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CHAPTER 15

WIRING AND ELECTRICAL DISTRIBUTION

INTRODUCTION

The distribution system is an extension of thegenerator. All electrical loads are connected inparallel with the generator terminals through con-nection points (nodes) at the switchboards and dis-tribution panels. Through proper design, largecables (feeders) provide power to bus bars insidethe switchboards and each distribution panel(Figure 15-1). The use of a single feeder cable willeliminate dozens of individual parallel cables thatwould have otherwise been needed for the connec-tion between the generator and each load.

The distribution system is also designed toprotect the overall electrical environment fromelectrical component casualties. Circuit breakersand fuses are installed in switchboards and distribu-tion panels to separate abnormally operating electri-cal apparatus from the rest of the system. Eachcircuit protective device, from the generator to theload, is set at decreasingly smaller ampacity incre-ments. When all overcurrent and short circuitprotective devices are properly selected and cor-rectly adjusted, selective tripping can be provided.

Selective tripping allows an abnormal circuit to beseparated from the electrical distribution system veryclose to the fault.

The switchboard receives power directlyfrom the generators. In turn, feeders extend fromthe switchboard circuit breakers to the power dis-tribution panels, lighting distribution panels, orlarge motor circuits. Branch circuits leave the dis-tribution panel circuit breakers and provide powerto individual loads.

GROUNDING

To understand the type of electrical systemused by the Army’s marine field, the term “ground-ing” must be understood. This is the mostmisunderstood term in electricity today. For themost part, Army vessels have an entirely ungroundedcurrent-carrying system. However, every electricaldevice is grounded.

The term "ground" refers solely to physicalconnections between conductive materials and theearth. Whether or not this conducting connection

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carries current is irrelevant. To help understand thisterm, start with these definitions from the NationalElectrical Code, Article 100:

Ground - a conducting connection,whether intentional or accidental, betweenan electrical circuit or equipment and theearth or to some conducting body thatserves in place of earth.

Grounded - connected to earth or to someconducting body that serves in place ofearth.

Grounded conductor - a circuit conductorthat is intentionally grounded (connectedto earth).

Grounding conductor, equipment - theconductor used to connect the noncurrent-carrying metal parts of equipment,raceways, and other enclosures to the sys-tem grounded conductor. In the case ofArmy watercraft, the hull of the vessel isthe grounded conductor.

WARNING

All electrical componentenclosures, switchboards, motorhousings, generator frames, andso forth must be grounded forsafety.

The definitions of ground and grounded do notstate whether or not the conductive material carriescurrent. Engineers ground components for tworeasons:

To carry current through a structural com-ponent to complete a circuit under normaloperating conditions.

To carry current through a structuralcomponent only under abnormal electri-cal conditions. This is not designed tocomplete a circuit for normal electricaloperations.

A ground can be either a current carrier undernormal operating conditions or a current carrier for

abnormal operating conditions. This depends onthe application of the hull connection.

The “grounded” system of the automobile hascurrent traveling through the chassis, engine block,and all connected metal. The body of the car repre-sents the negative conductors of its electrical system.All circuits are completed from the negative batteryterminal through the chassis, the electrical loads,positive wires, and back to the positive battery ter-minal. The ground symbol identifies the pointin the electrical circuit that connects to the metallicstructure. All the ground symbols in Figure 15-2 areconnected like a node, as if the entire automobileframe was a giant connector. This system is in factinsulated from earth by tires and is not a groundedsystem.

Current-Carrying Grounds

The emergency generator used on the 2K seriesLCU is an example of a current-carrying groundedelectrical system. The 24-volt DC battery startingand charging system is connected normally as acurrent-carrying ground. The main AC powerproduction portion, however, retains the insulatedconductors and does not use a current-carryingground for normal operations. Grounded current-carrying electrical systems are avoided wheneverpossible on watercraft because of the galvanic cor-rosion and electrical shock hazards. In this situation,hazards and corrosion are minimized through strictadherence to Subchapter J, Subpart 111.05-11(a)(2),Title 46, Code of Federal Regulations.

The DC part of the emergency generator primemover and power generation controls incorporatethe metal structure as a current-carrying structuralassembly of the generator. It is connected to the hull(grounded), and the automobile chassis is not. SeeFigure 20-4 for the diagram of this circuit.

Noncurrent-Carrying Grounds

The AC current-carrying conductors of theship service generator are not designed to come incontact with the structural components of the equip-ment. Instead, only the structure and metallicenclosures are connected together and connected tothe hull. All conductive equipment that surroundselectrical current-carrying conductors must begrounded; that is, connected to earth.

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Figure 15-3 shows the generator housing physi- in the system. Current will take the path of leasttally connected to the prime mover’s block. The resistance, around the soldier, through theprime mover may be directly bolted to the engine metal-to-metal connections, to the mounting, to thebed. The engine bed is connected to the hull and the hull and water, returning to earth.hull to the water.

A break in this normal metal-to-metal contact,from the generator housing to the vessel hull, maycome from the diesel generator set mountings. Toeliminate excessive generator vibrations during nor-mal operation, modern vessels do not have the primemover rigidly connected to the engine bed. Aresilient mount, not electrically conductive, acts as ashock absorber. A grounding strap or flexible shuntis attached from the generator housing to the enginebed. This connects the diesel generator set to theengine bed with a conductive path. In normal opera-tion, this is not a current-carrying ground.

This type of ground is used for safety. Shouldan abnormal electrical situation develop within thegenerator, a low-resistance conductive path isprovided for winding current to move to earththrough to the vessel’s hull. This is necessary toprevent current from using a human host as a con-ductor. Stray current will go to earth whenprovided a path to do so. The metallic connectionbetween the generator and the engine bed must nothave any resistance. If enough resistance is placedbetween electrical equipment and the vessel’s hull,a condition can exist where the soldier will conductcurrent because he has less resistance to ground thanthe equipment.

A low-resistance path is necessary to allowcurrent to flow to earth when an abnormal electri-cal condition exists. This means a clean, unpaintedmetal-to-metal contact surface. If vibration dam-pening is necessary, a grounding strap or flexibleshunt is mandatory to complete the connection.Additional information is in the Code of FederalRegulations, Title 46, Subpart 111.05.

