Voltage Restrained Overcurrent Protection; Figure 39: Modification Of Current Pickup Level For Voltage Restrained Overcurrent Protection - GE MiCOM P40 Agile Technical Manual

Chapter 6 - Current Protection Functions
4.1.2

VOLTAGE RESTRAINED OVERCURRENT PROTECTION

In Voltage Restrained Operation (VRO) mode the effective operating current of the protection element is
continuously variable as the applied voltage 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
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
●
V Dep OC I> Set
V Dep OC k Set
E00643

Figure 39: Modification of current pickup level for voltage restrained overcurrent protection

106
− <
V V 2
)
< − <
V 1 V 2
Current
setting
V Dep OC V<2 Set
Measured voltage
V Dep OC V<1 Set
P14x
P14xEd1-TM-EN-1