GE Mark VIe Instruction Manual page 16

Protection Redundancy, Triple Redundant Systems
A key tripping reliability feature is cross-tripping. The primary and backup systems initiate a trip independently, but can also
initiate a cross-trip for additional tripping redundancy. For example, a trip that originates in the backup protection can be sent
to the primary protection to close the control valves and de-energize the trip solenoids from the primary side. Another
example, the backup protection monitors communications from each controller, so it can be configured to initiate a trip on
behalf of the controllers.
Functionality for the backup protection system is application-specific and subject to the safety requirements dictated by code
and/or GE design practices for specific turbine types. In general, it complies with most industry standards. It is separate and
independent from the primary protection, with more functionality than required by most codes. As an example,
ANSI/API-670 requirements for overspeed protection are written for an (one) independent, triple redundant system. The
standard GE overspeed system for a heavy-duty gas turbine or a combined-cycle steam turbine consists of two triple
redundant protection systems with cross-tripping.
16 GEI-100728A Mark VIe Controls System Redundancy Options
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