can be obtained. Sensitivity in terms of fault resistance depends also
on the network parameters (nominal voltage, damping and detuning) as
described by equation below:
(Equation 120)
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],
I
F
is setting
EF current Str Val in primary amperes.
Consider next the following example:
Example 1. Definite time operation of IFPTOC, when Operation principle = “EF
current based”,
Operating curve type = “Definite time” is illustrated in
.
In the example, setting
EF current Str Val = 0.04*In (4 A with primary 100 A) and
DT stage Op time = 400 ms. Reduction factor =1.0. IFPTOC starts when estimated
fault current exceeds 4 A and operates after 400 ms, if start conditions are met. For
illustrating possible operating speed requirements of protection, limits of touch
voltage and earth potential rise durations defined in standard EN50522 scaled
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
599