As can be seen that the magnetizing inrush with this small transformer (2MVA used in the previous
example also) is very short, about 7 seconds, there is still over the nominal measurable current which
is seen only in the primary side of the transformer thus would cause clearly tripping of the differential
relay if tried to energize without magnetizing inrush blocking. When looking at the currents can be
noted that the fundamental component currents (which are used for differential calculations)
magnitudes are roughly as follows:
When remembering that in this example the transformer HV (primary) –side nominal current was
115.5A it yields to following:
In the set characteristics the differential currents would look like in the graph below.
Figure. 5.4.10. - 110. Differential currents in the energization of 2 MVA transformer.
Now this result is still very low considering of the magnetizing inrush current magnitudes but still the
differential relay would de nitely trip in this case if it would not be prevent from operating by 2
nd
harmonic blocking. Situation is the same with all of the setting variations calculated.
AQ-T216
Instruction manual
Version: 2.00
149
© Arcteq Relays Ltd
