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Three Phase measurements

  1. Jun 21, 2011 #1
    Hello all,

    Recently one of the power meters on one of our office's panelboards has been giving sensor garbage, calling the others' measurements into question.

    I have two 277/480Y transformers, one going to a two phase 480V duct heater and one going to the lighting (the meter reads three phase).

    The duct heater reads as follows:
    A 277.8V 0A 0%PF
    B 280.2V .6A -23.9%PF
    C 281.8V .5A 72.2%PF

    And the lighting:
    Load: .4KW
    A 280V 0A 0%PF
    B 278V 1.5A 99.9%PF
    C 0V 0A 0%PF

    There definitely seems to be at least one thing wrong: Why am I getting a negative PF for a duct heater? Apart from that, I'm unsure why I'm reading 0V on phase C for a supposed 3 phase unit. It isn't mislabeled; the meter is telling me three phase on the display. I'm not sure why lights would need 3PH power in the first place.

    I would like to be sure that something is wrong before I call for repairs again. Anything seem off?
  2. jcsd
  3. Jun 21, 2011 #2
    For the heater, the line-to-line load for 480 volts also means the current phase angles will be different relative to the line-to-neutral voltage sensing connections for B and C. The phase angle should be the same, but of opposite direction, on each. Technically, you're still consuming power through both, so the PF should still be positive. But with a resistive load, your PF should be nearly 100%, yet a L-to-L phase angle difference can confuse the readings. Combined, it should show the equivalent of 100%. But I don't really know how the meters work to handle that situation.

    Lights don't need three phase. But lights can be distributed among phases to keep things in balance. Yours apparently are not. And it appears that either phase C is not even connected, or the meter connection is not there. Everything is coming on over phase B (which is not necessarily the same phase as phase B on the heater). One way to approach balance is to have the heater on 2 phases like it is, and the lights on the remaining phase. How your transformer phase (mis-)wirings are rotated could in fact do that, anyway.

    How big are these transformers and meters? Got photos?
  4. Jun 21, 2011 #3
    The meter is the e-mon-d-mon 3000 series.

    http://www.emon.com/products_class3000.html" [Broken]

    Pictures on the way.
    Last edited by a moderator: May 5, 2017
  5. Jun 22, 2011 #4
    So this is not utility measurements, but just internal monitoring? Are the transformers utility transformers or smaller internal units? If non-utility, I'd like to know the primary voltage and type (delta or wye).
  6. Jun 22, 2011 #5
    They're utility. The monitors are set up to measure the office's (it's a leased space within a complex) individual consumption.
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