Electric warship new - Naval Postgraduate Schooledocs.nps.edu/dodpubs/topic/general/Electric_Warship.pdf · Electric warship new 3 14/2/03, 11:47 am. 4 Journal of Marine Design and

3No. B2 Journal of Marine Design and Operations

The electric warship VII - the reality

INTRODUCTION

In recent years a variety of papers, seminars and conferenceshave sought to provide detail and promote discussion onthe diverse range of issues that make up the electric warshipconcept. The same period has also seen a huge amount of

progress in enabling technologies that have made integratedelectric propulsion the system of choice for many new navalships. This paper looks to review the MoD’s Marine EngineeringDevelopment Strategy (MEDS), examining its role within theframework of the Equipment Pillar of the Royal Naval Strategic


Integrated electric propulsion (IEP) is an everyday reality as the power system solution fornaval platforms, embracing recent advances in enabling technologies to deliver cost-effective, survivable, power-dense solutions in a variety of applications. Founded on theMarine Engineering Development Strategy (MEDS) and supported by significant progressin the commercial marine sector, the defence community has embraced the potential ofIEP and is now looking at more advanced integrated full electric propulsion (IFEP) solutionsfor future platforms. This paper follows on from the earlier series of ‘Hodge-Mattick’ electricwarship papers and the ‘Newell-Young’ paper Beyond Electric Ship, and in doing so looksto put the United Kingdom Ministry of Defence’s (MoD) programmes and strategies intocontext, review the issues surrounding the introduction of IEP and provide an update onprogress towards achieving the electric warship.

Commander GT Little, Royal Navy Eng(Hons), MSc, MCGI, psc(j), Royal Navy,Commander SS Young, MSc, CEng, MIMechE, Royal Navy, and

Commander JM Newell, BSc, MSc, CEng, FIMarEST, Royal Navy

AUTHORS’ BIOGRAPHIESCommander Graeme Little, Royal Navy, joined the Royal Navyin 1984 as a marine engineer officer. On completion of his basictraining in 1985 he joined Royal Naval Engineering College(RNEC) Manadon to study for a first degree in marine engineering.Following successful professional training he joined HMSBirmingham in 1990 as the Deputy Marine Engineer Officer. Hesubsequently read for an MSc in electrical marine engineering atRNEC Manadon followed in 1994 by an appointment to the ShipSupport Agency as the project officer responsible for electricpropulsion systems. On promotion to Lieutenant Commander in1996 he joined HMS Sutherland as the Marine Engineer Officer.Following Staff Course, he was promoted to Commander in2000 and was appointed to the Warship Support Agency as thehead of the Electrical Power and Propulsion Systems specialistgroup where he is now serving.

Commander Stuart Young, Royal Navy, joined the Royal Navy in1977 and completed undergraduate and post-graduate trainingat the Royal Naval Engineering College in Plymouth. He hasundertaken a number of appointments at sea, including MarineEngineer Officer of HMS Norfolk, the Royal Navy’s first CODLAGfrigate. Shore appointments have included project officer for theprocurement of Warship Machinery Operator and MaintainerTrainers, lecturer at the Royal Naval Engineering College andMarine Engineering Liaison Officer with the United States Navy,based in Washington DC. He is currently the Electric ShipProgramme Manager within the UK’s Defence ProcurementAgency.

Commander John Newell, Royal Navy, joined the Royal Navy asan artificer apprentice in 1976 and joined BRNC Dartmouth onpromotion in 1978. On completion of his degree at RNECManadon and initial training as a marine engineer he served as theDeputy Marine Engineer Officer in HMS Sirius. He subsequentlytook a MSc in electrical marine engineering and served in the MoDas the project officer for pollution control equipment. He thenserved as the Marine Engineer Officer in HMS Boxer beforeundertaking the French Staff Course in Paris. On return to the UKhe spent 15 months with the Joint Planning Staff precursor to thePermanent Joint Headquarters (PJHQ) before becoming one ofthe appointers. He was promoted to Commander in 1997 andwas appointed as the head of the Electrical Power Distributionand Propulsion Systems specialist group within the Ship SupportAgency in March 1998. Commander Newell joined HMS Albionas Senior Naval Officer and Marine Engineer Officer in January2001.

Electric warship new 14/2/03, 11:47 am3

4 Journal of Marine Design and Operations No. B2


Plan and the Smart Acquisition Initiative. Recent progress andsuccesses will be reviewed along with a look at the enablingtechnologies and the ‘road map’ for managing the successfulintroduction of such technologies. The aim of the paper is toprovide the wider naval marine community with clarity of theMoD’s programme and to invite debate for marine systems of thefuture.

Perhaps by way of an overview it is worth reviewing the trendsin power and propulsion systems in recent years, noting that thereality of electric propulsion was successfully introduced in 1920in HMS Adventure and has seen widespread use in the submarinecommunity.

In the last decade of the 20th century, the Type 23 frigatedemonstrated the benefits that an electric architecture can bringto bear with the hybrid power distribution and propulsion systemknown as Combined Diesel Electric and Gas (CODLAG).

Building on the success of the Type 23 and the step change intechnology driven by the commercial sector, electric propulsion isthe reality as we enter the 21st century, with two Auxiliary Oilers(AO) and two Landing Platform Docks (LPD) shortly to enterservice. Both classes have integrated electric propulsion and bringturnkey commercial solutions to satisfy a naval application. Anartist’s impression of the LPD(R) is at Fig 1 together with an outlineschematic of the power generation and propulsion system at Fig 2.

Hard on the heels will be the replacement survey vessels,Type 45 destroyer and the Advanced Landing Ship Logistics, allembracing electric propulsion. The Type 45 solution is driven bythe requirement for a power dense system with reduced wholelife costs and challenging signature targets. The goal has beenmet by exploiting the commercial market and incorporating theUnited States’ integrated power system (IPS)-derived advancedinduction motor (AIM) development and the WR21 ICR gasturbine.

