Zone Selective Interlocking
5.1 ZSI
3WL/3VL circuit breakers with communication capability - PROFIBUS
System Manual, 03/2011, A5E01051353-02
109
5.1.6.2 Condition ZSI = ON and presence of a ground fault (G)
1. The overcurrent releases detect the ground fault and start the predefined delay times t
g
=
ground fault (G)
2. Each circuit breaker that detects the ground fault informs the higher-level breakers of the
detected ground fault (ZSI_OUT ⇒ ZSI_IN ⇒ ZSI_OUT ...)
3. Each circuit breaker that receives no information (ZSI IN) from subordinate grading levels
and detects the ground fault forces a short-circuit trip after 100 ms (t
ZSI
).
4. Otherwise a trip occurs at the end of the delay time t
g
(100 - 500 ms)
Result: The ZSI module switches off the ground fault after 100 ms in the next level to the
fault.
Overview of the times:
t
ZSI
= Guaranteed non-tripping time: 50 ms short-circuit/100 ms ground fault
t
sd
= From 80 – 4000 ms depending on the tripping unit ETU
t
g
= 100 – 500 ms
Plus the typical mechanical tripping time depending on the circuit breaker 20 – 40 ms
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