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Protection and Automation Functions
5.25 67 Directional Overcurrent/Earth Fault
The directional boundary can be used to discriminate between healthy and faulted feeders. The characteristic
angle is set to approximately 0° and the boundary at +90° used to detect the direction of the resistive compo-
nent within the residual current. Setting of the boundary is critical to discriminate between faulted and
unfaulted circuits. Setting 67GS Compensated Network to Enabled will set the directional boundaries to
± 87° around the characteristic angle, fine adjustment of the boundary may be necessary using the Charac-
teristic Angle setting.
[dw_7SR5_function67SettingExample7, 1, en_US]
Figure 5-46
The element measuring circuit can be subjected to only the cosine component of residual current i.e. to
directly measure the real (wattmetric) current due to losses. The current I
the measured phase angle between residual current and voltage and ∅ is the characteristic angle. This option
is selected by setting Ires Select to Ires Real. The characteristic angle should be set to 0°.
[dw_7SR5_function67SettingExample8, 1, en_US]
Figure 5-47
Application of a wattmetric power characteristic. The directional 50/51GS function element operation is
subject to an additional sensitive residual power element which operates only on the real (wattmetric) compo-
nent of residual power.
Isolated Networks
During earth faults on isolated distribution networks there is no fault current path to the source and subse-
quently no fault current will flow. However, the phase-neutral capacitive charging currents on the 3 phases
will become unbalanced and the healthy phase currents will create an unbalance current which flows to earth.
Unbalanced charging current for the whole connected network will return to the source through the fault
path. This will produce a current at the relay which can be used to detect the presence of the fault. On each
healthy circuit the unbalanced capacitive currents appear as a residual current which lags the residual voltage
by 90°. On the faulted circuit the charging current creates no residual but the return of the charging current
on the other circuits appears as a residual current which leads the residual voltage by 90°. The characteristic
angle should be set to +90°.
334
Adjustment Of Characteristic Angle
Cosine Component Of Current
Cos(θ - ∅) is calculated where θ is
RES
Reyrolle 7SR5, Overcurrent Protection Device, Device Manual
C53000-G7040-C014-1, Edition 11.2019
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