Danfoss frequency converter VLT® 6000 is a frequency converter designed specifically for HVAC applications. Thanks to the automatic energy optimization principle, the maximum number of nodes can be ensured for the motor: In addition to the built-in PID regulator, two feedback signals and two setpoints can be connected. Therefore, it is widely used in HVAC equipment.
Shanghai Jinxin Inverter Service Center recently received a Danfoss frequency converter VLT6000. When the customer delivered repairs, the inverter was used on site for several years and the external terminals could not be switched on recently. Since the load of the inverter is a HVAC fan, it needs to be repaired as soon as possible.
Inspection process:
The repaired Danfoss frequency converter model is VLT6052, a compact, IP20 frequency converter. The maintenance personnel first unscrew the screws on the top cover of the inverter, and then remove the control card, power supply card, and RELAY CARD of the inverter. Check the inverter's rectifier module and inverter module and found that the rectifier and inverter modules are not damaged, and the main circuit electrolytic capacitor is also good. Check the inverter's RELAY CARD and power supply card one after another. The test result is also good. Install the inverter completely and send power test on the input terminals L1, L2 and L3. It is found that there is no 24VDC voltage between the control terminals 12 and 20 on the variable frequency control card. Therefore, the reason why the inverter terminal cannot be turned on is that the 12 and 20 terminals do not have 24VDC voltage.
Failure Analysis:
The inverter's control card was opened and it was found that the inverter control card has obvious traces of fire and burnt behind terminal No.12. Since these two terminals are the 24VDC output of the inverter, the maximum load is 200MA and is electrically isolated from the supply voltage. Since the detection of the inverter power supply card has been confirmed and the switching power supply of the power supply card is operating normally, the reason for this is that there is a strong external string on the 12th terminal.
Repair process:
Remove the damaged components from the inverter's control card, clean the black parts, and replace the good components. Install the control card, perform the control card test, and pass the test result. Install the inverter completely, send power test to the inverter, balance the three-phase output voltage, pass the load test, meet the factory standards, and repair the inverter.
Maintenance experience summary:
The main reason for this type of fault is: a strong power entry is made on the No. 12 control terminal of the inverter control card, which may be caused by improper operation.
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