Enhancing Relay Performance - GE B30 Instruction Manual

ENHANCING RELAY PERFORMANCE

Setting
HIGH SET
8.6 Enhancing relay performance
8.6.1 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.
However, 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 can 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
breakpoint (
HIGH BPNT
The lower breakpoint (
table). The higher slope (
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 can be extended for buses that do not require the dynamic bus replica mechanism. This can 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.
8
8-12
Value Comments
5.54 The maximum spurious differential current is 2.77 pu. Due to limited accuracy of analysis and
the effect of DC saturation a security factor of 2 has been adopted. The highest internal fault
current is 14kA, or 11.67 pu giving a good chance to clear a number of faults by the unbiased
differential operation.
) could be increased to 22.88 pu (fourth column of the Limits of Linear Operations of the CTs table).
) could be increased to 4.58 pu (fifth column of the Limits of Linear Operations of the CTs
LOW BPNT
) could be decreased as no AC saturation is possible for the South bus CTs (see the
HIGH SLOPE
CHAPTER 8: APPLICATION OF SETTINGS
B30 BUS DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL