67 Directional Overcurrent/Earth Fault
Overview of Functions
Directional overcurrent and earth fault protection is used to provide discriminative graded protection where
the fault current can flow in either direction.
Structure of the Function
The directional overcurrent protection function has group dependent settings. These settings can be different
in each settings group – group numbers (Gn) 1 to 4.
The function monitors the primary system current direction using the 3 phase CT inputs e.g. CT1/2/3 and 3
phase VT inputs e.g. VT1/2/3.
The function elements determine the direction of current flow by measuring the phase angle of the current,
operate quantity, against the appropriate voltage, reference quantity.
If a protection element is set as non-directional then it will operate independently of the output of the direc-
tional detector. However, if a protection element is programmed for forward directional mode then operation
will occur only for a fault lying within the forward operate zone. Conversely, if a protection element is
programmed for reverse directional mode then operation will occur only for a fault lying within the reverse
operate zone.
Typically, to achieve consistent settings, the forward direction refers to current flow from the busbar or
towards the protected zone. The reverse current direction refers to power flowing into the busbar.
The function has 4 function element types:
•
Directional control of overcurrent elements (67)
•
Directional control of measured earth fault elements (67G)
•
Directional control of sensitive earth fault elements (67GS)
•
Directional control of calculated earth fault elements (67N)
5.25
5.25.1
5.25.2
Protection and Automation Functions
5.25 67 Directional Overcurrent/Earth Fault
324 Reyrolle 7SR5, Overcurrent Protection Device, Device Manual
C53000-G7040-C014-1, Edition 11.2019
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