ABB RED615 Technical Manual page 397

1YHT530004D05 D
615 series
Technical Manual
If the peak value of the differential current is very high, that is I
for the second harmonic blocking is desensitized (in the phase in question) by
increasing it proportionally to the peak value of the differential current.
The connection of the power transformer against a fault inside the protected area
does not delay the operation of the tripping, because in such a situation the
blocking based on the second harmonic of the differential current is prevented by a
separate algorithm based on a different waveform and a different rate of change of
the normal inrush current and the inrush current containing the fault current. The
algorithm does not eliminate the blocking at inrush currents, unless there is a fault
in the protected area.
The feature can also be enabled and disabled with the Harmonic deblock 2.H
parameter.
Fifth harmonic blocking
The inhibition of TR2PTDF operation in the situations of overexcitation is based
on the ratio of the fifth harmonic and the fundamental component of the differential
current (Id5f/Id1f). The ratio is calculated separately for each phase without
weighting . If the ratio exceeds the setting value of Start value 5.H and if blocking
is enabled through the Restraint mode parameter, the operation of the biased stage
of TR2PTDF in the concerned phase is blocked.The fifth harmonic ratios
I_5H_RAT_x are given in monitored data.
At dangerous levels of overvoltage, which can cause damage to the transformer,
the blocking can be automatically eliminated. If the ratio of the fifth harmonic and
the fundamental component of the differential current exceeds the Stop value 5.H
parameter, the blocking removal is enabled. The enabling and disabling of
deblocking feature is also done through the Harmonic deblock 5.H parameter.
GUID-A97464D1-3085-4F27-B829-11EEC47CA654 V1 EN
Figure 208: The limits and operation of the fifth harmonic blocking when both
blocking and deblocking features are enabled using the Harmonic
deblock 5.H control parameter.
Section 4
Protection functions
> 12 xIn, the limit
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