GE Industrial Solutions Entellisys System User Manual - Manual (Page 107)

Zone Selective Interlock 107
7
Each ZSI zone can be enabled or disabled independently by checking Enabled where
appropriate.
To send changes to the CPU, click OK or Apply. Once changes are sent to the CPU, the ZSI is
running on the CPUs.
NOTE: If changes made to the tier settings of member circuit breakers are committed to the
CPUs while the affected ZSI zones are not idle, the changes are accepted but do not take effect
until the ZSI zones enter idle states and can switch to using the new tier values.
NOTE: If some of the member circuit breakers do not communicate with CPUs, the ZSI zones
that these circuit breakers are members of switch to the new tier values until communication is
restored and it is confirmed that these circuit breakers are not in pickup state. On normally
functioning systems, if ZSI zones are not idle they switch to new tier values within several
seconds after changes were committed.
7.4.7.2 Operation
If a ZSI zone is enabled, every half cycle, ZSI evaluates the state of its member circuit breakers. If
ZSI detects that a member circuit breaker is in pickup state, it attempts to update all upstream
circuit breakers with new time delays and it logs the update as an event as shown in
Figure 7-11. This event log is the only indication that ZSI is working.
After a fault is cleared, ZSI restores all original time delays and no corresponding event is
logged.
NOTE: If the system loses communication with a member circuit breaker, for safety reasons,
ZSI assumes that the non-communicating circuit breaker is in pickup state and performs
protection tasks. As soon as the non-communicating circuit breaker starts communicating
again with the system, ZSI verifies whether circuit breaker is actually in pickup condition. If it is
not, ZSI restores all original time delays.