The electrical component housing that isproperly grounded will not become a deadly deviceto a soldier under abnormal electrical conditions.The current wiIl travel from the damaged generatorwindings, for example, to the generator housing.From the generator housing, the current will gothrough the shunt to the hull and earth. The currentdeveloped from the abnormal condition will bypassthe soldier. The soldier still provides more resis-tance than the correctly grounded components

THE EARTH

To properly understand how these differentgrounds fit into the vessel’s electrical system, theword “ground” must be understood as it wasoriginally used. Decades ago, when DC tugboatswere designed, the term “earth” was used insteadof ground. Still later, the tugboats were calledpositive ground systems. (Foreign cars used to betermed positive earth systems). Over the years,many individuals and contractors mistook the term“ground” for a negative ground (as referred to ontoday’s automobiles). Eventually all types of groundswere incorporated into the tugboats, and the truemeaning of the term “ground” was lost. Both earthand ground have their original roots in terra firma.However, today the importance of the earth’s electri-cal potential as a safety factor is realized.

Nikola Tesla, the father of alternating current,discovered the rotating magnetic field and developedthe Tesla coil used in radio and television today. In

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1900, he made one of his most important discoveries.He found that the earth could be used as a conductorand would respond to electrical vibrations. He calledthis terrestrial stationary waves. In one experiment,he lighted 200 lamps without wires from a distance of25 miles.

The earth has a continuous electrical currentthat flows in, over, and around itself. This currentseeks out equilibrium. In this way, it tries to establisha balance in its magnetic field. The potential of theearth is due to the transient electric currents that areelectromagnetically induced within the earth itself.The electrical potential (voltage) of the earth hasbeen measured. It is possible because of the condi-tions that form an electric cell-like device due to theelectrochemical differences in local conditions.

In effect, the earth is its own low-voltage gen-erator. The current produced is called telluric cur-rent. Telluric current, some believe, is caused by themotion of our sphere or the magma, the electricallyconductive sphere itself, and the presence of thegeomagnetic field. The earth is itself a generator andproduces its own difference in potential.

Therefore, it is advantageous to maintain ourvery precise current-carrying electrical systemsseparate from the earth. When there is current flowbetween one electrical terminal and the hull, it isusually due to an unintentional ground, carrying cur-rent within our own electrical system.

US ARMY VESSEL SYSTEMS

The Institute of Electrical and ElectronicsEngineers (IEEE) Standard 45, RecommendedPractice For Electrical Installations on Shipboard,recommends a dual voltage AC system of450/120 volts AC ungrounded. Army ports, Navalports, and Coast Guard facilities have 450 voltsreadily available for shore power hookups. Thesecond voltage (120 volts) should be obtainedthrough the use of transformers. This system isfound in many Army watercraft.

An ungrounded current-carrying systemmeans that all the current-carrying conductors areinsulated from other conductors, other structures,and earth. Each electrical component has a com-plete circuit from the generator to itself and back tothe generator through the use of these insulatedwires. Each current-carrying conductor has an

overcurrent protection device. This is because eachof the circuits to the electrical component is a dif-ferent potential than that of the hull (and the earth).

Even though Army vessels use theungrounded current-carrying system, all electricalcomponents must be grounded. The housings ofall motors, generators, and motor controller hous-ings must be directly connected to the hull. Theswitchboard housings, the distribution panels, thearmor wrapping surrounding the electrical cables,and the electrical appliance casings must have alow-resistance connection to the hull. Any metaldevice that houses a current-carrying conductormust have its enclosure grounded. This directconnection allows the flow of current to the hulland not through the engineer in the event of anabnormal electrical condition.

THE NEUTRAL

The neutral is a ground system that uses aninsulated current-carrying conductor and a directwiring connection to the earth. Onshore facilities,for example, the receptacle outlet, has three conduc-tor orifices: the neutral, a safety ground, and thephase conductor. The phase conductor is insulatedthroughout its circuit and retains the circuit breakerprotection. The neutral conductor is insulatedthroughout the circuit, normally without a circuitbreaker. Both the neutral and the phase conductorare current carriers under normal conditions. Theground wire is the safety circuit designed specificallyto carry current during an abnormal condition toprotect the operator.

The neutral, although an insulated current-carrying conductor, retains a single connection toearth. By connecting the neutral to earth, the earth’spotential is locally stabilized as a neutral potential.This provides safety on shore because two of thethree wires in every outlet receptacle will not createan electrical shock. The neutral and the ground arethe same potential as earth; hence there is no dif-ference in potential. There is no shock hazardbetween the neutral, the ground, and the earth.There remains only one “hot” wire even thoughthe neutral is a current carrier.

A very real danger would exist on shore if theearth was a very good conductor and had thepotential to encourage great current values tomove between the phase and earth. Since the earth

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is not capable of this current encouragement,electrocution from accidental contact with the phasewire is reduced (although not eliminated).

Watercraft generators or transformers can usethe center tap of a wye winding combination to derivea separate low voltage potential cheaply. The troublewith using a neutral current-carrying conductor as apotential stabilizing device is the connection to earth,directly through the hull. Army watercraft makelimited use of this low voltage potential. Since thevast majority of conductors on board the craft areinsulated current-carrying conductors, limited safetycan be derived from such a current.

Danger exists when a neutral is connected tothe hull because A, B, and C are always a differencein potential to the neutral. When the neutral is con-nected to the hull, the generator’s center is extendedas a node throughout the entire length of the shipincorporating all conductive materials connectedto the hull. Unlike the earth’s feeble ability toencourage current movement, the potentialdeveloped in the neutral connection will encourageany current from a difference in potential. Anyaccidental contact between any current-carryingconductor becomes potentially fatal. Unlike shorefacilities that make extensive use of the neutral con-ductor to carry current, watercraft rarely employsuch a circuit. All Army watercraft, with the excep-tion of a few branch circuits on the LSVs, have adifference is potential between any current-carryingconductor (A, B, C, L1, L2, or L3) and the neutralpoint of a generator or transformer. There is no gainin safety by grounding a neutral conductor unless theneutral can limit the number of current-carrying con-ductors that maintain an aboveground voltage.

Army watercraft no longer use the center-tapped neutral from the generator. Only the LSVuses the neutral connection from the wye trans-former to obtain this inexpensive low voltage value(Figure 15-4).

Figure 15-5 shows the optimum setup for ves-sels. It shows three single-phase transformers con-nected for three-phase power. Remember, it is themanner in which windings are connected, not thehousing that encases them, that provides the desiredvoltage and current values. Three single-phasetransformers can be wired in the same manner thatthe ship service armature windings were wired inChapter 7 to produce a given three-phase output.

The LSV using one three-phase transformer is wiredidentically.

Notice the neutral going to the hull from thesecondary transformer side. Note further thatthere are no circuit protective devices in theneutral conductors.

As long as the neutral conductor, carrying thecurrent to the electrical component, is the samepotential as the earth (or hull) that a soldier is incontact with, then there will be no difference inpotential between the soldier and the neutral con-ductor to cause injury. Without a difference inpotential, there is no current flow. However, extracare must be exercised when working between aphase and the hull.

