Switch Onto Fault Feature - ABB Relion Technical Manual

Section 6
Differential protection
6.1.3.12
110
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
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 (that is,
nd th
waveform, 2 or 5 harmonic content). In differential algorithm the user can 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 the 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

The transformer differential function 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
400kV Currents
Time [cycles]
nd
harmonic, and intervals of low current, and low
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Technical manual