Siemens SIPROTEC 7UT613 series Manual page 282

2 Functions
Voltage Sum
Current Phase Se-
quence
Voltage Phase Se-
quence
Broken Wire
282
If measured voltages are connected to the device and these are used, voltage sum
supervision is possible. A further prerequisite is that the displacement voltage (e-n
voltage of an open delta connection) at the same voltage measuring point is connect-
ed to the 4th voltage input U
voltages must equal three times the zero sequence voltage. Errors in the voltage
transformer circuits are detected when
U = |U + U + U – k
F L1 L2 L3
The factor k allows for a difference of the transformation ratio between the displace-
U
ment voltage inputs and the phase voltage inputs. By the settings of the rated voltages
and ratios (Subsection 2.1.4 under margin heading „Voltage Transformer Data") the
device is informed about these data. The dropout ratio is about 95 %.
This malfunction is signalled as „Fail Σ U Ph-E" (No. 165).
To detect swapped connections in the current input circuits, the direction of rotation of
the phase currents for three-phase application is checked. Therefore the sequence of
the zero crossings of the currents (having the same sign) is checked for each 3-phase
measuring location. For single-phase busbar differential protection and single-phase
transformers, this function would not be of any use and is thus disabled.
Especially the unbalanced load protection requires clockwise rotation. If rotation in the
protected object is reverse, this must be considered during the configuration of the
general power system data (Subsection 2.1.4 under „Phase rotation").
Phase rotation is checked by supervising the phase sequence of the currents, i.e. for
clockwise rotation.
I before I before I
L1 L2 L3
. The supervision of current rotation requires a minimum current of
| > 0,5 I
|I |, |I |, |I
L1 L2 L3 N
If the rotation measured differs from the rotation set, the annunciation for the corre-
sponding measuring location is output, e.g. „FailPh.Seq IM1" (No 30115). At the
same time, the common annunciation appears: „Fail Ph. Seq. I" (No 175).
If measured voltages are connected to the device and these are used, the voltage
phase rotation is supervised. On clockwise phase rotation this is done by supervising
the phase sequence of the voltages
U before U before U
L1 L2
This check is done as long as the voltages have a magnitude of at least
|U |, |U |, |U | > 40 V/√3
L1 L2 L3
. Wrong phase rotation is indicated by the alarm „Fail Ph. Seq. U" (No 176).
During steady-state operation the broken wire monitoring registers interruptions in the
secondary circuit of the current transformers. In addition to the hazardous potential
caused by high voltages in the secondary circuit, this kind of interruptions simulate dif-
ferential currents to the differential protection, such as those evoked by faults in the
protected object.
The broken wire monitor scans the transient behaviour of the currents of each phase
for every measuring location. The instantaneous currents are checked for plausibility
and continuity. If an instantaneous value does not correspond to the expected value,
a broken wire is considered. If the current decays strongly or drops abruptly to 0 (from
of the device. Then the sum of the three digitised phase
4
· U | > 25 V.
U EN
.
.
L3
7UT613/63x Manual
C53000-G1176-C160-2