WARNING

Never change the relationship ofthe circuit overcurrent protectivedevice and the neutral conductor.

The neutral wire must not have an independentovercurrent protective device installed unless thedevice can open the neutral and all the associatedphases in that circuit simultaneously.

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If the neutral opened and the other powersupply lead did not open, the motor would stop.There would no longer be a completed circuit to themotor. But there would be a difference in potentialat the faulty component housing and a difference inpotential in the hull the soldier contacts. If someonetouches the faulty motor housing, current would takethe only available path back to the earth – throughhim and the hull.

This is of such importance that neutrals will bestressed again when your understanding of the dis-tribution system is complete.

ELECTROLYSIS

In addition to safety reasons, the generator isnot connected electrically to the hull as a current-carrying conductor to prevent electrolysis.Electrolysis is the chemical process in which a sub-stance loses or gains electrons. Recall the operationof a battery. The battery developed an EMF bychemical means. Oxidation, or rust, is a chemicalprocess that reduces the number of electrons in asubstance because the electrons migrate to other

areas. Salt water and dissimilar metals connectedtogether for vessel construction create a very largechemical reaction. Electrons lost by the oxidizingmaterials are taken up by other metals lower downthe oxidation scale.

Some of these metals are called noble metals.Noble metals have an outstanding resistance tooxidation. Some noble metal oxidation rates in des-cending order are gold, silver, and platinum. Whenelectrons leave a metal, oxidation reduces thematerial. Hull and piping would deteriorate rapidlyif this condition were not properly addressed.

The steel hull is not one of the noble metals.However, steel is less easily oxidized than zinc. Zincsacrificial anodes are attached to the hull of thevessel. Electrons leave the zinc for the steel hullduring electrolysis. This provides a good degree ofprotection to the hull. For the zinc and steel toproperly provide protection, the zinc anode shouldnot be painted and retained at a size no smaller than50 percent of the original.

Electrolysis in the hull cannot be completelyeliminated, but it can be reduced. When stray

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currents are allowed to exist in the vessel’s hull,electrolysis, called galvanic corrosion, is greatlyincreased. Years ago, the 1466 class LCU was incor-rectly wired to the hull. The first indication of anextensive electrical problem was the hull’s unusualdeterioration. Electrically energizing the vessel’shull created a very large battery. The zinc anodesdissolved quickly, and the entire aft third of the hullbottom excessively deteriorated. After appropriatedocumentation was completed, the situation wascorrected.

VESSEL DISTRIBUTION SYSTEMCOMPONENTS

A vessel has an extensive electrical systemdesigned to carry out more functions than can befound in a small community. Lighting, instrumentpanels, steering systems, stoves, and so forth arespread throughout the vessel. Every electrical itemmust be serviced regularly. Locating the electricalwires can be frustrating. In an emergency situation,restoring electrical power for the dewatering and firepumps can mean the difference between life anddeath.

Chapter 10 discussed circuit breakers and fusesfor the protection of electrical circuits. It brieflymentioned the parts making up the circuit. Tounderstand the electrical distribution system, the dif-ferent system components need to be examined incloser detail.

Distribution Center

The distribution center controls the ship ser-vice generated power and shore power. Automaticovercurrent protective devices connected to the busmonitor and protect the feeders and branch circuits.

Feeder

The feeder consists of the cables that extendfrom the main switchboard to the distribution panels.In some cases, the feeder may provide power directlyto a large motor.

Bus Tie

The bus tie is the electrical connection betweenthe main and emergency switchboard bus bars. It isnot considered a feeder.

Emergency Switchboard

The emergency switchboard is a smaller ver-sion of the main distribution switchboard. Power isreceived either from the emergency generator or themain switchboard through a bus tie. Thisswitchboard provides power to vital services, includ-ing the fire main, communications, emergency light-ing, steering, and so forth. When the ship’s mainpower is lost, emergency power is automaticallyprovided by the emergency generators through theemergency switchboard by an automatic bus transfer(ABT) switch.

Motor Control Center (MCC)

The motor control center consolidates all themotor controlling equipment for all the major motorson board the vessel. Overcurrent and overloadprotection is provided to the motor and immediatecircuitry.

Distribution Panel

The distribution panel is an enclosed metalpanel that supplies power to components for a local-ized section of the vessel (Figure 15-6). Circuitbreakers or fuses are installed to protect the branchcircuits. The distribution panel has three bus bars(there is a fourth when the neutral is used). Whenthe distribution panel is used to provide three-phase power to loads, then each bus bar is con-nected to one terminal of a three-pole circuitbreaker (Figure 15-7). The other side of the circuitbreaker is connected to the loads.

If the distribution panel is used to supply single-phase power to loads, then only two of the bus barsare used, and a two-pole circuit breaker is employed(Figure 15-8).

NOTE: The same two bus bars areNOT used to supply all the power tothe loadsconnected in the single-phasedistribution panel.

To keep the three-phase generator balancedwith single-phase circuits, each phase (A-B, B-C, orC-A) is designed to carry a specific percentage of theload. The single-phase loads are equally dividedbetween the three phases. Each distribution panelreceives three-phase power. When single-phase

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loads are connected, the distribution panel dividesup the three phases so that each single-phase circuit(A-B, B-C, or C-A) has one third of the total poweravailable from that panel.

This electrical balance is continued by equallydividing the load at each panel throughout the vessel.All the other panels are divided in the same mannerbecause in the event of a distribution panel casualty,the overall generator load will be decreased evenlyacross the phases. The generator will still be electri-cally balanced.

Power Distribution Panel

This panel is generally dedicated as a source ofpower for operating other components, such as thepower supplied to the emergency batteries or toother distribution panels. More often, it can be dis-tinguished as a panel used to distribute three-phasepower to three-phase components.

Branch Circuits

These are the conductors that exist between thefinal overcurrent protective device in the distributionpanel and the load; for example, motors, lights, andreceptacle outlets.

Lighting Branch Circuits

These conductors supply power to lighting sys-tems, bracket fans, small heating appliances, circuits,and motors 1/4 HP or less.

Appliance Branch Circuits

These conductors supply power to the outletsfor the use of portable or nonfixed electricalapparatus.

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Communication Branch Circuits

These conductors supply power to com-munication, audio, and visual signaling devices.

Cables

These are heavy-duty conductors used tocarry current between a source and a load. Alter-nating current cables should contain all threecurrent- carrying conductors in a single cable tocancel out heating caused by inductive effects.

Distribution Cables

These cables are used for the power distribu-tion up to the rated voltage and ampacity of the cable.Low-voltage (600-volt) cables are generally found onArmy watercraft. They are used for most electricalconnections.

