ABB 615 series Technical Manual page 420

Section 4
Protection functions
414
In ungrounded networks, when the characteristic angle is -90°, the
measured residual power is reactive (varmetric power).
The fault direction is also indicated FAULT_DIR (available in the monitored data view),
which indicates 0 if a fault is not detected, 1 for faults in the forward direction and 2 for
faults in the backward direction.
The direction of the fault is detected only when the correct angle calculation can be made.
If the magnitude of the operating quantity or polarizing quantity is not high enough, the
direction calculation is not reliable. Hence, the magnitude of the operating quantity is
compared to the Min trip current setting and the magnitude of the polarizing quantity is
compared to Min trip voltage, and if both the operating quantity and polarizing quantity
are higher than their respective limit, a valid angle is calculated and the residual power
calculation module is enabled.
The Correction angle setting can be used to improve the selectivity when there are
inaccuracies due to the measurement transformer. The setting decreases the operation
sector. The Correction angle setting should be done carefully as the phase angle error of
the measurement transformer varies with the connected burden as well as with the
magnitude of the actual primary current that is being measured. An example of how
Correction angle alters the operating region is as shown:
Zero torque line
Correction angle
operate current
Backward
GUID-80D74A1C-3D75-4548-ABA5-318F2E65F91F V1 EN
Figure 200: Definition of correction angle
Maximum torque line
forward direction (RCA = 0˚)
-VG (Polarizing quantity)
IG (Operating quantity)
Forward
area
Minimum
Backward
area
1MAC059074-MB A
Forward
area
Correction angle
area
615 series ANSI
Technical Manual