[dw_7SR5_function67SettingExample9, 1, en_US]
Figure 5-41
Earth Fault Current In Isolated Network
Some customers prefer to use only the sine (reactive) component of the residual current which can be easily
achieved by setting
Ires Select
to
Ires Real
to select the operating current to I
RES
Cos(θ - ∅) and setting
the characteristic angle ∅ to +90°.
Minimum Polarizing Voltage
The correct residual voltage direction must be measured to allow a forward/reverse decision to be made.
Minimum polarizing voltage setting can be used to prevent tripping when fault conditions are such that signif-
icant residual voltage is not generated and the directional decision would be unreliable. The setting must
allow for error in voltage measurement due to VT inaccuracy and connection. It can be used to improve
stability under non-fault conditions during unbalanced load, when earth fault elements with very sensitive
current settings are applied. This is ensured by selecting a setting which is near to the minimum expected
residual voltage during fault conditions.
High impedance earthing methods, including compensated and isolated systems, will result in high levels of
residual voltage, up to 3 times normal phase to neutral voltage, during earth faults. The minimum polarizing
voltage can therefore be increased to allow very low residual current settings to be applied without risk of
operation during unbalanced load conditions.
Settings Menu
Functions > Protection > 67 > Gn 67
Parameter
Range
Settings
Default Gn1
Gn2
Gn3
Gn4
Char Angle
-95° to +95°, Δ 1°
45°
Minimum Voltage
1 V to 20 V, Δ 0.5 V
1 V
2-out-of-3 Logic
Enabled
Disabled
Disabled
5.19.5
Protection and Automation Functions
5.19 67 Directional Overcurrent/Earth Fault
286
Reyrolle 7SR5, Transformer Protection Device, Device Manual
C53000-G7040-C015-1, Edition 11.2019
