6.4.3.1
Settings for steps 1 and 4
n
means step 1 and 4.
x
means step 1, 2, 3 and 4.
DirModeSelx
: The directional mode of step
x
. Possible settings are
Disabled
/
Non-
directional
/
Forward
/
Reverse
.
Characteristn
: Selection of time characteristic for step
n
. Definite time delay and different
types of inverse time characteristics are available.
Inverse time characteristic enables fast fault clearance of high current faults at the same
time as selectivity to other inverse time phase overcurrent protections can be assured. This
is 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 have to be
a minimum time difference
D
t between the time delays of two protections. The minimum
time difference can be determined for different cases. 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 Manual (TM).
tx
: Definite time delay for step
x
. The definite time
tx
is added to the inverse time when
inverse time characteristic is selected.
Pickup"x"
: Operate residual current level for step
x
given in % of
IBase
.
TDn
: Time multiplier for inverse time delay for step
n
.
IMinn
: Minimum operate current for step
n
in % of
IBase
. Set
IMinn
below
Pickupx
for
every step to achieve ANSI reset characteristic according to standard. If
IMinn
is set above
Pickupx
for any step then signal will reset at current equals to zero.
tnMin
: 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
n
can never be shorter than the setting.
1MRK 511 286-UUS A
Section 6
Current protection
109
Application manual
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