Lesson nineteen Marine Electrical equipment The complete electrical plant on board ship is made up of power generation equipment,a distribution system and the many power utilising devices. Electricity is used for the motor drive of many auxiliaries and also for deck machinery, lighting, ventilation and air conditioning equipment A constant supply of electricity is essential for safe ship and machinery operation, and therefore standby or additional capacity is necessary together with emergency supply equipment Emergency equipment may take the form of an automatically starting emergency alternator or storage batteries may be used The complete range of electrical equipment will include generators, switch gear for control nd distribution, motors and their associated starting equipment and emergency supply arrangements Alternating or direct current Alternating current has now all but replaced direct current as the standard supply for all marine installations. The use of alternating current has a number of important advantages: for example, reduced first cost, less weight, less space required and a reduction in maintenance requirements. Direct current does how-ever offer advantages in motor control using, for example, the Ward-Leonard system which provides a wide range of speed Machine rating Motors and generators, both d. c and ac, are rated as Continuous Maximum Rated(CMR) machines. This means they can accept a considerable momentary overload and perhaps even a moderate overload for a longer duration Temperature affects the performance of all electrical equipment and also the useful life of the insulation and thus the equipment itself. The total temperature of an operating machine is a result of the ambient air temperature and the heating effect of current in the windings. Temperature rise is measured above this total temperature. Adequate ventilation of electrical equipment is therefore essential. Classification Societies have set requirements for the various classes of insulation. The usual classes for marine installations are E, B and F where particular insulation materials are specified and increasing temperature rises allowed in the order stated Depending upon the location, a motor or generator will have one of a number of possible types of enclosure. Drip-proof is most common and provides protection from falling liquids or liquids being drawn in by ventilating air. A watertight enclosure' provides protection for immersion under a low head of water for up to one hour. Weatherproof, "hose proof and'deck watertight provide immersion protection for only one minmet. " Totally enclosed'can also be acted ventilation from outside the flameproof enclosure is capable of withstanding an explosion of some particular flammable wa that may occur within it. It must also stop the transfer of flame, i.e. contain any fire or explosion Direct current generators A current is produced when a single coil of wire is rotated in a magnetic field. When the current is collected using a ring which is split into two halves, that is, a commutator, a direct or single direction current is produced. The current produced may be increased by the use of many turns of wire and additional magnetic fields With many coils connected to the commutator, sparking will occur as the current collectingLesson Nineteen Marine Electrical Equipment The complete electrical plant on board ship is made up of power generation equipment, a distribution system and the many power utilising devices. Electricity is used for the motor drive of many auxiliaries and also for deck machinery, lighting, ventilation and air conditioning equipment. A constant supply of electricity is essential for safe ship and machinery operation, and therefore standby or additional capacity is necessary together with emergency supply equipment. Emergency equipment may take the form of an automatically starting emergency alternator or storage batteries may be used. The complete range of electrical equipment will include generators, switch gear for control and distribution, motors and their associated starting equipment and emergency supply arrangements. Alternating or direct current Alternating current has now all but replaced direct current as the standard supply for all marine installations. The use of alternating current has a number of important advantages: for example, reduced first cost, less weight, less space required and a reduction in maintenance requirements. Direct current does how-ever offer advantages in motor control using, for example, the Ward-Leonard system which provides a wide range of speed. Machine rating Motors and generators, both d.c. and a.c. , are rated as Continuous Maximum Rated (CMR) machines. This means they can accept a considerable momentary overload and perhaps even a moderate overload for a longer duration. Temperature affects the performance of all electrical equipment and also the useful life of the insulation and thus the equipment itself. The total temperature of an operating machine is a result of the ambient air temperature and the heating effect of current in the windings. Temperature rise is measured above this total temperature. Adequate ventilation of electrical equipment is therefore essential. Classification Societies have set requirements for the various classes of insulation. The usual classes for marine installations are E,B and F where particular insulation materials are specified and increasing temperature rises allowed in the order stated. Enclosures Depending upon the location, a motor or generator will have one of a number of possible types of enclosure. ‘Drip-proof’ is most common and provides protection from falling liquids or liquids being drawn in by ventilating air. A ‘watertight enclosure’ provides protection for immersion under a low head of water for up to one hour. ‘Weatherproof’, ‘hose proof’ and ‘deck watertight’ provide immersion protection for only one minmet. ‘Totally enclosed ’ can also be used or an arrangement providing ducted ventilation from outside the manager space. A ‘flameproof ’ enclosure is capable of withstanding an explosion of some particular flammable was that may occur within it. It must also stop the transfer of flame, i.e. contain any fire or explosion. Direct current generators A current is produced when a single coil of wire is rotated in a magnetic field. When the current is collected using a ring which is split into two halves, that is, a commutator, a direct or single direction current is produced. The current produced may be increased by the use of many turns of wire and additional magnetic fields. With many coils connected to the commutator, sparking will occur as the current collecting