4.79
Date Code 20170927 Instruction Manual SEL-751 Relay
Protection and Logic Functions
Group Settings (SET Command)
q To Figure 4.38
Figure 4.54 Load-Encroachment Logic
Load-Encroachment Examples
EXAMPLE 4.8 Load-Encroachment Setting Example
Example system conditions:
Nominal Line-Line Voltage: 230 kV
Maximum Forward Load: 800 MVA
Maximum Reverse Load: 500 MVA
Power Factor (Forward Load): 0.90 lag to 0.95 lead
Power Factor (Reverse Load): 0.80 lag to 0.95 lead
CT ratio: 2000/5 = 400
PT ratio: 134000/67 = 2000
The PTs are connected line-to-neutral.
(90°)
(270°) (—90°)
(0°)(180°)
Example Settings
X
1
R
1
Positive-Sequence Threshold = (Phase Channels Nominal Rating) • (0.1)
Load In
ZLOUT
ZLOAD
Load Out
ZLIN
PLAF > ∠ Z
1
> NLAF
NLAR > ∠ Z
1
> PLAR
Pos.-Seq.
Threshold
|Z
1
| (Magnitude)
∠Z
1
(Angle)
V
1
I
1
V
1
I
1
Z
1
=
Relay
Word
Bits
ZLF
ZLR
Settings
ZLIN
(Load In
Region)
ZLOUT
(Load Out
Region)
ZLR = 19.00 Ω sec.
NLAR = 217°
PLAR = 162°
PLAF = 26°
NLAF = —18°
ZLF = 11.90 Ω sec.
1
1
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