Date Code 970103
Introduction
1-3
SEL-251, -2, -3 Instruction Manual
Sophisticated Multiple-Shot Reclosing Relay Includes Reset Inhibit and Sequence
Coordination
The reclosing relay allows up to four reclosing shots with separate, settable open interval timers
and reset interval timer. Overcurrent conditions during the reclosing relay reset interval inhibit
the reset interval timer. This prevents the reclosing relay from resetting when a trip condition is
imminent. A close failure timer can limit CLOSE output contact assertion. Reclose cancel
conditions are programmable. A programmable input can be used as a reclose enable input to
disable/enable the reclosing relay.
The SEL-251 Relay includes easily programmable sequence coordination to keep the relay in
step with line reclosers, preventing undesired tripping for faults beyond line reclosers.
Six Selectable Groups of Settings and Logic
The relay stores six setting groups. Select the active setting group by contact input or command.
Use these setting groups to cover a wide range of distribution feeder protection contingencies.
Selectable setting groups make the SEL-251 Relay ideal for bus-tie and substitute breaker
applications and other applications requiring frequent setting changes.
Circuit Breaker Monitor Tracks Breaker Performance and Helps Maintenance Planning
Separate circuit breaker trip counters differentiate and tally relay-initiated trips and external trips.
Running sums of interrupted current for relay and external trips indicate breaker wear and tear on
a pole-by-pole basis. Use these data to schedule breaker maintenance.
Trip failure logic provides alarm and breaker failure functions. A close failure alarm indicates
circuit breaker closing circuit or mechanism problems. The trip circuit monitor detects abnormal
open or short circuits in the circuit breaker tripping circuit or status input.
Fault Locator Reduces Line Patrol and Outage Time
The SEL-251 Relay includes a fault locator which uses fault type, prefault, and fault conditions
to provide an accurate estimate of fault location without communications channels or special
instrument transformers, or source impedance information, even during conditions of substantial
load flow and fault resistance. Fault locating reduces line patrol and outage time.
Analyze Operations Using Event Reports
Eleven-cycle event reports triggered by user selected conditions provide the current, voltage, and
sequence-of-events information you need to understand relay and circuit breaker performance, as
well as stress on the feeder for every fault.
Comprehensive Metering Supports Protection, Operation, and Demand Analysis
The relay measures phase, negative sequence, and zero-sequence voltage and current, as well as
MW and MVAR. Demand and peak demand values for current, MW, and MVAR are also
available. Metering also supports protection, because you can inspect the quantities monitored