Siemens SIPROTEC 7UT613 series Manual page 55

7UT613/63x Manual
C53000-G1176-C160-2
Current comparison for common winding of an auto-transformer:
If during configuration of the functional scope in section 2.1.3 a pure current compar-
ison via each winding has been selected, then the example of figure 2-7 applies.
Besides the common winding terminals of the sides S1 (full winding) and S2 (tap) with
the assigned 3-phase measuring locations M1 and M2, one more side S3 is defined at
the starpoint terminals with the 3-phase measuring location M3. In this way, a current
comparison can be realised over each of the three transformer windings, i.e. each
phase with its 3 measuring locations.
Such current comparison is more sensitive to 1-phase earth faults in one of the trans-
formers than the normal differential protection. This has a certain importance consid-
ering that 1-phase earth faults are the most probable faults in such banks. By means
of the parameter setting at address 105 PROT. OBJECT = Autotransf.Autotr.
node, the current comparison protection of the auto-transf. node is supported.
On the other hand, the compensation winding cannot and must not be included into
this protection even if it is accessible and equipped with current transformers. This ap-
plication variant is based on the current law in that all currents flowing in to a winding
must total to zero. In auto-transformers with stabilising winding, the stabilising winding
should be protected separately (e.g. with time overcurrent protection). During setting
of address 105 PROT. OBJECT = Autotransf., a stabilising winding can be includ-
ed.
The current transformer X1 in figure 2-7 is not required. In order to realise an earth
overcurrent protection or a restricted earth fault protection in this arrangement, you
can feed the sum of the three currents measured at M3 to an auxiliary 1-phase current
input of the device. An example of a connection, where a measuring location M3
serves as 3-phase measuring location for the current comparison and where simulta-
neously the total current 3I
tion I
of the device, is available in the annex.
X1
of the transformer set is led to a 1-phase measuring loca-
0
2.1 General
55