Control Engineering
The closer control of machinery operating conditions, eg cooling water temperature and pressure, permits machinery to be run at its optimum design conditions, making for fuel economy and reduced maintenance.
Automation can carry out some tasks far more effectively than men in other areas it is less effective. For example, the monitoring of machinery operating conditions such as temperatures and pressure can be carried out by a solid-state alarm scanning system at the rate of 400 channels/sec giving a degree of surveillance wihcih would be impossible by human observation. Conversely the detection of a noisy bearing a leaky gland or a cracked pipe is scarcely possibly by automatic means. The balance between the possible and the necessary would be achieved in this case by combining automatic monitoring of all the likely fault conditions, with routine machinery space inspection say twice daily.
Classification societies
The class notation of a ship granted by a classification society, is a mark of approval of its standard, and it indicates that the vessel has been built to specific rules and thereafter periodically surveryed. It is the practice to include in the notation a special mark for ships designed to operate with periodically unmanned engine rooms, e.g. Lloyds Register add U.M.S. to the 100A1 notation to signify approval of operation with unattended machinery spaces.
The granting of special notations is also subject to the ship being built in conformity with rules or recommendations concerning automation. The principal international classification societies are Lloyds Register of Shipping, the American Bureau of shipping, Detnorske Veritas, Bureau Veritas and Germanischer Lloyd.
CONTORLS FOR GENERATORS
In unattended machinery installations it is necessary to provide certain control facilities for the electrical generating plant. These may vary from simple load sharing and automatic starting of the emergency generator, to a fully comprehensive system in which generators are started and stopped in accordance with variations in load demand.
Medium-speed propulsion plants normally use all-diesel generating plant. Turbine ships obviously use some os the high quality steam generated in the main boilers in condensing or back pressure turbo charger generators, with a diesel generator for harbour use. The usual arrangement on large-bore diesel propulsion systems is a turbogenerator employing steam generated in a waste-heat boiler, plus diesel generator for manoeuvring, port duty, and periods of high electrical demand.
Diesel generators
The extent of automation can range from simple fault protection with automatic shut-down for lubricating oil failure, to fully automatic operation. For the latter case the function to be carried out are:
- Preparation for engine starting
- Starting and stopping engines according to load demands
- Sychronisation of incoming sets with supply
- Circuit breaker closure
- Load sharing between alternators
- Maintenance of supply frequency and voltage
- Engine/alternator fault protection
- Preferential tripping of non essential loads
When diesel generators are arranged for automatic operations, it is good policy to arrange for off-duty sets to be circulated with main engine cooling water so that they are in state od readiness when required. Pre-starting preparations are then simply limited to lubricating oil priming.
It is necessary to provide fault protection for lubricating oil and cooling services, and in a fully automatic system these fault signals can be employed to start a standby machine, place it on line, and stop the defective set. In some installations, automatic controls carry out the sequence as far as synchronisation, and leave final circuit breaker closure to the engineer.
Turbo-generators
The starting and shut-down sequences for a turbo-generator are more complex than those needed for a diesel-driven set, and fully automatic control is therefore less frequenctly encountered. However, the control facilities are often less frequently encountered. However, the control facilities are often centralized in the control room, together with sequence indicator lights to enable the operator to verify each step before proceeding to the next. Interlocks may also be employed to guard against error.
The start up sequence given below is necessarily general, but it illustrates the principal and may be applied to remote manual or automatic control:
- Reset governor trip lever
- Reset emergency stop valve
- Start auxiliary L.O. pump
- Start circulating pump
- Apply gland steam
- Start extraction pump
- Start air ejectors
- Open steam valve to run-up turbine
Where a waste heat boiler (economizer- a word form economy) is used to supply steam to a turbo-alternator, control of steam output is normally controlled by a three way valve in the exhaust uptake, the position of which is regulated in accordance with steam demand. Surplus waste-heat is then diverted to a silencer.
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