Tech Focus: Power plant alarm systemson Mar 13, 2012
Step 4: Alarm Documentation and Rationalisation
Alarm Documentation and Rationalisation (D&R) is a consistent methodology for rationalising, prioritising, documenting, and revising alarms. D&R involves a thorough re-examination of an existing alarm system to ensure it complies with the alarm philosophy. D&R is also an important task in designing new alarm systems.
During D&R, a team of knowledgeable people discuss each configured and possible alarm, verifying that each alarm should exist. It is then verified that all alarms represent an abnormal situation that requires operator action, and these genuine alarms assigned an appropriate priority.
During this process, any duplicate alarms can also be eliminated. The alarm causes, consequences, and proper operator responses are then documented for every alarm. Any special alarm handling e.g. special logic or advanced techniques must also be included so that operators are made aware of any hidden dependencies that could be disruptive.
Performing a D&R creates a Master Alarm Database, which is the collection of proper settings and information for each alarm.
This document will be used in the rest of the process for state-based alarm management, flood suppression, audit and enforcement mechanisms, management of change, and for operator information during commissioning and operation.
Step 5: Alarm System Audit and Enforcement
Proper Management of Change (MOC) is an essential practice. Without it, benefits achieved from proper design or alarm improvement efforts can be lost in a relatively short period.
Alarm audit and enforcement is a software function that periodically and automatically checks for differences between the current alarm settings and the Master Alarm Database.
It then reports any differences, and may optionally restore the system to the proper settings. This functionality helps manage the ongoing, and often undocumented, changes made by operators and others, in order to ensure the alarm system remains in the proper configuration.
Step 6: Implement Real-Time Alarm Management
Power generation is a complex process subject to many abnormal situations including equipment trips, unit trips, and post-outage restarts. One way to help operators deal with the many challenges of power generation alarming is to employ sophisticated, real-time alarm management capabilities.
Alarm shelving is the operator-initiated temporary suppression of alarms in a highly controlled manner, and we recommend a software solution since paper-based procedures and tracking processes have historically been proven to be both cumbersome and unreliable. Limits should be placed on suppression authorisation and duration. Accurate lists of suppressed alarms should be very easily available and reviewed at shift change.
State-based alarming is the adaptation of the alarm system to the current operating mode of the facility. This can include partial generation, load shedding, startup, spinning reserve, or similar modes. State-based alarming dynamically modifies the alarm system settings in predetermined ways based on detecting changes in the process state. This ensures that alarms are always meaningful and accurate.
Alarm flood suppression is the dynamic management of pre-defined groups of alarms based on triggering events, such as equipment trips. They are characterised by the annunciation of a large number of alarms in a short period, which overwhelms the operator and renders the alarm system unusable. The risks of having a major process upset or an accident are much higher during an alarm flood.
Step 7: Control and Maintain Alarm System Performance
Processes and sensors change over time, and alarm behaviour will change with them. Alarms working correctly now may become nuisances or malfunction in the future. Therefore, alarm system Key Performance Indicators should be developed and routinely reported to appropriate personnel.
Additionally, effective management of change methodologies, as well as an ongoing program of system analysis and correction of problems as they occur, is needed to maintain an effective alarm system. Modern alarm management software is an essential element to monitoring and maintaining alarm system performance.
Overloaded and malfunctioning alarm systems continue to negatively impact the profitability, safety, and environmental performance of such facilities worldwide.
The rapid development of Middle East power networks is resulting sub-optimal alarm management, but it is also an opportunity for the region’s power generation
companies to start as they mean to go on – with reliable and profitable operations.
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