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Protection Question No.47 – Earth fault setting calculation

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  • #360
    abbas

      Are there any criteria or normal practice for setting calculation of earth leakage protection in impedance earthed electrical systems?
      Are there any criteria or normal practice for setting calculation of earth leakage protection in impedance earthed electrical systems?

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    • #1672
      Hamid

        In impedance earthed networks which subjected to earth leakage concerning, the earth fault current is limited to a value in the range app. 10 to 1000 ampere. In this systems, the feeders is equipped with earth fault protection which fed either from a core-balance CT or from the residual connection of the 3 line CTs.When the residual connection of 3 line CTs is applied, the operating level should not be set below %6 of the CT nominal current. This is due to the fact that in the event of an inter-phase short-circuit , the current transformers may start to saturate in a non-symmetrical manner, and this could cause spurious operation of a relay whose operating level is set too low. If a relay supplied from a ring (core-balance) CT, the pick

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