WHY ELECTRIC PROPULSION ANDWHAT IS IT?

Electric propulsion brings together efficiency, flexibility,survivability and, perhaps most importantly, reductions in costof ownership. Captured simply, reduced numbers of primemovers, integrated systems, flexibility in layout and provencommercial precedent make it a credible solution to the require-ment.

Electric propulsion systems fall into three broad categories,namely hybrid, integrated (IEP) and integrated full (IFEP). Theterms electric ship and electric warship are also used. They can bedefined as follows:● Hybrid - similar to the T23 frigate, where mechanical drive

and electric drive systems are combined.● IEP - where a common power source is utilised for both

ship services and propulsion system, with the propulsionbeing purely electric. T45, AO and LPD(R) are examples.

● IFEP - takes the IEP concept further by incorporatingadvanced power electronics and energy storage into thearchitecture to give further cost and operational benefits.

● Electric ship - incorporates advanced prime movers andwidespread electrification of auxiliaries into the IFEParchitecture.

● Electric warship - where novel high-power weapons andsensors are incorporated to take advantage of the highsystem powers available.

Fig 3 looks to put the various system configurations intocontext.

THE MARINE ENGINEERINGDEVELOPMENT STRATEGYThe current strategy

The first Marine Engineering Development Strategy wasendorsed in 1996. It aimed to achieve significant life cycle costreductions, whilst meeting naval requirements, by exploitingworld-wide industrial and commercial developments. Only ifnaval requirements could not be met would development ofspecific equipment be funded. It envisaged achieving this throughthe development and introduction of advanced-cycle gas tur-bines within an integrated full electric propulsion architectureand the electrification of auxiliaries. Development of industrypartnering and international co-operation opportunities wasencouraged.

Much has been achieved. Since 1996 every major shipordered for the Royal Navy has had an integrated electricpropulsion system. The selection of IEP for the T45 means thatlife cycle cost benefits will now be achieved earlier than envis-aged in 1996. The electric ship technology demonstrator isexpected to start testing in spring 2002. This builds on the T45concept and introduces new power conversion systems andadvanced energy storage concepts to accrue further LCC ben-efits with high system integrity, particularly under damage orfault conditions.

The Marine Engineering Development Programme (MEDP) ismore than just electric ship, it covers all marine engineeringtechnologies where MoD-funded work is needed to ensure thatnew technologies meet the requirements of future ships. Workeither recently completed or currently on-going includes.● Integrated waste management.● Fire-fighting systems.● Upper deck systems.● Improved roll-stabilisation.● Composite pressure vessels.● Non-thermal plasma for Nox/particulate removal for die-

sel exhausts.● Fuel cross-flow micro-filtration.● Electrical actuation of hydrodynamic control surfaces.

The Equipment PillarThe Marine Engineering Development Strategy does not

exist in isolation and its pursuit over the next two to three yearsis a key element of the Equipment Pillar of the Royal NavalStrategic Plan. The Equipment Pillar outlines the Navy’s con-cerns regarding reliability, manning levels and through-lifecosts of current equipment and indicates how these could beimproved by:● Exploiting the concept of smart acquisition, closely align-

ing needs of through-life fighting power with specifiersand designers of equipment, focusing on ease of opera-tion, maintenance, reliability and longevity, efficient man-ning and operating costs.

● Seeking innovative ways of monitoring and employingtrends in technology, especially encouraging potential fornon-warfighting technology to improve conduct of rou-tine business.




THE DRIVERS FOR CHANGETechnology

Technical progress over the last five years has been far morerapid than envisaged in 1996. The step change to integratedpower architectures, with all the ensuing benefits, has now beentaken. Future development will be more evolutionary rather thanrevolutionary, and the benefits will be obtained through equip-ment, rather than system development.

Development of the first ICR gas turbine (the WR21) hasbeen completed and the engine system selected as the primarypower source in the T45. Propulsion motor technology hasallowed a power-dense advanced induction motor to be selectedfor the T45. Many manufacturers around the world are nowdeveloping permanent magnet motors of various topologies,and major breakthroughs have recently been achieved in super-conducting motor technology. Semiconductor developmentcontinues unabated, as predicted, and further major advancesare expected over the next few years. In many areas, commercialshipping has embraced future technologies earlier than navies;podded drives are an excellent example of an equipment now inwidespread commercial use whilst still under assessment by themajor navies. Fuel cell development, driven by automotiverequirements, is progressing rapidly and to the extent that off-the-shelf solutions may be available within the foreseeablefuture. The choice of fuel, and its production, transportationand storage remains a major issue.

As a result, further MoD-funded development — except toaddress shock or signature issues and other specific naval issues— is probably unnecessary but technology assessment in order toascertain suitability is very important. This assessment is bestconducted through the medium of the proposed Ministry-ledMarine Engineering Centre of Excellence, utilising the availableexpertise to make strategic decisions that have the full backing ofboth MoD and industry. These achievements and a re-assessmentof trends need to be reflected in any revised development strategy.

Smart Acquisition - The new environmentSmart Acquisition was introduced within the Ministry of

Defence in 1999 and adds clarity to the acquisition process whichwas not available to the original strategy in 1996. It refined theconcept of capability-led requirements and defined a new acqui-sition cycle, with clear decision points and therefore clear win-dows in which technologies needed to be sufficiently mature inorder to be selected as candidate solutions. It defined incrementalacquisition and technology insertion. More investment duringthe early project stages is encouraged is order to reduce risk, andclose liaison with industry is regarded as essential. Although theoriginal strategy anticipated many aspects of smart acquisition,the revised strategy needs to stress further how marine engineer-ing development fits into the smart acquisition framework.

