current transformer connections

Discussion in 'General Electronics Chat' started by ibegbu_e, Nov 8, 2009.

  1. ibegbu_e

    Thread Starter New Member

    Nov 8, 2009
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    0
    Can anyone help me,
    I intend to connect 3 CTs in series. These 3 CTs are connected on a 3 phase AC lines. My aim is to connect all CTs together and rectify the output which I will connect to analog/digital converter to be able to monitor voltage drops on the lines.
    Is this configuration possible. Do I connect the CTs in series of paralell. Do I rectify the outputs of the CTs individually and connect the DC outputs in series.
    Thanks
     
  2. JDT

    Well-Known Member

    Feb 12, 2009
    658
    85
    If I understand you correctly, you are going to have a current transformer on each phase of a three-phase supply.

    You cannot connect the three secondaries in series or parallel. Each secondary must be separately loaded with a low resistance (usually only a few ohms). The secondary of the current transformer must always be loaded - or shorted. Otherwise high voltages can be developed across the open secondary.

    A small voltage is developed across this resistance which is normally amplified and then rectified to produce a DC voltage that is proportional to the AC current. You can, if you want, add these DC voltages to produce a DC voltage that is proportional to the total current in all three primaries (the phases).

    I don't understand how you can use this to measure the voltage drop on the lines. Please explain more.
     
  3. ibegbu_e

    Thread Starter New Member

    Nov 8, 2009
    16
    0
    Thanks JDT
    This answers all my question completely. Thanks you.
    About measuring voltage drop was posted in error
    The only thing I do not understand it the connection of resistor. Do you mean I should connect this accross the terminal of each CT
    Thanks
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    The manufacturer of your current transformers will have data about sizing the scaling resistors for a predictable response. But, yes, those resistors do get connected across each CT.
     
  5. ibegbu_e

    Thread Starter New Member

    Nov 8, 2009
    16
    0
    Thank you!
     
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