Switch Onto Fault Feature - ABB REG650 Technical Manual

Section 6
Differential protection
6.1.3.12
102
I_A
I_B
I_C
ANSI05000343 V1 EN
Figure 36: Inrush currents to a transformer as seen by a protection IED. Typical is
a high amount of the 2
low rate-of-change of current within each period.
Cross-blocking between phases
With the cross-blocking function, one of the three phases can block operation of the
other two phases due to the harmonic pollution of the differential current in that phase
nd
(that is, waveform, 2 or 5
control the cross-blocking between the phases via the setting parameter CrossBlockEn.
When parameter CrossBlockEn=Enabled 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=Disabled, any cross blocking between phases will be
disabled. It is recommended to use the value Disabled 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
400kV Currents
Time [cycles]
nd
harmonic, and intervals of low current, and
th
harmonic content). In differential algorithm the user can
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Technical Manual