RiskRisk management is a key tool in the acquisition process. In

the assessment phase the user’s requirements will be developedinto the more detailed system requirements. At each stage the riskassociated with attaining the requirements will be assessed. Thetechnology development and demonstration within the MEDP isa primary means of mitigating this risk. In addition the technologyspecialists within the proposed Marine Engineering Centre ofExcellence (primarily the Marine Equipment Integrated Projects

teams within the UK’s Warship Support Agency) can advise onthe risks associated with attaining the required capability. Thus adialogue needs to be established between all the relevantstakeholders.

EnvironmentalRoyal Navy ships are required to operate world-wide and must

therefore comply with all applicable environmental legislation.Indeed, the long life-cycle of warships means that the design mustanticipate future requirements. Commercial waste treatmenttechnologies may be applicable to the naval requirement butwould need to be made significantly more compact to facilitateinstallation on a surface warship or submarine. Furthermore,warships are required to stay at sea for far longer periods and shoresupport facilities for disposal of waste stored onboard may not beavailable. The goal of achieving a zero-emission warship, acrossthe operational profile, remains.

The environmental impact of ships throughout their life cyclemust also be assessed and minimised. This requires examinationof environmental impact during build, in-service maintenanceand on disposal. Within the automotive industry the manufactur-er’s responsibilities are clear cut and increasing. Similar trends canbe expected in other fields, including marine.

The future availability of fossil fuels must also be considered.Fossil fuels are predicted to remain in significant use for 40 yearsor more. However, cost will increase through this time frame andat some point it will become more cost-effective to use analternative. The Royal Navy will be governed by commercialtrends in this respect but needs to monitor trends closely andinitiate development to ensure that warships can operate withinthe wider future fuel economy.

OperationalThe operational capabilities required from future warships

continue to develop. Specific capabilities of future power andauxiliary systems will, of course, vary but there will be a numberof requirements that are generic. These include:● Increasing power density, to minimise impact on overall

ship design.● Extended range, requiring highly efficient power systems.● High availability.● Low manning.● Increased stealth and improved signature control.

A STRATEGY FOR THE 21ST CENTURYTaking these factors into account, the following strategy for

marine engineering development in support of the Royal Navy’sfuture capability requirements is proposed:● Maintain awareness of technology and its capabilities by

monitoring and assessing technology innovation andindustrial capabilities and trends whilst maintaining theElectric Ship Programme Office as a focal point for themonitoring of industrial and commercial technology trendsand utilising the Marine Engineering Centre of Excellencefor the dissemination and assessment of applicable tech-nologies.

● Identify the warship acquisition risks which can be miti-gated through marine engineering system solutions.

● Develop mitigation strategies that satisfy the prime con-tractor (or potential prime contractor), satisfy the DEC




and Warship IPT and are within our ability to fund andmanage to completion within required time-scales.

● Build on success of original MEDS and the electric shipconcept, with emphasis on facilitation of incrementalacquisition and technology insertion through the use ofopen systems.

● Maintain focus on LCC reductions through equipmentdevelopment within the IFEP architecture, technologytrends, including fuel cells, podded drives and smartsystems, and integration of high-power weapons andsensors.

● Take into account external influences, including increas-ing environmental legislation and trends in future fuels.

● Gain effective pull-through into service by ensuring thatsufficient de-risking is undertaken, results of de-risking areavailable for those who need it (whilst protecting IPR) andindustrial capability to deliver solutions is maintained,particularly through competition.

● Maximise value-for-money through internationalco-operation.

Thus the aim of the Marine Engineering Development Strategyis:

To achieve the required capability whilst generating ongo-ing reductions in life-cycle costs, through the leveraging oftechnology to mitigate the associated warship acquisitionrisks.

THE ELECTRIC WARSHIP - EXPOSEDAs discussed previously, the all-electric ship embodies the

IFEP concept with the additional enablers of advanced-cycle gasturbines and wider electrification of auxiliaries.

It is however the IFEP architecture and possible solutionswhich offer the most exciting possibilities; in terms of oper-ability, capability and reduced cost of ownership. The frame-work that is IFEP is founded on a number of enabling sub-systems; high power generation, high power distribution,energy storage and conversion, low power distribution, auto-mation systems and propulsion systems. Within these base-line sub-systems a bespoke architecture can be produced, anexample of which is at Fig 4.

The overall concept for the baseline architecture is oneof flexibility of design solution with a range of technologiesable to meet the demands of the system. It is these tech-nologies which have been the focus of MEDP and themarine engineering community and will form the basis ofthe next section. Before reviewing the technologies it isworth highlighting the importance of a generic baselinesolution in the context of understanding and maximisingthe synergy between various platform architectures; a keytheme in realising the potential of IFEP. Given a genericbaseline allows system level design assessments to be madetogether with supporting a technology development focus.It must, however, be remembered that at the system andsub-system level a number of themes need to be understoodif the system is to be optimised effectively, these include:hullform; power system architecture; energy storage; oper-ability; user demands; and, field effects.

Hullform. The hullform solution drives the IFEP solution,primarily from a power density perspective but with support-

ing considerations of signature, survivability and shock. Thespectrum of hullforms is bounded by the larger carrier-basedhullform (steel is cheap and air is free solution - although thisis not an entirely valid statement) and the exacting require-ments of a submarine platform. The middle ground occupiedby the destroyer and frigate, whether multi- or monohull,completes the picture. This is not the entire picture as IFEP isalso relevant to smaller vessels, but the requirements that setthe main contenders apart is installed power which is signifi-cantly greater than those anticipated for minor war vessels. Thehuge benefit of the IFEP solution is that premised on thecurrently-accepted range of hullforms possible for warshipsdriven by naval architecture and weapon and sensor solutions,the IFEP concept can be designed to fit. This will not gounchallenged as the required bounds of power density fromboth gravimetric and volumetric perspectives are placed underconsiderable pressure and the demands for increases in bothare made.

