2.19
Date Code 20080103 Instruction Manual SEL-351S Relay
Installation
Making Rear-Panel Connections
Voltage Input Rating
The serial number sticker on the relay rear panel indicates the continuous
voltage input rating, which is 300 Vac for the SEL-351S.
This voltage rating applies to the three-phase voltage inputs (VA-N, VB-N, VC-N)
as well as to the VS-NS voltage input. The voltage rating is in units of V
LN
when the relay is wye connected (three-phase, four-wire), or V
LL
when the
relay is delta connected (three-phase, three-wire). The following two
subsections explain the wye and delta voltage input connections.
The part number sticker on SEL-351S relays manufactured with firmware
revision R108 (or higher) indicates “300 V Wye/Delta.” The part number
sticker on previously manufactured SEL-351S relays indicates “300 V Wye.”
If older SEL-351S relays (with firmware revisions R102 through R107) are
upgraded to R108 (or higher) firmware, they too can be wye connected or
delta connected, provided that the voltage rating is not exceeded.
Wye-Connected Voltages (Global Setting PTCONN = WYE)
Any single voltage input (i.e., VA-N, VB-N, VC-N, or VS-NS) can be connected to
voltage up to 300 V continuous. Figure 2.17–Figure 2.22 and Figure 2.25–
Figure 2.27 show examples of wye-connected voltages. 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 on page 3.36 and Frequency Elements on page 3.49.
Delta-Connected Voltages (Global Setting PTCONN = DELTA)
SEL-351S relays with firmware revision R108 (or higher) can be configured
via Global Setting PTCONN = DELTA to accept an open-delta PT connection.
Phase-to-phase voltage up to 300 V continuous can be connected to the relay
when it is connected as shown in Figure 2.28 or Figure 2.29. This connection
requires an external jumper between VB (terminal Z10) and N (terminal Z12).
In this configuration, the relay cannot measure zero-sequence voltage (3V
0
)
because the open-delta connection blocks zero-sequence voltage information.
Relay functions that require 3V
0
voltage may be disabled, unless another 3V
0
voltage source is supplied to the relay via voltage input VS-NS (see Broken-
Delta VS Connection (Global Setting VSCONN = 3V0) on page 2.20).
Referring to Figure 2.28 and Figure 2.29, when Global Setting PTCONN =
DELTA, the relay interprets the voltage signal detected across voltage input
VA-N as V
AB
, and the voltage signal detected across voltage input VC-N as V
CB
(or –V
BC
). Phase-to-phase voltage V
CA
is derived internally (V
CA
= V
CB
–
V
AB
). The relay does not use the voltage signal detected across voltage input
VB-N, 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 12.8.
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 on page 3.36 and Frequency Elements on
page 3.49.
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