Schweitzer Engineering Laboratories SEL-351A - Figure 4.12 Zero-Sequence Voltage-Polarized Directional Element (Low-Impedance Grounded Systems)

4.24
SEL-351A Relay Instruction Manual Date Code 20080213
Loss-of-Potential, Load Encroachment, and Directional Element Logic
Directional Control for Neutral-Ground and Residual-Ground Overcurrent Elements (Not in SEL-351A-1)
q From Figure 4.13 and Figure 4.14; w to Figure 4.15 and Figure 4.16.
Figure 4.12 Zero-Sequence Voltage-Polarized Directional Element (Low-
Impedance Grounded Systems)
The 3V
0
input to Figure 4.12 may be either a calculated value (when global
settings VSCONN = VS and PTCONN = WYE) or a measured value (when
global setting VSCONN = 3V0). See Zero-Sequence Voltage Sources on
page 4.15.
I
N
3V
0
If Z0F Setting > 0, Forward Threshold = 1.25 • Z0F — 0.25 •
I
N
3V
0
If Z0F Setting ≤ 0, Forward Threshold = 0.75 • Z0F — 0.25 •
Forward Threshold:
I
N
3V
0
If Z0R Setting < 0, Reverse Threshold = 1.25 • Z0R + 0.25 •
I
N
3V
0
If Z0R Setting ≥ 0, Reverse Threshold = 0.75 • Z0R + 0.25 •
Reverse Threshold:
Note: 1∠Z0MTA = One Ohm at the Zero-Sequence Line Angle
Direction Element Characteristics
R0
X0
Forward Threshold
Reverse Threshold
Z0 PLANE
w
R32N
F32N
Forward
Reverse
"S" listed in
setting ORDER
50NF
Enable
Forward
Threshold
32NE
Reverse
Threshold
50NR
Re[3V
0
•(I
N
•1
∠
Z0MTA)*]
|I
N
|
2
Z0 =
I
N
3V
0
Relay
Word
Bits
Relay
Word
Bit
Relay
Word
Bit
Relay
Word
Bit
"Forward"
Outputs
q
"Reverse"
Outputs
q
Courtesy of NationalSwitchgear.com