Zsi Function - Siemens SENTRON VL Series System Manual

5.1.4

ZSI function

The ZSI function (ZSI = Zone Selective Interlocking) offers full selectivity with an extremely
short delay time (t
in the distribution system in the short-time-delayed S range and G range of the trip
characteristic.
S range = short-time-delayed short-circuit
protection
G range = ground fault protection
The benefit of ZSI is all the greater the higher the number of grading levels in large and
meshed networks, and the longer the resulting delay times for standard time grading.
By shortening the break time, the ZSI function significantly reduces stress in the switchgear
in the event of a short-circuit and/or ground fault.
Note
The ZSI function is only effective in the case of short-time-delayed short-circuit protection S
up to the level of the preset maximum short-time-delayed short-circuit protection. If the short-
circuit current exceeds this permissible maximum value, the short-circuit current is so great
that instantaneous tripping of the circuit breaker always takes place in order to protect the
system.
3WL/3VL circuit breakers with communication capability - PROFIBUS
System Manual, 03/2011, A5E01051353-02
) regardless of the number of grading levels and the location of the fault
ZSI
Zone Selective Interlocking
=> t = 50 ms
ZSI
=> t = 100 ms
ZSI
5.1 ZSI
107