ABB RELION REX640 Technical Manual page 588

Protection functions
where t
module. Pre-fault time moment is at least
moment.
Revert time setting should be set high enough (default value is 300 ms), because
during a high(er) ohmic fault the increase speed (gradient) of the magnitude of
U may be slow, refer to example in
o
ms. Earth fault is detected by GFC module slightly after that, at time instant t
marked with red dot, when magnitude of U
an indication of detected earth-fault output EF_IND is activated.
Figure 337: Illustration of operation of General Fault Criterion (GFC) module and the meaning of
setting Revert time
Fault current estimation and validity check
Operation of IFPTOC is based on estimating the magnitude of earth-fault current
flowing in the fault spot, or on touch voltage magnitude derived from the earth-
fault current estimate.
In compensated network, the magnitude of fundamental frequency earth-fault
current depends on the network damping (
resistance (
588
(1) equals the first time instant, when earth fault is detected by the GFC-
FLT
In case of secondary testing of IFPTOC function, the pre-fault time in the
test file must be longer than
300 ms, then pre-fault time in the test file must be longer than 600 ms.
Indication of detected earth fault is available in Recorded data:
indication .
R
) and can be written as:
F
Revert time before earth fault occurrence
Figure 337 , where earth-fault occurs at time 0
exceeds setting
o
2xRevert time . For example, if Revert time =
I I
), detuning (
d
1MRS759142 F
FLT
Voltage start value . As
EF
U
), voltage ( ) and fault
v PE
REX640
Technical Manual
(1)