RY Input to Step Down Transformer 230/115 v, Neutral Ground Voltage

Discussion in 'The Projects Forum' started by HST20, Jan 2, 2016.

  1. HST20

    Thread Starter New Member

    Jan 1, 2016
    3
    0
    Hi,
    I have a step down transformer which inputs are connected to RY phase of 3 phase 3 wire system.
    The outputs of the transformer are COM, 230v & COM, 115v. If i check the voltage between each COM & Voltage,
    the voltages are shown correct, but there is voltage difference between two COM terminals about 55v.
    Is it normal? or something wrong with the T/F?

    and
    I am giving 230 v supply from transformer to Motor Drive which has 3 terminals COM, 230v, GND.
    the voltage between GND & COM is showing about 55v, recently the drive gone bad,
    is this the cause for that?
    Neutral to ground supposed to be below 5v but it is showing 55-60v...
     
  2. sailorjoe

    Member

    Jun 4, 2013
    361
    63
    Do you have a part number or a datasheet for the transformer? And can you draw a schematic of how you are hooking everything up, please? Helpers need these details to provide accurate help.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,571
    2,381
    It sounds as though the secondary neutral is not re-referenced to earth ground?
    Max.
     
  4. HST20

    Thread Starter New Member

    Jan 1, 2016
    3
    0
    Shall i connect secondary neutral to ground directly?
    to get rid off that earth to neutral problem.
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,571
    2,381
    Normally when a transformer is used, then the secondary is galvanically isolated from the primary so you have lost the earth ground reference, so yes, it is normal to take the neutral to either a new qualified earth point or to the primary service earth conductor if present.
    Max.
     
    HST20 likes this.
  6. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Measuring voltages between two isolated transformer windings with an AC Voltmeter whose input impedance is =>10MegΩ is bound to read garbage...
     
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