Central operating station (cos)

Central operating station (cos) COMPARISON OF SYSTEMSSystems, telemetering or control, may be either pneumatic, hydraulic, or electronic-electric, or combination.Hydraulic systems are generally more restricted in application. Basically the technique is as for pneumatics but fluid cannot be allowed to escape and a recovery-storage system is required. Advantages of Pneumatic system: Less expensive initially, this is in spite of tubing and air supply costs.No heat generation and safe in explosive atmosphere.Less susceptible to power supply variation, but do have appreciable time lags.Direct application, without transducers, to large final power actuators.

Advantages of an electronic system:Small and adaptable with cheap flexible transmission lines.No moving parts can however generate heat.Stable, generally accurate and very short time lags.Low power consumption, Direct application to computer but often needs final control element transducers.

Advantages of hydraulic system:Nearly instant response as fluid is virtually incompressible.It can readily provide any type of motionIt can have accurate position controlIt has high amplification of power

Control In Different Section in Central Operating Station (COS)

Permits a one man operation of the power plant through bridge control of the propeller from full ahead or full astern.It is the centralized area from observing and operating the major components of the system.The nerve center of the automated engine room

CONTROLS FOUND IN THE COMBUSTION SECTION

Control of main steam pressureControl of fuel oil pressureControl of air to burnersControl of superheated temperatureControl of water levelControl of feed water regulating valveControl of feed pump speedBurner Management Control of burnerFail safe protection

CONTROLS FOUND IN THE SERVICE SECTION

Ship service air supplyCentral air supplyFire pump system Fresh water systemSea water service system Generator information Evaporator information

CONTROLS FOUND IN THE PROPULSION SYSTEM

Throttle controlEngine order telegraph Shaft speed tachometersMain Lub oil pumpsMain vacuum controlMonitoring systemCondensate system Temperature control

Monitoring SystemsTo replace the human operator, who would normally carry out the rule of monitoring any operation, automatic monitoring systems must be introduced. Monitoring systems vary in both size and complexity, ranging from a simple make-break switch operated by pressure to activate an alarm, to a sophisticated sequential scanning system.

Sequential monitoring of sensors and comparison of readings with a stored data bank of alarm limit settings. Some modern systems can have over 6000 monitoring points around the ship.Data acquisition and storage on computer tapes or disks for later reference. Some ships now will automatically transmit this data by satellite to the company headquarters for statistical analysis.

Data logging of monitored processes, with trend analysis computer VDU displays.Assessment of the machinery operating conditions, and automatic adjustment to provide the optimum operating conditions for the prevailing conditions. This particular facility may be used to adjust the speed of a ship in passage to give the greatest fuel economy possible.

Machinery condition monitoring. The machinery may be fitted with sensors to monitor the combustion process and general health of the engine to aid efficient running and predictive maintenance schedules.

Alarm SystemsWithin the rules and regulations are features which must be included into the design of control equipment, in particular the alarm system. 4, 5, 6, Alarm systems are associated with control and safety systems and are normally an integral part of the monitoring system. The design must allow the alarm system to function independently of any control or safety system, where practical, so that the alarm system will still function if there is a fault in these other systems.

There are many other different features which may be fitted to alarms systems and these include:automatic reset where the alarm will automatically reset after normal conditions have been restored (but this would not be acceptable to classification societies unless the alarm has already been accepted or acknowledged); manual reset where the alarm must be manually reset after normal conditions are restored; lock in on fleeting alarms where the alarm condition is still displayed even though the fault condition has quickly appeared and then disappeared;time delay to prevent raising of spurious alarm signals; event recorder which prints out a record of the alarm details and the sequence and time of alarms;first up or first out enabling identification of the first alarm that operated within a group or flood of alarms.

Engine Room AlarmsMachinery fault alarm systems A system of alarm display must be provided which ensures identification of faults in the propulsion plant, and other essential machinery. Audible and visual alarms are to be operated when a fault condition arises and the fault selection system must inform the engineers of the precise nature of the fault.

Automatic shutdown systems When certain plant variables (e.g. lub oil pressure) exceeded prescribed upper or lower limits, the operation of the main propulsion plant or other essential machineries (e.g. electrical generation plant) may become dangerous, or result in costly damage. Hence there must be shutdown system which causes the machinery involved to shutdown in the correct sequence. In all cases alarms would be triggered in the main console and on the bridge.

Bilge level alarm system An alarm system must be provided to warn the liquid in the machinery space when the bilge has reached a high level. Automatic starting of the bilge pump is not advisable because of the possibility of pollution.

Fire Detection Alarm SystemA fully automatic fire detection system must be fitted in the machinery space in all UMS certified ships, satisfying the following conditions:A fire detector indicator panel is to be located on the bridge, in such a position that a fire in the machinery space cannot make it inoperative. When the engine room consist of more than on compartment the alarm panel should be sectionalized.

The audible fire alarm must have a tune which clearly distinguishes it from all other alarmsFailure of the fire detection alarm system power supply must be indicated by visual and audible means.Detector heads, or an approved design must be fitted so that all potential fire hazards are guarded.The fire detection alarm system must be capable of being tested, and manually triggered.

