GE Industrial Solutions Entellisys 5.0 User Manual - Manual (Page 23)

System components 23
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1.3.9 CPU
The CPU is a rack-mount industrial computer running a real-time operating system. The CPU
provides the processing capability to support all switchgear functions. Two redundant CPUs
(CPU A and CPU B) are used per lineup, supporting up to 30 circuit breakers.
The CPUs run simultaneously. If one CPU has an issue, the other continues to run providing
redundancy. One CPU should be running at all times to maintain the highest level of protection.
In the event that the Messenger-to-CPU communication network is down or power to the CPU is
not available, the EntelliGuard Messenger will provide back-up overcurrent protection
functionality.
The redundant CPUs are synchronized by a common connection to a synch clock. Each CPU has
a slot for synch clock, although only one synch clock is used per system. The synch clock is
programmed for either 60 Hertz or 50 Hertz frequency operation.
Each CPU has two slots for optional discrete I/O cards.
Figure 1-11 Redundant CPUs with synch clock connection
1.3.10 Synch clock
To maintain system synchronization, a mechanism exists to provide a single sampling time
source. This time source is provided on a separate hardware card, called the Synch Clock. The
Synch Clock sits in CPU A and has a connection to CPU B.
In the event of an issue with the Synch Clock or its connections, the CPUs fall-back to software
synch functionality. When this occurs CPU A maintains full functionality. As time drifts, CPU B
may suspend advanced multi-source protection and may not be able to provide metering
information for the circuit breakers without PTs. If CPU A is powered down to provide
maintenance, CPU B will continue to run all functions.