Power system architecture. At the heart of the ‘powerstation’ is the system architecture, on which the solutionwill hang; in the case of IFEP a number of options are stillpresented as viable. The traditional architecture of a ringdistribution with centralised switchboards and electricaldistribution centres (EDCs) offers, in most part, a goodbaseline solution against which other ‘more novel’ solu-tions can be gauged. Novel approaches to EDC architecturesprovide inherent flexibility and system redundancy withfurther enhancement possible using change-over switchesand uninterruptible power supplies (UPS). Looking at aslightly more novel approach leads us to the much courted‘zonal concept’, whereby the distribution system, togetherwith all the supporting systems, is zoned with at least twomethods of supplying energy within a zone. Central to thisarchitecture is a zonal power supply unit (ZPSU) and zonalenergy storage unit (ZESU). Extremely attractive, the zonalconcept infers increased survivability and operability butnot without an element of technology and integration risk;a decision that will be informed by the MoD’s energystorage philosophy.

Energy storage. A wide range of technologies exist to supporta profusion of possible requirements; indeed it is this thatsupports the need for a platform, if not pan-platform, energystorage philosophy. The requirements range from the equipment-based UPS, commonly found in weapons and sensors, throughsub-system requirements such as steering, to the most onerousdemands of propulsive ride-through, more of which later. Again,this issue is far from concluded and cannot be viewed in isolation,as together with architecture and the ZPSU/ZESU debate, thisneeds a much broader focus. Assessment of technologies will bebased on demonstration in the ESTD and the MoD’s energystorage strategy.

Operability. Often described as the panacea for the platformsystems, IFEP and its variants, provides a huge step forward inflexibility of operation and system survivability, to name but two.However, a note of caution - realising the full potential of the plantcan only be achieved if it is fully understood and not, as someprotagonists suggest, left to ‘come out in the wash’ as more isunderstood and experience gained. Operability is a key strand andmust be understood at the earliest point in the design process.Central to the operability debate is the issue of single generator




operation (SGO), a subject which has attracted a huge amount ofinterest, notably from the operating community. The technicalcommunity has not helped themselves on this one as the termSGO conjures up all sorts of issues in the minds of the operators.However they have now been articulated clearly and it has beendemonstrated, with some clarity, that SGO does not result inreduced system availability when balanced against the ship han-dling constraints, operational state and provision of energy stor-age. The concept of minimum generator operation (MGO) em-braces SGO fully and is perhaps a far more relevant description ofthe operating procedures.

User demands. As wider electrification becomes a reality thedemands on the power system increase, this is best illustrated aswe focus on the possible next generation of weapons and sensors,or indeed those of aircraft launch and recovery. The user demandsneed to be understood from the outset if the design solution is tobe flexible enough to accommodate technology insertion and,indeed, the capacity to support demands from the outset. Not justconfined to weapon systems and sensors, the implication ofincreased electrification of auxiliary systems needs to be under-stood and quantified.

Field effects. Subject to much recent focus for both in-service and newbuild projects, the effects of electromagneticfields have been raised as an area of concern for hybrid and IEPinstallations, from signature and safety perspectives. Whilstthe issue cannot be dismissed out of hand it equally must notbe made too much of, and a number of approaches are in handto manage this effectively. From a safety perspective, measure-ments are being taken on current classes and it is planned tocarry out similar trials onboard LPD(R) and AO as they enterservice. Any potential further problems can be reduced signifi-cantly by up front design and focus on shielding and installa-tion. The issue of signatures is being assessed but cannot bediscussed in this paper.

The generic baseline and system framework allows for a moreholistic approach to system and platform design, primarily froma technology insertion perspective - an important point as theplatform visions of the future begin to move into and out of focus!Outwith these system design issues, it must be recognised that arange of enabling technologies are central to IFEP, a number ofwhich, together with the review of risks are outlined in the nextsection.

Framing the technologyAs mentioned previously, the key thread must be under-

standing and managing the risk, both from equipment andplatform perspectives. To articulate the technical risk requiresa formal risk review across the enabling technologies, theoutcome of which will provide generic and platform-specificrisk assessments across the technology, thereby framing thetechnology issues and underpinning future development. Fig5 captures the high-level technology enablers within which theanalysis will be undertaken.

Before reviewing the technologies it is worth reiterating thecentral themes for MEDS and AES; power density, risk, whole-lifecosts, efficiency, environment and survivability. These criteriaframe the focus on technology of power generation, high powerdistribution, energy storage and distribution, and low powerdistribution.

Power generation, Gas turbines are established as the

power-dense, efficient and environmentally-sound solution tothe problem of installed power. Coupled with conventionalgenerator technologies, the high power generation capability,vested currently in the WR21 GTA and the ACL GTA looks toprovide the surface platforms with the bulk of their power wellinto the late part of the 21st century. Technology focus for thefuture is reliant on established construction techniques withpossible trends to super-conducting and permanent magnettechnology. Before moving away from generation it is worthyof note to raise the issue of fuel cells. The jury is still out andthe MoD focus has, at best, until recently been uncoordinated.Whilst the short term possibilities are limited, advances in fuelstorage and cell technology will undoubtedly make fuel cells afuture attractive low power energy source. Industry is develop-ing the fuel cell as a clean and efficient source of energy. Futurework may concentrate on the use of alternative fuels (egmethanol or hydrogen) and its safe storage and handling in ashipboard environment. This work will be driven by the needto identify an alternative to conventional fossil fuels by themiddle of the 21st century.

