Date Code 20010731 Breaker Logic 3-1
SEL-352-1, -2 Instruction Manual
SECTION 3: BREAKER LOGIC
INTRODUCTION
The predefined logic schemes of the SEL-352 Relay provide protection for several circuit
breaker (CB) failure modes:
Failure to clear a fault (five available schemes for fault current conditions)
Failure to trip under load (load current conditions)
Failure to complete trip sequence due to trip resistor(s) or close resistor(s) remaining
inserted (thermal protection of close and trip resistors)
Failure to close (current unbalance)
Failure while open (flashover conditions)
Loss-of-dielectric pressure
Failure of the breaker 52A contact to indicate operation (breaker alarm logic)
Each of the protection schemes is implemented in SEL
OGIC
®
control equations, giving relay
engineers unparalleled flexibility in adapting the relay to their needs. This flexibility is
simplified by selecting the predefined schemes. Set the scheme setting to CUSTOM to make
changes to the predefined logic.
BREAKER FAILURE RELAYING OVERVIEW
Ideally, when a fault occurs on a power system, the primary protection for the system operates to
remove the faulted equipment from service. Zones of protection are arranged to minimize
service disruption when local primary protection operates. When local protection fails to clear a
fault, backup protection clears the fault, sometimes removing more equipment from service than
the primary protection would have during correct operation.
Both local and remote backup protection are available to the system protection engineer.
Remote backup consists of overlapping, time-coordinated protection zones, which can operate if
a fault outside the instantaneous protection zone persists. Local backup protection uses
redundant equipment, which operates to clear a fault if primary protection fails. The extent of
redundancy depends on the availability of resources, the overall system impact, and the
importance of the load.
Breaker failure relaying is one form of local backup protection. Consider using breaker failure
relaying instead of remote backup if any of the following conditions are true:
Remote backup fault clearing time is greater than maximum allowed fault clearing
time due to system stability or equipment damage considerations.
Critical loads are lost due to remote fault clearing, which can be maintained using
local breaker failure relaying.
Remote fault clearing is sequential, requiring the local fault contribution to be cleared
before remote relaying can detect the fault.
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