Switch Onto Fault Feature - ABB REG650 Technical Manual

1MRK 502 034-UEN -
5.1.3.12
Technical Manual
IEC05000343 V1 EN
Figure 37: Inrush currents to a transformer as seen by a protective IED.
Typical is a high amount of the 2
current, and low rate-of-change of current within each period.
Cross-blocking between phases
Basic definition of the cross-blocking is that one of the three phases can block
operation (that is,tripping) of the other two phases due to the harmonic pollution of
the differential current in that phase (that is, waveform, 2
content). In differential algorithm the user can control the cross-blocking between
the phases via the setting parameter CrossBlockEn=On.
When parameter CrossBlockEn=On cross blocking between phases is introduced.
There is no time settings involved, but the phase with the operating point above the
set bias characteristic (in the operate region) will be able to cross-block other two
phases if it is itself blocked by any of the previously explained restrained criteria. If
the start signal in this phase is removed, that is, reset from TRUE to FALSE, cross
blocking from that phase will be inhibited. In this way cross-blocking of the
temporary nature is achieved. It should be noted that this is the default
(recommended) setting value for this parameter.
When parameter CrossBlockEn=Off, any cross blocking between phases will be
disabled. It is recommended to use the value Off with caution in order to avoid the
unwanted tripping during initial energizing of the power transformer.

Switch onto fault feature

Transformer differential function in the IED has a built-in, advanced switch onto
fault feature. This feature can be enabled or disabled by a setting parameter
SOTFMode. When enabled this feature ensures quick differential protection
tripping in cases where a transformer is energized with a more severe (minor faults
cannot be discovered) internal fault (for example, forgotten earthing 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, when the power transformer is
Section 5
Differential protection
nd
harmonic, and intervals of low
nd th
or 5 harmonic
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