High power distribution, The ac/dc debate is still farfrom resolved, indeed which way we fall will primarily bedriven by the industrial focus and the level of risk. The ac/dcsubject is as emotive as ever and the decision point is fastapproaching. Switchgear and cables cannot be readily di-vorced from this debate and will play a key role in thesolution. Switchgear rated for the perceived IFEP architecturesis on the limits of its capability and a number of options suchas the hybrid switch and novel breakers are being assessed fortheir applicability to marine systems. Related to this are theissues of switchboard design and a possible trend away fromcentralised to, perhaps, distributed switching and thereafter,perhaps, embedded protection - one step at a time possibly,but this is an area that we must progress as the exactingprotection and switching requirements increase. The lastissue within this area is that of cables, and whilst we areconfident that the issues of EM fields, buildability and shockcan be managed with existing technology, we need to look athow we might embrace busbars or more novel systems for thefuture. At present all such systems are prohibitively expen-sive for the gains in ease of build and similar.

Energy storage and conversion, Noting the profusion ofpossible solutions to meet the varied demands on energy storage,it is difficult to progress any one technology without havingarticulated the architecture and energy storage philosophy. Ingeneral terms, the industrial base is making the enabling technol-ogy available, it is how we grasp this technology for the navalmarine environment that presents the greatest challenge. Return-ing briefly to ESTD, flywheel technology and a regenerative fuelcell are being assessed for power system suitability at the zonal andbulk levels of power.

Low power distribution, Not wishing to open the ac/dcdebate or indeed repeat the high-power discussion, this section isbest left looked at from a system perspective. System issues arevery much architecture-dependent and we must be aware of theimportance of the transversal issue with the high-power system.Current solutions include transformed supplies but the technol-ogy is ‘here and now’ for bi-directional static power converters andperhaps presents a viable solution for platform incremental acqui-sition.




SWITCHGEAR - THE DC CHALLENGE - AFOCUS

Not a focus for previous electric warship papers, switchgear ishowever worthy of mention as a key enabling technology, particu-larly for a potential dc distribution system where the interruptionof fault currents is more onerous than for comparable ac systems.The reason for this is simply that an ac circuit breaker can interruptat or around current zero whereas a dc breaker must create acurrent zero either by forcing the current to zero by controlling thearc voltage or, creating a current zero by commutating the currentaround an opening contact. In addition the dc circuit breakerdesign is driven by the arc energy that can be dissipated, mindfulthat a dc breaker will be much larger than its equivalent rated accounterpart, and the need to minimise the rise of fault current.The technology solutions to these problems are high-speed aircircuit breakers and hybrid breakers.

Air circuit breakers. The mechanism during a fault is thecontrol of the arc within the arc chute whereby an increasedresistance of an established arc reduces the circuit current so thatthe arc cannot be maintained by the circuit voltage and the currentis reduced to zero. The control of the arc is achieved by naturalelectromagnetic and thermal forces assisted by a magnetic field;technology which is well established. Currently available at up to3kV, 8kA with a breaking capacity of 60kA, the move to voltagesin excess of 5.6kV for the electric warship application will needdevelopment, but the more onerous rating is containable withincurrent technology.

Hybrid circuit breakers. Combining a fast mechanical switchand power electronics, hybrid circuit breakers utilise either zerocurrent or zero voltage switching, both of which are illustrated atFig 6 and described below.

Zero current switching. The mechanical switch carries theload current until a short circuit is detected whereby the switchopens, the power electronic switch is then triggered and aresonant current is established in the L-C network with a reversecurrent flow at the mechanical switch. The voltage across thecapacitor rises and the varistor begins to conduct, which dissi-pates the inductive energy within the circuit and the current dropsto zero.

Zero voltage switching. The mechanical and power electronicswitches are triggered simultaneously but the time constants ofthe mechanical switch allows a parallel conducting path to beestablished within the power electronics. As the mechanicalswitch opens, the arc voltage shifts the current flow fully to theparallel power electronics path. The commutation provided bythe power electronics then extinguishes the arc and with theelectronic switch turned off with the mechanical switch open, theremaining energy is dissipated within the varistor.

Issues. The hybrid breakers provide improved current limit-ing overfast-acting air circuit breakers with a significant reduction,almost elimination, of arcing. The hybrid variants are very similarbut the trade-off is between the bulky resonant circuit required inthe zero current switch compared to the need for switchgeardevelopment. The technology has been implemented in proto-type designs but no production arrangements have been takenforward. In a marine application the constraints are the mechani-cal and power electronic switches, with current limiting onlyachievable at the planned ratings if the mechanical opening forceand time to open are in the order of 35kN and 1.6 milliseconds1.

Propulsion systems. A huge subject area, broadly captured

by the propulsion motor (PM) system and the transmission/propulsor system. Comprising a drive and motor, power densityand signature direct these technologies which have seen a hugeamount of industrial and government effort in recent years. Theadvanced induction motor (AIM) is currently the preferred solu-tion, and is shown at Fig 7, but the industry pack of chasingtechnologies is focused on taking PM system developments tomeet the demands of pods, low displacement and novel hullformapplications. Whether it will be a derivative of the AIM, apermanent magnet machine or indeed a super-conducting ma-chine, is a long way from being resolved, indeed the MoD isactively pursuing a PM strategy to assess where best to focus itsefforts and, perhaps more importantly, its money! Again industryis actively pursuing and solving the technical issues surroundingthe novel PM technologies and this looks to be an area ofsignificant industry-led work in the near term. In support of this,power electronic devices and system developments continueapace and a number of maturing PM system combinations nowfeature advanced pulsed width modulated (PWM) converters.

The three technology areas - conventional, permanent magnetand superconducting - all offer high power density (volumetricand gravimetric) efficient solutions. Whilst the technologies areall at varying stages of maturity, the key is that they would all seemto have a role to play in the next generation of warships, albeit notall technologies are suited to all applications. Fig 8 looks toprovide a snapshot of motor technology to put each of thecontender technologies into perspective.

Of course Fig 8 is only half of the story, particularly the powerdensities, and the motor technologies cannot be compared inisolation; any longer term assessment will need to include theconverter and auxiliaries and this is the subject of the MoD’spropulsion motor strategy.