Control Cables

These are multiple parallel conductor cablesused for —

Control circuits where an electrical signalenergizes a magnetic control device tophysically open or close the main contactsof a motor. The control cable does notcarry the main motor operating current,but only the current used in energizing thecoil of the magnetic control device.

Indicating circuits in meters and otheraudio and visual indicating apparatus.

Communication, electronic, and othersimilar circuits.

Signal Cables

Signal cables of twisted pairs of conductorcables are used for signal transmission. Eachtwisted pair of conductors will have a shield toprevent interference.

Portable Cords

Portable cords are used for the temporary con-nection of portable appliances. They are not to beused for fixed wiring. They must conform withNAVSEA 0981-052-8090 [40].

DISTRIBUTION CABLE AND WIRE MARKINGSYSTEMS

Color coding allows the engineer/enginemanto follow electrical circuits throughout a vesselwithout having to physically touch each cable. Thecolor can be continuous throughout the length ofthe conductor, or the color noun-nomenclature,such as red, is printed every 24 inches on the insula-tion of the conductor.

The following are newer color designations fordistribution cables:

2 conductors - black, red, or white.

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3 conductors - black, red, blue, or white.

4 conductors - black, red, blue, orange, orwhite.

Older wire designations are as follows:

Alternating current:

Phase A: black.Phase B: white.Phase C: red.

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Direct current:

2 wire DC: positive(+) black.negative (-) white.

3 wire DC: positive (+) black.negative (-) red.

Table 15-1 gives the newer color designations forcontrol and signal cables.

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Cable Tags

Embossed metal tags are used to identifycables throughout the vessel. The tags are located atthe distribution panel and the component. Tags arealso attached to the cables where penetration of thebulkhead is necessary. The tag code will start withthe type of circuit it is. Army vessels use P to indicatepower distribution panel cables, L for lighting dis-tribution panel cables, and E for emergency distribu-tion cables. If there is a number preceding that letter,this identifies the cable in the distribution panel. Thenext numbers indicate the voltage carried in thatcable, such as 400 or 200. Any additional numbersabove the whole hundred value are used to distin-guish the differences between two like voltage dis-tribution panels. For example, in the cable tag3P-401–

3 indicates the third wire in distributionpanel P-401.

P indicates that this cable acts as a power-supplying cable or that it provides three-phase AC to its loads.

An L would indicate a lighting or single-phase AC supply panel cable.

4 with two additional digits means thatthere is 400 to 499 volts in that cable.. Ifthere was only one additional digit, thenthe voltage in the cable would be what isactually printed. For example, 24 indi-cates 24 volts.

01 distinguishes the cable’s source. Thisidentifies the difference between the P-401distribution panel and the P-400 distribu-tion panel.

Wire Construction Details

With the addition of a set of prints, theengineer/engineman can locate all the necessaryelectrical components on his vessel. To make themost use out of the wiring construction detailsand to help distinguish between single and three-phase AC circuits, a basic understanding isneeded. The wire construction detail is the codeused for determining the current-carryingcapacity, insulation material, shielding, applica-tion, and so forth. This information may be found in

the IEEE Standard 45 manual However, it is notnecessary to understand everything about these intri-cate codes. There are some basic rules that can beeasily applied. The following details are found on thedistribution system prints:

2SJ-14.

DSGU-14.

MSCU-10.

TSGA-100.

This text will examine only the frost and lastcharacter and the numbers. The first character indi-cates the number of individual conductors in thecable; 2 obviously means that there are two conduc-tors in the cable. D means that there is a doubleconductor in the cable, or the same as 2. M standsfor multiple conductors, and there may be severalunused conductors for future electrical growth. Tstands for a triple conductor, so there will be threeconductors in the cable. If the last letter is an A orB, then the cable is armor-shielded. The last num-bers indicate the size of the conductor in thousandsof circular roils (KC MIL). Thus, 14 indicates thatthe area is 14,000 circular roils. The 100 indicatesthat there is a 100,000-circular mil area. It wouldbe easy to identify the difference between the twocables. The TSGA- 100 will be much larger thanthe 2SJ-14 cable.

This basic understanding is useful in locatingthe wire on the vessel after seeing it in the blueprints.Additionally, if there are two conductors in a cable,the cable cannot carry three-phase power. Wire size,application, and distribution panel location will helpyou locate components when troubleshooting.

Shipboard Electronic Equipment Wire MarkingSystems

The following explanation is an example of thetype of conductor marking used in shipboardelectronic equipment. These conductors may becontained in cables within the equipment. Cableswithin equipment are usually numbered by themanufacturer. These numbers are found in the tech-nical manual for the equipment. If the cables con-nect equipment between compartments on a ship,they will be marked by the shipboard cable number-ing system previously described.

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On the conductor lead, at the end near thepoint of connection to a terminal post, spaghettisleeving is used as a marking material and insulator.The sleeve is marked with identifying numbers andletters and then slid over the conductor.

The marking on the sleeve identifies the con-ductor connections to and from by giving the follow-ing information (Figure 15-9):

The terminal from.

The terminal board to.

The terminal to.

These designations on the sleeve are separatedby a dash. The order of the markings is such that thefirst set of numbers and letters reading from left toright is the designation corresponding to the terminalfrom which the conductor runs. Following this is thenumber to the terminal board to which the conductorruns. The third designation is the terminal to whichthe conductor runs.

For example, as shown in Figure 15-9, the con-ductor is attached to terminal 2A of terminal board101 (terminal from 2A on the spaghetti sleeving).The next designation on the sleeving is 401, indicatingit is going to terminal board 401. The last designationis 7B, indicating it is attached to terminal 7B of TB401. The spaghetti marking on the other end of theconductor is read the same way. The conductor isgoing from terminal 7B on terminal board 401 “to”terminal 2A on terminal board 101.

It may be necessary to run conductors to unitswhich have no terminal board numbers; for example,a junction box. In this case, an easily recognizableabbreviation may be used in place of the terminalboard number on the spaghetti sleeving. The desig-nation JB2 indicates the conductor is connected tojunction box 2 (Figure 15-10).

In the same manner, a plug would be identifiedas P. This P would be substituted for the terminal boardnumber marking on the sleeve. A complete descriptionof shipboard electronic equipment wire markingis in NAVSEA Publication 0967 LP 1470010,Dictionary of Standard Terminal Designations forElectronic Equipment.

