Hitachi Relion 670 Series Applications Manual page 106

Section 7
Impedance protection
ANSI05000283 V2 EN-US
Figure 50:
The outer boundary of oscillation detection characteristic in forward direction RLdOutFw should be set
with certain safety margin K
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
400kV when the rated voltage of the line under consideration is higher than 400kV. The outer boundary
RLdOutFw obtains in this particular case its value according to equation 22.
100
LdAngle_PHS
Impedance diagrams with corresponding impedances under consideration
compared to the minimum expected load resistance R
L
© 2017 - 2023 Hitachi Energy. All rights reserved
LdAngle_PSD
R
ANSI05000283-2-en.vsdx
with the ratio between actual voltage and
L
1MRK511407-UUS Rev. N
R
. When the exact
Lmin
Phasor measurement unit RES670
Application manual