Chapter 1 Ships Electrical Systems Safety & Maintenance

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ChapterOne:ShiPs'electrical systems- safetYand maintenance ShiF' Ehctricd System Electrical Disgrams Electrical Sefely ElcctricShock lnsulalbD Resistsnce Testing 'festing Insulalion ContinuilyTestinS, Multimcters Dbdc Tests Currenl Clampmeters Live-LineTesters GencralEleclricalMaintenance

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I ntroduclion l his chaptcr Prcscnlsan overview ol a shiP'sclcctric l sl stcnr and dcseribcsvarioustypesof circuit rliagrams uscd i|l clectric t work. llasic clectrical :alely precautions and electrical testing fllcthods itrc outlincd toScther wilh a dcscripttottof gcncral clcctrical muinl€nance. Ships' clcctricNl system Auxiliary scrviceson btlarrl ship range frrttn cngitrc rtxrnl putltpsand lans' dcck winchesand windlasscstr.rgcncral lighting, catcrirrgand air conditionrng. Elcctrical power is usedtodrive 'l the nrajority ,rf thcse auxiliary scrviccs. hc clectricllpo$cr svslcltl()tl bturd ship is designed to providc a sccurcsupply t0 tll Irads with ildcquittc htlill in pr()tccti()nf()t lhe equipment and 'fhc gcncral schctneof a ship s ch;ctrieal Powcr system is conlmon t(t opcrarinS,pcrsttntrcl. n e a r l ya l l s h i p s . l{o 2 €1,€RGEirY )aoI G€IIERATOR OENERAIOR G€NERAIOR

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hc gcncrators(liotnctintescallcrl ithctnators) producc the clcetriealprwcr' lt is collcclcd al the main switchboard and thcn tlistrihutcd t(! thc various auxiliary *.-rviccsconlprilinE lhe

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v clectricalload. An emergencygeneratorand€mcrgencyswirchboardmainrainsuppliesin the cventof a main power failure. compare thisgcnerallayout with the systemon yourship. Notc the grearsimilaririesand also note the differences- all ships' systemsdiffer in some res1rcct. The generatorsmay bc driven by a dieselengine.by a steamor gasturbine, or by the main propulsionengine.The rype of prime mover is dererminedby the designof rhe ship and by cconomicfactors. The power rating ofth€ generatorsis determinedby the powerdemandof the electricalload. Largepassengcrshipshavethreeor four largegeneratorsratedat 2MW or more to supplythe ertcnsivc hotel serviceson board. A cargoship may havetwo maingeneratorslypically rated from 350to l000kW which are sufficientto supplythe engineroom auxiliarieswhile at scaand thc winchesor cranesfor handlingcargo while in port. The limiied load required during an cmergencyrequiresthat the emergencygeneratorsmay be ratedfrom about l0kW for a small coasterto about 300kWor more for a cargoliner. The shipbuildermustestimaiethe number and power rating ofthe requiredgeneratorsby assessing the pnwerdemandof the load for all situationswhether at seaor in port. Electrical power on board ship is commonlygeneratedar 440V,60Hz (somerimes380V, 50 Hz). These values have been adopted becausethey are standard shore practice in the Americasand in Europe. Shipswith a very largeelectricalpowerdemandmay be designedto operateat 3.3kV and even6.6kV, or higher. The BritishStandardand IEC definirionof LOW VOLTAGE is between50V acand 10fi)V ac (the IEC give this definirionro harmonizeBritishand Europeanstandards). Lightingandother domesticsuppliesusuallyoperatear I | 5V or 220V,single-phase. Transformers are used to reduce rhe /0r(,)Vgeoeraaedvoltage to this safer volragelev€I. Where ponable equipment is to be usedin dangerous,hot and damp locations,it is advisableto op€rateat 55V or even 24V suppliedagain by a srep-d()wnrransformer.Occasionally, transformersare also usedto step up volrages.e.g. supplyinga large3.3kV bow thrustel motor from a 4zl0Vswitchboardsupply. Batteriesfor variousservices operateat I2V or 24Vbut somerimcs highervoltagesareused. Elcctricrl dlrgrrms Thereare variOustyp€sof diagramwhiehattcnrptt(| sh()whow an clcctricalcircuitoperates. Symbolsareusedto represent itemsof equipment.Thc shipbuiltter providesa completesctof ships'electricaldiagrams.lt is imgrrtantthat you\iudy rhesedragrams to bc abl,jto readand understandthem compctently,and to usethem as an aid in kxating electricatfaults. A BLOCK DIAGRAM showsin simplifiedform themaininrer-relationships of theelemenrs in a sysl€m,andhow the systemworksor may bc operai€d.Suchdiagramsareoft€n usedto depictcontrolsystemsand oiher complcxrelarionships.

