3-Phase Generator, unequal voltages

Discussion in 'General Electronics Chat' started by Bobert, Jan 8, 2010.

  1. Bobert

    Thread Starter New Member

    Jan 8, 2010
    3
    0
    I have a 3-phase, 480V generator that is running but offline. The Voltmeter reads as follows:

    1-2 = 140V
    2-3 = 480V
    3-1 = 140V

    Shouldn't these all read 480V? The ammeter reads zero on all three phases. I noticed the voltage differences after I went to replace the "Generator Power Available" indicator bulb and it burned out the second I installed it.
     
  2. Duane P Wetick

    Active Member

    Apr 23, 2009
    408
    19
    It looks like winding 1 is not generating any voltage. Have you taken a megger reading (ohms > 0.5M) of all windings to ground? Or you may have an open winding leg at 1, because 2-3 winding reading looks good.

    Regards, DPW [ Everyone's knowledge is in-complete...Albert Einstein]
     
  3. Bobert

    Thread Starter New Member

    Jan 8, 2010
    3
    0
    Thank you for the reply. I don't have access to a megger at the moment, though there is no ground showing on the Ground Detection lights. I just shut off the generator and realized the meter rests at 140V, so those readings were actually zero. Would that indicate an open winding like you said?

    I turned the generator back on and tested the voltage across the back of the meter (there is a positive terminal and a negative terminal) and from each terminal to ground.

    1-3:
    POS to NEG = 0
    POS to GRD = 0
    NEG to GRD = 0

    2-3:
    POS to NEG = 120
    POS to GRD = 120
    NEG to GRD = 0

    3-1:
    POS to NEG = 0
    POS to GRD = 120
    NEG to GRD = 120
     
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