P.3.306
SEL-411L Relay Protection Manual Date Code 20151029
Protection Functions
87L Master, Outstation, and Loss of Protection Logic
87L Master, Outstation, and Loss of Protection Logic
When in the master mode, the 87L function depends on communications with
all other scheme relays and requires adequate accuracy of data
synchronization. When in outstation mode, a given relay may or may not be
capable of tripping the local line terminal, depending if it communicates with
the master.
To provide you fine control of 87L backup functions according to your
preferences, the relay offers detailed information about the present ability of
the 87L function to detect line faults.
Depending on the application and the state of the required channels at any
given time, the 87L function of the relay can be in one of the following states.
➤ A master capable of receiving all required information and able
to properly synchronize current data, calculate differential
current, and act upon information to provide such functionality
as 87L protection, fault identification logic, and multi-ended
fault location.
➤ A permanent outstation that serves the local current to a remote
master (not all channels installed).
➤ A temporary outstation (normally a master) upon a loss of a
channel or loss of current data synchronization and unable to
use the current data.
➤ When in an outstation mode, the relay may or may not be
capable of tripping from the 87L via the 87DTT (depending
upon whether the connected remote relay is in the master state
and depending if the 87DTT is configured via the E87DTT
setting at the receiving outstation relay).
Relay Word bits flag the previously listed states; you can use default relay
logic and SEL
OGIC control equations to control other relay functions. The
following three Relay Word bits describe the state of the 87L function.
➤ 87MTR—the relay is in the master mode; it receives usable
data from all terminals within the zone and calculates the
differential signal and associated quantities. If this bit is
deasserted, the relay performs no differential calculations but
forces differential currents to zero.
➤ 87SLV—the relay receives data from some but not all line
terminals, or it cannot use the received data for differential
protection, primarily because of a lack of synchronization; the
relay performs no differential signal calculations but forces
differential currents to zero.
➤ 87LST—the 87L function is unavailable and inoperable for
internal faults. The function will not trip as a master
(autonomously) or as an outstation from the 87DTT (because it
does not communicate with the master, or the 87DTT function
is disabled at this relay terminal).
Figure 3.214–Figure 3.216 show logic diagrams for establishing the state of
the 87L function.
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