ABB REG650 Technical Manual page 278

Section 10
Secondary system supervision
272
• The magnitude of the phase current in the same phase is higher than the setting
IPh>
• The circuit breaker is closed (CBCLOSED = True)
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 occur
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 CBCLOSED input to FALSE. In this way
only the first criterion can activate the delta function.
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Technical Manual