Module 6Electrical Power Sources

A. Where the electrical power requirements are normally supplied by two or more generators operating in parallel, arrangements are to be provided e.g. by load shedding, so that the remaining generators are kept in service in the event of loss of a generator. The load shedding schedule should take account of the essential services, particularly with regard to those necessary for the safe automatic shut down of the plant, and the alarm system.

B. In addition to this, an emergency generator must be provided, which is outside the machinery space. This should be automatically started when the normal generators plant fails. It must be of sufficient capacity to power all essential electrical equipment for storage and propulsion including all necessary automatic sequential operations, alarm panels, and essential machinery space lighting. This power should be available within 5 seconds of loss of service generation plant.

C. In addition to this, the alarm self monitoring equipment including the fire alarm system may have separate battery supply which comes into use should the emergency generator fail.

Safety Systems

Safety is of paramount importance in any control system. A safety system is a system which reduces dangers and risks of injury to personnel and damage to machinery. Any safety system should operate automatically to prevent endangering both personnel and machinery.

Typical Safety Systems1. Machinery Auto start-up

These systems are provided with a stand-by device which will automatically start in the event of the running device failing through a fault condition. The start-up of the stand-by device must restore the normal operating conditions and give an alarm on failure of the online device.Electrical generators can be arranged with automatic start-up, which can be initiated by a failure of the running generator, or by the electrical load for one generator. In the latter case the switchboard must also be fitted with automatic synchronizing equipment to allow the two generators to run in parallel and load share.

2. Reduction of Power

With this safety system the machinery output power is temporarily reduced to meet the prevailing conditions. There are several situations which may trigger this device, the most common being excessive high temperatures, low pressures or high loads on the machinery.3. Emergency generatorsAn emergency generator must be provided, which is outside the machinery space. This should be automatically started when the normal generators plant fails. It must be of sufficient capacity to power all essential electrical equipment for storage and propulsion including all necessary automatic sequential operations, alarm panels, and essential machinery space lighting. This power should be available within 5 seconds of loss of service generation plant.

4. Machinery Shut Down

With the shut down safety system the machinery is protected from critical conditions by shutting off the fuel supply or power supply thereby stopping the machinery. In some cases a shut down will follow a reduction of power if the prevailing conditions continue to develop into a critical situation or if no remedial action is taken after a certain time period.

5. Bilge level detection system

An alarm system must be fitted to provide warning when the content of the machinery space bilge wells has reached a predetermined level. This level must be low enough for the contents of the bilges not to overflow onto the tank tops.

Bilge water moving over the tank tops is particularly dangerous for several reasons.

It can be a fire hazard, especially if there is oil in the bilge water. A local fire could rapidly spread through the machinery space.There is danger of free surface effect on the stability of the vessel.There is a possibility water damage to electrical cables and motors, from splashing.Some ships are fitted with automatic pumping for bilges. Before the bilge level reaches the alarm level a float controller will activate the bilge pump, open the required valves and activate the bilge pump. The system must be designed to avoid causing pollution or masking an actual leak situation.

6. Fire detection alarm systemsThe fire detector indicator and alarm system must be situated in such a position that fire in the machinery spaces will not make it inoperative. Commonly it is sited on the bridge or in a special fire control centre.

Fire DetectorsIn order to assess the efficiency of the various types of fire detectors it is necessary to consider the fire spectrum. Most ship fires start extremely slowly; frequently a smoldering or glowing fire can burn for some time, the lack of oxygen or fuel preventing it spreading. In many recorded cases, it was only after the opening of a door or the fracturing of a fuel line that caused the fire to burst into open flames, thus causing a sharp rise in temperature.

Photoelectric smoke detectorsThis detector will detect smoke based on the percentage of obstruction or reflection produced by the visible particles in the smoke. A number of types are available, all of which contain a light source and a photoelectric receiver. Dependent on the design of the device, an alarm will be raised upon an increase or decrease in the light transmitted to the receiver, owing to the obstruction or reflection of the light source.

Infra red flame detectorWhere it is known that a risk likely to involve flame at a very early stage, it is possible to detect the electromagnetic radiation from the flame and avoid the delay of waiting for smoke, combustion products of heat to reach the detector.

Heat detectorsThe most commonly used heat detector heat is the rate of rise/fixed temperature type, which is dual action thermostat operating at a predetermined temperature or when the temperature rises unusually quickly, as would occur in the case of a fast burning fire, in which case the detector would operate and raise an alarm before the fixed temperature setting was reached.Operation depends on differential movement of two bimetallic strips, wound as springs on a common axis, with one spring is shielded. Fast temperature change produces differential movement and closure of contacts affixed to the springs, causing an alarm to be raised before the fixed temperature stop is reached.

7. Control Panels

The following features are incorporated in control panels: Audible fire alarm circuitsidentification of zone of fireAutomatic change-over from normal power supply to emergency power supplySystem fault alarm circuits

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