POWER DISTRIBUTION

The wires and cables in the distribution systemare expressed as a single line between the powersupply source and the component. Instead of show-ing the actual number of conductors, only one line isillustrated. While the distribution wire diagrammore closely resembles the actual cable runs, thecomplete circuits necessary for electrical operationare missing. The wire construction details becomevery informative now. The wire construction detailsstate, rather than illustrate, the actual number ofcurrent paths in the component’s circuit.

As an example, Figures 15-11 through 15-21illustrate the power distribution system from anLCU.

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Three-phase AC is developed in the genera- TSGA-30 cable (Figure 15-11). The TSGA-30 indi-tors. The AC is fed to the switchboard through a cates three large 30,000-circular mil conductors.

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Three-phase AC enters the distributioncenter’s main switchboard through a three-pole cir-cuit breaker (Figure 15-11 [a]). When this main cir-cuit breaker is closed, power is provided to three busbars inside the switchboard. Each bus bar (b) carriesone phase of the generator’s power. The bus bars areactually a mere connection point on this switchboard.The actual bus in Figure 15-11 has been expanded forclarity.

Current is available from the main distributionswitchboard to the power distribution panel (P-400)through the three-pole circuit breaker (c) andTSGA-100 feeder (d).

A cable tag P-400 indicates that 450 volts aresupplied to the power distribution panel number 400(Figure 15-12). The feeder is protected by the circuitbreaker in the main distribution switchboard (c).The TSGA-100 feeder is larger than the TSGA-30generator cable because the TSGA-100 feeder mustcarry current from both generators when operatingin parallel.

The power distribution panels do not have anycircuit breakers for the entering feeder. The feederis connected to three bus bars in the power distribu-tion panel P-400. In this manner, current is available,through a common contact point, for all the three-phase branch cables and feeder cables. Current isconnected to the cables through three-pole circuitbreakers (e).

Where the cable goes can be determined byusing the blueprints. In the same way, a defectivemotor can be identified, and then the source of itspower (and circuit breaker) can be determined fromthe motor cable tag.

A three-phase 450-volt motor is connected tothe feeder tagged P-408 (f). Refer to Figure 15-13.

After the cable passes through a disconnectswitch (DS) (Figure 15-13 [g]) and enters a controller(C), the wire is branched into four directions.

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P-408-C indicates the first of three control cir-cuits used with this motor. Each circuit is tagged withthe controllers number and wire number P-408. Thisis followed by an alphabetical designation P-408-C.This wire is also a MSCU-10. This indicates thatthere are multiple conductors as would be expectedfrom a station that controls the raise, stop, and lowerof a ramp motor (h), unarmored, and of limiteddiameter.

P-408-A 2SJ-14 indicates that this handcrankinterlock limit switch is part of a two-wire, single-phase circuit in the same way the slack cable limitswitch (P-408-B) is connected.

The motor uses the same size cable as thefeeder that powers the controller. This is necessarybecause of the high current draw from the motor.

Skip the elementary branch circuit P-407, andrefer to feeder P-409, Figure 15-12, at the powerdistribution panel. P-409 TSGU-9 indicates a cablegoing to power distribution panel P-409 in the airconditioning compartment (Figure 15-14). Thisfeeder also carries three-phase current to three busbars inside the P-409 power panel.

Power is provided to all the three-phasebranch circuits through three-pole circuitbreakers. Individual branch circuits are desig-nated by the first number on the tag, such as lP-409,2P-409, and 3P-409. 4P-409 is a spare provided

for future electrical growth. Note the location iden-tification of the 3/4-HP motor vent (2-30-1) and the7.5-KW heater (1-31-1) in the air conditioning com-partment.

Now return to the P-400 power distributionpanel and begin with feeder P-402. Feeder P-402TSGU-14 is of special interest. This three-phase,450-volt feeder is going to provide the 120-voltsingle-phase power necessary to operate the light-ing and single-phase branch circuits. TSGU-14enters three 10-kVA single-phase delta-delta connected step-down transformers (Fig-ure 15-15). When three single-phase transformersare connected together delta-delta, this connec-tion provides increased system reliability and theproper electrical three-phase relationship neces-sary to operate the lighting circuits.

The secondary side of the transformer bank islabeled L-100. This indicates that the cable will go tothe lighting distribution panel using the TSGA-100cable.

Notice that the secondary cable is larger indiameter than the primary cable (TSGU-14 versusTSGA-100). This is because a reduction in the volt-age of a step-down transformer means an increase inthe current on the secondary side of the transformers.With an increase in current, an increase in conductorsize is necessary.

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The L-100 TSGA-100 feeder enters the light- panels through the three-pole circuit breakers.ing distribution panel (L-100, Figure 15-16) and Feeders L-101 and L-103 identify themselves as feed-connects to three bus bars. Three-phase power is ing three-phase current to lighting panels of likestill maintained in the lighting distribution panel. designations.Three-phase power is distributed to other lighting

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Tagged feeder L-101 TSGU-9 has three con-ductors entering lighting distribution panel L-101(Figure 15-17). Each conductor connects to one ofthe three bus bars. Since lighting panel L-101 hasonly branch circuits distributing single-phase powerto the loads, only two bus bars at a time are used.Figure 15-17 shows phases A and C (i) supplyingcurrent to the 1L-101 branch circuit. Branch 6L-101is supplied by phases A and B (j). Branch 3L-101 issupplied with power from B and C (k). This keeps

the load equally distributed across the distributionpanel and the windings in the generator. Notice howall these branch circuits are two-conductor wires.

In this case, 1L-101/2SJ-14 and 2L-101/2SJ-14supply the aft engine room lighting system.3L-101/DSGU-14 provides power to the oil waterseparator motor and controls. The D in DSGU-14indicates that there are only two wires. This meansthat the motor must be single phase.

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Return to the lighting distribution panelL-100 in Figure 15-16. The L-102 feeder providespower to the isolation transformer bank. Again,the most effective way to use the benefits derivedfrom a transformer bank results when three single-phase transformers are connected delta-delta. Inthis situation, the transformers do not step up or stepdown the voltage. The diameter of the conductor isthe same on the primary side as it is on the secon-dary side of the transformer (Figure 15-18). Thetransformers are not used to increase or decreasethe voltage. In this situation, the isolationtransformers provide a nonmechanical electrical

connection between the L-100 lighting panel and theL-102 lighting distribution panel.

The branch circuits in the L-102 distributionpanel example are very prone to abuse. This vessel’supper and lower deck receptacles receive theirpower from this panel. Receptacles are availablefor use by personnel not necessarily proficient inthe electrical crafts. All types of equipment can beconnected to receptacles. This is not to say that alltypes of equipment should be connected here, mere-ly that improper conditions are likely to presentthemselves. All transformers prevent catastrophic

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electrical system damage by opening up on theirsecondary side before the short circuit condition canbe passed throughout the distribution system. Theisolation transformer bank exists for this sole pur-pose of protecting the electrical environment. Theisolation bank neither steps down nor steps up thevoltage. If this nonmechanical electrical link werenot provided for, a short circuit condition can resultin an electrical casualty of the L-100 lighting paneland end all single-phase power from the panel.

