ABB RELION REX640, Техническое руководство, Страница: 609 / 1960

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
[A]
0.05 702 V/R
Emax
0.10 496 V/R
Emax
0.20 351 V/R
Emax
0.50 222 V/R
Emax
1.00 157 V/R
Emax
2.00 111 V/R
Emax
5.00 70 V/R
Emax
10.00 50 V/R
Emax
In some countries, safety during an earth fault is defined in terms of highest
allowed earth potential rise (EPR) as a function of fault duration. As an example,
in Finnish national Electrical Safety Regulations 89 define highest allowed earth
potential rise as a function of fault duration as shown in table below.
Table 630: Highest allowed EPR values based on Electrical Safety
Group Highest allowed EPR [V], when earth fault is automatically
disconnected within time
t
[sec]
a 750V/√ t
b 2000V/√
t
c 3000V/√
t
d 500V/√
t
e1 750V/√ t
e2 1000V/√
t
The regulations of
Table 630
are implemented into IFPTOC. In case
Operation
principle = “EF current based”, setting Maximum earthing Ris is used to convert
the highest allowed earth potential risevalues into corresponding earth-fault current
values. Setting
IEEE multiplier is set to equal the highest allowed voltage value,
for example for group d,
IEEE multiplier = 500. Conversion of the highest allowed
earth potential rise value to the highest allowed earth-fault current magnitude with
setting
Maximum earthing Ris is shown in Table 631
.
Setting
Maximum earthing Ris in primary ohms is selected based on the maximum
earthing resistance encountered in protected feeder.
Table 631: Conversion of the highest allowed earth potential rise value into corre-
sponding earth-fault current values according to the Electrical Safety Regulations
1MRS759142 F Protection functions
REX640
Technical Manual
609