Mounting and Commissioning
3.3 Commissioning
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
424
3.3.14 Checking the Earth Current Differential Protection
Preparation
The primary test checks correct integration into the system, especially the CT connection. Before commencing
any primary tests, make sure that the configured object is actually the one you want to protect. To do so, verify
the settings used in the configuration of the protection function, Power System Data 1 and in the protection
function itself.
Before test commencement, set the earth current differential protection (address2101 REF PROT.) to Block
relay, or interrupt the trip command lines.
Primary tests of power units are performed with the generator itself. On transformers, a low-voltage test source
is used.
Before the test, the CT connections have to be visually checked for correctness.
Note
When performing the short-circuit test (3-phase short-circuit) for the earth current differential protection, check
that the three current transformers (side 1 or side 2 – whichever side is used for the earth current differential
protection) are identical in design. To do so, read out the percentages of the operational measured values 3I0-
1 and 3I0-2 (in DIGSI under Differential Protection Measured Values). If the CTs are well matched, the values
must be zero. Values that are not zero must be taken into account for the protection settings.
Primary Test with Generator
This test is performed in addition to the current test. For this the protection must be set to maximum sensitivity.
Zero voltage release must be blocked (address 2103 REF U0>RELEASE = 0).
For the test, one phase is earthed and the generator is excited (see the following Figure). The test current may
not exceed the admissible negative-sequence current. If this current amounts e.g. to I
2adm.
= 10 % I
N,G
, the test
current must be less than 30 % I I
N,G
. On the other hand, the current is determined by the low-resistance star-
point earthing. 10 % of the rated generator current is sufficient for testing.
Figure 3-27 Testing the earth current differential protection on the generator
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