89 with setting
Maximum earthing Ris
in primary ohms i.e. the maximum earthing
resistance encountered in protected feeder.
Group Highest allowed EPR values [V] converted into corresponding
permissible fault current, I
Fp
[A],when earth fault is automatically
disconnected within time t [sec]
a (750 V/
Maximum earthing Ris
)/√t
b (2000 V/
Maximum earthing Ris
)/√t
c (3000 V/
Maximum earthing Ris
)/√t
d (500 V/
Maximum earthing Ris
)/√t
e1 (750 V/
Maximum earthing Ris
)/√t
e2 (1000 V/
Maximum earthing Ris
)/√t
It is important to note, that:
1. Minimum effective earth-fault current magnitude (considering the effect of
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.
2. 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.
3. 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 IEEE80” is selected.
Setting
Maximum earthing Ris
is needed to scale the touch voltage
and earth potential rise requirements defined in standard IEEE80 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
earthing and touch voltages.
When
Operating curve type
= “Inverse time IEEE80” is selected, then
setting
UTp multiplier
is not effective.
Consider next the following example with
Operating curve type
= “Inverse time
IEEE80”:
Example 3. Inverse time operation of IFPTOC, when
Operation principle
= “EF-
current based” and
Operating curve type
= “Inverse time IEEE80” is illustrated in
Figure 347
. Start value for operation is set to be 0.02*In (2 A). IFPTOC is set to have
minimum operate time 100 ms and maximum operate time of 5000 ms. Setting
IEEE
multiplier
is 500 and setting
Maximum earthing Ris
is 10 ohms.
Reduction factor
=
1.0. For illustrating the operating speed requirement of protection, limits of earth
potential rise durations defined in Finnish national Electrical Safety Regulations 89
scaled the into corresponding earth-fault current requirements using the maximum
earthing resistance R
Emax
(setting
Maximum earthing Ris
) encountered in protected
feeder are shown for reference.
Protection functions
1MRS759142 F
610 REX640
Technical Manual
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