ABB RELION REX640 - Page 615

1. Settings Reduction factor and Maximum earthing Ris are used to scale the
estimated effective earth-fault current value into corresponding touch voltage
or earth-potential rise estimate.
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 632: Permissible touch voltages U
Tp
and earth potential rise U
E
values
as a function of the fault duration t
f
according to standard EN50522 with U
Tp
multiplier as a parameter
Fault duration t
f
[sec.]
Permissible touch
voltage, U
Tp
, U
Tp
multiplier = 1.0 [V]
Permissible earth
potential rise, U
E
,
U
Tp
multiplier = 2.0
[V]
Permissible earth
potential rise, U
E
,
U
Tp
multiplier = 4.0
[V]
0.05 716 1432 2864
0.10 654 1308 2616
0.20 537 1074 2148
0.50 220 440 880
1.00 117 234 468
2.00 96 192 384
5.00 86 172 344
10.00 85 170 340
3. Minimum touch voltage or earth potential rise magnitude (considering the
effect of Reduction factor ), which must be exceeded for the function to start, is
defined with setting Touch Vol Str Val . It is important to set setting Touch Vol
Str Val 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 = “Touch
voltage based” and Operating curve type = “Inverse time EN50522” is
selected. Setting Maximum earthing Ris is needed to scale the estimated
effective earth-fault current value to corresponding touch voltage or
earth potential rise value.
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.
Minimum practical value for setting Touch Vol Str Val is 0.5% of
CT primary current multiplied by setting Maximum earthing Ris . For
example, in case CT primary current is 200 A, and Maximum earthing
Ris = 10 ohm, then minimum practical value for setting Touch Vol Str
Val is 0.5%*200 A*10 ohm = 10 V. For CT with 400 A primary current,
then minimum practical value for setting Touch Vol Str Val is 0.5%*400
A*10 ohm = 20 V. The lower setting Touch Vol Str Val is used, the
higher sensitivity in terms of fault resistance can be obtained. Sensitivity
1MRS759142 F Protection functions
REX640
Technical Manual
615