-Uo (Polarizing quantity)
Forward area
Io (Operating quantity)
RCA = -90˚
Maximum torque line
Backward area
Minimum
operate current
Forward area
Backward area
Figure 189: Definition of relay characteristic angle, RCA = -90° in an isolated network
Characteristic angle should be set to a positive value if the operating
signal lags the polarizing signal and to a negative value if the operating
signal leads the polarizing signal.
Type of network
Recommended characteristic angle
Compensated network
0°
Unearthed network
-90°
In unearthed 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 operate current setting and the
magnitude of the polarizing quantity is compared to
Min operate 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:
1MRS758755 C
Protection functions
REC615 & RER615
Technical Manual
379
