Three Phase Power Phase Loss Detection

Discussion in 'General Electronics Chat' started by Doug16214, Jul 10, 2008.

  1. Doug16214

    Thread Starter New Member

    Jul 10, 2008
    I have many contacts with Electricians out in the field that argue the point that they CAN measure the presence of all three phases in a three phase power system with a voltmeter or wiggins.

    I contend that due to the configuration of the utility's transformer, it is impossible to measure the presence of all three with anything short of an oscilloscope or a special meter.

    Comments ?


  2. recca02

    Senior Member

    Apr 2, 2007
    Are we talking about fault detection? At what point? After generator transformer?
  3. SgtWookie


    Jul 17, 2007
    If the secondary is delta-wound, you will indeed have a tough time with just a meter.
    If the secondary is wye-wound, it's easy. Disconnect the load at the service panel, and measure each phase to neutral.
  4. theamber

    AAC Fanatic!

    Jun 13, 2008
    Why do you say they can't? Yes they can if they know which configuration they are, for example here I copy this two from my Ugly's to you:
    120/240 Delta high leg
    A(black)to B(orange)=240
    B(orange) to C(Red)=240 >High leg.
    Neutral(white) to A(black)=120
    High leg to Neutral=208

    120/208 4 wire system (WYE Connected)
    A(Black) to B(Red)=208
    B(Red) to C(Blue)=208
    Neutral(White) to B (red) or to C(blue)=120
    REd to White=120

    You need to buy the Ugly's Electrical References booklet.
    But if you are talking about the phase sequence they cannot with the voltmenter but they can use a circuit with a capacitor an two light bulbs in Y of equal filament resistances and wattage they can see the intensities of the lamps. The cap. has to be sized to have the same reactance at system frequency(you can calculate with the formula) the cap. introduce a phase shift of 90 which is greater than 0 but less than 120 this will skew the values between the lamps. All this is in the book here.
    Last edited: Jul 10, 2008