ABB REL650 - Page 169

• K
L
= 0.9 for lines longer than 100 miles
• K
L
= 0.85 for lines between 50 and 100 miles
• K
L
= 0.8 for lines shorter than 50 miles
Multiply the required resistance for the same safety factor K
L
with the ratio between actual
voltage and 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
81.
min
0.9 137.2 123.5
L L
RLdOutFw K R= × = × = W
EQUATION1343 V1 EN (Equation 81)
It is a general recommendation to set the inner boundary RLdInFw of the oscillation
detection characteristic to 80% or less of its outer boundary. Exceptions are always
possible, but must be considered with special care especially when it comes to settings of
timers tP1 and tP2 included in oscillation detection logic. This requires the maximum
permitted setting values of factor kLdRFw = 0.8. Equation 82 presents the corresponding
maximum possible value of RLdInFw.
RLdInFw = kLdRFw·RLdOutFw = 98.8W
EQUATION1344 V2 EN (Equation 82)
The load angles, which correspond to external δ
Out
and internal δ
In
boundary of proposed
oscillation detection characteristic in forward direction, are calculated with sufficient
accuracy according to equation 83 and 84 respectively.
155.75
2 arc tan 2 arc tan 64.5
2 2 123.5
d
æ ö
æ ö
ç ÷= × = × = °
ç ÷
ç ÷
× ×
è ø
è ø
S
Out
Z
RLdOutFw
EQUATION1345 V1 EN
(Equation 83)
max
155.75
2 arc tan 2 arc tan 76.5
2 2 98.8
d
æ ö
æ ö
ç ÷= × = × = °
ç ÷
ç ÷
× ×
è ø
è ø
S
In
Z
RLdInFw
EQUATION1346 V1 EN (Equation 84)
The required setting tP1 of the initial oscillation detection timer depends on the load angle
difference according to equation 85.
1MRK 506 334-UUS A Section 6
Impedance protection
163
Application manual