Description
2.10 Zone-selective interlocking ZSI
3WA1 air circuit breaker
196 Equipment Manual, 02/2023, 92310000002-06
The following figure shows a ZSI system with one fuse and four circuit breakers. Due to
the adjustable delay t
ZSI
, the break time can be reduced by a ZSI system even when
fuses and circuit breakers are used simultaneously.
The delay t
ZSI
of the short-time-delayed short-circuit protection is matched to the fuse -
F1 with 0.2 s in the following example. The grading times t
sd
of the short-time-delayed
short-circuit protection ST of the upstream circuit breakers are unchanged.
For the power distribution system with three grading levels, faults A, B and C are
considered in more detail.
The left side of the figure shows the settings of the ZSI function and the delays for the
short-time-delayed short-circuit protection ST.
Fault scenario A
• The -F1 fuse switches off the short-circuit according to its characteristic curve.
• Depending on the level of the short-circuit current, the two -Q3 and -Q1 circuit
breakers can also be excited by the short-circuit current.
In this case, the -Q3 circuit breaker does not receive a control signal at the ZSI
interface port A from a downstream grading level and would trip after the delay t
ZSI
0.2 s if a pick-up is pending.
In the event of an excitation, it would send this excitation as a control signal via the
ZSI interface port B to the -Q1 circuit breaker.
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