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4.52
SEL-351A Relay Instruction Manual
Date Code 20080213
Loss-of-Potential, Load Encroachment, and Directional Element Logic
Directional Control Settings (Not in SEL-351A-1)
Figure 4.28 Wattmetric Element Operation for Ground Fault on Feeder
The sum of settings 32WFP and 32WRP must be 0.1 watts secondary or
greater:
32WFP + 32WRP
≥
0.1 watts secondary
In Figure 4.28 , the calculated wattmetric value for a forward fault is a negative
value (shown as WF), while that for a reverse fault is a positive value (shown
as WR). Again, corresponding settings 32WFP and 32WRP are both entered
as positive values, with some margin of sensitivity. The above “0.1 watts
secondary” rule is effectively the minimum distance between settings 32WFP
and 32WRP in the wattmetric plane (setting 32WFP is put on the “negative”
side of the wattmetric plane: i.e., “–32WFP”; see
Figure 4.13 ).
32WD—Wattmetric Delay (Petersen Coil Grounded System)
Setting Range:
30.00–999,999.00 cycles
If preceding setting ORDER does not contain P (Petersen Coil directional
element is not enabled) or the model does not have a 0.2 A nominal neutral
channel (
IN
), then setting 32WD is not made or displayed.
Settings Considerations for Petersen Coil Grounded Systems
The Petersen Coil elements require a zero-sequence voltage source, which is
calculated from voltages V
A
, V
B
, and V
C
when the relay is wye-connected
(global setting PTCONN = WYE and VSCONN = VS), or which is measured
from the
VS channel when the relay is connected to a broken-delta 3V
0
source
and global setting VSCONN = 3V0. Three of the required Petersen Coil
element settings, 59RES, 32WFP, and 32WRP, depend on the type of 3V
0
voltage source and on the PTR and PTRS group settings.
When VSCONN = VS and the relay is wye-connected (PTCONN = WYE), the
3V
0
source is in secondary volts on the
VA
,
VB
,
VC
input terminal base. In fact,
3V
0
is calculated from the measured V
A
, V
B
, and V
C
voltages. The 59RES,
32WFP, and 32WRP settings are set in terms of this same base.
An example system similar to Figure 2.21 , with wye-connected PTs (PT ratio
7200:120; setting PTR = 7200/120 = 60) and a core-flux summation CT (CT
ratio 50:5; setting CTRN = 50/5 =10), is used to demonstrate the required
setting scaling.
Net capacitive behind
Relay 1 (under-
compensated system)
Relay 1 / Faulted Feeder 1
Calculated "negative"
wattmetric value
(forward fault)
Net inductive behind
Relay 1 (tuned or over-
compensated system)
0
V
0
V
0
V
I
0(1)
I
0(1)
Calculated "positive"
wattmetric value
(reverse fault)
Capacitive in
front of Relay 2
I
0(2)
Relay 2 / Unfaulted Feeder 2
WF
WR
Courtesy of NationalSwitchgear.com