•
The checks must be performed on one device per phase for each phase. In the following you can find
some more information on summation transformers.
•
However, each check is restricted on one current pair, i.e. on the one traversing testing current. Informa-
tion on vector group matching and vectors (except the phase angle comparison of the traversing current
= 180° at the sides tested) or similar is not relevant.
Summation Transformer Connection
If summation transformers are used, different connection possibilities exist. The following clarifications are
based on the normal connection mode L1-L3-E. This connection variant and the connection mode L1-L2-L3 are
shown in the following figures.
1-phase primary tests are to be preferred, since they evoke clearer differences in the measured currents. They
also detect connecting errors in the earth current path.
The measured current to be read out in the operational measured values only corresponds to the testing
current if 3-phase symmetrical check is performed. In other cases there are deviations which are listed in the
figures as factor of the testing current.
[mischwandlerl1l3e-7ut612-021026-rei, 1, en_GB]
Figure 3-43 Summation Transformer Connection L1-L3-E
[mischwandleranschlussl1l2l3-wlk-030710, 1, en_GB]
Figure 3-44 Summation transformer connection L1-L2-L3
Deviations which cannot be explained by measuring tolerances may be caused by connection errors or
matching errors of the summation transformers:
•
Switch off the test source and the protected object and earth it,
•
Check the plant connections to the device and the test arrangement and correct them.
•
Repeat test and re-check the current magnitudes.
The phase angles must be 180° in all cases.
Check the differential and restraint currents for each phase.
If single-phase primary checks cannot be carried out but only symmetrical operational currents are available,
polarity or connecting errors in the earth current path with summation transformer connection L1-L3-E will
not be detected with the before-mentioned checks. In this case, asymmetry is to be achieved by secondary
manipulation.
Mounting and Commissioning
3.3 Commissioning
384 SIPROTEC 4, 7UT6x, Manual
C53000-G1176-C230-5, Edition 09.2016
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