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Diagrams like this state the tuncti()n ol cach bkrck but usually givc n. inlornrution of thc comfxlnents in each bklck nor how thc bkxks arc intcrconnccted A SYSTEM DIAGRAM shows thc murn lcltures of a systcm and irs b()unds. without necessarilyshowing causc-lo-effcct. lts matn use is to illustratC lhc ways ()f operating the

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sFtcm. Detril is omined in order to make the diagram as clear as possible,and so easily undcrstood.

A CIRCUIT DIACRAM shows,lN FULL, the functioningof a circuit. All csscntialp.tt! rnd conncctiom are dcpictedby meansof symbolsarrangedto showthe opcrationesclcrly .r pcriblc bur without rcgard lo the physicallayout of lhe various ilcms, thcir p$lt or conncc'tions. o(

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Thc clectrical connectionsof rhe above m(Nor starteJ are clearly shown in the simPlest poesibleway. A most important F)int is that no attempl is madeto showthc movinSconlacls of e rclay or conlactor alongside the coil that operatcs therh (whcrc they aac actually

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physicallylocated).l'. tead the coil and its related contacls are identified by a common numb€roi leil€r. 'cc' drivestwo auxiliarycontactsidentifiedas 'ccl' and 'cr2'. For cxarnPle:contactorcoil

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Eachwire connectionis identified by a numberwhich maybe found on a numbcredsleeveon cach wirc at its termination on a component in ihe actual starter' Allhough there are international agreementsas to ihe symbol to be uscd 1o r€present elecrricil componentsyou must be preparedto meel variousdifferent symbolsrepresenting thc samc oomponent.For example: a coil can be represenledas

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The useof a circuil diagramis to enablethe readerto understandthe operationof the circuit, to follow eachscquencein the operation from lhe momentof initiatinBthe operation(e.g. by prescing a'stan' bution)to the final act (e.g.startingof the motor)' lf the equipmentfailsto operatJ correctly, lhe reader can follow the sequenceof operalions until he comesto the opcntion that has failed. He can then examine all the componentsinvolved in that faulty opcration (and only thos€ componentsneed be examined)and so locate the fauhy componint. He hasno needto examineother componentsthat are known to functioncorteclly and haveno influenceon the fauli; his work is simplified. A circuit diagramis an essentialtool in trouble shooting. A WIRING DIAGRAM showslhe detailedwiring and conneciionsbetweencomponcntsor itcmsof equipment,and in somecas€sthe routeingofthcscconnections-A wiring diagmmof an ilem ofequipmenl showsthe componentsin the approximatePosilionth€y occuPyin rhc actual equipment. The compon€nt may be shown complete(e.9. a contaclor coil togethcr with all Ge conractsit drives) or may bc simply representedby a blcrckwith th€ necessarry of linecan be usedto diffclcntialebelween terminalsclearlymarked.Differentthicknesses 'I'he wiring diagrambelowis of the samestartershown powerandcontrol circuii conneclions. for the previouscircuit diagram. z------a-----\

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A wiring diagrammay be of a fairly simplecircuit, but it is quite difficult to useit to work out opcrationof the circuit.The purposeof a wiringdiagramis to imtruct the wiring thc sequential lt is of little usein troubleshootingapartfrom mrn how to constructandconnecttheequipment. components andtcrminals. idcntifyingthecxactpositionof suspect QUESTION What are you to do if difficultiesarisein locatinga fault on an item of equipmentand only a wiring diagram is available? ANSWER It may well savetime andtroubleto conv€rtthe wiringdiagraminto a muchsimplerand morc usefulcircuitdiagram.Whenconvertinga wiring diagraminto a circuitdiagramcertainbasic rules and conventionsshould be followed. l. Every sequenceshould be drawn from left to right and from top to bottom (where prssible). 2. Each stageshould be in order of occurrencefrom left to right. 3. All contactsand componentswhich are in seriesshould be drawn in a straight line (where possible)with the componentthey conlrol. 4. All contactsand componentswhich are in parallelshouldbe drawn sideby sideand at the samelevel to emphasisetheir parallel function. 5. All major componentsop€ratingat bus-barvoltageshouldbe drawn at lhe samelevel (or alignedhorizontally)to help identify the rer;uiredcomponentsquickly. 6. All contactsshouldbe shown'open'or 'closed'as in their NORMAL or unenergiscd condition.

There are other conventionsbut lhesecover the main pointsof g