ABB 650 series, Technical Manual

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example, a forgotten grounding on the transformer LV side. 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.
6.1.3.13 Logic diagram
The simplified internal logics, for transformer differential protection are shown in the
following figures.
1MRK 502 048-UUS A
Section 6
Differential protection
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Technical manual