Schweitzer Engineering Laboratories SEL-351-5, Instruction Manual

Page: 165 / 706

4.21
Date Code 20070117
Instruction Manual SEL-351-5, -6, -7 Relay
Loss-of-Potential, Load Encroachment, and Directional Element Logic
Directional Control for Neutral Ground and Residual Ground Overcurrent Elements
q From Table 4.2 ; w to Figure 4.15 and Figure 4.16 .
Figure 4.9 Negative-Sequence Voltage-Polarized Directional Element for
Neutral Ground and Residual Ground Overcurrent Elements
I
2
V
2
If Z2F Setting
>
0, Forward Threshold = 1.25 • Z2F — 0.25 •
I
2
V
2
If Z2F Setting
≤
0, Forward Threshold = 0.75 • Z2F — 0.25 •
Forward Threshold:
I
2
V
2
If Z2R Setting
<
0, Reverse Threshold = 1.25 • Z2R + 0.25 •
I
2
V
2
If Z2R Setting
≥
0, Reverse Threshold = 0.75 • Z2R + 0.25 •
Reverse Threshold:
Note: 1
∠
Z1L = One Ohm at the Positive-Sequence Line Angle
Direction Element Characteristics
R2
X2
Forward Threshold
Reverse Threshold
Z2 PLANE
32QGE is highest
w
R32QG
(Reverse)
F32QG
(Forward)
Best Choice
Ground
Directional
Logic
50QF
Enable
Forward
Threshold
32QGE
Reverse
Threshold
50QR
q
Re[V
2
•(I
2
•1
∠
Z1L)*]
|I
2
|
2
Z2 =
I
2
V
2
Relay
Word
Bits
Relay
Word
Bit
Relay
Word
Bit
Relay
Word
Bit
choice that is asserted