ABB RELION 620 Series Technical Manual page 533

1MAC504801-IB E
5.1.5
620 series ANSI
Technical Manual
within the trip time up counting, the reset timer is activated. If the drop-off time exceeds
Reset delay time, the trip timer is reset.
The BLOCK input can be controlled with a binary input, a horizontal communication input
or an internal signal of the relay program. The activation of the BLOCK input prevents the
BLK2H output from being activated.
It is recommended to use the second harmonic and the waveform based
inrush blocking from the transformer differential protection function 87T
if available.
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.
Protection-related functions
Section 5
527