Sel 411L - Page 138

P.3.30
SEL-411L Relay Protection Manual Date Code 20151029
Protection Functions
87L Differential Elements
Note that the relay has a dedicated mechanism for protecting the line in a
temporary stub bus configuration, and that you should not use the 87CTWL or
87CTXL SEL
OGIC control equations for stub bus control of the 87L function
(see Stub Bus Condition for more details).
The 87CTWL and 87CTXL Relay Word bits signal inclusion or exclusion,
respectively, of a given current terminal of the relay in the 87L function.
87CTPWL and 87CTPXL
These settings control polarity of a given relay current input terminal, W and
X respectively, as the local inputs to the 87L function.
Set the setting to "P" if the corresponding current is wired with polarity
consistent with the other currents of the 87L zone. The 87L function will use
the current directly as wired.
Set the setting to "N" if the corresponding current is wired with polarity that is
the inverse of other 87L zone currents. The 87L function will invert the sign of
the current before using it.
Note that the polarity setting applies to the 87L function only.
The current transformers are most commonly wired with a consistent polarity
for the 87L zone of protection, so these settings will typically be set to "P" at
all relays of the 87L scheme.
87CTP1R, 87CTP2R, and 87CTP3R
These settings specify the CT primary nominal currents for remote Relays 1,
2, and 3, respectively, allowing the relay to scale the remote currents for
different CT ratios and ratings.
If a given remote relay uses a single current terminal as its local input to the
87L function (either the W or X current terminal), the corresponding
87CTPxR setting is the nominal primary current of the CT connected to the
current terminal in use.
If a given remote relay uses both current terminal as its local inputs to the 87L
function (both the W or X current terminals), such as in dual-breaker
applications, the corresponding 87CTPxR setting is the higher of the two
nominal primary currents of the CTs connected to the two current terminals of
the remote relay.
87LTAPW and 87LTAPX
These read-only settings are the tap values the relay uses to scale its local
currents connected to the W and X current terminals, respectively, to per-unit
values for use in the 87L function.
The relay allows ratio matching with the taps in a range of 5–50 if the relay is
a 5 A nominal relay, and within a range of 1–10 if the relay is a 1 A nominal
relay.
You can apply 1 A and 5 A nominal CTs in the same 87L scheme.
The relays calculate the tap values as follows.
Equation 3.33
87LTAPW
CTBASE
CTRW
------------------------ 87LTAPX,
CTBASE
CTRX
------------------------==