2.1 General
47
7UT613/63x Manual
C53000-G1176-C160-2
The main protected object is a two-winding transformer YNd with an earthed starpoint
at the Y-side. Side
S1 is the upper voltage side (Y), side S2 is the lower voltage side
(d). This definition of the sides for the main protected object (and only for it) is the basis
for the formation of the differential and restraint currents used in the differential pro-
tection.
For the side S1 2 measuring locations
M1 and M2 exist. The currents that are mea-
sured there belong to the side S1, their sum flowing on side 1 in the protected zone of
the main protected object. The position of the busbar isolator is not important here.
Likewise, the polarity of the currents is not yet considered under topology aspects.
At the lower voltage side, side S2 also has two measuring locations
because of its
branch point to the auxiliaries system circuit: M3 and M4. The sum of these currents
flows into the low voltage side (S2) of the main protected object.
The 4 measuring locationsM1 to M4 are assigned to the sides of the main protected
object, thus assigned measuring locations
. They are the basis for the measured value
processing of three-phase currents for the differential protection. Basically, the same
applies to a single-phase transformer; Here, only the measured currents of the mea-
suring locations are connected in two-phase.
Measuring location
M5 is not assigned to the main protected object, but to the cable
feeder, which is not related in any way to the transformer. M5 is thus a non-assigned
measuring location. The currents of this measuring location can be used for other pro-
tection functions, e.g. for 3-phase overcurrent protection for protection of the cable
feeder.
In 3-phase busbar protection there is no difference between measuring locations and
sides; both correspond with the feeders of the busbar.
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