IEC 62241-2004 pdf – Nuclear power plants – Main control room – Alarm functions and presentation.
1 Scope and object This International Standard provides the functional requirements for the alarm systems in the main control room of nuclear power plants. It gives definitions of the terms used for alarm functions. It also establishes the human factors requirements and the design guidelines for alarm presentation for the main control room of nuclear power plants. NOTE The alarm functions can be implemented in a dedicated system (alarm system) or preferably be an integrated part of the main control room HMI (Human-Machine Interface) system. It specifies the alarm functions including those for the selection and definition of original alarm signals, alarm signal processing (e.g., event sequence processing, static and dynamic prioritisation), alarm display processing (e.g., alarm suppression) and the use of associated display devices (e.g., Visual Display Unit (VDU), conventional alarm fascia, mural display), with acknowledge and reset sequences, and other related matters. Under abnormal conditions or plant transient conditions in the nuclear power plant, many alarms occur simultaneously. For this reason, the alarm functions of the main control room of nuclear power plants require special considerations for human factors engineering and system configuration, to avoid operator misunderstandings and to provide the operator with adequate information. Therefore, the scope includes special alarm functions based on human factors for monitoring and operation of nuclear power plants. It does not cover specific alarm systems, such as the fire alarm and security alarm systems. The object of this Standard is to establish a common international understanding of the underlying functional design basis of alarm systems for control rooms, covering the corresponding functional requirements, the human factors requirements and design guidelines for the alarm functions and alarm presentation for the main control room of nuclear power plants.
3 Terms and definitions For the purposes of this document, the terms and definitions given in IEC 60964, as well as the following definitions, apply. NOTE When the same term is defined in IEC 60964 and in this standard, the definition given in this standard applies. 3.1 alarm item of diagnostic, prognostic, or guidance information, which is used to alert the operator and to draw his or her attention to a process or system deviation NOTE Specific information provided by alarms includes the existence of an anomaly for which corrective action might be needed, the cause and potential consequences of the anomaly, the overall plant status, corrective action to the anomaly, and feedback of corrective actions. Two types of deviation may be recognised: – unplanned – undesirable process deviations and equipment faults; – planned – deviations in process conditions or equipment status that are the expected response to but could be indicative of undesirable plant conditions. 3.2 alarm acknowledgement action, which operators are required to carry out to show that they have recognized an alarm presented to them 3.3 alarm avalanche condition where a large number of alarms appear within a short time at a rate exceeding the operator’s capacity to take them into account 3.4 alarm coding method of highlighting an object of concern visually or audibly, with the intention of drawing the operator’s attention to the object 3.5 alarm control set of alarm presentation control functions, which support the operators in recognizing alarm status correctly and in a timely manner NOTE Alarm acknowledgement, silence, and reset are typical examples of alarm control.
3.6 alarm display processing alarm signal processing functions or mechanisms, which are used in controlling or enhancing alarm presentation, for example, grouped alarms, alarm suppression NOTE The alarm display processing operates on the alarms identified by the alarm signal processing (q.v.) logic. 3.7 alarm fascia alarm display consisting of a set of alarm tiles 3.8 alarm reduction or filtering alarm signal processing function or mechanism which has the aim of reducing the number of alarms for operator attention NOTE Filtering or reduction are generic terms. 3.9 alarm generation alarm signal processing function or mechanism, which is used to generate an alarm based on a logical combination of pre-defined alarm signals and non-alarm binary signals (e.g., component status signals) NOTE See also under alarm signal processing logic. 3.10 alarm legend caption identifying an alarm 3.11 alarm message alarm phrase identifying an alarm, which is used typically in VDU-based alarm displays NOTE It may be associated with supplemental information such as the time of alarm activation, the threshold, and the trend of a corresponding process. It is also used to mean a string of speech-based audible announcements, representing an alarm, which may be associated with guidance or other supplemental information.