Platform management systems (PMS). These have longbeen the key to achieving manpower savings, and work is underwayon how to specify systems, in performance requirements terms,which support the operating and manning philosophies of thefuture navy. This work will be further enhanced by developmentsin smart systems, which will be able to identify failures anddamage, and reconfigure themselves automatically without op-erator intervention.

DELIVERING CAPABILITYReturning to the theme of strategy and how this and the

technology can be embraced and engaged as platform systemsolutions, Fig 9 puts forward a roadmap for technology within theframework of capability, requirement and timescales. These boundsare extremely pertinent to the longer term focus of the electricwarship concept and system design and technology integrationfor future platforms. The key thread throughout is risk and howit is identified, owned and managed by the various stakeholders;notably the MoD, the prime contractors’ offices (PCOs), systemintegrators and equipment suppliers the balance of which needsto be developed if the capability is to be delivered.

Mindful of the common thread of risk, the roadmap looks tocapture the main themes and how the stakeholders need to beintegrated and relevant to ensure that the obvious synergy isexploited. Within the bounds of the roadmap, here are a fewthoughts. Procurement of future platforms is now focused ondelivering capability by the most cost-effective means, with thekey themes being that of ‘requirements engineering’ and risk




aversion - basically PCOs are tasked to deliver a capability to timeand cost, and they are not paid enough to embrace additional risk.It is in the management of the dichotomy of risk aversion and theintroduction of technology in which the MoD can be mosteffective with the combination of MEDP, partnerships withindustry and collaboration. It is the MoD’s informed customerstatus and ability to identify and mitigate risk that underpinsmuch of the Smart Procurement Initiative - notably the balance ofCOTs, development of commercial solutions and bespoke navaldevelopment. How then against such a background can it beensured that the work being undertaken within the MEDPprogramme is not nugatory and that our future ships fullyembrace IFEP? The answer is, in principle, easy to identify; inpractice it is much harder to implement. Fundamentally it isimperative that the risks are captured from technical, programmeand platform perspectives so that a coherent risk register ismaintained - this functionality is vested with the Electric ShipProgramme Office, thereafter the key is how to translate the riskprocess into design, development and technology insertion. Inmaking this transition it is essential that PCOs and the widerindustrial base are ‘onboard’. The drivers here, in addition tothose of risk management, are the need to reduce cost of owner-ship with effective support packages, the emphasis towardscommercial off the shelf equipments, and the trend away fromnaval standards towards best practice, wherever that may bevested. The AO, LPD(R) and Type 45 have been provided asalmost turnkey solutions, thereby minimising risk and thereforecost. As system and equipment trends move away from thecommercial sector, the overriding issue must be ‘partnership’ andthis is the area in which the MoD can bring a huge amount ofexperience and knowledge to bear. A key focus for technologyinsertion and de-risking is the Electric Ship Technology Demon-strator (ESTD).

ELECTRIC SHIP TECHNOLOGYDEMONSTRATOR

The ESTD is a joint programme between the UK and Francewhich looks to de-risk IFEP technology so that it becomes anattractive option for future ship propulsion system prime contrac-tors. The schematic of ESTD is at Fig 10. Broadly speaking itincludes a half ship set of equipment with representative powergeneration and distribution systems linked by two static powerconverters. The 20 MW propulsion motor drives a dynamic four-quadrant load, enabling the system to be demonstrated through-out the complete operating envelope. The zonal distributionsystem, and inclusion of both zonal and bulk energy storagecomplete the picture. The supporting aims of ESTD are:● To identify and de-risk IFEP system integration issues,

including system stability, fault identification and protec-tion and harmonic distortion levels.

● To validate equipment and system software models toreduce or eliminate need for shore testing of future warship power/propulsion systems.

● To generate ILS data.● To assess signature issues.● To inform future platform baseline designs and provide

supporting evidence for technology pull-through.● To support the development of power and propulsion

requirements for future warships.● Inclusion of some T45-specific equipment will also allow

the facility to be used for shore integration testing (SIT) forType 45 systems once the majority of ESTD testing hasbeen completed.

One of the key issues for ESTD is how it will be utilised beyondthe current testing programme to manage technology insertionand incremental system design; this presents a unique opportu-nity for the wider naval power system stakeholders to be engagedin this important programme.

THE REALITY - AN INSIDE VIEWThis section will look at the all electric warship from the reality

of a practitioner’s perspective with the emphasis on operatingchallenges related in the most part to LPD(R) experiences butequally applicable to the wider concept. The single line diagramat Fig 2 should be used to support references to the LPD(R)system.

There are several key features that will make electrical propul-sion a success or a failure in warships. We must of course adopta safe system of work but with many examples available fromindustry, the merchant marine and of course the Royal FleetAuxiliary (RFA), this is a well-trodden path. More crucially wemust differentiate between an all electric ship and an all electricwarship in that we take these latter platforms into operationaltheatres where we can expect some damage, even if minor, and wecannot afford to take away propulsion or electrical services fromthe command. This leads to a focus on operation, fire-fighting anddamage control, equipment design, onboard organisation andtraining, all of which are discussed below:

Safe system of work and compartment accessA safe system of work to include Health and Safety and other

statutory requirements is essential if the system is to be operatedsafely, noting the requirement to have established procedures formaintenance and operation by naval and civilian personnel.Wherever possible standard RN practice has been adopted buthigh voltage requires additional precautions including hazardmarkings for compartments, hazard signage, restricted accessprocedures and CCTV monitoring of all compartments desig-nated HV. Routines are required both by contractors and visitorswith restricted access regulations controlled by either a ‘day pass’or ‘contractors pass’. Contractors requiring access to HV com-partments will need to be briefed on the hazards and will requirea limitation of access prior to unescorted access/work in thesespaces. None of these issues is insurmountable but they need tofeature in the baseline design for an IFEP solution as the presenceof HV will limit access and require control procedures.

