ABB RELION REX640 Technical Manual page 749

1MRS759142 C
REX640
Technical Manual
Irrespective of the operating quantity selected, directional calculation
is always determined using the negative-sequence current.
Directional calculation
Directional calculation compares the negative-sequence current phasor with the
negative-sequence voltage phasor, that is, the polarizing quantity. The directional
operation can be selected with the Directional mode setting. The options are "Non-
directional", "Forward" or "Reverse" operation. By setting the value of Allow Non Dir
to "True", the non-directional operation is allowed when the directional information
is invalid.
The Characteristic angle setting is used to turn the directional characteristics. The
value of Characteristic angle should be chosen so that all the faults in the operating
direction are seen in the operating zone and all the faults in the opposite direction are
seen in the non-operating zone. The value of Characteristic angle depends on the
network configuration.
Reliable directional calculation requires that both negative-sequence current and
negative-sequence voltage quantities exceed certain minimum amplitude levels. The
minimum amplitude level for the negative-sequence current is set with the Min
operate current setting. The minimum amplitude level for the polarizing quantity, that
is, the negative-sequence voltage, is set with the Min operate voltage setting. If the
amplitude level of the operating quantity or polarizing quantity is below the set level,
the direction information of the corresponding phase is set to "unknown". If the
negative-sequence voltage before the fault situation is below Min operate voltage, the
voltage direction cannot be determined.
The value for the Min operate voltage setting should be carefully
selected since the accuracy in low signal levels is strongly affected by
the measuring device accuracy.
Timer
Once activated, Timer activates the START output. The time characteristic is
according to DT. When the operation timer has reached the value set by Operate delay
time, the OPERATE output is activated if the operating signal persists.
In a drop-off situation, that is, if a fault suddenly disappears before the operate delay
is exceeded, the timer reset state is activated. If the reset timer reaches the value set by
Reset delay time, the operate 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 operation time. The value is available
in the Monitored data view.
Section 4
Protection functions
743