Description
2.10 Zone-selective interlocking ZSI
3WA1 air circuit breaker
192 Equipment Manual, 02/2023, 92310000002-06
Fault scenario A:
• The -Q4, -Q3 and -Q1 circuit breakers detect the short-circuit. Via the ZSI system,
circuit breaker -Q3 is informed of the pick-up of -Q4 and circuit breaker -Q1 is
informed of the excitation of -Q3. This prevents tripping of the circuit breakers -Q3
and -Q1 with delay t
ZSI
.
• The -Q4 circuit breaker does not receive any pick-up information from a downstream
circuit breaker at the ZSI interface port A. Therefore, the -Q4 circuit breaker trips
after the adjustable delay t
ZSI
for the short-time-delayed short-circuit protection.
• If the fault current cannot be switched off by the -Q4 circuit breaker, tripping of -Q3
and -Q1 as back-up protection takes place in each case after the parameterized delay
time t
sd
.
The fault current does not flow through the -Q2 and -Q5 circuit breakers and they are
therefore not considered in more detail.
Fault scenario B:
• The -Q3 and -Q1 circuit breakers detect the short-circuit. Via the ZSI system, circuit
breaker -Q1 is informed of the pick-up of -Q3. This prevents tripping of -Q1 after the
delay t
ZSI
.
• The -Q3 circuit breaker does not receive any pick-up information from a downstream
circuit breaker at its ZSI interface port A. Therefore, the -Q3 circuit breaker trips after
the adjustable delay t
ZSI
for the short-time-delayed short-circuit protection.
• If the fault current cannot be switched off by the -Q3 circuit breaker, tripping of -Q1
as back-up protection takes place after its delay time t
sd
.
Fault scenario C:
• The -Q1 circuit breaker detects the short-circuit and does not receive any information
about the pick-up of a downstream circuit breaker.
-Q1 therefore trips after the delay t
ZSI
.
In this example, it can be seen that the load on the power distribution system in the
event of a short-circuit is significantly reduced by the ZSI system.
The following table lists the delays of the ETU600 electronic trip unit until the trip
command for the three fault cases.
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