Siemens SIPROTEC 4 7UT6 Series Manual page 69

the currents of the 3-phase measuring locations M1 and M2 flow into the autoconnected winding, the 1-
phase earth fault current is measured at the auxiliary measuring location X3. The 3- phase measuring location
M3 is irrelevant for the restricted earth fault protection. Since the assignment of the 3-phase measuring loca-
tions and of the auxiliary measuring location is also defined by the topology, you only need to set auto-
connected for the restricted earth fault protection REF PROT. AT. This is also true if the autoconnected
winding has more than one tap.
But the restricted earth fault protection can also act upon an object other than the main protected object. In
Figure Topology of a three-winding transformer as main protected object and a neutral reactor arranged
outside of the protected zone as a further protected object; right hand 3-phase illustration of the neutral
reactor the main protected object is a three-winding transformer with the sides S1, S2 and S3. The 3-phase
measuring location M5, on the other hand, belongs to the neutral reactor. You have now the option to use the
restricted earth fault protection for this reactor. Since for this further protected object no sides are defined,
you can assign here the restricted earth fault protection to the 3-phase measuring location M5, which is not
assigned to the main protected object: set address 413 REF PROT. AT to n.assigMeasLoc5.
By the assignment of the auxiliary measuring location X4 to the 3-phase measuring location M5, it is defined
that the 1-phase earth fault current measured at X4 belongs to the neutral reactor connected to M5 (Section
2.1.4 Power System Data 1
7UT613/63x provides a second earth fault differential protection. With a YNyn transformer, for example, that
is earthed at the two starpoints, you can realize a restricted earth fault protection for each of the two wind-
ings. Or you can use the first restricted earth fault protection for the earthed winding of a transformer and the
second for another protected object, e.g. a neutral reactor. Set address 414 REF PROT. 2 AT following the
same considerations as for the first restricted earth fault protection.
Further 3-phase Protection Functions
A reminder: the single-phase power transformer is treated like a three-phase power transformer (without
phase L2). Therefore, the three-phase protection functions apply also for this (except the overcurrent protec-
tion for zero sequence current and asymmetrical load protection).
These further protection functions can operate on the main protected object or on a further protected object.
The possibilities depend on the definitions made in the topology.
For the main protection object, you normally choose one side for which the protection function will be effec-
tive. If in the example shown in
(Section 2.4.1 General) as a backup protection on the high-voltage side, you set address 420 DMT/IDMT Ph
AT to Side 1. The phase overcurrent protection then acquires the sum of the currents flowing through the
measuring locations M1 and M2 (for each phase) towards the transformer.
You can also set the phase overcurrent protection to be effective for one single measuring location of the
main protected object. If in the same example you want to use the overcurrent protection as a protection for
the auxiliaries system circuit, you set address 420 DMT/IDMT Ph AT to Measuring loc.3.
Finally, you can also set the overcurrent protection to be effective for another protection object, i.e. assign it
to a 3-phase measuring location which is not assigned to the main protection object. To do so, you select that
measuring location. In the example shown in
tion for the cable feeder by setting address 420 DMT/IDMT Ph AT to Measuring loc.5.
As the above examples show, the protection function can be assigned as desired. Generally speaking:
•
Where a 3-phase protection function is assigned to a measuring location, the currents are acquired at this
location, regardless of whether it is assigned to the main protected object or not.
•
Where a 3-phase protection function is assigned to a side (of the main protected object), the sum of the
currents flowing in at this side from the measuring locations assigned to it is acquired (for each phase).
•
Please note also that the earth overcurrent protection will receive from the auxiliary measuring location
assigned here not only its measured value, but also circuit breaker information (current flow and manual-
close detection).
The same basic principles apply to the two additional overcurrent protection functions. With reference to the
example in Figure
voltage side by setting address 420 DMT/IDMT Ph AT= Side 1 (as above), the second overcurrent protec-
tion as protection of the station's own requirement feeder (address 430 DMT/IDMT Ph2 AT = Measuring
SIPROTEC 4, 7UT6x, Manual
C53000-G1176-C230-5, Edition 09.2016
under margin heading "Assignment of Auxiliary 1-phase Measuring Locations").
Figure 2-2 you want to use the time overcurrent protection for phase currents
2-2, the first overcurrent protection can be determined as reserve protection at the high-
Figure 2-2, you can use the overcurrent protection as a protec-
Functions
2.1 General
69