Siemens SIPROTEC 4, User Manual

Page: 184 / 734

[stromsymmetrieueberwachung-020313-kn, 1, en_US]
Figure 2-71 Current symmetry monitoring
Voltage Symmetry
During normal system operation, balance among the voltages is expected. Since the phase-to-phase voltages
are insensitive to ground faults, the phase-to-phase voltages are used for balance 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 connected to phase-to-phase voltages and the displacement voltage V
0
, then the third
phase-to-phase voltage is calculated accordingly. From the phase-to-phase voltages, the device generates the
rectified average values and checks the balance of their absolute values. The smallest phase voltage is
compared with the largest phase voltage.
Asymmetry is recognized if
| V
min
| / | V
max
| <
BAL. FACTOR V
as long as | V
max
| >
BALANCE V-LIMIT
. Where V
max
is the highest of the
three voltages and V
min
the smallest. The symmetry factor
BAL. FACTOR V
(address 8103) represents the
allowable asymmetry of the conductor voltages while the limit value
BALANCE V-LIMIT
(address 8102) is
the lower limit of the operating range of this monitoring (see Figure 2-70). Both parameters can be set. The
dropout ratio is about 97%.
This fault is signalled after settable delay time with
Fail V balance
.
[spannungssymmetrieueberwachung-020313-kn, 1, en_US]
Figure 2-72 Voltage symmetry monitoring
Functions
2.12 Monitoring Functions
184 SIPROTEC 4, 7SJ62/64, Manual
C53000-G1140-C207-8, Edition 08.2016