Basler BE1-CDS220, Instruction Manual

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4-18 Protection and Control BE1-CDS220
The characteristic of the Restrained Element function is the same as that for the phase differential shown
in Figure 4-10 with the exception that maximum restraint is always used. This comparator has a slope
setting and a minimum pickup setting. The slope setting is the ratio of operate current to restraint current.
The minimum pickup setting determines the minimum sensitivity. If the ratio of operate current to restraint
current is above the slope setting and the operate current is above the minimum pickup setting, the
87NDPU (87 neutral element picked up) logic output is set.
A timer provides security from misoperation on false residual caused by CT saturation during a through
fault. If the transient monitor function from the 87 phase differential function detects CT saturation, the
87NDT trip logic output is routed through the timer. The timer should be set longer than the normal
clearing time for a fault just outside the zone of protection to allow it to ride-through until the external fault
is cleared.
If the target is enabled for this function, the target reporting function will record an 87ND target when the
87NDT logic output is TRUE and the fault recording function trip logic expression is TRUE. See Section 6,
Reporting and Alarm Functions, Fault Reporting, for more details on the target reporting function.
BESTlogic Settings for Neutral Differential
BESTlogic settings are made from the BESTlogic Function Element screen in BESTCOMS. Figure 4-16
illustrates the BESTCOMS screen used to select BESTlogic settings for the 87ND function. To open the
BESTlogic Function Element screen, select Percentage Differential from the Screens pull-down menu.
Then select the 87ND tab. Select the BESTlogic button for 87ND. Alternately, these settings can be made
using the SL-87ND ASCII command.
Figure 4-16. BESTlogic Function Element Screen, Neutral (87ND)
At the top center of the BESTlogic Function Element screen is a pull-down menu labeled Logic. This
menu allows viewing of the BESTlogic settings for each preprogrammed logic scheme. A custom logic
scheme must be created and selected in the Logic pull-down menu at the top of the screen before
BESTlogic settings can be changed. See Section 7, BESTlogic Programmable Logic.
Enable the 87 function by selecting its mode of operation from the Mode pull-down menu. To connect the
element's input, select the button for the input in the BESTlogic Function Element screen. The BESTlogic
Expression Builder screen will open. Select the expression type to be used. Then, select the BESTlogic
variable, or series of variables to be connected to the input. Select Save when finished to return to the
BESTlogic Function Element screen. For more details on the BESTlogic Expression Builder, see Section
7, BESTlogic Programmable Logic. Select Done when the settings have been completely edited.