ABB RELION REX640 Technical Manual page 593

1MRS759142 F
and has thus value of 1. 0pu (xU
middle column is shown residual voltage, phase currents and fault current estimate
during a higher ohmic earth fault (R
fault U
magnitude of fault current is reduced proportionally to residual voltage. In the
right-hand column the effect of fault resistance is compensated by scaling the fault
current estimate by dividing it with the per unit value of residual voltage. With fault
resistance compensation, the operation speed of IFPTOC can be accelerated during
high(er) ohmic earth faults.
Figure 339: Illustration of fault resistance compensation functionality in IFPTOC. Left-hand column:
galvanic earth fault (R
setting Ena R Compensation = "Disable". Right-hand column: a higher ohmic earth fault (R
F
ohm) with setting Ena R
Note that it is the "effective" earth-fault current estimate which determines
operation of IFPTOC. "Effective" earth-fault current includes the effect of user
setting
Effective earth-fault current estimate,
Setting
scale down the estimated earth-fault current magnitude. Setting
allows e.g. consideration that not all the earth-fault current (I
through "remote" earth. See illustration in Figure 7. A portion of the earth-fault
current (I
Only current which flows through earth (I
(earth potential rise, EPR, also called as ground potential rise GPR), which must
REX640
Technical Manual
reduces and thus also the magnitude of fault current is reduced. But the
o
= 0 ohm). Middle column: a higher ohmic earth fault (R
F
Compensation = "Enable".
F
Reduction factor :
Reduction factor is a user defined reduction factor, which can be used to
) may have alternative return paths, e.g. through cable sheaths/screens.
SCR
, U = Nominal phase-to-earth voltage). In the
n_PE n_PE
= 3000 ohm). During a higher ohmic earth
F
:
) will introduce rise of earth potential
E
Protection functions
= 3000 ohm) with
F
= 3000
F
(Equation 115)
Reduction factor
) will flow back
F
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