Should an electrical casualty damage one of thetransformers, the other two can be connected open-delta. The number of phases does not change.With the loss of one of the three transformers, apower reduction to approximately 58 percent isnecessary to prevent the open-delta from becomingoverloaded.

In another example, three single-phase trans-formers are used to step down the 450 volts to 120 voltsand provide the same protection to the P-400 power panel

Return to lighting panel L-100 (Figure 15-16)and locate feeder L106/TSGA-23. This feeder goesto lighting panel L-106 in the pilot house (Fig-ure 15-19). From here, a very important systemcan be traced out – the emergency power supply.

From the lighting panel L-106, follow feeder5L-106/DSGU-9 to the battery charger. From thebattery charger to the loads, the cables will now belabeled as P for power. The batteries directlycharged by the battery charger provide the power

supply to the emergency power panel P-24. Noticehow the circuit protective devices (fuses) are graphi-cally represented in Figure 15-20. Each conductorhas circuit protection.

Troubleshooting usually starts with the iden-tification of a defective electrical component. Thepower supply will then be sought out. The tag on thewire of the component will indicate its source ofpower; for example, the lighting distribution panelL-101. This allows the engineer/engineman towork backwards from the component, isolatingand de-energizing only the circuit needing service.

EMERGENCY POWER AND LIGHTING

Personal involvement with new state-of-the-artelectrical equipment and their appropriate manualswill complete your knowledge of the electrical sys-tem. This field is undergoing major changes thatpreclude this text from encompassing all aspects ofthe distribution system. The emergency power andlighting system should be one of the first systems youbecome comfortable with.

If the power should fail on board a vessel, livesand property are jeopardized. Many vessels regaincontrol of their electrical systems through the use ofan emergency generator and emergencyswitchboard. The generator is provided with its ownstarting system. When power is lost, the emergencygenerator must be able to automatically start andprovide power to the emergency switchboard withina few moments.

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Transferring power from ship to shore requiresthe momentary interruption of ship’s power becausemost Army vessels are not equipped to cogenerate (orrun in parallel with) shore power utility companies.Make provisions to ensure the emergency generatorwill not start during this momentary interruption.

The emergency generator power supply is madeavailable to either the main distribution center or theemergency distribution switchboard through an auto-matic bus transfer (ABT) switch and the bus tie. Nor-mally, the ship service generators supply power to theemergency switchboard from the main distribution cen-ter through a circuit breaker and automatic bus transferswitch. When power is lost, the ABT switch automati-cally connects the emergency generator to the emer-gency switchboard. The ABT simultaneouslydisconnects the main distribution switchboard from theemergency switchboard. This allows all the emergencypower to be supplied to the vital services connected tothe emergency switchboard. For unusual conditions,manual switches may allow the emergency generator toprovide power to the main distribution center. Caremust be taken not to overload the emergency generator.

The circuits connected to the emergencyswitchboard are determined by the design of thevessel. Some of these vital services are the —

Steering gear.

Fire pump.

Emergency lighting.

Emergency bilge pump.

Interior communications.

Main and emergency radio.

Loran and radar.

Additional information may be obtained in theIEEE Standard 45, Section 36.

SWITCH BOARDS

The operator monitors the power from thegenerators through the main power distributionswitchboard. The marine engineer/engineman hasthe critical task of putting the generators on line. Online means that the generator is supplying powerthrough the switchboard to the loads. If a generatoris coming on line, this indicates that the generator isoperating and waiting to furnish power to theswitchboard.

The information below is provided as ageneral guide for the junior and senior marineengineman in the operation of the AC switchboard.In all cases, equipment should not be operatedwithout first consulting the manufacturer’smanuals and appropriate Army technical manuals.Look for additional information pertinent to the

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operation of the 2000-series LCU and logistics sup-port vessel (LSV).

The following is based on the proceduresnecessary to operate and parallel the generic ACbrushless generators. Every prime mover and genera-tor manufacturer has its own specific needs and in-terrelated requirements for paralleling generators.Unlike many selective tasks you may have performedin the past, the act of paralleling generators dependson many outside influences.

Prime Mover

Currently, the Army vessel inventory uses theCummins, Detroit, and Caterpillar diesels as theprime mover to provide the motion necessary toproduce an electromotive force. To become a goodelectrician, you must first be a good mechanic.Nowhere is it more evident than when generatorsneed to be paralleled. In order to parallel gener-ators, the prime movers must be in proper workingorder. The diesels need to be mechanically soundand properly tuned. The governors must be setproperly. Before you ever consider major adjust-ments on the distribution switchboard, you must con-sult the operator and maintenance manual of theprime mover. If the prime movers do not operatewith the expected speed characteristics, then there isno possible way for you to compensate for theirinaccuracies at the switchboard.

Speed Droop

The efficient operation of a generator is notenough. Both generators must operate with the sameefficient characteristics. Each generator must betuned up individually, but their speed droop settingmust be collectively consistent. The reason the speeddroop is set is to establish a defined engine speed atno load and full load.

When a large electrical load is suddenlyplaced on the generators, the speed of their primemover drops. This is because it is harder for thediesel to turn the generator rotor with the strongermagnetic field. The magnetic field in the rotor hadto increase to compensate for the increase inelectrical demand. How spontaneously the twogenerator prime movers react to this decrease inspeed depends on the speed droop setting of the

individual governors. The increase infield strengthand armature current acts as a magnetic break,reducing diesel RPM.

Speed droop allows a decrease in diesel speedas the load is applied. In keeping with the elementarybasics of this manual, the electronic speed and volt-age controls of the new 2K LCUs will not be directlyaddressed. Although all functions presented arecomparable between all generator sets, consultationof the specific manufacturer’s manual is mandatory.General understanding of speed droop is bestpresented by the basic PSG governor function foundon the 1600 series LCUs. Much of the followinginformation is reprinted with permission of theWoodward Governor Company.

Speed droop is increased by moving the externalknurled knob forward on the governor and decreased(toward zero droop) by moving the knurled knobtoward the back of the governor. The droop settingmust be made by trial and error because there is nocalibration point (on these models). If it has not beenpreviously set, the engineer must move the knob backand forth until he achieves the proper droop settingbetween full load and no load.

The procedure below is recommended by theoriginal manufacturer’s manual, incorporated withinthe initial TMs (Figure 15-21).

