LS Industrial Systems Metasol Series, Технический каталог, Страница: 87 / 156

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Technical catalog for Susol & Metasol ACB
Technical catalog for Susol & Metasol ACB
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Picture 6. ZSI Operation Principle Picture 7. ZSI Applied in Power Supply
This ZSI technique allow breakers to exchange communication signals and to provide more precise discrimination
at upstream trip unit level. For instance (see picture 6), ZSI technique is applied to D2 and D1, and hypothesize
that both trip units detected the fault in downstream area. For this case, D2 is activated instantaneously and sends
its delay signal (pre-arranged) to D1. D1 breaker operates its breaking function if the fault event is not eliminated
after its delay time.
ZSI (Zone Selective Interlocking)
To further explanations, another example is illustrated on picture 7 where three breakers are installed in series.
Suppose each CB3, CB2, and CB1 breaker under picture 7 is predetermined its operating time as follows.
If fault occurred in downstream of CB2(fault point #2 from the picture), without ZSI technique the breaker will
function after 0.1second (its original prearranged delay time) however with ZSI technique the breaker will
recognize it as an accident. Because CB3 breaker can not monitor the fault current at fault point #2, and failed to
send its ZSI signal to CB2. Therefore, CB2 breaker detects fault currents and from not receiving ZSI signals will
perceive that this accident should be dealt at its level. For this case, CB2 operates instantaneously after sending
its ZSI signals. For CB1 breaker, it operates after 0.2 seconds which is prearranged for its delay time after
receiving ZSI signals.
In other words, a breaker with ZSI technique will operate under following these three cases.
1) Case 1 : Fault current was detected, however ZSI signal was not received � The breaker is responsible for an
instantaneous operation. If there is a breaker in upstream, send ZSI signals to the breaker, and operate
instantaneously.
2) Case 2 : Fault current was detected, and received ZSI signals
�
If there is a breaker tied with ZSI signal in
upstream, send ZSI signal and operate at prearranged delay time.
3) Case 3 : Fault current was not detected. But ZSI signal was received when fault current did not reach its short
time delay range. � Even though there is a breaker tied with ZSI signal, it will not send ZSI signal. It
operates after its prearranged delay time.
1) CB3-No Forced Time
Delay
2) CB2-Delay Time 0.1S
3) CB1-Delay Time 0.2S
Forced Time
Delay : 0.2S
Forced Time
Delay : 0.2S
CB1
CB2
CB3
Instantaneous
Operation Logic wait
instruction
D
1
D
2
Trip
Unit
Trip
Unit
Instantaneous
Operation
Fault Point 2
Fault Point 1
Forced Time
Delay : 0.1S
Zone selective
interlocking