Schweitzer Engineering Laboratories SEL-351-5, Instruction Manual

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9.42
SEL-351-5, -6, -7 Relay Instruction Manual
Date Code 20070117
Setting the Relay
Settings Explanations
Potential Transformer
Ratios and PT
Nominal Secondary
Voltage Settings
Refer to Current and Potential Transformer Ratios (See Settings Explanations
on page 9.37) on page SET.1 .
Relay setting PTR is the overall potential ratio from the primary system to the
relay phase voltage inputs
VA-VB – VC-N . For example, on a 12.5 kV phase-to-
phase primary system with wye-connected 7200:120 V PTs, the correct PTR
setting is 60. For the same 12.5 kV system connected through 12470:115 V
PTs in an open-delta configuration (global setting PTCONN = DELTA, and
the relay wired as shown in
Figure 2.22 ), the correct PTR setting is 108.44.
Relay setting PTRS is the overall potential ratio from the synchronizing or
broken-delta voltage source to the relay
VS-NS
voltage inputs. For example, in
a synchronism check application (global setting VSCONN = VS), with phase-
to-ground voltage connected from a 12.5 kV phase-to-phase primary system
through a 7200:120 V PT, the correct PTRS setting is 60.
In an application that uses a broken-delta PT connection to create a 3V
0
zero-
sequence voltage signal (global setting VSCONN = 3V0, and the relay VS-NS
terminals wired as shown in Figure 2.21 ), the step-down transformer, if
present, must also be included in the overall PTRS ratio calculation. For
example, if there are three PTs connected wye (primary)/broken delta
(secondary) with ratios of 7200:120, and a 400:250 step-down instrumentation
transformer in the circuit, the correct PTRS setting is 60 • 1.6 = 96.00.
Settings PTR and PTRS are used in event report and METER commands so
that power system values can be reported in primary units.
Settings PTR and PTRS are also used when global setting VSCONN = 3V0,
to scale the measured VS voltage into the same voltage base as voltage inputs
VA-VB
–
VC-N
for certain functions, as shown in Table 9.7 and Table 9.8 . If no
PTs are connected to voltage inputs
VA-VB
-
VC-N
, make setting PTR the same
value as setting PTRS.
The ratio of the PTRS and PTR settings (PTRS/PTR) must be less than 1000
and greater than 0.001 when VSCONN = 3V0.
Table 9.9 Main Relay Functions That Change With VNOM = OFF
Relay Function When VNOM = Numeric Value When VNOM = OFF
Undervoltage block for
frequency elements: 27B81 Requires all three voltages V
A
, V
B
, V
C
(when PTCONN = WYE) or V
AB
, V
BC
, V
CA
(when PTCONN = DELTA) to be greater
than setting 27B81P in order to deassert
Requires one voltage V
A
(when PTCONN = WYE) or
V
AB
(when PTCONN = DELTA)
to be greater than setting
27B81P in order to deassert
Load encroachment logic
(enable setting ELOAD) Available Not available (can
only set ELOAD = N)
Negative-sequence and positive-sequence
voltage polarized directional elements Available 32QE is disabled, F32P/R32P
disabled, ground directional
element ORDER setting choice
“Q” not selectable
Phase and negative-sequence element direc-
tional control (
Figure 4.23 and Figure 4.24 )
Available Not available (defaults to “nondi-
rectional” in levels DIR1–DIR4
Loss-of-Potential Logic (enable setting ELOP) Available Not available
(can only set ELOP = N);
Output Relay Word bits disabled
(LOP = logical 0, V1GOOD =
logical 0)