The magnetizing inrush current in a 2 MVA transformer is over quickly, in about seven seconds.
Afterwards there is still the nominal measurable current (seen only in the transformer's primary side)
which would cause the differential relay to trip if energized without magnetizing the inrush blocking.
Looking at the currents more closely one can see that the input values of the fundamental frequency
currents (used for differential calculations) are roughly as follows:
In our previous example the transformer's nominal current on the HV (primary) side was 115.5 A; with it
we can count the following:
The graph below shows how the differential currents look like when used in the set characteristics.
Figure. 5.4.29 - 164. Differential currents in the energization of a 2 MVA transformer.
While the results are very low compared to the magnetizing inrush current magnitudes, the differential
relay would still definitely trip without the 2
nd
harmonic blocking. The situation is the same with all of the
calculted setting variations.
A
AQ
Q-M257
-M257
Instruction manual
Version: 2.07
310
© Arcteq Relays Ltd
IM00021
Summary of Contents for AQ-M257
Page 1: ...AQ M257 Motor protection IED Instruction manual...
Page 2: ......
