2.15
Date Code 20080213
Instruction Manual
SEL-351A Relay
Installation
Making Rear-Panel Connections
System frequency is determined from voltage connected to voltage input
VA-N
.
Additionally, voltage input
VS-NS
measures frequency on the other side of an
open breaker for synchronism check applications. See subsections
Synchronism Check Elements (Not in SEL-351A-1)
.
Throughout this Instruction Manual, relay functions, specifications, or
features that are different for delta-connected and wye-connected PTs are
identified, either with “wye-connected” and “delta-connected” text, or with
“PTCONN = WYE” and “PTCONN = DELTA” text.
Synchronism Check VS Connection (Global setting VSCONN = VS)
NOTE:
The VS channel is not
supported in the SEL-351A-1.
When setting VSCONN = VS, voltage input
VS-NS
operates in its traditional
role of voltage input for the synchronism check elements.
–
,
show examples of synchronism
check voltage inputs applied to voltage input
VS-NS
. See
Elements (Not in SEL-351A-1) on page 3.36
SEL-351A relays with firmware revisions R104 and earlier do not have a
VSCONN setting. In these relays, voltage input
VS-NS
operates in its
traditional role of voltage input for synchronism check (as if setting
VSCONN = VS).
Broken-Delta VS Connection (Global setting VSCONN = 3V0)
In SEL-351A relays with firmware revision R105 or higher, global setting
VSCONN = 3V0 adjusts the relay to accept a 3V
0
zero-sequence voltage
signal connected to voltage input
VS-NS
. This signal is usually derived from
PTs connected wye (primary)/broken-delta (secondary):
V
S
= V
A
+ V
B
+ V
C
= 3V
0
.
This signal is passed to certain relay functions that require zero-sequence
voltage, such as zero-sequence voltage-polarized ground directional elements
or Wattmetric and incremental conductance elements (for Petersen Coil
grounded systems). Because setting VSCONN = 3V0, these elements use the
3V
0
zero-sequence voltage measured by the
VS-NS
voltage input, even if wye-
connected PTs are connected to voltage inputs
VA-VB-VC-N
(PTCONN = WYE;
see
). With this wye-connection, 3V
0
zero-sequence voltage is
calculated from voltages V
A
, V
B
, and V
C
(3V
0
= V
A
+ V
B
+ V
C
) for metering,
but this calculated 3V
0
is not used elsewhere when VSCONN = 3V0.
To prevent a broken-delta voltage source from exceeding the rated voltage of
the relay voltage inputs, some applications require an external step-down
transformer.
show the PT wiring,
including an instrumentation step-down transformer, for using voltage input
VS-NS
as a zero-sequence voltage source. Group setting PTRS accommodates
the ratio of the step-down transformer. See
Settings Explanations on page 9.34
for an example setting of PTRS when VSCONN = 3V0. For a complete listing
of the changes caused by setting VSCONN = 3V0, see
,
,
and related discussions.
Selecting global setting VSCONN = 3V0 disables the synchronism-check
element. Therefore, input terminals
VS-NS
cannot be used for 3V
0
zero-
sequence voltage measurement and as a synchronism check voltage input, at
the same time.
Summary of Contents for SEL-351A
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