4.3.4.3 Functionality
The high-impedance differential protection function 87A, 87B, 87C is a general
differential protection. It provides a phase-segregated short circuit protection for the
busbar. However, the function can also be used for providing generator, motor,
transformer and reactor protection.
The function starts and operates when the differential current exceeds the set limit. The
operate time characteristics are according to definite time (DT).
The function contains a blocking functionality. It is possible to block the function outputs,
timer or the whole function.
4.3.4.4 Operation principle
The function can be enabled and disabled with the Operation setting. The corresponding
parameter values are “Enable” and “Disable”.
The operation of 87A, 87B, 87C can be described with a module diagram. All the modules
in the diagram are explained in the next sections.
1MAC059074-MB A Section 4
Protection functions
615 series ANSI 551
Technical Manual
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