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NOTE: A very accurate tachometermust be used to determine the speeddrop. The same tachometer must beused for both generators. This willeliminate any calibration errors orerratic tachometer response.

The Detroit diesel manual for the speed droopadjustment on the 4/71, PSG governor is supple-mented as follows:

Operate the prime mover until the oil is upto operating temperature.

Position the governor speed droop adjust-ing knob midway.

With the throttle in the RUN position,adjust the engine speed 5 percent abovethe recommended full-load speed.

Apply a full electrical load on the engine.Ensure that motors are providing themajority of the load. An inductive loaddemonstrates the current action in the ACsystem better than the resistive load fromthe stove, electric heaters, or lights.

Remove the rated load. After the speedhas stabilized, the diesel speed should be 5percent higher for no load than for fullload.

Adjust the governor speed droopaccordingly.

Adjust both generators the same way.

If the speed droop is not accurately establishedbetween the two prime movers, balanced electricaldistribution cannot be obtained.

Generator Voltage Droop

Voltage droop is the decrease in the normalgenerator voltage due to an increase in load current.The decrease in voltage from no load to full load isexpressed as a percentage of the full-load voltage:

Percentvoltage = (no-load voltage - full-load voltage) x 100droop full-load voltage

This is another adjustment that is necessary toproperly parallel AC generators. The droop controlshould be set so that a given amount of reactivecurrent applied separately to each generator willcause identical reductions in output voltage.

A large increase in current draw is followed bya slight decrease in voltage. This voltage drop needsto be compensated for accurately and consistently byboth generators.

The procedure below is a general guidance tobe used in accordance with appropriate technicaland manufacturer’s manuals. It is designed to clarifyelectrical procedures only.

Before adjusting for voltage droop, the droopcontrol is initially set in the mid position. Shorepower is secured. To adjust for voltage droop–

Operate both prime movers at rated speedand voltage until the prime movers and theregulators have stabilized.

Remove all electrical load from the mainbus by opening the feeder circuit breakersand the main circuit breakers of any addi-tional distribution panels connected to themain bus.

Close one generator circuit breaker. Withthe voltmeter selector switch in the BUSposition, adjust the automatic voltage con-trol to 465 volts. Open the generator cir-cuit breaker.

Repeat this procedure for the other generator,except do not open the generator circuit breakerafter the last adjustment. Leave this generator online. Then –

Close enough circuit breakers to loadthe generator with reactive loads. Donot exceed the current or power factorrating of the generator.

With the integral unit/parallel switch in theOFF position (ensure that the generatorsare not electrically linked for operation inparallel), adjust the droop control for thedesired voltage droop percentage at theavailable reactive load. A voltage drop ofthree percent will generally result in

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acceptable reactive load sharing withoutunacceptable voltage regulation. Consultyour manufacturer’s manual. If the avail-able reactive current is less than the ratedreactive current, set the droop control togive a proportionally higher bus voltage.

NOTE: The load should be motors.Motors provide the inductive reactancenecessary for this setting.

Open the generator circuit breaker of thegenerator adjusted instep 5. Repeat steps4 and 5, and adjust the droop control of thesecond generator. The reactive load andthe voltmeter selector switch (BUS posi-tion) must be the same as used for the firstgenerator. Identical loads and meters areparamount in duplicating the droop char-acteristics necessary to perform the adjust-ment as properly as possible. The samevoltmeter must be used for each machine.

Record the dial position of each of the twodroop controls. This will allow promptcorrection of unintentional control distur-bances. Once the voltage droop is set,minor changes in reactive load should becorrected by an adjustment of the auto-matic voltage control and not the droopcontrol.

PLACING AN ALTERNATING CURRENTGENERATOR ON LINE

Before trying to start the generator, ensure thefollowing:

Make sure the associated generator circuitbreakers are open. If a generator is startedand the circuit breakers to both generatorsare closed, the voltage surge to the genera-tor that is not operating will destroy thecomponents in its rotating rectifier.

Place the selector switch in a position thatindicates an individual generator is operat-ing, that is, unit or single unit operation.

Place the voltage regulator in the auto-matic position.

NOTE: A complete understanding ofthe manufacturer’s manual is necessary.Many generator electrical systems arenot designed to be warmed up or operatedat below rated speed with the voltageregulator in operation. Failure to complywith the manufacturer’s recommendationwill damage the voltage regulator.

NOTE: Many generator electricalsystems are not designed to be operatedwith the voltage regulator field open.

To place one generator on line –

Start the prime mover and bring the gen-erator set up to speed.

Adjust the generator for rated voltage.

Adjust the frequency for 60 hertz by adjust-ing the speed of the prime mover.

When it has been determined that the gen-erator is operating at the required voltageand frequency, connect the bus to thefeeders by closing the appropriate circuitbreaker. The generator is now on line.

PARALLEL OPERATION OF ALTERNATINGCURRENT GENERATORS

The voltage setting of AC generators is themost critical setting for paralleling. The voltage ofeach generator must be set exactly the same. Since avessel is subjected to extensive vibration and salt aircorrosion, it is advisable to check the calibration ofall the meters regularly.

The voltmeter should always reflect the ratedvoltage of the machine. In a perfect scenario, bothgenerators will reflect the exact rated voltage. How-ever, this is not often the case. Voltage settings arecritical because any voltage difference between thegenerators will increase the reactance between thetwo generators. This will require the generator tosupply extra current to overcome this wasted power.(Review Chapter 6 on inductive reactance.) Thismeans increased heat in the electrical system andextra demand from the generators.

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An expedient way to check the calibration ofthe voltmeter is as follows:

Start and operate number one generatoronly.

With the number two generator off, turnthe number two generator voltmeter to theBUS position.

Now the number one voltmeter and the numbertwo voltmeter are reading the same voltage source.If everything is correctly calibrated, then both meterswill read the same voltage from the number onegenerator.

If both generator voltmeters do not displaythe same voltage reading, then there is an inconsis-tency. If you adjust each generator according to itsown meter readings, then the voltage differencestill exists. As an expedient measure, you can main-tain the voltage difference as noted above, when eachvoltmeter is monitoring its own generator. Eventhough the meters are not identical, the voltages willbe. Final paralleling voltage adjustment will com-pensate for any inconsistency.

In paralleling, it is more effective to have boththe voltages slightly below or both voltages slightlyabove the rated voltage than for one generator to beonly 1 volt above and the other generator at exactlythe rated voltage. Differences in voltage increaseelectrical system reactance. The increased currentand subsequent increase in heat decrease the lifeexpectancy of components. In any application, whenan inconsistency is found with the equipment, correctit immediately or refer it to a higher echelon ofmaintenance.

