Schweitzer Engineering Laboratories SEL-351-5, Instruction Manual

Page: 54 / 706

2.14
SEL-351-5, -6, -7 Relay Instruction Manual
Date Code 20070117
Installation
Making Rear-Panel Connections
equation V
CA
= V
CB
– V
AB
. The relay does not use the voltage signal detected
across the
VB-N
terminals, which should effectively be zero due to the jumper
between
VB
and
N
. Unfiltered (raw) event reports are the only means by which
signals applied to relay voltage terminals VA-N , VB-N , and VC-N can be directly
observed. See Unfiltered Event Reports With PTCONN = DELTA on
page 12.9 .
Frequency is measured from the voltages connected to terminals
VA-VB
; and
VS-NS when the synchronism check elements are enabled and the relay is
properly wired (see Synchronism Check Elements on page 3.33 and Frequency
Elements on page 3.46 ).
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)
When setting VSCONN = VS, voltage input
VS
is in its traditional role of
voltage input for the synchronism check elements. Figure 2.10 – Figure 2.13 ,
Figure 2.22 , and Figure 2.23 show examples of synchronism check voltage
inputs applied to relay terminals VS-NS . See Synchronism Check Elements .
SEL-351-5, -6, -7 relays with firmware revisions up to and including R308
function as if VSCONN = VS, although global setting VSCONN is not
actually available in these relays.
Broken-Delta VS Connection (Global Setting VSCONN = 3V0)
In SEL-351-5, -6, -7 relays with firmware revision R309 or higher, global
setting VSCONN = 3V0 adjusts the relay to accept a 3V
0
zero-sequence
voltage signal connected to voltage input VS . 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). These elements will use the VS channel measured 3V0
even if a calculated 3V0 is available (when the relay phase voltage inputs are
supplied by wye-connected PTs and PTCONN = WYE).
To prevent a broken-delta voltage source from exceeding the rated voltage
(150 V or 300 V) of the relay voltage inputs, some applications require an
external step-down transformer.
Figure 2.6 , Figure 2.8 , and Figure 2.21 show
the PT wiring, including an instrumentation step-down transformer, for using
relay terminals
VS-NS
as a zero-sequence voltage source. Group setting PTRS
accommodates the ratio of the step-down transformer. See Settings
Explanations on page 9.37 for an example setting of PTRS when VSCONN =
3V0. For a complete listing of the changes caused by setting VSCONN = 3V0,
see
Table 9.7 , Table 9.8 and related discussions.
Selecting global setting VSCONN = 3V0 disables the synchronism check
element. Therefore, input terminals
VS-NS cannot be used for 3V0
measurement and as a synchronism check input at the same time.