118 9424200994 Rev N
Pickup Calculations
The differential value is calculated as shown in Equation 17 and Equation 18 and displayed in
BESTCOMSPlus metering and on the front-panel display.
If CT Flip Setting = Yes, then Iop = IG
Phase CT Ratio
Ground CT Ratio
× 3I0
Equation 17. Iop Calculation when CT Flip Setting = Yes
If CT Flip Setting = No, then Iop = IG
+
Phase CT Ratio
Ground CT Ratio
× 3I0
Equation 18. Iop Calculation when CT Flip Setting = No
Pickup and Trip
The Pickup output occurs first, followed by the Trip output.
Pickup
The Pickup output becomes true when the Minimum Iop setting is exceeded. In BESTlogicPlus, the
Pickup output can be connected to other logic elements to annunciate the condition, control other
elements in logic, and start the fault recorder (logic element FAULTTRIG).
Assertion of the Pickup output initiates a timer that begins timing to a trip. The duration of the timer is
established by the Time Delay setting. A Time Delay setting of zero (0) makes the 87N element
instantaneous with no intentional time delay.
If the pickup condition subsides before the element delay expires, the timer and Pickup output are reset,
no corrective action is taken, and the element is rearmed for any other fault occurrences.
Trip
The Trip output becomes true if a fault condition persists for the duration of the element Time Delay
setting. In BESTlogicPlus, the Trip output can be connected to other logic elements and to a physical
relay output to annunciate the condition and to initiate corrective action. If a target is enabled for the
element, the BE1-11g will record a target when the Trip output becomes true. See the Fault Reporting
chapter for more information about target reporting.
Current-Polarized Directional Scheme
Figure 73 shows the current-polarized directional scheme. The CT Flip setting is “YES” for this scheme.
With the assumed positive current direction, 3I0 and IG are in phase for an internal fault and are out of
phase for an external fault.
Element Blocking
The Block input provides logic-supervision control of the element. When true, the Block input disables the
element by forcing the Trip and Pickup outputs to logic 0 and resetting the element timer. Connect the
element Block input to the desired logic in BESTlogicPlus. When the element is initially selected from the
Elements view, the default condition of the Block input is a logic 0.
Neutral Current Differential (87N) Protection BE1-11g
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