ABB Relion 650 Series Technical Manual page 281

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1MRK 506 326-UUS B

The first criterion means that detection of failure in one phase together with high current for the

same phase will set the output. The measured phase current is used to reduce the risk of false

fuse failure detection. If the current on the protected line is low, a voltage drop in the system (not

caused by fuse failure) is not by certain followed by current change and a false fuse failure might

The second criterion requires that the delta condition shall be fulfilled in any phase at the same

time as circuit breaker is closed. Opening circuit breaker at one end and energizing the line from

other end onto a fault could lead to wrong start of the fuse failure function at the end with the

open breaker. If this is considering to be an important disadvantage, connect the 52a input to

FALSE. In this way only the first criterion can activate the delta function.

Line distance protection REL650

Technical manual

Secondary system supervision