Energy Meter Data

squelchea
squelchea Registered Users Posts: 6 ✭✭
in PV Installers Forum - NEC, Wiring, Installation #1
GooD Day !

Guys,
Can you share your thoughts on why there was time the Meter reads Neg Values on Power ? See below attachment.

TIA
Tagged:
· Share on Twitter

Comments

  • squelchea
    squelchea Registered Users Posts: 6 ✭✭
    #2
    Attachment.
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,609 admin
    #3
    I cannot tell from your report. There appears to be some "scaling" in current and/or voltage to get Watts (none of the current * voltage = power math seems to work out).

    In general, there is some math going on. Power = Voltage * Current * Cosine (angle between voltage and current).

    Depending on the "phase angles" between the voltage and current (and this appears to be a three phase circuit), that will determine the direction of power flow.

    In general, power only flows one way (from utility lines to loads). There are conditions where the power flow can be reversed (energy is moved from one phase to another), or you can even generate power back into the grid (a gasoline/diesel engine driving an induction motor will generate power).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    edited August 2017 #4
    My guess is simply a system that isn't accurate at low values (ie, needs calibration).    

    With non sinusoidal loads (common now), angle doesn't work to get from RMS amps and RMS volts to watts.

    I am available for custom hardware/firmware development

    · Share on Twitter

Categories