ABB Relion 670 Series Applications Manual page 114

Section 7
Impedance protection
ANSI05000283 V2 EN-US
Figure 50: Impedance diagrams with corresponding impedances under consideration
The outer boundary of oscillation detection characteristic in forward direction
be set with certain safety margin K
When the exact value of the minimum load resistance is not known, the following approximations
may be considered for lines with a rated voltage of 400 kV:
• K = 0.9 for lines longer than 100 miles
L
• K = 0.85 for lines between 50 and 100 miles
L
• K = 0.8 for lines shorter than 50 miles
L
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 400kV.
The outer boundary
108
LdAngle_PSD
LdAngle_PHS
compared to the minimum expected load resistance R
L
RLdOutFw obtains in this particular case its value according to equation 22.
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R
R
ANSI05000283-2-en.vsdx
with the ratio between actual
L
Phasor measurement unit RES670
1MRK 511 407-UUS Rev. J
RLdOutFw should
.
Lmin
Application manual