Date Code 20010625
Application Settings for SEL-311L Relays
14-47
SEL-311L Instruction Manual
A
PPLICATION
S
ETTING
87L21P—D
IFFERENTIAL
P
ROTECTION WITH
P
ILOTED
S
TEP
-D
ISTANCE
B
ACKUP
Set APP = 87L21P in the SEL-311L to configure the relay for differential protection, including
•
Four zones of phase- and ground-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.
•
Communications-assisted trip logic. Six available tripping schemes provide
transmission line protection with the help of communications. No external coordination
devices are required. See
Section 5: Trip and Target Logic
.
•
Four directional ground-overcurrent elements (67G1T/67G2T/67G3T/51GT).
These elements may be used to coordinate with existing directional ground-overcurrent
protection schemes, provide fast piloted tripping for forward faults, and provide Zone 3
reverse-fault blocking for communications-assisted 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 = 87L21P, the SEL-311L:
1. Configures itself as full-function differential relay. All differential and tapped load
settings are available.
2. Configures itself as a four-zone step-distance phase-mho and ground-mho relay for
distance protection. (E21P* = 4, E21MG* = 4)
3. Enables one phase-overcurrent and four ground-overcurrent elements:
•
50P—instantaneous/definite-time phase-overcurrent element (E50P* = 1)
•
50G1-3—instantaneous/definite-time ground-overcurrent element (E50G* = 3)
•
51G—inverse-time ground-overcurrent element (E51G* = Y)
*
Note:
These settings are hidden.
4. Displays the enable settings for:
•
Loss-of-potential (ELOP = Y1)
•
Communications-assisted trip schemes (ECOMM = N)
•
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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