Siemens siprotec 7SA522, User Manual

Page: 367 / 628

Functions
6-219
7SA522 Manual
C53000-G1176-C119-2
Broken Conductor A broken conductor of the protected line or in the current transformer secondary circuit
can be detected, if the minimum current
%$/$1&(,/,0,7
flows via the feeder. If a
current symmetrie failure is detected and the minimum current is below the threshold
3ROH2SHQ&XUUHQW
(address 1130, refer to subsection 6.1.3), an interruption of this
conductor may be assumed. After approximately 5 s the device issues the alarm
“
)DLO&RQGXFWRU
”.
Voltage Symmetry During normal system operation, a certain degree of voltage symmetry can be as-
sumed. The symmetry is monitored in the device with a magnitude comparison. The
smallest phase voltage is compared to the largest. Non-symmetry is detected when
|U
min
| / |U
max
| <
%$/)$&7258
as long as |Umax| >
%$/$1&(8/,0,7
U
max
is the largest and U
min
is the smallest of the three voltages. The symmetry factor
%$/)$&7258
provides a measure of the voltage unsymmetry, the threshold value
%$/$1&(8/,0,7
defines the lower limit of the operating range for this monitoring
function (refer to Figure 6-116). Both parameters can be set. The reset ratio is approx.
97 %.
This failure is alarmed by “
)DLO8EDODQFH
”.
Figure 6-116 Voltage symmetry monitoring
Voltage Phase
Rotation The verification of the faulted phases and the phase preference, direction measure-
ment and polarization with quadrature voltages usually demand clockwise rotation of
the measured values. The phase rotation of the measured voltages is checked by
monitoring of the voltage phase sequence.
U
L1
before U
L2
before U
L3
This check takes place if each measured voltage has a minimum magnitude of
|U
L1
|, |U
L2
|, |U
L3
| > 40 V/
√
3
In the event of negative phase rotation, the alarm “
)DLO3K6HT
” is issued.
If the system has a negative phase rotation, this must have been set during the con-
figuration of the power system data (Sub-section 6.1.1). In such event, the phase ro-
tation monitoring applies to the corresponding opposite phase sequence.
U
min
V
%$/$1&(8/,0,7
slope:
%$/)$&7258
U
max
V