13
Air Circuit Breakers
BT2 series
Zone selective interlock
Zone selective interlock (ZSI function) (for M25, M26, H26, P25 and P26, optional)
21
22
23
24
21
22
23
24
21
22
23
24
21
22
23
24
Note: 21,22,23,24 serve as the wiring teminals of secondary circuit.
Busbar
Release delay t
2
Zone1
Circuit breaker
at higher level
Control line
Control line
Busbar
Release delay t
2
Zone2
Fault
Control line
Control line
Busbar
Zone3
Down stream circuit breaker
When pieces of circuit breakers are linked together up and
down, zone selective interlock (ZSI) can ensure fully-selective
protection of circuit breakers at higher or lower level so as to
reduce the range of action by fault and the breaking time of
circuit breakers. This function serves for short-time delay short
circuit (I
2
t OFF) and ground-fault protection of circuit breakers.
As the sketch shown above, control lines can interlock with
pieces of circuit breakers.
After detecting the fault, the intelligent controller (zone 2) will
send out a signal to circuit breakers (zone1) at higher level and
check whether the signal of circuit breakers (zone 3) at lower
level arrives. If circuit breakers at lower level send out a signal,
the circuit breaker will be on at the time duration of release
delay; if circuit breakers at lower level don't send out a signal,
the circuit breaker will break off instantly no matter whether the
release has the protection of delay.
Note: The end 23 and 24 should be shortcircuited.
Intelligent controller
