To ensure the reliable and stable operation of high-voltage frequency converters and minimize downtime, daily use and maintenance are crucial. Especially after a period of shutdown or storage, high-voltage frequency converters require maintenance and testing before being put back into operation. During long-term storage, condensation may occur on the high-voltage frequency converter due to changes in ambient temperature. This condensation can form on the circuit boards, power devices, and heat sinks. This liquid water, mixed with dust, can cause cable joints, terminals, screws, and other components to rust, damaging electrical insulation and even creating a direct circuit, leading to frequency converter malfunction. To ensure the stable operation of high-voltage frequency converters, the following steps are necessary:
1. Visual inspection:
Before powering on, check whether the inverter's appearance is deformed and whether the cabinet door is deformed. Open the cabinet door and check for any abnormalities inside, such as dampness, rust, corrosion, electrical discharge, detachment, or foreign objects.
2. Drying and dehumidification treatment:
The high-voltage frequency converter is dried and dehumidified using ventilation and heating methods. An electric heating fan (industrial type with a power greater than 3000W, requiring the hot air to oscillate) is used to blow air onto the high-voltage frequency converter to raise the internal temperature. As the temperature rises, the relative humidity decreases. The drying time is controlled according to the degree of moisture in the frequency converter (care must be taken to avoid damaging optical fibers and cables during drying due to high temperatures).
For inverters with minor moisture issues, ventilation and dehumidification can be achieved using the built-in fan on the top of the inverter cabinet. Manually force the top fan to operate, allowing fresh air from outside to enter the inverter cabinet, ensuring uniform humidity inside and outside the cabinet, and removing moisture from the inverter. Ventilation time should be at least 8 hours.
3. Clean the dust:
If a frequency inverter is not cleaned of dust promptly after a period of inactivity, it will affect the heat dissipation of the internal components, potentially leading to damage over time. Before resuming operation, a thorough cleaning of the inverter cabinet is essential. Use a vacuum cleaner to remove dust from the cabinet and unit surfaces (do not use a blower to remove dust from the inverter; if using a blower, ensure the dust is expelled from inside the inverter cabinet and to the outside).
For equipment that has been in operation for more than 3 months or is located in harsh environments, remove the power units. Take each unit outdoors and clean off the dust using a blower or compressed air. When removing units, be careful not to snag or damage the fiber optic cables. When blowing off dust, avoid touching the circuit boards and power devices. After cleaning, tighten all connectors on the unit circuit boards. Check the tightness of the screws on the power devices. Also, use a multimeter to test for any damaged fuses. Clean the dust inside the power cabinet while removing the unit. For 5000 series models, carefully wipe the unit connectors with a cloth dampened with a small amount of alcohol, and only operate the unit again after the inverter has completely dried.
After six months of operation, or in harsh environments, transformers require cleaning to remove dust. Use a blower to remove dust from between the high and low voltage windings of each winding. Check for foreign objects between the core and coils, broken or exposed connecting wires, and discoloration or blackening of the coils.
4. Cleaning dust from the filter screen:
During use or long-term storage, dust will accumulate on the filter of the frequency converter. It is essential to clean the filter thoroughly before using the frequency converter. After removing the filter, it can be cleaned with a hairdryer or compressed air. If the dust is not very sticky, the filter can be washed with water and dried before use.
5. Inspection of primary and secondary circuit cables:
Check the tightness of all cable connections and inspect each cable for abnormal discharge marks, strange odors, discoloration, cracks, or damage. Verify the correctness of the primary input and output high-voltage cables and the correct phase sequence. Use a multimeter to ensure the high-voltage power supply line and motor wires are not mixed up. Check that the wiring is secure, the stress is reasonable, and the contact surfaces are appropriate. Always inspect the primary cable wiring after inverter maintenance to prevent backfeeding.
Secure all control terminals, adapter plugs, and external terminals inside the frequency converter cabinet. Check that the cabinet, PE, and signal ground are reliably grounded.
6. Cable insulation inspection:
After a long period of shutdown, when resuming operation of a high-voltage variable frequency speed control device, insulation testing of the high-voltage cables should be performed. Use a 2500V megohmmeter to measure the phase-to-ground and phase-to-phase insulation resistance separately. The high-voltage variable frequency speed control device can only be started after the insulation test is passed. When testing the output cable insulation, the cable should be disconnected to prevent damage to the power devices.
7. Transformer inspection:
Tighten the lead terminals, pins, grounding screws, and busbar screws. If any are loose, remove the screws or replace the spring washers and screws until good contact is achieved. Use a 2500V megohmmeter to test the primary side insulation of the transformer.
8. Control unit inspection:
Check that the control box is securely installed, that all control boards are firmly inserted, and that each terminal on the boards is securely fastened. Check that the fiber optic connector on the PWM board is secure. Check that the fiber optic cable is not bent at an excessive angle or subjected to excessive force.
9. Room preheating:
Before powering on a high-voltage frequency converter, the ambient temperature must be above 0 degrees Celsius to prevent damage to the internal components. Depending on the site environment, the frequency converter room should be heated or the air conditioner should be set to heating mode to ensure the room temperature reaches above 0 degrees Celsius.
10. Power unit capacitor activation:
If the frequency converter has been stored for more than 3 months, the power module needs to be charged and discharged 3 times. Each charge should last for 30 minutes to completely discharge the unit's electricity before charging again. This re-discharge of the capacitors activates the capacitors in the module.
11. System preheating:
Do not immediately put the system under load after all testing is completed. Connect the high-voltage power supply to make the high-voltage frequency converter ready, and the converter will enter hot standby mode. The hot standby time should be greater than 2 hours; if the storage time is too long, the hot standby time should be extended. During the frequency converter's hot standby, the top fan rotates to expel air from the inside of the frequency converter and activate the capacitor modules in the power unit.
12. Cleaning of the frequency converter room:
The inverter room for high-voltage frequency converter operation must be kept clean and should be cleaned regularly according to the actual site conditions, keeping the floor clean. Maintain humidity and prevent water leakage. In dusty environments, ensure the room is sealed. Keep cable trenches dry and clean.
Note:
After testing the high-voltage variable frequency speed control device, carefully check for any missing screws and wires to prevent small metal objects from causing short circuits in the device.
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