ABB 615 Series ANSI, Technical Manual

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Section 5
Protection related functions
615 series ANSI 385
Technical Manual
5.1.5 Application
Transformer protections require high stability to avoid tripping during magnetizing inrush
conditions. A typical example of an inrush detector application is doubling the pickup
value of an overcurrent protection during inrush detection.
The inrush detection function can be used to selectively block overcurrent and
ground-fault function stages when the ratio of second harmonic component over the
fundamental component exceeds the set value.
Other applications of this function include the detection of inrush in lines connected to a
transformer.
Figure 186: Inrush current in transformer
It is recommended to use the second harmonic and the waveform based
inrush blocking from the transformer differential protection function 87T
if available.