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IndustryArena Forum > Maintenance in General > Maintenance DIY Discussion > VSD / VFD / inverter - 122 VAC on PE?
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  1. #1
    Join Date
    Jun 2011
    Posts
    21

    VSD / VFD / inverter - 122 VAC on PE?

    Hi all,

    I'm looking for a bit of guidance here from those in the know.

    I have a single phase to three phase 3kw inverter. When I plugged it in to the mains 244VAC 50Hz (UK) the RCD tripped instantly this is before starting the drive. Connecting the motor makes no difference.

    On investigation I am getting exactly half the input voltage 122VAC 50Hz on the Protective Earth circuit. This again does not change with motor connected or not or drive running or not.

    Apart from this obvious safety issue the drive seems to perform fine!

    My question to all the VSD gurus is what where should I be looking for the issue? I know enough to know that this is likely to be in the rectification of the 244VAC but where why would it end up on the PE? Rectifier shorting to the heat sink?
    Coupling Capacitor shorted to earth.... not sure why it would be coupled to earth rather than to neutral.

    Basically I am stumped and don't have enough knowledge to narrow down the fault finding process.

    Finally I know that RCD's give issues with inverter drives but my understanding is that this is due to harmonics or induced currents when the drive is running and to me does not seem to be my issue.

    Any theories or assistance is very welcome

  2. #2
    Join Date
    Dec 2003
    Posts
    24216
    What make of VFD?
    I suspect that either the VFD has a suppression circuit that is referenced to earth ground or there is an aberrant leakage somewhere in the VFD itself allowing enough leakage to ground.
    Does it stay powered if you remove the earth connection?
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  3. #3
    Join Date
    Jun 2011
    Posts
    21
    Hi Al,

    It is a Siemens Micromaster vector see here Siemens Micromaster Vector Inverter Motor Drive Converter Single Phase to 3 | eBay
    Don't go off the name plate details in the photo as they are wrong if you want that off the drive I can post those.

    If I disconnect the earth it works fine. 122v is between Live (or Neutral)and the PE. It really has me baffled I cant see any damage in fact the VFD looks remarkably clean for its age.

    I have two other 240v single Phase to 240v Three phase VFDs and the cheap Chinese one has 28 VAC between the PE and live the IMO (Japanese) has 148Vac but neither of these trip the RCD so I am stumped.

    Al

  4. #4
    Join Date
    Dec 2003
    Posts
    24216
    It sounds like either a design flaw for RCD use, or a defect in the unit?
    You could always remove the cover and see if you can see any connections or suppression devices connected to the frame.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

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