Toshiba GR200 Series Instruction Manual page 116

Line differential protection ied

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As shown above, the positive-sequence impedance is used when determining settings for

phase faults.

Single-phase-earth fault

Figure 2.10-2 shows the power system in the event of a single-phase-earth fault. It is very

difficult to measure precisely the distance to the fault point for a single-phase-earth fault. This

is because the impedance of the zero-sequence circuit including the earth return is generally

different from the positive-sequence impedance. Therefore, the faulted phase voltage is not

simply proportional to the faulted phase current.

It is necessary to analyze the impedance seen by the relay in the event of a single-phase-

earth fault according to the method of symmetrical components. Figure 2.10-3 shows an

equivalent circuit for a single-phase-earth fault based on the method of symmetrical

components. If we define the positive-sequence, negative-sequence and zero-sequence voltages

as being V 1 F, V 2 F and V 0 F, then the voltage at the relaying point of each symmetrical circuit

will be given by the following equations based upon the assumption that the positive-sequence

Figure 2.10-1 Phase-to-phase fault

Figure 2.10-2 Single-phase-earth fault

6F2S1914 (0.49)

GRL200 (Soft 033 & 037)

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