This variant has definite time delay.
Directional functions
For all the directional functions there are directional start signals STFW: fault in the
forward direction, and STRV: fault in the reverse direction. Even if the directional
function is set to operate for faults in the forward direction, a fault in the reverse
direction will give the start signal STRV. Also if the directional function is set to
operate for faults in the reverse direction, a fault in the forward direction will give the
start signal STFW.
Non-directional earth fault current protection
This function will measure the residual current without checking the phase angle. The
function will be used to detect cross-country faults. This function can serve as
alternative or backup to distance protection with phase preference logic. To assure
selectivity the distance protection can block the non-directional earth fault current
function via the input BLKNDN.
The non-directional function is using the calculated residual current, derived as sum
of the phase currents. This will give a better ability to detect cross-country faults with
high residual current, also when dedicated core balance CT for the sensitive earth fault
protection will saturate.
This variant has the possibility of choice between definite time delay and inverse time
delay (
TimeChar
parameter). The inverse time delay shall be according to IEC
60255-3.
For trip, the residual current 3I
0
shall be larger than the set level (
INNonDir>
).
Trip from this function can be blocked from the binary input BLKNDN.
When the function picks up, binary output signal STNDIN is activated. If the output
signal STNDIN remains active for the set delay
tINNonDir
or after the inverse time
delay the binary output signals TRIP and TRNDIN get activated.
Residual overvoltage release and protection
All the directional functions shall be released when the residual voltage gets higher
than a set level
UNRel>
.
In addition, there is also a separate non-directional residual over voltage protection,
with its own definite time delay
tUN
and set level
UN>
.
For trip, the residual voltage 3U
0
shall be larger than the set level (
UN>
).
Trip from this function can be blocked from the binary input BLKUN.
When the function picks up, binary output signal STUN is activated. If the output
signal STUN is active for the set delay
tUNNonDir
, the binary output signals TRIP
and TRUN get activated. A simplified logical diagram of the total function is shown
in Figure
.
Section 8
1MRK502052-UEN B
Current protection
398
Technical manual
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