Schweitzer Engineering Laboratories SEL-351A, Manual

Page: 51 / 666

2.17
Date Code 20080213
Instruction Manual SEL-351A Relay
Installation
Making Rear-Panel Connections
collapse of secondary voltage V
A
(V
A
= 0) in the broken-delta secondary,
note that voltage V
S
is 180 degrees out-of-phase with voltage V
A
(from
voltage input
VA-N
).
Use the METER command (via serial port or front panel) to compare
these voltage phase angles. If the phase angle difference between V
S
and
V
A
is 180 degrees (within a few degrees), then the polarity of voltage
input
VS
is deemed correct. If the phase angle difference between V
S
and
V
A
is 0 degrees (again, within a few degrees), then the secondary wires
from the broken-delta secondary in Figure 2.8 need to be swapped in
connection to voltage input
VS-NS
.
Figure 2.9 Resultant Voltage V
S
from the Collapse of Voltage V
A
in the
Broken-Delta Secondary (Compared to the Wye-Connected Power System
Voltages)
Open-Delta Connected PT Example
Figure 2.10 Broken-Delta Secondary Connection to Voltage Input VS,
Open-Delta Connected PTs
NOTE:
“3V0” in the METER command
(via serial port or front panel) is
derived internally from the
VA-VB-VC-N
voltage inputs, not from voltage input
VS-NS , regardless of setting VSCONN.
V
C
V
B
V
A
V
S
VS
NS
Setting
VSCONN = 3V0
Open Circuit
for Test
VB
N
Setting
PTCONN = DELTA
A B C
VA
V
AB
VC
Step-Down
Transformer
SEL-351 Relay
Broken-Delta
Open-Delta
V
CB
V
A
V
B
V
S
V
C
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