Polarity Issue

Polarity Issue

  1. When viewing a electricity meters in Raw Data "Before Polarity, CT & VT Ratio" all three phases (Pa | Pb | Pc) should be either negative, or positive. 
    If all 3 are the same, a negative polarity can be set by changing the polarity setting. Data for "After Polarity, CT & VT Ratio" should then reflect correctly. 
  2. When one, or two of the phases are negative, this needs to be corrected on site. 
    This is done by either
  1. disconnecting the physical CT, and turning it around, 
  2. or alternatively the 2 secondary wires from the CT that connects to the meter terminal can be reversed. 
  1. Alternative Problems: 
    When seeing negative polarities, the following could be causes that do not require the above action. 
  1. Phase Rotation 
    The image below shows a meter with a phase rotation issue. This cannot be solved by changing CT polarities on site. See "Phase Rotation" section for more information. 
  2. Solar or another form of energy generation
    When seeing negative polarities, it is important to ensure there is no on-site energy generation taking place. 
    This can generally be seen by looking at the energy profile over multiple days, where loads will be positive, and drop during daylight hours, reaching a low peak mid day (potentially negative), and then go up as the solar energy reduces.  
    Confirm with on-site contacts before making system changes if it is not clear that there is on-site generation taking place. 
  3. Very Low Loads
    When a large CT is measuring very low loads (3000/5A CT measuring 5 Amp load) it can often look like phase rotation due to CT inaccuracies at very low loads. 


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