Power Plant Instrumentation and Control Handbook

3. Annunciation and Sequence of Event: Preamble

Both annunciation and sequence of event (SOE) could be a part of the DCS as well as installed as an independent system. The alarm annunciator is initiated by a trouble/fault signal (contact) that brings the trouble at any part of the plant to the notice of operating personnel. The SOE stores and records various events in sequence so that the event can be studied and analyzed in a more precise manner to detect the root cause of the problem. A story cannot be properly understood if the sequence of events is lost. Similarly, after any trip and/or any major fault it is most important to know the entire SOE: How did it happen and what are the consequences? The first event is not always the root cause ...