mainly used in radial fed networks but can also be used in meshed networks. In meshed
networks, the settings must be based on network fault calculations.
To assure selectivity between different protections, in the radial network, there has to be a
minimum time difference Dt between the time delays of two protections. To determine the
shortest possible time difference, the operation time of protections, breaker opening time
and protection resetting time must be known. These time delays can vary significantly
between different protective equipment. The following time delays can be estimated:
Protection operate time: 15-60 ms
Protection resetting time: 15-60 ms
Breaker opening time: 20-120 ms
The different characteristics are described in the technical reference manual.
tx
: Definite time delay for step
x
. The definite time
tx
is added to the inverse time when inverse
time characteristic is selected. Note that the value set is the time between activation of the
start and the trip outputs.
INx>
: Operate residual current level for step
x
given in % of
IB
.
INx>Max
and
INx>Min
should only be changed if remote setting of operation current level,
INx>
, is used. The limits are used for decreasing the used range of the
INx>
setting. If
INx>
is
set outside
INx>Max
and
INx>Min
, the closest of the limits to
INx>
is used by the function. If
INx>Max
is smaller than
INx>Min
, the limits are swapped.
kx
: Time multiplier for the dependent (inverse) characteristic for step
x
.
IMinx
: Minimum operate current for step
x
in % of
IB
. Set
IMinx
below
INx>
for every step to
achieve ANSI reset characteristic according to standard. If
IMinx
is set above
INx>
for any step,
signal will reset at current equals to zero.
txMin
: Minimum operating time for inverse time characteristics. At high currents, the inverse
time characteristic might give a very short operation time. By setting this parameter, the
operation time of the step can never be shorter than the setting.
IMinx
Operate me
Current
tx
txMin
IEC10000058
IEC10000058 V2 EN-US
Figure 96: Minimum operate current and operate time for inverse time characteristics
In order to fully comply with the curves definition, the setting parameter
txMin
shall be set to
the value which is equal to the operate time of the selected IEC inverse curve for measured
Section 7 1MRK 505 370-UEN D
Current protection
164 Busbar protection REB670
Application manual
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