Alarm Types; Controller Alarm Subsystem - GE Mark VIe System Manual

7.2 Alarm Types

Standards for alarming define five types that occur in the Mark VIe control system as follows:
Process alarms are created to annunciate abnormal conditions in the plant equipment that the operator needs to be
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aware of or take action on. The focus of the alarm management system is based on capturing, filtering, visualizing, and
analyzing these process alarm messages. Typically, the word alarm is used to mean a process alarm, since that type is
most commonly used and experienced in the field.
Hold list alarms advise the operator that an automatic sequence is on hold. Then, the operator can choose to override
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the hold if permitted by the protective logic. Holds are typically used in steam turbine controls. An example hold list
alarm is the notification used with controlling the thermal expansion in steam turbines.
Diagnostic alarms alert the operator to fault conditions in the control equipment (such as a power supply failure) or an
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interruption in network communications (issue with cabling or switches).
• Events are important normal occurrences in the operation of a plant such as the closure of the generator breaker.
• Sequence of Events (SOE) provide a ±1 ms time stamped message whenever a field contact opens or closes. This
precision is particularly useful in determining the root cause of trips in a power plant that is subject to trips from
electrical equipment and grid dynamics. To be effective, time synchronized sequence-of-events reporting is needed
throughout the plant. In general, ±1 ms resolution is available on native Mark VIe and Mark VIeS discrete input modules
for dc contacts and available with less resolution for ac contacts. Time resolution for third-party I/O on fieldbus networks
is application-specific.
The maximum number of new alarms that can be processed are as follows:
• A burst load of 400 alarm transitions are supported in a single frame without missing a transition in the internal queue.
• A constant load of 100 alarm transitions per second are supported without missing a transition in the internal queue.

7.3 Controller Alarm Subsystem

The Mark VIe and VIeS controllers contain an embedded alarm subsystem that can handle the following data types:
• Boolean Alarms
• Analog Alarms (not available with Mark VIeS controller)
• Boolean Events
• Boolean Holds
Beginning with ControlST V04.04, the following limits to the number of data types are enforced by the ToolboxST
application during the build operation of the Mark VIe, EX2100e, and LS2100e controller:
• There can be a maximum of 4096 Boolean Alarms, Analog Alarms, and Holds, but this includes a limit of 512 Holds
• Boolean Events are limited to 2048
The state information of each alarm, including the Hold state and the Acknowledged state, is stored in the alarm queue of the
controller. There are several benefits to having the persistent alarm state information stored in the controller itself rather than
in the HMI:
• If an HMI fails, the alarms are still in the controller. Another HMI can obtain the information from the controller making
all the alarms and their state available for viewing. Neither alarms nor their state are lost.
• Multiple HMIs may be used to view alarms simultaneously since each HMI only needs to get information directly from
the controller.
• Each alarm has a timestamp of when it became active. If an alarm transitions to inactive and then back to active, the latest
time stamp of when the alarm became active is retained.
• In a redundant controller set, the alarm queue is synchronized so that if one controller fails the other(s) have the alarms.
During normal operation, the designated controller sends the alarm states to the HMI and to the other controllers to keep
them in sync. If a controller fails and is replaced, the new controller will initialize its state from the designated controller.
Therefore, alarms are not lost if one of the controllers in a redundant set reboots.
168 GEH-6721_Vol_I_BP GEH-6721_Vol_I Mark VIe and Mark VIeS Control Systems Volume I
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