ABB RELION REX640 Technical Manual page 592

Protection functions
When setting
Where
component (n = 1, 2, 3, 5, 7 and 9).
In case there is fault resistance included in the fault current path, the effect of fault
resistance is to decrease the value of earth-fault current as shown by
The downscaling of fault current magnitude can be estimated to be proportional
to the magnitude of per unit value of residual voltage, refer to
setting
resistance and then earth-fault current estimate becomes independent of actual
fault resistance value. This is done by dividing the fault current estimate with per
unit value of residual voltage (< 1pu):
Estimate for "fault resistance compensated" earth-fault current,
This means that with setting
fault resistance magnitude, the earth-fault current estimate matches the value that
would be valid if the fault would be a galvanic one (fault resistance equals zero).
Thanks to this feature the fault is always seen and treated as a galvanic fault
regardless of possible fault resistance. This functionality allows acceleration of
protection operation speed during high(er) ohmic earth fault when fault current
magnitude is low.
Figure 339
voltage, phase currents and fault current estimate during a galvanic earth fault (R
= 0 ohm). During a galvanic fault U
592
Enable harmonics = "Enable":
is the magnitude of the n
In case of frequency adaptive system measurements, only 2
harmonics are calculated.
Ena RF Compensation = "Enable", user can compensate the effect of fault
In case IFPTOC is used to detect high(er) ohmic earth faults, all start
Voltage start value , EF current Str Val or Touch Vol Str Val )
thresholds (
must be set according to sensitivity requirements. Otherwise
Compensation may not be effective during actual high(er) ohmic earth
fault.
Ena RF Compensation = "Enable", the effect of
In case of setting
harmonics are not taken into account i.e. fault current estimation is
based only on fundamental frequency component.
illustrates this concept: In the left-hand column is shown residual
th
harmonic negative-sequence current
Ena RF Compensation = "Enable", regardless of actual
equals system nominal phase-to-earth voltage
o
1MRS759142 F
(Equation 112)
(Equation 113)
nd rd th
, 3 and 5
Equation 106
.
Equation 106
. With
:
(Equation 114)
Ena RF
F
REX640
Technical Manual