4.1.2 VOLTAGE RESTRAINED OVERCURRENT PROTECTION
In Voltage Restrained Operation (VRO) mode the effective operating current of the protection element is
continuously v
ariable as the applied v
oltage varies between two voltage thresholds. This protection mode is
considered to be better suited to applications where the generator is connected to the system via a generator
transformer.
With indirect connection of the generator, a solid phase-phase fault on the local busbar will result in only a partial
phase-phase voltage collapse at the generator terminals.
The voltage-restrained current setting is related to measured voltage as follows:
● If V is greater than V<1, the current setting (Ιs) = Ι>
● If V is greater than V<2 but less than V<1, the current setting (Ιs) =
KI I KI
V V
V V
> + > −
( )
− <
< − <
2
1 2
● If V is less than V<2, the current setting (
Ιs) = K.Ι>
where:
● Ι> = Over current stage setting
● Ιs = Current setting at voltage V
● V = Voltage applied to relay element
● V<1 = V Dep OC V<1 Set
● V<2 = V Dep OC V<2 Set
E00643
Measured voltage
Current
setting
V Dep OC V<1 Set
V Dep OC V<2 Set
V Dep OC k Set
V Dep OC I> Set
Figure 39: Modification of current pickup level for voltage restrained overcurrent protection
Chapter 6 - Current Protection Functions P14x
106 P14xEd1-TM-EN-1
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