ABB RELION 670 Series Applications Manual page 106

Section 7
Impedance protection
• 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
RLdOutFw
EQUATION1343 V1 EN-US
It is a general recommendation to set the inner boundary
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
oscillation detection logic. This requires the maximum permitted setting values of factor
= 0.8. Equation
RLdInFw
EQUATION1344 V3 EN-US
The load angles, which correspond to external δ
oscillation detection characteristic in forward direction, are calculated with sufficient accuracy
according to equation
d
= ×
2 arc tan
Out
EQUATION1345 V1 EN-US
d
= ×
2 arc tan
In
EQUATION1346 V1 EN-US
The required setting
difference according to equation 27.
d
=
tP 1
EQUATION1347 V1 EN-US
The general tendency should be to set the
possible to further increase the external load angle δ
boundary of the oscillation detection characteristic. The minimum required value is calculated
according to the procedure listed in equation 28, 29,
100
RLdOutFw obtains in this particular case its value according to equation 23.
= × =
K R 0.9 137.2 123.5
L L min
24 presents the corresponding maximum possible value of
= ×
kLdRFw RLdOutFw
25 and 26
æ
Z
S
ç
ç
×
2 RLdOutFw
è
æ
Z
S
ç
ç
×
2 RLdInFw
è
max
tP1 of the initial oscillation detection timer depends on the load angle
d
- ° -
76.5 64.5
=
In Out
× ° ×
f 360 2.5 360
si
× = W
= W
98.8
and internal δ
Out
respectively.
ö
æ ö
155.75
÷ = ×
2 arc tan
ç ÷
÷
×
2 123.5
è ø
ø
ö
æ ö
155.75
÷ = × =
2 arc tan
ç ÷
÷
×
è 2 98.8 ø
ø
°
=
13.3 ms
°
tP1 time to at least 30 ms, if possible. Since it is not
, it is necessary to reduce the inner
Out
30
with the ratio between actual
L
RLdInFw of the oscillation detection
tP1 and tP2 included in
RLdInFw .
boundary of proposed
In
= °
64.5
°
76.5
and 31.
1MRK 511 364-UUS A
(Equation 23)
kLdRFw
(Equation 24)
(Equation 25)
(Equation 26)
(Equation 27)
Application manual