Siemens siprotec SJ62 User Manual page 190

Voltage Symmetry
Current and Voltage
Phase Sequence
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015
During normal system operation (i.e. the absence of a short-circuit fault), symmetry
among the input voltages is expected. Because the phase-to-phase voltages are in-
sensitive to ground connections, the phase-to-phase voltages are used for the sym-
metry monitoring. If the device is connected to the phase-to-ground voltages, then the
phase-to-phase voltages are calculated accordingly, whereas if the device is connect-
ed to phase-to-phase voltages and the displacement voltage, then the third phase-to-
phase voltage is calculated accordingly. Whereas if the device is connected to phase-
to-phase voltages and the displacement voltage V
voltage is calculated accordingly. From the phase-to-phase voltages, the protection
generates the rectified average values and checks the symmetry of their absolute
values. The smallest phase voltage is compared with the largest phase voltage. Asym-
metry is recognized if:
| < BAL. FACTOR V as long as | V
| V | / | V
min max
V is the highest of the three voltages and V
max
BAL. FACTOR V is the measure for the asymmetry of the conductor voltages; the limit
value BALANCE V-LIMIT is the lower limit of the operating range of this monitoring
(see Figure 2-60). Both parameters can be set. The dropout ratio is about 97%.
This malfunction is reported as „Fail V balance".
Figure 2-60 Voltage symmetry monitoring
To detect swapped phase connections in the voltage and current input circuits, the
phase sequence of the phase-to-phase measured voltages and the phase currents
are checked by monitoring the sequence of same polarity zero transitions of the volt-
ages.
Direction measurement with normal voltages, path selection for fault location, and
negative sequence detection all assume a phase sequence of "abc". Phase rotation
of measurement quantities is checked by verifying the phase sequences.
Voltages: V before V
A B
Currents: I before I before I
A B
before V and
C
.
C
2.11 Monitoring Functions
, then the third phase-to-phase
0
| > BALANCE V-LIMIT. Where
max
the smallest. The symmetry factor
min
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