Project Description

SEL-311C Transmission Protection System

SEL-311C Transmission Protection System

Apply the SEL-311C Relay for protection, reclosing, monitoring, and control of transmission lines.

Features include a four-shot recloser, patented capacitance voltage transformer (CVT) transient overreach logic to enhance security of Zone 1 distance elements, and overcurrent elements with directional control, monitoring, and metering. Apply three-pole tripping logic, or select the SEL-311C-2 for single-pole tripping. The SEL-311C comes standard with EIA-232 serial ports as well as a 10/100 BASE-T Ethernet port for local/remote access and system integration. IEEE C37.118 compliant synchrophasors are included for improved situational awareness.

Functional Overview

 SEL-311C Functional Overview
16SEC Access Security (Serial, Ethernet)
21 (P, G) Distance (Phase Mho, Ground Mho, Ground Quad)
25 Synchronism Check
27 Undervoltage
50 (P, G, Q) Overcurrent (Phase, Ground, Neg. Seq.)
51 (P, G, Q) Time-Overcurrent (Phase, Ground, Neg. Seq.)
52PB Trip/Close Pushbuttons
50BF Breaker Failure Overcurrent
59 Overvoltage
67 (P, G, Q) Directional Overcurrent (Phase, Ground, Neg. Seq.)
68 Out-of-Step Block/Trip
79 Autoreclosing
81 (O, U) Over-/Underfrequency
85 SEL MIRRORED BITS Communications
DFR Event Reports
HMI Operator Interface
LGC Expanded SELOGIC Control Equations
MET High-Accuracy Metering
PMU Synchrophasors
SER Sequential Events Recorder
BRM Breaker Wear Monitor
LDE Load Encroachment
LOC Fault Locator
SBM Station Battery Monitor


Front- and Rear-Panel Diagrams

SEL311C- Front Panel SEL311C- Rear Panel
Front Rear


Distance Protection

Increase transmission line loading, reduce equipment damage, and improve system stability with phase and ground distance elements. The SEL-311C Transmission Protection System provides four zones of phase mho, ground mho, and ground quadrilateral distance elements. The SEL-311C-1 features the ability to connect either wye or delta voltage transformers (VTs) for phase distance protection.

Subcycle Distance Protection

The SEL-311C-3 adds three zones of high-speed phase mho and ground mho distance elements to provide subcycle tripping times.

Breaker Failure Detection

Quickly detect failed circuit breakers with the built-in breaker failure detection elements and logic. The high-speed breaker failure element drops out less than one cycle after successful breaker operation, even with subsidence current.


Restore service following transient faults by using programmable four-shot breaker autoreclosing with synchronism and voltage check logic.  The synchronism check function compensates for breaker close time, frequency, magnitude, and angle differences between the two voltage sources used for synchronism.

Fault Location

Calculate accurate distance-to-fault measurements with the impedance-based fault locator. Obtain fault resistance calculations for enhanced fault studies.

Load Shedding

Operate six levels of frequency elements as either an under- or overfrequency element. The frequency elements are suited for applications such as under-frequency load shedding and restoration control systems.

Communications-Assisted Tripping

SchemesConfigure protection for transmission lines without any need for external coor-dination devices. The SEL-311C includes settings for permissive overreaching transfer trip(POTT),directional compar-ison unblocking (DCUB), and directional comparison blocking (DCB) schemes.

Out-of-Step Blocking and Tripping

Detect stable or unstable power swings with out-of-step detection logic. Enhance security with out-of-step blocking to block distance elements during stable swing conditions. Implement out-of-step tripping during unstable power swing conditions to maintain a generation load balance.

Innovative Logic for Secure Operation

Use loss-of-potential logic to detect blown potential transformer (PT) fuses and disable distance and directional elements that are affected by voltage. Recognize coupling capacitor voltage transformer (CCVT) transients during Zone 1 faults with built-in CCVT detec-tion logic. Delay the distance element during CCVT transients to prevent a Zone 1 distance overreach and improve sensitivity.


411L 421 311C 311L 387L
Distance Protection
Line Current Differential
Breaker Failure Protection f f
Undervoltage Load Shedding f f f f
Series-Compensated Lines + +
21G Mho Ground Distance
21XG Quad Ground Distance
21P Mho Phase Distance
25 Synchronism Check
27/59 Under-/Overvoltage f
49 Thermal f f
50 (N,G) Overcurrent (Neutral, Ground)
50P Phase Overcurrent
50Q Negative-Sequence Overcurrent
51 (N,G) Time-Overcurrent (Neutral, Ground)
51P Phase Time-Overcurrent
51Q Negative-Sequence Time-Overcurrent
67 (N,G) Directional Overcurrent (Neutral, Ground)
67P Phase Directional Overcurrent
67Q Negative-Sequence Directional Overcurrent
81 Under-/Overfrequency
87L Line Current Differential
Programmable Analog Math
Out-of-Step Block and Trip
Load-Encroachment Supervision
Single-Pole Trip + +
Zone/Level Timers
Pilot Protection Logic
79 Automatic Reclosing
Number of Controlled Breakers 2 2 1 1 1
Fault Locating
Traveling Wave Fault Location +
Subcycle Distance Elements + + +
SELogic Control Equations
Nonvolatile Latch Control Switches
SELogic Remote Control Switches
SELogic Local Control Switches +
Display Points +
Mirrored Bits Communications
Substation Battery Monitor
Breaker Wear Monitor
Trip Coil Monitor f f f f
Event Report (Multicycle Data)
Sequential Events Recorder
Instantaneous Meter
DNP3 Level 2 Outstation + +
IEC 61850 Communications + + + +
Synchrophasors (SEL Format)
Synchrophasors (IEEE C37.118 Format)
Accepts Delta Voltage Transformers +
Connectorized (Quick Disconnect) Available + + +
Configurable Labels +
Standard Feature
+ Model Option
f This function may be created using settings

Product Literature