Siemens siprotec 7SA522 User Manual page 367

Broken Conductor
Voltage Symmetry
Voltage Phase
Rotation
7SA522 Manual
C53000-G1176-C119-2
A broken conductor of the protected line or in the current transformer secondary circuit
can be detected, if the minimum current %$/$1&( , /,0,7 flows via the feeder. If a
current symmetrie failure is detected and the minimum current is below the threshold
3ROH2SHQ&XUUHQW (address 1130, refer to subsection 6.1.3), an interruption of this
conductor may be assumed. After approximately 5 s the device issues the alarm
")DLO &RQGXFWRU".
During normal system operation, a certain degree of voltage symmetry can be as-
sumed. The symmetry is monitored in the device with a magnitude comparison. The
smallest phase voltage is compared to the largest. Non-symmetry is detected when
| < %$/ )$&725 8
|U | / |U
min max
as long as |Umax| > %$/$1&( 8/,0,7
U is the largest and U
max
%$/ )$&725 8 provides a measure of the voltage unsymmetry, the threshold value
%$/$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 ")DLO 8 EDODQFH".
U
min
V
76G6I8@ÃVGDHDU
Figure 6-116 Voltage symmetry monitoring
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 before U before U
L1 L2
This check takes place if each measured voltage has a minimum magnitude of
|U |, |U |, |U | > 40 V/√3
L1 L2 L3
In the event of negative phase rotation, the alarm ")DLO 3K 6HT" 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.
is the smallest of the three voltages. The symmetry factor
min
slope:
76GÃA68UPSÃV
U
max
V
L3
Functions
6-219