Problems with motor fans and speed controllers

Discussion in 'General Electronics Chat' started by Electricsix, Feb 26, 2009.

  1. Electricsix

    Thread Starter New Member

    Feb 26, 2009
    Hello all,

    I hope you can help me out. I have supplied a number of 400V / three phase variable speed drives to a customer who connected them to their fan motors in star. The motors are 400V Δ/690V γ. The motors ran for about 1 year and then started to burn out. When an investigation was carried out as to why the motors failed the incorrect wiring was discovered and the replacement motors were rewired correctly in Delta.

    The new, correctly wired motors have been running for a week and over the last day or so the variable speed drives have begun to fail. There is a permanent short circuit trip on the output of the VSD. This indicates that the power module of the drive has been damaged. This short circuit is present even when the motor has been disconnected from the VSD

    Some Facts

    The current overload limits on the VSDs were initally set and remain as per the delta value on the motor name plates.

    The VSDs have overload protection.

    The motor speed / VSD output was controled by a remote analogue speed reference and fluctuated between 20Hz and 50Hz.

    Acceleration and decelleration times are set in the VSD so that there was sufficent time for the fan to gain speed without drawing excessive current, and reduce speed without the danger of excess voltage being generated by the motor and entering the output of the drive.

    Out of 10 VDSs that were supplied 5 have failed in the last day. The failure rate of the drives in question is less the 0.1% and other units in this maufacturing batch have not failed. The fact that all these VSDs have failed at approximately the same time and this coencides with the motors being wired correctly, I have to assume there is an exernal factor causing them to fail.

    My questions are:

    Why did the motors burn-out, if the overload limits of the VSD were set as per the Delta value?

    Why, when the motors were subsequently re-wired correctly did the inverters start to fail?

    Many thanks for you help.


  2. ifixit

    AAC Fanatic!

    Nov 20, 2008
    Call the maker of the VSD, explain your situation and they will then tell you what has gone wrong.

    Good Luck,

  3. Electricsix

    Thread Starter New Member

    Feb 26, 2009
    I have spoken to the VSD manufacturer, unfortunately they have a vested interest in removing any blame from their product, so their explanations possibly do not include the whole story.

    My electrical knowledge is broad but not detailed enough in this particular area to make my own assumptions.