System operation and manning of HV spacesThe HV system will be operated via the platform management

system (PMS). For the LPD(R) system, the normal practice will beto run continuously in parallel, de-isolated with the minimumnumber of generators required (minimum generator operation(MGO) leading to single generator operation (SGO)) at State 3. AtState 1, all generators may be required but the system will remainde-isolated.

Because of the late change to electric propulsion during thedesign phase of the LPD contract, some HV equipment built toIP23 is located in main machinery spaces. This means that thespaces concerned need to be disconnected from the live systembefore any water-based extinguishers can be used to tackle a fire




or before any attempt is made to control a flood. System discon-nection procedures for the isolation of the HV system in the eventof fire/floods need careful consideration to ensure that the appro-priate action is taken without endangering personnel and maxim-ising availability of the propulsion system to the command.Likewise, careful thought must be given when operating in SGOmode to ensure that a total electrical failure (TLF) does not occurif the affected compartment contains the only running primemover. It is also possible to lose main motor excitation if isolationsare carried out in the incorrect sequence. A series of hard-wiredtrips allow rapid disconnection of the HV system.

The PMS system consists of a Pentium-based PC systemcommunicating via a dual redundant ethernet with battery-backed power supplies. This reversionary power source is locatedin the forward switchboard and could perhaps be split into zonedpower supplies to make the system more resilient to actiondamage in upgrades or future platforms.

Manning of machinery spaces at State 1 should not be undulyaffected by the possible hazards of exposure to HV (we have for along time manned magazines), but should be primarily driven bythe operational gains of manning secondary or local machinerycontrol positions as well as the ability to carry out immediate firstaid action. This approach must also be balanced against theavailability of manpower and the increased risk of exposure toinjury from action damage within a large machinery space. HenceHV compartments will not be manned at State 3 but will be atState 1. The mobile party (the cavalry!) needs to be best locatedto cover all main machinery spaces; particularly any unmanned atState 1. They need good communications and a high degree ofindividual protection.

Fire-fighting and damage controlThe recommended fire-fighting approach is to always

maintain a continuous aggressive attack using appropriatefirst aid fire-fighting appliances. Should high voltage equip-ment within the compartment be correctly protected bycorrectly IP-rated enclosures, then AFFF and HPSW hosesmay be used without restriction, although the inherentdangers of unprotected lower voltage systems must also betaken into account. Should the compartment become unten-able it should be evacuated and closed down prior to usingthe fixed suppression system. The process of closing downand isolating the compartment should be initiated as early asreasonably possible with the available manpower.

How then to first aid fire-fight in HV compartments? Thesuggested solution is to replace AFFF extinguishers and hose reelswith portable CO2 and dry powder extinguishers to maintain theaggressive attack without isolating equipment, although compart-ment isolation prior to initial attack on the fire could also beconsidered. Kill Cards will indicate HV compartments and alsocompartments through which HV cables pass, and how to isolatepower to these cables. There is however no need to isolate spacesprior to CO2 drench although direct injection of CO2 onto HVequipment is not supported.

Electrical isolations for fire-fighting and the use of foam blanketswill depend on the IP rating of high voltage equipment whichshould be a minimum of IP55 for a compartment below thewaterline and/or with fluid systems running through it (low voltagesystems must also be considered). The ability to isolate equipmentfrom outside the compartment is essential and there should be a

clear indication at the compartment entrance, and possibly on theequipment, as to whether high voltage equipment is still live.

Normal re-entry into any space requires the fire-fighting teamto be protected behind a water wall. Whilst this may remainsensible during peacetime operations, it probably is not if we wishto protect the HV system from water ingress and maintainpropulsion to the command at State 1.Fig 11 summarises the range of fire and flood scenarios.

Equipment designThe selection of IP ratings for equipment must take into due

consideration the siting and possible consequences of fire-fight-ing and flooding taking place in the immediate vicinity. Wecannot afford to evacuate a space and abandon the prime moversor other equipment contained within. The number of systemsadjacent to HV equipment should be minimised and, whereunavoidable, pipework should be continuous. CO2 injectionports on HV equipment will not be fitted; rather compartment orequipment fire suppression systems should be installed.

Onboard organisation and qualificationsThe organisation to be employed for the ‘day to day’ opera-

tion/maintenance of the HV system is shown at Fig 12.

TrainingThere is the requirement for the provision of a training/joining

video for the education of the ship’s company not involved in theday-to-day working of HV equipment. This video may also haveto be made available to potential contractors to also make themaware of the potential hazards. Training organisations such asFOST will be required to input proposed training scenarios andalso they will have to be informed of any limitations that HV mayplace on proposed training (eg charged hoses, training smoke,etc). FOST currently use exercise smoke during operational seatraining and this may have an impact on HV installations.

High voltage policyThe preceding paragraphs highlight a number of themes for

high voltage systems, all of which will be captured in the MLS1-sponsored HV Policy Document. The document looks to providethe wider naval marine power system community with guidanceon the specification, design, installation, test and operation of HVpower systems in warships together with the wider issues oftraining and infrastructure. In the longer term it is hoped toincorporate the policy guidelines within the requirements docu-mentation for future platforms, notably on all safety-related issuesbut in the near term the plan is to issue the document for ‘buy in’from the wider naval power system community.

THE CHALLENGESNotwithstanding the specific technical issues mentioned, a

number of other challenges also face the effective implementationof IFEP. Whilst not exhaustive, the Top ‘X’ challenges includesintegration, electrical standards, equipment strategies, maintain-ing innovation whilst minimising risk, embracing automation andsystem analysis. The following takes each of these issues in turn.

Integration. The integration of the complex IFEP architectureis a significant challenge to system and equipment designers andan area which needs the requisite focus at all stages of the designprocess. Integration issues include system stability, operability,




compatibility - notably EMC, physical issues and system transver-sals. Experience has shown that the transversals issue is the mostdifficult to manage as boundaries are established between systemsand sub-systems; the management of which needs system levelco-ordination. On the theme of integration, the physical integra-tion and buildability of solutions is extremely important and mustbe a significant focus during the design process.

