Sel 411L - Figure 3.34 Disturbance Detection Logic Responding to Local and Remote Signals, Stub Bus, and Test Mode

P.3.61
Date Code 20151029 Protection Manual SEL-411L Relay
Protection Functions
87L Differential Elements
bus protection is responsible for protecting the local stub bus, so it is not
susceptible to misoperations for communications or remote relay problems in
any case.
Figure 3.34 Disturbance Detection Logic Responding to Local and Remote
Signals, Stub Bus, and Test Mode
As Figure 3.35 shows, the local disturbance detection logic responds to as
many as two sets of local currents (W and X current terminals of the local
relay) and the local voltage you select for the 87L function.
Local disturbance detection uses a given current terminal (W and X,
accordingly) if you have configured this current terminal as an input to the
87L function. The 87CTWL and 87CTXL Relay Word bits, respectively,
signal if the corresponding current is an input to the 87L function.
The logic uses the adaptive disturbance detection algorithm (explained later
and shown in Figure 3.37) to check full-cycle filtered current phasors
(positive-sequence [IA1WF] and zero-sequence [I0WF]) for disturbance. If
either the positive-sequence or zero-sequence current phasors show a sign of
disturbance (a magnitude change, angle change, or a combination), in either
the W or X local current terminals, the current path of the local disturbance
detection asserts.
In addition, to cater for weak feed conditions, the local disturbance detector
checks the positive-sequence, negative-sequence, and zero-sequence in the
voltage terminal (Y or Z) that you have configured through use of the
87LINEV setting. If any one of the positive-sequence, negative-sequence, or
zero-sequence voltage phasors shows a sign of disturbance (a magnitude
change, angle change, or a combination), in the Y or Z local voltage terminal,
whichever is in use, the voltage path of the local disturbance detection asserts.
If all local currents configured under 87CTnL settings are lower than 10
percent of its CT nominal—as checked by the positive-sequence level—the
local disturbance detector is forced to assert. This ensures symmetrical
operation between the local and remote disturbance detectors.
The logic inhibits the voltage path under LOP condition to prevent spurious
and potentially permanent assertion of the 87DDL Relay Word bit when you
cannot trust the voltage source. Note that 87LINEV should be set to the same
voltage terminal as the main protection functions of the relay (see Current and
Voltage Source Selection). When the relay uses an alternate voltage source
upon assertion of the ALTV SEL
OGIC control equation, the LOP logic
monitors the alternate voltage source you have selected through use of the
ALINEV setting. Note that this setting may be different from the 87LINEV
setting that the 87L function uses. Therefore, logic inhibits the voltage path of
the disturbance detection upon assertion of ALTV, and the local disturbance
detector responds to changes in the local current signals only. Once asserted,
the 87DDL Relay Word bit stays asserted for at least 10 power cycles, using
the dropout timer to ensure reliable operation of the supervised 87L elements
and the 87DTT logic.
Note that the local disturbance detection logic executes in the master or
outstation mode; there are no differential quantities involved. Moreover, the
logic executes on local currents and voltages prior to their alignment with
87DDL
Relay Word Bits
87DDR
87TEST
ESTUB
Relay Word Bits
87DD