KYORITSU KEW 6016, Инструкция по эксплуатации

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9. LOOP/ PSC/PFC
9.1 Principles of measurement of fault loop impedance and PFC
If an electrical installation is protected by over-current protective devices including circuit
breakers or fuses, the earth loop impedance should be measured.
In the event of a fault the earth fault loop impedance should be low enough (and the
prospective fault current high enough) to allow automatic disconnection of the electrical
supply by the circuit protection device within a prescribed time interval. Every circuit must
be tested to ensure that the earth fault loop impedance value does not exceed that specified
or appropriate for the over-current protective device installed in the circuit. The KEW6016
takes a current from the supply and measures the difference between the unloaded and
loaded supply voltages. From this difference it is possible to calculate the loop resistance.
TT System
For a TT system the earth fault loop impedance is the sum of the following impedances;
●Impedance of the power transformer secondary winding.
●Impedance of the phase conductor resistance from the power transformer to the location of
the fault.
●The impedance of the protective conductor from the fault location to the earth system.
●Resistance of the local earth system (R).
●Resistance of the power transformer earth system (Ro).
The figure below shows (dotted line) the Fault loop impedance for TT systems.
Fig.22