for setting
EF current Str Val
is 0.5%*400 A = 2 A. The lower setting
EF
current Str Val
is used, the higher sensitivity in terms of fault resistance
can be obtained. Sensitivity in terms of fault resistance depends also
on the network parameters (nominal voltage, damping and detuning) as
described by
Equation 120
.
When
Operating curve type
= “Inverse time EN50522” is selected, then the
protection operate time as a function of estimated effective earth-fault current
(taking into account the effect of settings
Reduction factor
and
Enable harmonics
)
is according to equation below:
(Equation 121)
In IFPTOC function, the preferred presentation of operation timer characteristics
is by plotting the protection operate time as a function of permissible/estimated
earth-fault current as illustrated in figures from
Figure 343
,
Figure 344
and
Figure
345
.
Consider next three examples with
Operating curve type
= “Inverse time EN50522”:
Table 628: Comparison of operation times given in EN50522 with IFPTOC. The
theoretical operate time of IFPTOC has been calculated assuming CB delay Comp =
0 s
EN50522, U
tp
[V] EN50522, t
f
[sec] IFPTOC, t
f
Theoretical [sec]
716 0.05 0.04
654 0.1 0.12
537 0.2 0.20
220 0.5 0.50
117 1 1.00
96 2 1.59
86 5 5.02
85 10 8.48
Example 2a. Inverse time operation of IFPTOC, when
Operation principle
= “EF-
current based” and
Operating curve type
= “Inverse time EN50522” is illustrated
in
Figure 343
. Start value for operation is set to be 0.02*In (2 A if primary 100
A). IFPTOC is set to have minimum operate time 100 ms and maximum operate
time of 5000 ms. Setting
UTp multiplier
is 1.0 and setting
Maximum earthing Ris
is
10 ohms. Reduction factor = 1.0. For illustrating the operating speed requirement
of protection, limits of touch voltage durations defined in standard EN50522
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.
1MRS759142 F
Protection functions
REX640
Technical Manual
603
To Next Page
Loading...