Electrical standards. Existing power system standards arenot sufficiently robust to support IFEP and IEP architectures.Fundamentally, standards reflect conventional systems and arenot sufficiently flexible to be adapted to suit novel systems. Insupport of this a review is being undertaken to propose a policyfor IEP and IFEP systems covering issues as diverse as powersystem standards, safety, Design constraints and working prac-tices. This is even more relevant in view of the high voltageimplications. The MoD’s HV Policy Document will look toprovide the framework for naval marine power system standards.

Equipment strategies. Building on the themes of risk, theoverarching MEDS and its implementation through the centre ofmarine engineering excellence, equipment and system strate-gies are essential to the electric warship aspirations. A numberof strategies are being written which look to draw together therequirements, platform risks, timescales and industry focus toproduce the supporting justification for equipment develop-ment, the outcome of which will inform development and thewider stakeholding community. Within DOpsE, a Directorate ofthe Warship Support Agency, system strategies are being pro-duced to support medium (10 year) and long (25 year) termvisions, which look to provide a coherent focus across themarine engineering community embracing the MEDP and ele-ments of both the Corporate (CRP) and Applied (ARP) ResearchProgrammes.

Innovation. Innovation will always be constrained by riskand the desire to minimise any impact on the performance,cost and acquisition timescales of a future warship. However,without innovation, technology will stagnate and the futureRoyal Navy will face increasing support costs and degradingperformance and capability compared to other, more adven-turous, navies. A balance must therefore be struck. This can beachieved through establishing a thorough appreciation offuture technologies and their assessment, through the MEDPand the expert eye of the Marine Engineering Centre ofExcellence. The risks associated with innovation can then befully quantified, and effective, focused risk-mitigation put inplace. As a result the likelihood of the pull-through of innova-tive technologies into service by the warship prime contractorwill be enhanced.

Wider strategy. The marine engineering aspects are focused,but the lack of coherent strategies or, in some cases, coherencybetween strategies in the wider naval service creates difficulties.Notably, the lack of a weapon engineering equivalent to MEDSremains a concern and it is imperative that the future require-ments of combat systems are identified as a priority to ensure that

the platform solution can meet the demands, primarily in termsof power requirements and possible requirements for pulsedenergy. Manning, support and similar strategies do, however,exist but it is essential that coherency is maintained betweenthem.

Automation. Central to the platform system solution, theplatform management system (PMS) and its derivatives providethe operability and functionality of the system - the main concernhowever is that of integration. PMS needs to be embraced at theoutset and become an integral part of the design solution. Oftenseen as the ‘cure all’ for system functionality and integration, it isimportant that it is not left to pick up the design deficiencies fromthe system and equipment integration.

System analysis. As the focus moves away from platformshore test facilities, a function of cost and time, the emphasis onalternative mechanisms to assess system and equipment perform-ance has come to the fore. The spectrum of activities in supportof the analysis is bounded by full scale test and simulationbalanced with prototyping and equipment tests. The trend to-wards simulation is worthy of note, with both MoD and industryembracing it to balance equipment and system development. Thestrength of this approach is flexibility and cost, and the ability tomodel at component, equipment, sub-system and system levels.Already naval marine power system modelling has produced amodelling blockset to assess system and sub-system issues in a‘fuel to thrust’ approach, the outline schematic for which is at Fig13. The functionality of the models allows assessment of dynamicperformance, system transients, external impacts and bounds ofoperation. Validation of models remains a key theme along withthe issue of models containing proprietary information, whichmust be resolved if the goals are to be realised. The simulationvision is to maintain a database of models for all power systemsand equipment, with all new systems and equipment beingdelivered with a validated model - wishful thinking, perhaps, butessential if we are to realise the full potential of simulation.

SUMMARYThe last year has seen a huge amount of activity in both the

electric ship and electric warship arenas, notably with the realityof the electric warship and the coming of age of the integratedelectric propulsion concept in the guise of LPD(R) and Type 45.In support of these vessels and within the framework of smartacquisition, the marine engineering development plan has soughtto maintain momentum and relevance with a number of notablesuccesses, primarily that of ESTD. The emphasis is now, as ever,on cost-effective capability for the marine engineering solutionand it is hoped that this paper has gone some way to demonstratehow the MoD is looking to take this forward in partnership withindustry with the focus very much towards incremental acquisi-tion and technology insertion.

REFERENCES1.EA Technology Report 5435, HV DC Switchgear Feasibility

Study dated 3 Jul 01.

© Controller, Her Majesty’s Stationery Office, London 2001.© British Crown Copyright 2001/MoD. Published with the permission of the Controller of Her Britannic Majesty’s Stationery Office.




Fig 1: The reality of the electric ship

Fig 3: The usual suspects

Fig 4: Baseline architecture or marker in the sand




Fig 2: LPD(R); the single line diagram




Fig 6: The hybrid switch schematic

Fig 7: The advanced induction motor

Fig 5: Framing the technology




Fig 10: ESTD schematic

Fig 9: A technology roadmap

Fig 8: Motor development compared




Fig 13: IEP Model; the software realisation

PERSONNEL TRAINING

Authorising Authority (FOSF ashore) HVA

Authorising Engineer (MEO-May have nominated deputies) MCQ +AP+local assessment

Authorised Persons AP+local assessment

Competent Person (CP) Video + detailed briefing

HV Aware (Remainder of ship's company) Video + briefing

MEOOW1 As CP

Fig 12: Onboard organisation

Fig 11: Fire and flood scenarios and responses


Documents

Electric warship new - Naval Postgraduate Schooledocs.nps.edu/dodpubs/topic/general/Electric_Warship.pdf · Electric warship new 3 14/2/03, 11:47 am. 4 Journal of Marine Design and