ABB RED615 Technical Manual page 432

Section 4
Protection functions
426
To calculate the directional differential current ID_COSPHI, the fundamental
frequency amplitude of both the residual and neutral currents has to be above 4
percent of In. If neither or only one condition is fulfilled at a time, the cosφ term is
forced to 1. After the conditions are fulfilled, both currents must stay above 2
percent of In to allow the continuous calculation of the cosφ term.
Second harmonic blocking
This module compares the ratio of the current second harmonic (I
the set value Start value 2.H. If the ratio (I
the BLK2H output is activated.
The blocking also prevents unwanted operation at the recovery and sympathetic
magnetizing inrushes. At the recovery inrush, the magnetizing current of the
transformer to be protected increases momentarily when the voltage returns to
normal after the clearance of a fault outside the protected area. The sympathetic
inrush is caused by the energization of a transformer running in parallel with the
protected transformer connected to the network.
The second harmonic blocking is disabled when Restraint mode is set to "None"
and enabled when set to "Harmonic2".
Timer
Once activated, the timer activates the START output. The time characteristic is
according to DT. When the operation timer has reached the value set by Minimum
operate time, the OPERATE output is activated. If the fault disappears before the
module operates, the reset timer is activated. If the reset timer reaches the value set
by Reset delay time, the reset timer resets and the START output is deactivated.
The timer calculates the start duration value START_DUR which indicates the
percentage ratio of the start situation and the set operate time. The value is
available through the Monitored data view.
Blocking logic
There are three operation modes in the blocking functionality. The operation modes
are controlled by the BLOCK input and the global setting "Configuration/System/
Blocking mode" which selects the blocking mode. The BLOCK input can be
controlled by a binary input, a horizontal communication input or an internal signal
of the IED program. The influence of the BLOCK signal activation is preselected
with the global setting Blocking mode.
The Blocking mode setting has three blocking methods. In the "Freeze timers"
mode, the operate timer is frozen to the prevailing value. In the "Block all" mode,
the whole function is blocked and the timers are reset. In the "Block OPERATE
output" mode, the function operates normally but the OPERATE output is not
activated.
The activation of the output of the second harmonic blocking signal BLK2H
deactivates the OPERATE output.
0
_2H / I ) value exceeds the set value,
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_2H) and I to
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615 series
Technical Manual