Date Code 20010625
Application Settings for SEL-311L Relays
14-21
SEL-311L Instruction Manual
A
PPLICATION
S
ETTING
87L21—D
IFFERENTIAL
P
ROTECTION WITH
S
TEP
-D
ISTANCE
B
ACKUP
Set APP = 87L21 in the SEL-311L to configure the relay for differential protection and:
•
Three zones of phase and ground step-distance backup protection. Unused zones may
be set to OFF. For example, set overreaching ground distance elements OFF when
neighboring protection uses directional ground overcurrent.
•
Two directional ground-overcurrent elements (67G1T/51GT). These elements may be
used to coordinate with existing directional ground overcurrent protection schemes.
•
One phase-overcurrent element (50P1). This element may be used with switch-onto-
fault logic. Consider using switch-onto-fault logic when applying line side PTs, and
when relay potentials are unavailable before breaker closing.
When APP = 87L21, the SEL-311L:
1. Configures itself as full-function differential relay. All differential and tapped load
settings are available.
2. Configures itself as a three-zone step-distance phase-mho and ground-mho relay for
distance protection (E21P* = 3, E21MG* = 3).
3. Enables overcurrent elements:
•
50P—instantaneous/definite-time phase-overcurrent element (E50P* = 1)
•
50G—instantaneous/definite-time ground-overcurrent element (E50G* = 1)
•
51G—inverse-time ground-overcurrent element (E51G* = Y)
*
Note:
These settings are hidden.
4. Displays the enable settings for:
•
Loss-of-potential (ELOP = Y1)
•
Reclosing (E79 = N)
•
CCVT transient protection (ECCVT = N)
•
SEL
OGIC
variables (ESV = N)
•
SEL
OGIC
Latch bits (ELAT = N)
•
SEL
OGIC
Display points (EDP = 3)
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