GE B90 UR Series, Instruction Manual

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10-10 B90 Low Impedance Bus Differential System GE Multilin
10.6 ENHANCING RELAY PERFORMANCE 10 APPLICATION OF SETTINGS
10
10.6ENHANCING RELAY PERFORMANCE 10.6.1 USING SETTING GROUPS
In the example of the South bus, CT-2 is the weakest (most prone to saturation) CT dictating values of some settings. How-
ever, CT-2 may not be a part of the South bus protection zone if the S-2 switch is opened. As the position of the switch must
be provided for the dynamic bus replica, the status of the switch may be re-used to control the setting groups and apply
more sensitive settings if the weakest CT is not part of the bus zone at a given time. For example, if the S-2 switch is
opened while the S-6 switch is closed, the CT-4 becomes the weakest CT connected to the South bus. The higher break-
point (
HIGH BPNT
) could be increased to 22.88 pu (fourth column of the Limits of Linear Operations of the CTs table). The
lower breakpoint (
LOW BPNT
) could be increased to 4.58 pu (fifth column of the Limits of Linear Operations of the CTs table).
The higher slope (
HIGH SLOPE
) could be decreased as no AC saturation is possible for the South bus CTs (see the external
fault calculation tables for each circuit).
The concept could be implemented by using:
• FlexLogic to process the status signals in order to identify the weakest CT.
• Setting Groups to switch dynamically from one setting group to another (adaptive settings).
This approach may be extended even further for buses that do not require the dynamic bus replica mechanism. This could
include approximation of the total bus fault current using positions of all switches and breakers and optimizing the settings
depending on the amount of stress imposed on the CTs in any particular bus configuration.