Logic Diagram - ABB REG650 Technical Manual

1MRK 502 043-UUS B
6.1.3.13
Technical Manual
a transformer is energized with a more severe (minor faults cannot be discovered)
internal fault (for example, forgotten grounding on transformer LV side for example,
after a regular service). The feature is based on the waveform check. If a severe
internal fault exists, then, during energization the magnetic density in the iron core
will be low and high sinusoidal currents will flow from the very beginning. In this case
the waveform block algorithm removes all its three block signals in a very short
interval of time. This quick reset of the waveblock criterion will temporarily disable
the second harmonic blocking feature of the differential protection function. This
consequently ensures fast operation of the transformer differential function for a switch
onto a fault condition. It shall be noted that this feature is only active during initial
power transformer energizing, more exactly, under the first 50 ms. When the switch
onto fault feature is disabled by the setting parameter SOTFMode, the waveblock and
second harmonic blocking features work in parallel and are completely independent
from each other.

Logic diagram

The simplified internal logics, for transformer differential protection are shown in the
following figures.
Section 6
Differential protection
103