Floating voltage safety issue

Discussion in 'The Projects Forum' started by sridharan_eee, Feb 27, 2013.

  1. sridharan_eee

    Thread Starter New Member

    Feb 27, 2013
    1
    0
    Hi everybody
    Greetings to you!! I am a new member of this forum.

    I am working as a Designer in a private company, currently working on 1500W switching power supply for a US based customer.

    The product converts 3ph AC into power factor corrected DC output (375VDC, 6A current).

    Customer raises an issue that "What is the floating voltage between +Ve terminal to ground and -Ve terminal to ground". Iam new to this topic of user safety. He also wants to provide a circuit that can detect a leakage from any of +ve or -ve terminals to ground chassis.

    Request you to kindly guide me with your suggestions and guidance pls.
    Thanks
    Sridhar
     
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,395
    1,607
    I believe you have a rare case of the customer not being right, but before I comment I am not sure what these ve voltages are, are they the main output of the supply? What is this "ground?" Is the ground common to the chassis, the supply output, or some other point?
     
  3. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    First of all there should be magnetic trip switch on the AC side for leakage current.

    Then the case should have a solid ground connection which will not corrode, break off and all this. For this power class, preferably more than one connection.

    Then wire a voltage divider to the case, and a service ground. Monitor that with a controller. Unscrew etc. the grounding, and observe the voltages you get, float it with some mA 400 Volts AC (be careful here).

    Remember wires always could break off, corrode, someone may service it and not rewire it correctly.

    For power electronics with 3phase 400 volts, you have to be clever and think of all sort of unthinkable occurances.

    If you are new to safety, work together with someone who has years of experience with that.

    A 400V AC short will vaporize good wires instantly with a loud bang and shoot small projectiles. Much worse than 240v single phase.

    You must observe minimum distances, use high quality terminals designed for this voltage, and proper cables. The cable terminations must be sound. Think about corrosion here which in the worst case, can cause a fire.

    I saw terminals melting at about 5A from an unsound cable termination. It caused arcing, which in turn heated up the metal, so much as to melt the plastic.
     
  4. #12

    Expert

    Nov 30, 2010
    16,351
    6,840
    375V x 6A = 2250 watts
    You are working with the kind of power that explodes when you make a mistake.
    You are new to safety issues?
    You are in over your head.
    Get help from a competent person immediately!
     
  5. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    Do you have a schematic, with grounds (Earth and circuit) labeled?

    I Don't understand your question, and as stated above, this isn't an area where being unsure is a good thing.
     
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