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Shock At Input Terminals Of Drive After Switching The Power Off


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Recently we have faced some problem in AC drive . Whenever we switched off ac power of the drive, there was a ac voltage generated at input terminals. This voltage was present as long as the DC link was present.and reduced proportinally.All the lamps and other logic contactors were chattering. This drive is having thyristorised rectifier stage.

I am unable to find the exact cause of happening . There is absoultly no other problem with drive. I have not obsrved such things in any other drive. What may be the reasons.?

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Hello VST


This is probably an Active Front End drive that can regenerate during deceleration and it has probably been set up so that under normal deceleration, it is regenerating. This would cause it to stop quicker.


A standard VFD can not generate AC on the input.


Best regards,


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  • 3 weeks later...
  • 1 month later...
No Sir,

This is not an active front end. this is normal standaone drive with thyristorised rectifier inside.This observations have been noted recent versions.






It sounds like you have had a partial failure of one of the components in the converter section of the VFD. (The part that changes AC line voltage to DC) If you could let us know what type of drive this is, so that I can find an electrical diagram, or if you could post a diagram of the converter, we may be able to tell you what type of failure you are likely to have had.



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