I.2
SEL-351A Relay Instruction Manual Date Code 20080213
Using the SEL-251 and SEL-267 Relay Settings in the SEL-351A Relay
Main Differences Between Settings for the SEL-251, SEL-267, and SEL-351A Relays
Main Differences Between Settings for the SEL-251,
SEL-267, and SEL-351A Relays
Basic Protective
Functions
The overcurrent functions in these products are very similar. For
nondirectional overcurrent protection, the settings from the SEL-251 and
SEL-267 relays can be easily converted to the appropriate SEL-351A settings.
The following settings descriptions give the equivalent setting names and
scaling for these three specific products:
➤ SEL-251-3
➤ SEL-267-5
➤ SEL-351A
For other model numbers, refer to the appropriate Instruction Manual.
Line Impedance Parameters
SEL-251-3 and SEL-267-5 relays:
R1, X1, R0, X0 (ohms primary)
These impedance values have to be converted to ohms secondary (magnitude
and angle) for the SEL-351A.
Equation I.1
Equation I.2
Equation I.3
Equation I.4
Phase Overcurrent and Time-Overcurrent Pickup Settings
SEL-251-3: Enter directly into SEL-351A phase elements (e.g., 50P1P, 51PP).
SEL-267-5: Convert setting to secondary units, then enter into the SEL-351A
phase elements.
Equation I.5
Phase Time-Overcurrent Element Curve Settings
SEL-251-3 and SEL-267-5 relays: Append a “U” in front of the 51C
(SEL-251-3) or 51PC (SEL-267-5) setting value and enter into the SEL-351A
51PC setting.
Z1MAG
CTR
PTR
------------
R1
2
X1
2
+• =
Z0MAG
CTR
PTR
------------
R0
2
X0
2
+• =
Z1ANG ARCTAN
X1
R1
-------
⎝
⎛
=
NOTE: The RS and XS settings for
current limiting reactor impedance in
the SEL-251-3 have no equivalent
settings in the SEL-351A.
Z0ANG ARCTAN
X0
R0
-------
⎝
⎛
=
A secondary
A primary
CTR setting()
----------------------------------=
Courtesy of NationalSwitchgear.com
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