Sel 411L - Page 434

P.3.326
SEL-411L Relay Protection Manual Date Code 20151029
Protection Functions
Protection Application Examples
The current distribution factors are as follows:
C
1
= 0.358, C
0
= 0.427
and
K
P
= 0.34  –84.3°
Note that this value will be near the Y axis in the lower half of the Alpha Plane
and on the edge of the 87LP characteristic when you apply typical settings.
We can conclude that the phase differential will operate for resistive faults of
as much as 100  at maximum load.
The equations for K
2
and K
0
are as follows:
Equation 3.121
We obtain the following by substituting the previously calculated values for
C
1
and C
0
,
K
2
= 1.8 0.° and K
0
= 1.34  2.28°
Note that these values will be close to the X axis on the right-hand side of the
Alpha Plane. Clearly, the negative-sequence and zero-sequence elements are
not impacted by load and will operate for higher fault resistance values.
Enable the 87LQ and 87LG elements to provide coverage beyond the value
provided previously.
The fault calculations show that we can apply default settings for the pickup,
radius, and blocking angle of the differential elements. Choose the following:
87LPP := 0.5 Pickup 87LP Element (OFF, 0.1–2 pu)
87LPR := 6 Radius 87LP Element (1.2–8)
87LPA := 195 Block Angle 87LP Element (90–270°)
87LQP := 0.25 Pickup 87LQ Element, Sec. Mode (0.1–2 pu)
87LQR := 6 Radius 87LQ Element, Sec. Mode (1.2–8)
87LQA := 195 Block Angle 87LQ Element, Sec. Mode (90–270°)
87LGP := 0.25 Pickup 87LG Element (OFF, 0.1–2 pu)
87LGR := 6 Radius 87LG Element (1.2–8)
87LGA := 195 Block Angle 87LG Element (90–270°)
87LPPS := 0.6 Pickup 87LP Element, Sec. Mode (0.1–2 pu)
87LPRS := 7.2 Radius 87LP Element, Sec. Mode (1.2–8)
87LPAS := 234 Block Angle 87LP Element, Sec. Mode (90–270°)
87LQPS := 0.3 Pickup 87LQ Element (OFF, 0.1–2 pu)
87LQRS := 7.2 Radius 87LQ Element (1.2–8)
87LQAS := 234 Block Angle 87LP Element (90–270°)
K
2
1C
1
–
C
1
---------------= K
0
1C
0
–
C
0
---------------=