PARALLEL OPERATION ANDSYNCHRONIZING

Use the following sequence to parallel twogenerators:

Make sure both generator sets are up tooperating temperature and rated speed.

Place one generator on line as earlierdescribed.

Set the voltage regulator toAUTO-MATIC.

Set the voltage on each machine.

Set the frequency of both machines. Thefrequency represents the speed of the gen-erator prime mover. A change in theprime mover speed changes the frequency.The generator on line should indicate 60hertz. The generator that will be placed online should be slightly higher than 60 hertz.This is because the generator that will beplaced on line will eventually be placedunder load, reducing its speed slightly.One generator is operating at full load(with speed droop), and the other gener-ator is operating at no load.

Place the synchronizing switch in the incom-ing generator position. The synchronizingscope lets you see when the generators areoperating in phase and to see the relation-ship between the differing speeds of thetwo prime movers. The synchronizingpointer must rotate in the FAST direc-tion. This indicates that the generatorthat will be coming on line is operatingfaster (more revolutions per minute) thanthe generator online. If the synchronizingscope pointer rotates in the SLOW posi-tion, this indicates that the speed of thegenerator that will be placed on line ismoving too slowly. Ensure that the pointeris moving slowly in the FAST direction ata speed where you can accurately close theincoming generator circuit breaker at the12 o’clock position.

When the synchronizing pointer is at the 12o’clock position, close the incoming genera-tor circuit breaker.

Observe the kilowatt load at once. Adjustthe kilowatt load by adjusting the speedof the prime movers. This is to balancethe load between both generators. Eachgenerator should share the kilowatt loadevenly.

Check the frequency of the generators andadjust both prime mover speeds together,if necessary, to maintain 60 hertz.

Check the ammeters. Check the voltmeters.If you had 40 amperes on one ammeter

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before you paralleled the generators andnow you observe 25 amperes on eachammeter, then the voltage is not exact. Thisis because 25 amperes plus 25 amperes doesnot equal 40 amperes. The total powerproduced between the two generators isnow 50 amperes, and therefore 10 extraamperes are being produced to overcomethe increased reactance. Adjust one voltagein minute proportions until you have thelowest total current reading. This is howyou will finally eliminate the extra reac-tive loads due to any inconsistencies inthe voltmeters. Do not drop below ratedvoltage. Only one voltage needs to beadjusted.

Place the integral unit/parallel switch inthe position that indicates both generatorsare operating in parallel. This switchprovides an electrical link between the twogenerator sets and helps maintain paralleloperation.

Recheck all meters. Adjust each ammeterand kilowatt meter so that they show anevenly distributed load.

FLOATING ON THE LINE

Once a generator is paralleled, its voltage andspeed are determined by the bus. At the instant youthrow the switch, the generator is connected to thebus, but it is not delivering power. It is said to be“floating” on the line. If you try to reduce the speedof the prime mover, the generator continues to run atrated speed. How is that possible? There is notenough mechanical power to drive the generator thatfast. Therefore, the generator draws electricalpower from the bus. It actually runs as a motor.

If you try to increase voltage by increasing DCexcitation to the generator’s field, terminal voltagewill appear to remain the same. You have actuallyincreased the generated voltage of one generator, butit does not show.

Why is it that the terminal voltage does notchange? The extra generated voltage produces areactive current flow into the bus. This current doesnot deliver any active (usable load) power. Only byincreasing the prime mover speed will the generatoraccept its share of the load.

SHUTTING DOWN THE GENERATORS

To shut down the generators –

Place the integral unit/parallel switch in aposition that indicates which generator isto remain on line.

Transfer the entire load to the generator toremain on line by simultaneously increas-ing the speed of the generator and decreas-ing the speed of the generator that will beshut down.

When the transfer is almost complete(again check with applicable manuals),open the main circuit breaker of the gen-erator to be secured.

Recheck your voltage and frequencymeters.

Secure the prime mover as required.

Now you may continue to operate on one unitor continue to shut down the other generator asfollows:

Reduce the electrical load as much as pos-sible by securing equipment and openingfeeder circuit breakers to the electricaldistribution system.

Open the generator main circuit breaker.

Shut down the prime mover as applicable.

Remember, never perform any maintenance,servicing, or operating without first consulting theappropriate technical manuals.

ELECTRONIC GOVERNORS

Newer vessels designed for the Army will beusing the electronic fuel control (EFC) and govern-ing system. The following information is provided asintroductory information only. In-depth informationwill be made available at the junior and senior marineengineer levels. Specific information is availablefrom the vessel technical manuals andmanufacturer’s manuals.

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The EFC system will be made up of three basicunits (Figure 15-22):

Electronic speed sensor, magnetic pickup(MPU).

Electronic control box, governor control.

Electronic actuator, fuel delivery.

The elimination of most throttle controls andlinkages means that the system is less maintenance-intensive than current fuel control systems.

The MPU is an electromagnetic componentmounted through the flywheel housing (Figure 15-23).The MPU is a permanent magnet with the circuitfrom the governor control tightly wrapped around it.The MPU comes in close proximity with the teeth ofthe flywheel. As the teeth from the flywheel movepast the magnetic field from the MPU, the MPU’smagnetic field becomes distorted. The motion of thedistorted magnetic field induces an EMF into thegovernor control circuit wrapped around the magnet.As the flywheel teeth move further past the MPU,another portion of the MPU field becomes distortedin a like but opposite manner. This magnetic field

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motion in the MPU induces an EMF in the oppositedirection as previous. The single-phase ACdeveloped in the MPU is sent to the governor control.The cycles per second can be easily converted torevolutions per minute. This provides the governorwith an indication of prime mover speed. The fasterthe flywheel turns, the faster the induced EMF fre-quency. In this manner, the governor control sensesthe changes in speed.

The governor control interprets these speedchanges and, depending on the setting of the con-trols, provides an electrical signal to the actuatorport.

The actuator is basically a solenoid valve thatadmits fuel to the diesel in a quantity determined bythe signal from the governor control. The slower the

speed of the prime mover, the more the governorcontrol electrically opens the fuel port. The fasterthe prime mover speed, the smaller the quantity offuel delivered through the actuator port.

The most important information for thejunior and senior marine engineman concerns thebatteries. The batteries provide the voltage andcurrent necessary for operating the electronic fuelcontrol system. This equipment is set up so thatthe generator prime mover cannot functionwithout the batteries fully operational. Althoughprovided with manual means to override this sys-tem, normal operation is prohibited. Emergencygenerators will not start automatically nor will theship service generators continue to operate shouldthe batteries fail to provide the necessary power forthe EFC control circuits.

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