3.3 Commissioning
419
7UT613/63x Manual
C53000-G1176-C160-2
Such test records are especially informative on power transformers when they are trig-
gered by the switch-on command of the transformer. Since the inrush current may
have the same effect as a single-ended infeed, but which may not initiate tripping, the
effectiveness of the inrush restraint is checked by energising the power transformer
several times.
The trip circuit should be interrupted or the differential protection should be switched
to DIFF. PROT. = Block relay (address 1201) during these tests in order to avoid
tripping.
Conclusions as to the effectiveness of the inrush restraint can be drawn from the re-
cording of the differential currents and the harmonic contents. If necessary the inrush
current restraint effect can be increased (= smaller value of the 2nd harmonic in
address 1271 2. HARMONIC) when trip occurs or when the recorded data show that
the second harmonic content does not safely exceed the restraining threshold (ad-
dress 1271). A further method to increase inrush restraint is to set the crossblock
function effective or to increase the duration of the crossblock function (address 1272
CROSSB. 2. HARM) (For further details refer to the setting information for differential
protection under „Harmonic Restraint“).
Note
Do not forget to switch on the differential protection (address 1201) after completion
of the test.
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