be considered from electrical safety perspective. Setting
Reduction factor
= 1.00
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
E
) will introduce rise of earth potential
(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).
In case of setting
Ena RF Compensation
= “Enable”, actual earth-fault
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 check
Validity of earth-fault current estimate is defined with settings
EF validity Op
mode
and
EF validity Min Curr
.
EF validity Op mode
has three options “Resistive”,
“Resistive, Reactive” and “No Validity”.
Validity of earth-fault current estimate is based on evaluating the polarity
of the measured admittance (Y
o
= I
o
/U
o
) at fault ignation. The accuracy
of I
o
and U
o
should be therefore as good as possible. Especially the
measurement of I
o
should be based on accurate Core Balance CT (CBCT).
The validity of earth-fault current estimate is based on evaluating the polarity of
the measured admittance (Y
o
= I
o
/U
o
) during the fault ignition moment (during
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
Protection functions
1MRS759142 F
594 REX640
Technical Manual
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