Alarm Overview; Alarm System Architecture - GE Mark VIe System Manual

7

Alarm Overview

Alarm management is a vital component to operating and maintaining equipment in power generation or other industrial
plants. Reporting of abnormal conditions and trips (with accurate descriptions and high-resolution time tags to identify the
origin) are vital to minimizing mean-time-to-repair (MTTR). The Mark VIe control with the ControlST software suite
provides solutions for alarm management, prioritization, classification, measurement, and reporting.

7.1 Alarm System Architecture

Each Mark VIe unit control (such as a turbine control) has its own embedded alarm detection and management system to
ensure the integrity of its data. Alarm logic is embedded in the overall unit control logic, and runs at the same frame rate,
synchronous with the control logic. Therefore, any trip emanating from the control due to a condition such as low lube oil
pressure will have a first-out alarm time tag assigned during the same data frame as the trip command. Since trips are
significant events, they are initiated locally from sensor inputs and internal algorithms. The unit alarm management system is
immune to failures of peripheral networks and supervisory equipment. Should a network malfunction occur, local alarm logic,
time tags, and messages are retained in the local controller and are available to operator stations upon restoration of the
network.
In normal operation, each unit control communicates its alarm messages and local high-resolution time tags to operator
stations where they are combined into the overall plant alarm management system. The integrity of the time stamps that the
operator sees depends on the system time synchronization, which consists of time coherence and time accuracy. Within a unit
control, there is ±1 ms time coherence between time stamps in controllers due to the distributed nature of its I/O. Time
synchronization on the I/O networks is implemented with IEEE-1588 Precision Clock Synchronization Protocol. In addition,
there is ±2 ms time coherence between any two units on the control network (UDH), which is implemented with Network
Time Protocol (NTP).
A time-server is normally provided for plant-wide time synchronization. The server communicates on the control network
(UDH) and information network (PDH) with ±1ms accuracy between a plant data point and a time source such as a global
positioning satellite (GPS). IRIG-B is a commonly used synchronization protocol.
Alarm Overview GEH-6721_Vol_I_BP System Guide 165
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