Annunciation systems

These systems give early warning of impending trouble to allow personnel to take corrective action prior to a shut-in, and provide informa- 

Annunciator panels should be in a central location with alarm annunciators and shutdown annunciators grouped separately. The first alarm and the first shut-down normally sound a horn and are annunciated. This is called first-out indication. Subsequent shutdown or alarm signals received by the panel are either not annunciated or are annunciated in a different manner so that the operator can determine the initiating cause of the process upset. 

Alarm signals may come from the output signal used to control an operational valve. Shutdown signals should come from a completely separate instrument not dependent upon a normally used output signal for operation. 

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An alarm annunciation system that eliminates operator information overload during major plant transients. 

HUMAN FACTORS PROGRAM PLAN -ANNUNCIATOR SYSTEMS... 

NUREG/CR-3217, "Near-Term Improvements for Nuclear Power Plant Control Room Annunciator Systems", U.S. Nuclear Regulatory Commission, April 1983. 

Alarms are provided as part of the "human engineered" control complex (see CESSAR-DC, Chapter 18) and are included in the plant computer annunciator systems. After passing through the alarm unit, the amplified accelerometer signals are multiplexed, filtered, digitized, and transmitted to a computer for further analyses. The computer maintains data storage, performs comparisons, develops trends, and performs analyses to enhance the signal characteristics. 

NUREG/CR-3217, "Near -term improvements for nuclear power plant control room annunciator systems," issued April 1983. 

Dousing Water System/Suppression Pool System Fuel Handling System Annunciation System... 

Another serious distraction to a process operator is the multiple alarm event, where a single event within the process results in iTuuti-ple alarms. When the operator must individually acknowledge each alarm, considerable time can be lost in silencing the obnoxious annunciator before the real problem is addressed. Air-handling systems are especially vulnerable to this, where any fluctuation in pressure (for example, resulting from a blower trip) can cause a number of pressure alarms to occur. Point alarms (high alarms, low alarms, status alarms, etc.) are especially vulnerable to the multiple alarm event. This can be addressed in one of two ways ... 

Safety systems are typically divided into emergency trip/shutdown functions, controlled (slow) shutdown, alarm activation, or startup annunciation of auxiliary equipment such as oil pumps. 

Alarms are used to alert operators of serious, and potentially hazardous, deviations in process conditions. Key instruments are fitted with switches and relays to operate audible and visual alarms on the control panels and annunciator panels. Where delay, or lack of response, by the operator is likely to lead to the rapid development of a hazardous situation, the instrument would be fitted with a trip system to take action automatically to avert the hazard such as shutting down pumps, closing valves, operating emergency systems. 

An alarm system consists of sensors that detect different types of events an arming station that is used to turn the system on and off a control panel that receives information, processes it, and transmits the alarm and an annunciator that generates a visual and/or audible response to the alarm. When a sensor is tripped it sends a signal to a control panel, which triggers a visual or audible alarm and/or notifies a central monitoring station. A more complete description of each of the components of an alarm system is provided below. 

Once a sensor in an alarm system detects an event, it must communicate an alarm signal. The two basic types of alarm communication systems are hardwired and wireless. Hardwired systems rely on wire that is run from the control panel to each of the detection devices and annunciators. Wireless systems transmit signals from a transmitter to a receiver through the air—primarily using radio or other waves. Hardwired... 

In addition to the abbreviated LCD display on the fire alarm panel, an annunciator should be provided to graphically display facility conditions in all areas. Often this annunciator is an additional panel provided with the fire alarm system, which contains a graphic display or representation of the plant or area being monitored as well as illumination capabilities which identify the status of all monitored plant areas. 

More and more commonly, fire alarm panel data is transferred to a safety instrumented system (SIS) for graphic annunciation though the SIS human-machine interface (HMI). 

Where releases of flammable or toxic chemicals are possible, a flammable or toxic gas alarm system is often established as part of the plant emergency alarm system. Best practices require different types of alarms to be annunciated differently, both audibly and visually. For example, the toxic alarm stations may be provided with a blue light to distinguish them from fire alarm stations that are red. A consistent color system for lights should be adopted. 

A main control and annunciator panel should be installed when the fire alarm system requires more than a single alarm zone. The panel should be installed in the control room or other continuously staffed location. Separate detection zones should be provided for each distinct fire area and identified by a permanent label. A detailed map of the area should also be provided at the annunciator that identifies which zone relates to which annunciator lamp. Systems with more than ten separate zones should be provided with an electric or electroniczone "mimic" panel showingthe location of all alarms on the graphic display of the platform. Basic arrangements of equipment and system design should be in accordance with NFPA 72. A locked main fire panel and control cabinet should be provided. 

The original GC control system took the form of a central room which monitors the flowllne6, oil, water, and utility sections, plus a smaller satellite control room monitoring the gas compression and gas conditioning section of the plant. Closed loop process control, such as separator liquid level, pressure, flow and temperature control were handled by local pneumatic analog controllers. The key process variables are displayed in the control room via electronic instrumentation. All the key process and equipment trouble alarms are annunciated m the control rooms, plus the on/off status of key machinery and open/close status of key valves are displayed. 

The Fluid Flame energy systems are designed to run themselves without the need for full-time operators. The system is fully automated and is equipped with annunciators to alert operators when problems arise. A number of electrical process controllers are used to maintain constant temperatures in the bed and in the vapor space of the combustion cell in order to provide steam at constant pressure. Signals from these controllers dictate the feed rate from the metering bin and the amount of excess air fed into the system. The temperature is controlled in order to maintain constant parameters throughout the system and to keep temperatures below the slagging temperatures of the ash. Normal temperature variation is less than +5C° (9F°), and the response time to process variations is rapid. 

Trips shall be provided to annunciate (audible and visual) and scram the reactor for exponential power level rate Increases having periods of 15 seconds or less. Trips and instrumentation ranges shall be fixed when the reactor power level is in this range (lO" to 10 ). The xesponse tlme of the system shall be k seconds or less. Geometric distribution of transducers is not important in first four decades of this range (10 7 to 10 3), All transducers shall be located in one general area to monitor ths same power level. 

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