ABB RELION REX640 Technical Manual page 594

Protection functions
be considered from electrical safety perspective. Setting
means that 100% of earth-fault current flows back through "remote" earth and thus
100% of earth-fault current will introduce rise of earth potential.
Figure 340: Simplified illustration and explanation of setting Reduction factor. Only
fault current which flows through earth (I
(earth potential rise, EPR, also called as ground potential rise, GPR).
Magnitude of the estimated effective earth-fault current is given in Recorded data:
Fault current (fundamental frequency magnitude)
•
Fault current rms (rms-value).
•
In Monitored data the magnitude of estimated effective earth-fault current is given
in as:
FLT_CURRENT (fundamental frequency magnitude)
•
FLT_CURR_RMS (rms-value).
•
Validity check
Validity of earth-fault current estimate is defined with settings
mode and EF validity Min Curr . EF validity Op mode has three options "Resistive",
"Resistive, Reactive" and "No Validity".
The validity of earth-fault current estimate is based on evaluating the polarity of
the measured admittance (Y
the transient phase of fault). Admittance is calculated utilizing cumulative phasor
summing technique (CPS). The measured "transient admittance" is converted into
equivalent current value by multiplying it with nominal phase-to-earth voltage value
594
Ena RF Compensation = "Enable", actual earth-fault
In case of setting
current value affected by fault resistance is then not available in
Monitored/Recorded data, but the monitored/recorded current value is
fault resistance compensated.
Validity of earth-fault current estimate is based on evaluating the polarity
of the measured admittance (Y
of I and U should be therefore as good as possible. Especially the
o o
measurement of I should be based on accurate Core Balance CT (CBCT).
o
= I
o o
) will introduce rise of earth potential
E
= I /U ) at fault ignation. The accuracy
o o o
/U ) during the fault ignition moment (during
o
1MRS759142 F
Reduction factor = 1.00
EF validity Op
REX640
Technical Manual