in terms of fault resistance depends also on the network parameters
(nominal voltage, damping and detuning) as described by
Equation 126
.
(Equation 126)
where U
PE
is the nominal phase-to-earth voltage [V], I
d
is the total system damping
[A], I
v
is the detuning [A], U
F
is setting
Touch Vol Str Val
in primary volts and R
E
is
setting
Maximum earthing Ris
in primary ohms.
When
Operating curve type
= “Inverse time EN50522” is selected, then the
protection operate time as a function of estimated touch voltage
(taking
account the effect of
Reduction factor
) is according to
Equation 127
:
(Equation 127)
In IFPTOC function, the preferred presentation of operation timer characteristics
is by plotting the protection operate time as a function of permissible/estimated
touch voltage as illustrated in
Figure 350
,
Figure 351
and
Figure 352
.
Consider next three examples with
Operating curve type
= “Inverse time EN50522”:
Example 5a. Inverse time operation of IFPTOC, when
Operation principle
= “Touch
voltage based”,
Operating curve type
= “Inverse time EN50522” and setting
UTp
multiplier
= 1.0 is illustrated in
Figure 350
. Start value for operation is set to be 20 V
(setting
Touch Vol Str Val
). IFPTOC is set to have minimum operate time 100 ms and
maximum operate time of 5000 ms (settings
IDMT stage Min Op Tm, IDMT stage
Max Op Tm
). Maximum earthing resistance value encountered in the protected
feeder is set to be 10 ohms (setting
Maximum earthing Ris
) and Reduction factor
= 1. For illustrating the operating speed requirement of protection, limits of touch
voltage durations defined in standard EN50522 are shown for reference.
Protection functions
1MRS759142 F
616 REX640
Technical Manual
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