PRACTICAL MARINE ELECTRICAL KNOWLEDGE PDF
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Email: [email protected] cittadelmonte.info British Library Cataloguing in Publication. Hall, Dennis T. Practical Marine Electrical Knowledge. - Second. Written for marine and electrical engineers, this book provides up-to-date information on ships' electrical systems to support the knowledge requirements of . Download Best Book Practical Marine Electrical Knowledge, Download Online Practical Marine Electrical Knowledge Book, Download pdf Practical Marine.
Be the first to review this product. Clearly written and extensively illustrated, this publication provides a comprehensive source of reference for management and operational level marine engineers, electrical engineers and electricians with limited experience of modern electrical applications, and students currently studying marine and electrical engineering. The book covers the fundamentals, operating principles and safe working practices of most electrical systems and automation found on board, including appliances, their circuits and common troubleshooting practices. Circuit Calculations. Electrical Diagrams. Electrical Safety.
Practical marine electrical knowledge download
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Marine Electrical -Dennis.T.hall
Why not review it? If you have a question about this product, please contact us directly. Submit Review. Ships with very large electrical loads have generators operating at high voltages HV of 3. Such high voltages are economically necessary in high power systems to reduce the size of current, and so reduce the size of conductors and equipment required.
Operating at such high voltages is becoming more common as ship size and complexity increase. Offshore oil and gas production platforms operate at up to The frequency of an AC power system can be 50 Hz or 60 Hz. In Europe and most of the world, the national frequency is 50 Hz, but it is 60 Hz in North America and in a few other countries.
The most common power frequency adopted for use on board ships and offshore platforms is 60 Hz. This higher frequency means that motors and generators run at higher speeds, with a consequent reduction in size for a given power rating. Lighting and low power single-phase supplies operate at the lower voltage of V, which is derived from power step-down transformers connected, with their primary windings, to the V V system.
The electrical energy is routed through the main switchboard, then distributed via cables to section and distribution boards, and ultimately to the final load consumers. The circuit breakers and switches are the means of interrupting the flow of electric current. The fuses and relays protect the distribution system from the damaging effects of large fault currents.
Figure 2. The system is called a radial, or branching, system and it has a simple and logical structure. Each item of load is supplied at its rated voltage via the correct size of cable and is protected by the correctly rated protection device. The main board supplies bulk power to motor group starter boards often part of the main board , section boards and distribution boards.
Protection, eg circuit breakers and fuses strategically placed throughout the system, automatically disconnects a faulty circuit within the network. Transformers interconnect the high voltage and low voltage distribution sections of the system. The operational state of a distribution system is constantly monitored by the power management system for active and reactive load sharing, voltage, current and frequency power factor is also often monitored.
Protection appliances monitor for over and undervoltage, overcurrent, over and under frequency, reverse power and earth faults. The required electrical services are broadly considered as main and emergency supplies. For ships built in Europe, a V, three-phase system is common.
Three-phase AC V, 50 Hz earthed neutral systems can also be found on board. If a generator overload condition develops, the power management system PMS disconnects non-essential services in a defined order at set time intervals, eg: The order of tripping varies with the ship type. When sufficient non-essential load has been The main electrical load is divided into essential and non-essential services.
Essential services are for the safety of personnel and for the safe navigation and propulsion of the ship and they may be supplied directly from the main switchboard or via section boards or distribution boards. Emergency supplies are necessary for loads required to handle a potentially dangerous situation.
To maintain generator operation during an overload, a preferential load shedding arrangement is employed. This is achieved by an analogue current monitoring relay, called a preference trip relay. If a generator overload develops, the preference trip relay sets an alarm and acts to trip selected non-essential loads. This reduces the generator load so that it may continue to supply essential circuits, maintaining its nominal load.
In the majority of cases, the preference trip protection is incorporated into a combined electronic relay or programmable logic control- based PMS that also monitors generator over and undervoltage, overcurrent and reverse power. Emergency supply An emergency electrical power service must be provided in the event of a main power failure. This is for emergency lighting, alarms, communications, watertight doors and other services necessary to maintain safety and permit safe evacuation of the ship.
Regulations require that the emergency power source is a generator, batteries or both. The emergency power source must be self-contained and not dependent upon any other engine room power supply. A battery, when fully charged, is self- contained. An emergency generator must have an internal combustion engine as prime mover and have its own fuel supply tank, starting equipment and switchboard in the near vicinity. The emergency supply should automatically operate as quickly as possible but not later than 45 seconds after the failure of the main source of power.
Emergency batteries should be arranged so that they are switched into service immediately following a main power failure. Emergency generators can be hand cranked, but are usually automatically started by compressed air or a battery to ensure immediate run-up following a main power failure. Other cranking options should be provided to ensure safety, eg cranking by means of the electric starter driven with a set of batteries or with a hydraulically driven starter accompanied by a hand-driven pump and hydraulic accumulator.
Although regulations may permit a battery to be the sole source of emergency power, in practice a suitable battery may be physically very large and so a diesel-driven generator is usually installed, with its own starting battery large enough to sustain several consequent starting attempts or to air start hydraulic start supply. On passenger ships, SOLAS Chapter II-1, Part D, requires that the primary emergency power supply is provided by a diesel-driven generator for up to 36 hours 18 hours for non-passenger vessels.
In addition, an emergency transitional battery must also be installed to maintain vital services mainly lighting for a short period — typically a minimum of 3 hours.
This emergency battery is to ensure that a total blackout cannot occur in the transitional period between loss of main power and the connection of the emergency generator. A typical distribution system, incorporating emergency power supplies, is shown in Figure 2.
