1. Setting
Maximum earthing Ris
is used to scale the touch voltage and earth
potential rise requirements defined in standard EN 50522 into corresponding
earth-fault current requirements.
2. Setting
UTp multiplier
enables operation based on permissible earth potential
rise U
E
, by scaling of the permissible time-touch voltage characteristics given in
standard EN 50522 with Setting
UTp multiplier
, see table below.
Table 627: Permissible touch voltages U
Tp
and earth potential rise U
E
values
given in standard EN50522 converted into equivalent permissible earth-fault
current I
Fp
values as a function of the fault duration t
f
. Conversion is made
with parameter R
Emax
, which is the setting
Maximum earthing Ris
in primary
ohms i.e. the maximum earthing resistance encountered in protected feeder.
Fault duration t
f
[sec.]
Permissible touch
voltage, U
Tp
converted into
corresponding
permissible fault
current, I
Fp
, U
Tp
multiplier = 1.0 [A]
Permissible earth
potential rise,
U
E
converted
into corresponding
permissible fault
current, I
Fp
, U
Tp
multiplier = 2.0 [A]
Permissible earth
potential rise,
U
E
converted
into corresponding
permissible fault
current, I
Fp
, U
Tp
multiplier = 4.0 [A]
0.05 716 V/R
Emax
1432 V/R
Emax
2864 V/R
Emax
0.10 654 V/R
Emax
1308 V/R
Emax
2616 V/R
Emax
0.20 537 V/R
Emax
1074 V/R
Emax
2148 V/R
Emax
0.50 220 V/R
Emax
440 V/R
Emax
880 V/R
Emax
1.00 117 V/R
Emax
234 V/R
Emax
468 V/R
Emax
2.00 96 V/R
Emax
192 V/R
Emax
384 V/R
Emax
5.00 86 V/R
Emax
172 V R
Emax
344 V/R
Emax
10.00 85 V/R
Emax
170 V/R
Emax
340 V/R
Emax
3. Minimum effective earth-fault current magnitude (considering the effect of
setting
Reduction factor
), which must be exceeded for the function to start,
is defined with setting
EF current Str Val
. It is important to set this value
according to required protection sensitivity.
4. With
IDMT stage Min Op Tm
setting user can define minimum allowed operate
time for IFPTOC i.e. this is the minimum allowed operate time of IFPTOC.
5. With
IDMT stage Max Op Tm
setting user can define maximum allowed operate
time for IFPTOC i.e. this is the maximum allowed operate time of IFPTOC
although IDMT timer would define slower operate time.
Parameter defining maximum earthing resistance, setting
Maximum
earthing Ris
must be always set in case
Operation principle
= “EF current
based” and
Operating curve type
= “Inverse time EN50522” is selected.
Setting
Maximum earthing Ris
is needed to scale the touch voltage and
earth potential rise requirements defined in standard EN 50522 into
corresponding earth-fault current requirements.
Setting
Reduction factor
considers the fact that only part of the earth-
fault current (I
F
) will flow back through “remote” earth and introduces
earth potential rise and touch voltages.
Minimum practical value for setting
EF current Str Val
is 0.5% from CT
primary current. For example, in case CT primary current is 200A, then
minimum practical value for setting
EF current Str Val
is 0.5%*200 A =
1 A. For CT with 400 A primary current, then minimum practical value
Protection functions 1MRS759142 F
602 REX640
Technical Manual
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