ABB RELION 670 Series Applications Manual page 355

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1MRK 504 152-UEN B

IEC09000225 V1 EN-US

Figure 216: Impedance diagrams with corresponding impedances under consideration

The outer boundary of oscillation detection characteristic in forward direction

should be set with certain safety margin K

resistance R

following approximations may be considered for lines with rated voltage 400 kV:

= 0.9 for lines longer than 150 km

= 0.85 for lines between 80 and 150 km

= 0.8 for lines shorter than 80 km

Multiply the required resistance for the same safety factor K

voltage and 400kV when the rated voltage of the line under consideration is higher than

Application manual

. When the exact value of the minimum load resistance is not known, the

IEC09000225-1-en.vsd

compared to the minimum expected load

with the ratio between actual

Impedance protection