There is no standard electrical supply arrangement as all ships differ in some respect. Both the main and the emergency consumers are supplied by the main service generators during normal operating conditions.
In the event of an emergency, only the emergency services are supplied by the emergency generator. The emergency power system must be ready and available at all times and this level of reliability requires special care and maintenance.
The system must be tested at regular intervals to confirm that it does operate correctly.
The testing is normally carried out during the weekly emergency fire and boat drill practice sessions. The main generators are not shut down, but the emergency power sources are energised and connected to supply the emergency services for the period of the practice session.
The emergency generator may be used as the main power supply during lay time either in single mode or in parallel with one of main generators. Independence of the emergency power supply from other auxiliaries of the main engine plant must be ensured. Similar systems ashore are normally earthed to the ground.
An earthed system has the supply neutral point connected to earth. A circuit consists of two parts: Three basic circuit faults that can occur are shown in Figure 2. The size of fault current that will occur depends on the overall impedance left in the circuit under fault conditions.
The majority of earth faults occur within electrical equipment due to an insulation failure or a loose wire, which allows a live conductor to come into contact with its earthed metal enclosure. To protect against the dangers of electric shock and fire that may result from earth faults, the metal enclosures and other non-current carrying metal QUESTION A 10 A motor operates from a V insulated system.
The supply cables have a total impedance of 0. Such earth bonding of equipment ensures that it always remains at zero volts. High voltage systems 3. The ohmic value of each earthing resistor is usually chosen so as to limit the maximum earth fault current to not more than the generator full load current. Such a neutral earthing resistor NER is usually assembled from metallic plates.
The use of such an earthed HV system means that a single earth fault will cause current to flow in the neutral connection wire. Certain essential loads eg steering gear can be supplied via a transformer, with its secondary winding unearthed to maintain security of supply in the event of a single earth fault.
Regulations insist that tankers have only insulated distribution systems. This is intended to reduce danger from earth fault currents circulating in the hull within hazardous zones, which may cause an explosion of the flammable cargo. An exception allowed by regulating bodies occurs where a tanker has a 3. Such a system is permitted providing that the earthed system does not extend forward of the engine room bulkhead and into the hazardous area. Electrical supplies forward of the engine room bulkhead are usually three-phase V insulated 2.
The faulted electrical equipment would be immediately isolated from the supply and so rendered safe. However, the loss of power supply could create a hazardous situation, particularly if the equipment was classed essential, eg steering gear.
The large fault current could also cause arcing damage at the fault location. This is the important point: An insulated distribution system, therefore, requires two earth faults on two different lines to cause an earth fault current to flow. This has led to the development and use of earth fault indicator instruments.
One common type of earth fault monitor connects a small DC voltage to the distribution system. Any resulting DC current is a measure of the insulation resistance of the system. The injection-type instrument limits the maximum earth fault monitoring current to only 1 mA compared with about 60 mA for earth lamps , and the meter indicates insulation resistance directly in k?
The monitor triggers an alarm when its set value is reached. This type of arrangement has been developed to meet regulations that demand that circuits in or passing through hazardous zones must be continuously monitoring the system insulation resistance.
Visual and audible alarms are given if the insulation resistance falls below a pre-set value. An earth fault monitor should be fitted to the main and emergency switchboards to indicate the presence of an earth fault on each isolated section of a distribution system, eg on the V and V sections. An earth fault monitor can be either a set of indicator lamps or an instrument or both to show the system IR value to earth.
Earth indication lamps in a three-phase AC system are arranged as shown in Figure 2. When the system is healthy no earth faults , the lamps glow with equal half brilliance. If an earth fault occurs on one line as illustrated in the line 3 earth fault example in Figure 2. The other lamps experience an increased voltage so will glow brighter than before. Earth indication lamps have been the most common method used for many years and are an inexpensive installation that is easy to understand.
If the motor is healthy no earth faults , the phasor sum of the currents measured by the CT is zero. The earth fault monitor on the switchboard shows the presence of an earth fault on the distribution system. It is up to the maintenance staff to trace search for the exact location of the fault and then to clear it as quickly as possible. The generator full load current is: So its ohmic value has to be: Electrical Distribution 27 The method of earth fault clearance will be described fully for an example lighting distribution circuit, as shown in Figure 2.
If the earth fault monitor on the V lighting distribution board DB indicates the presence of an earth fault, miniature circuit-breakers F1, F2, F3 and F4 are sequentially opened and closed in turn until the earth fault monitor indicates the earth faulted circuit. If this is circuit breaker F2, which supplies a distribution fuse board DFB for lighting circuits, then, as there is no earth fault monitor, an IR tester must be used to determine which is the faulty lighting circuit.
At this DFB, fuse-pair No. All fuse-pairs are checked in turn to confirm whether healthy or faulted. The earth fault must then be on that particular circuit.
Practical Marine Electrical Knowledge
In practice, circuits cannot be randomly disconnected in this way. Some vital service may be interrupted, such as causing the main engines to stop, possibly in dangerous narrow waters. If the IR is low then the earth fault lies on the conductors beyond the switch.
At lamp 1, remove the fitting and disconnect the conductors as shown to further break down the circuit. Use the IR tester on each of these disconnected leads. If one conductor is indicated as having an earth fault suppose it is the conductor between lamp 1 and lamp 2 then the earth fault lies at lamp 1 or lamp 2 or on the conductor.
Both lamp fittings must now be opened and visually inspected to trace the exact location of the earth fault. The method of tracing the earth fault is that of continually breaking down the circuit into smaller and smaller sections until it is finally located.
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