The relay stores the last twelve event reports in a buffer. You can examine any full length
report stored in the relay using the EVENT command. The relay clears the event buffer
when relay power is interrupted or when you make a setting or logic change.
The relay stores event summaries corresponding to each of the twelve events. Summaries
contain operation data such as event type, event date and time, fault type and location,
maximum phase current near the middle of the fault, and fault duration. Use the HISTORY
command to view summaries for events reports stored in the relay history buffer.
Section 4: EVENT REPORTING has further information regarding the generation, content,
and analysis of event reports and summaries saved by the relay.
Fault Locator
The relay calculates a fault location from data stored in the event report. The fault location is
determined for event records in which any triggering relay elements listed above are picked
up, unless they are picked up in the first seven rows of prefault data or picked up only in the
last five rows of the event report.
The actual fault location algorithm is composed of two steps. First the fault type must be
determined, then the location can be calculated.
For the event reports, the fault type is determined independently from the relay element
operations. The involved phases are determined by fault current comparison.
Once fault type is determined, the fault locator employs the Takagi algorithm to locate the
fault. Using prefault and fault data, it compensates for errors introduced by fault resistance
or the presence of load flow. If the event record does not provide prefault data, the relay
gives a location based on a simple reactance measurement.
Although the fault location computation takes several seconds, the relay can handle faults in
quick succession, such as those occurring in a reclosing sequence. This is because the fault
data are stored, then processed later. For example, suppose three faults occur within a few
seconds. The data from each is stored as it occurs. Fault location computations begin with
the first (oldest) fault and proceed until all three faults are processed.
Metering
The meter function shows the values of ac current, voltage, and real and reactive power
measured by the relay (see Section 3: COMMUNICATIONS, METER command). You can
execute the METER command locally or remotely to check breaker conditions.
Date Code 920508
Specifications
SEL-221F, -1 Instruction Manual
2-27
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