What is the purpose of Prospective Earth Fault Current measurement in a 3 phase DB

Good afternoon

On a 3 phase DB what is the purpose of measuring the PEFC?

I know we measure the prospective short circuit current between L1,L2,L3 and N and then double the highest reading. 

This is the Prospective Fault Current which is being recorded.

Why should we waste time with prospective earth fault current?

Are there cases where PEFC is higher than PSSC?

Thanks

Parents
  • There is a note at the bottom of the BEAMA article I linked to about certain parts of England and Wales having LV Interconnected Pairs, not a generally an issue. Which I presume is part of these projects, presumably with the local network being fed from multiple points rather than just one transformer PSCC readings are going to be very variable.

    https://www.enwl.co.uk/globalassets/innovation/smart-street/smart-street-key-docs/smart-street-design-and-operation-of-lv-interconnected-networks-study.pdf

    and

    innovation.ukpowernetworks.co.uk/.../lv-interconnected-pairs

  • That study includes some odd ideas - almost everything else we know about losses says higher voltages are better.

    "Conservation voltage reduction (CVR)
    Electrical equipment made for the European market, including household appliances and
    lighting, is designed to operate most efficiently in the region of 220 to 230 volts. This
    equipment can, however, operate adequately at voltages in the region of 200 volts. If power
    is delivered at voltages higher than these optimum levels, energy is consequently wasted "

    Boiling a kettle or heating a room faster is not a loss it is a saving, as is obvious by thinking about boiling it very slowly, the as then it never gets warm. A 1kW kettle is a lot slower than 1/3 of a 3kW one,  as heat is lost during the process, and a 100W kettle never boils at all. So, boiling adiabatically in a fraction of a second with megawatts would be ideal but is sadly impractical.
    Anything electronic with a switch mode regulator will draw more current at lower line voltage to compensate, so the wiring losses are higher.
    I do now wonder now about the rest of the thinking.

    Mike

Reply
  • That study includes some odd ideas - almost everything else we know about losses says higher voltages are better.

    "Conservation voltage reduction (CVR)
    Electrical equipment made for the European market, including household appliances and
    lighting, is designed to operate most efficiently in the region of 220 to 230 volts. This
    equipment can, however, operate adequately at voltages in the region of 200 volts. If power
    is delivered at voltages higher than these optimum levels, energy is consequently wasted "

    Boiling a kettle or heating a room faster is not a loss it is a saving, as is obvious by thinking about boiling it very slowly, the as then it never gets warm. A 1kW kettle is a lot slower than 1/3 of a 3kW one,  as heat is lost during the process, and a 100W kettle never boils at all. So, boiling adiabatically in a fraction of a second with megawatts would be ideal but is sadly impractical.
    Anything electronic with a switch mode regulator will draw more current at lower line voltage to compensate, so the wiring losses are higher.
    I do now wonder now about the rest of the thinking.

    Mike

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