-Uo (Polarizing quantity)
Forward area
Io (Operating quantity)
RCA = -90˚
Maximum torque line
Backward area
Minimum
operate current
Forward area Backward area
Figure 241: 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:
1MRS757644 H
Protection functions
620 series
Technical Manual
471
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