul of the Frequency Inverter: 

The overhaul items for the frequency inverter include:

Fans:

Component Status Assessment:

Fans are common spare parts in frequency inverters. Fan damage can be categorized into electrical damage and bearing damage. If the fan experiences electrical damage, it will not operate, which can be detected during routine inspections. Once detected, the fan should be replaced immediately. Bearing damage can be identified by a noticeable increase in noise and vibration during operation, indicating that the fan should be replaced as soon as possible. According to the inverter manual, it is recommended to replace the fan after a certain period of use (typically around three years).

Replacement Procedure:

It is recommended to use original fan spare parts; however, if original parts are difficult to obtain or the delivery time is too long, suitable substitutes may be considered. The substitute must match the original in terms of shape, installation dimensions, power supply, power consumption, airflow, and quality.

Post-Replacement Testing:

After replacing the fan, perform a test run to observe the airflow, operational noise, and vibration. Allow the fan to run continuously for about half an hour and monitor the overall temperature rise of the unit. If everything is normal, the replacement (or substitution) can be considered successful.

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Main Filter Capacitor:

Component Status Assessment:

The main filter electrolytic capacitor is another commonly used spare part in frequency inverters. If a capacitor shows signs of leakage, swelling, or a ruptured safety vent, it should be replaced immediately. During routine inspections, pay attention to the capacitance value. If the capacitance drops by more than 15% from the nominal value, it should be replaced promptly. According to the inverter manual, it is also advisable to replace the capacitor after a certain period of use. The lifespan of the main circuit filter electrolytic capacitor is closely related to the ambient temperature of the inverter. Proper maintenance and a good installation environment can significantly extend the lifespan of the capacitor.

Replacement Procedure:

It is recommended to use original capacitors; however, if they are difficult to obtain or the delivery time is too long, suitable substitutes may be considered. The substitute must match the original in terms of installation size, length (equal to or less than the original), voltage rating, nominal operating temperature (greater than or equal to the original), and total capacitance (close to the original).

Post-Replacement Testing:

After replacing the capacitor, perform a test run at full load for 2 hours. If the capacitor does not overheat, the replacement can be considered successful.

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High-Power Resistor:

Component Status Assessment:

Inspect the surface color of the high-power resistor. For cement resistors, check for cracks on the surface. If the resistor shows obvious signs of aging (e.g., discoloration, severe cracking), it should be replaced.

Replacement Procedure:

It is recommended to use original resistor spare parts; however, substitutes may also be used. The substitute should have a similar power rating and resistance value to the original, and the installation method and dimensions must match the original.

Post-Replacement Testing:

After replacing the resistor, perform a test run with three cycles of power off and on, paying attention to the time interval between power cycles. Then, run the inverter at full load for half an hour. If everything is normal, the replacement can be considered successful.

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Contactors or Relays:

Component Status Assessment:

Contactors or relays generally have a lifespan based on the number of operational cycles. If this limit is exceeded, they should be replaced. If poor contact is detected during routine inspections, replacement is necessary.

Replacement Procedure:

It is recommended to use original spare parts; however, substitutes may also be used. The substitute must have the same contact capacity and coil specifications as the original, and the installation method and dimensions must match the original. The quality of the substitute should also be comparable.

Post-Replacement Testing:

After replacing the contactor or relay, perform a test run with repeated actuation of the contactor. Then, run the inverter at full load for half an hour. If everything is normal, the replacement can be considered successful.

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Structural Components:

Component Status Assessment:

The plastic casing of the inverter may be damaged by impact, and replacement should be considered based on the extent of the damage. If the internal mounting screws of the inverter show signs of slippage or rust, they should be replaced.

Replacement Procedure:

The casing must be replaced with original spare parts, while screws and other structural components can be replaced with products of the same specifications and quality.

Post-Replacement Testing:

After replacing screws, ensure they are tightened securely. Perform a full load test to ensure that excessive contact resistance does not cause overheating.

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Operation and Display Unit:

Component Status Assessment:

If the operation and display unit of the inverter shows missing displays or non-functional buttons, it should be replaced.

Replacement Procedure:

Replacement should be carried out with original products or compatible upgrade substitutes.

Post-Replacement Testing:

After replacing the unit, power on the inverter to check if the display and functions operate normally.

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Printed Circuit Board (PCB):

Component Status Assessment:

In principle, printed circuit boards should not be replaced unless severe overheating or scorching is observed during routine inspections.

Replacement Procedure:

Replacement should be carried out with original spare parts.

Post-Replacement Testing:

After replacing the PCB, conduct a full load test for about one hour. If the operation is normal, the replacement can be considered successful.