22
6LE007331A
The Zone Selective Interlocking function is designed to reduce electrodynamic stress in
the electrical power distribution system (conductors and busbars) when time selectivity is
activated.
It applies to the upstream section of the electrical power distribution system and requires
the upstream and downstream circuit breakers to be connected by a cable. This connection
makes it possible to enable or inhibit the tsd and/or tg time delay depending on the location of
the short circuit fault.
When the Zone Selective function is activated on a circuit breaker, it inhibits its time delay
settings and has an almost instantaneous trigger time.
When it is not activated, the circuit breaker operates according to its trigger time delay
settings.
The Zone Selective Interlocking function is supplementary to time selectivity (tsd and tg time
delay). Under no circumstances can it replace it.
It is applicable to short time delay protection and ground fault protection.
Here are two examples to explain the functioning.
Q1
Q2
Q3
Q4
a)
b)
STD2 /
Cmn2
STD1 /
Cmn1
STD2 /
Cmn2
STD1 /
Cmn1
STD2 /
Cmn2
STD1 /
Cmn1
STD2 /
Cmn2
STD1 /
Cmn1
Zone Selective Interlocking: Example
First, circuit breakers Q1, Q2, Q3, Q4 are set to their respective thresholds enabling the
expected time selectivity to be activated.
Fault example a):
-
In the event of a fault downstream of circuit breaker Q3
, circuit breakers Q1, Q2 and
Q3 detect the fault at the same time. Thanks to the connection cable between the circuit
breakers, circuit breaker Q3 informs circuit breaker Q2 that it has detected the fault. Circuit
breaker Q2 then informs circuit breaker Q1 that it has also detected the fault. Circuit
breakers Q1 and Q2 then maintain their respective time delays so that circuit breaker Q3
can eliminate the fault according to its protection settings.
The types of protection device
3.7 Zone Selective Interlocking function (ZSI)
