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The electric warship VII - the reality
The electric warship VII - the reality
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
Integrated electric propulsion (IEP) is an everyday reality as the power system solution for
naval platforms, embracing recent advances in enabling technologies to deliver costeffective, survivable, power-dense solutions in a variety of applications. Founded on the
Marine Engineering Development Strategy (MEDS) and supported by significant progress
in the commercial marine sector, the defence community has embraced the potential of
IEP and is now looking at more advanced integrated full electric propulsion (IFEP) solutions
for future platforms. This paper follows on from the earlier series of ‘Hodge-Mattick’ electric
warship papers and the ‘Newell-Young’ paper Beyond Electric Ship, and in doing so looks
to put the United Kingdom Ministry of Defence’s (MoD) programmes and strategies into
context, review the issues surrounding the introduction of IEP and provide an update on
progress towards achieving the electric warship.
AUTHORS’ BIOGRAPHIES
Commander Graeme Little, Royal Navy, joined the Royal Navy
in 1984 as a marine engineer officer. On completion of his basic
training 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 HMS
Birmingham in 1990 as the Deputy Marine Engineer Officer. He
subsequently read for an MSc in electrical marine engineering at
RNEC Manadon followed in 1994 by an appointment to the Ship
Support Agency as the project officer responsible for electric
propulsion systems. On promotion to Lieutenant Commander in
1996 he joined HMS Sutherland as the Marine Engineer Officer.
Following Staff Course, he was promoted to Commander in
2000 and was appointed to the Warship Support Agency as the
head of the Electrical Power and Propulsion Systems specialist
group where he is now serving.
Commander Stuart Young, Royal Navy, joined the Royal Navy in
1977 and completed undergraduate and post-graduate training
at the Royal Naval Engineering College in Plymouth. He has
undertaken a number of appointments at sea, including Marine
Engineer Officer of HMS Norfolk, the Royal Navy’s first CODLAG
frigate. Shore appointments have included project officer for the
procurement of Warship Machinery Operator and Maintainer
Trainers, lecturer at the Royal Naval Engineering College and
Marine Engineering Liaison Officer with the United States Navy,
based in Washington DC. He is currently the Electric Ship
Programme Manager within the UK’s Defence Procurement
Agency.
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Commander John Newell, Royal Navy, joined the Royal Navy as
an artificer apprentice in 1976 and joined BRNC Dartmouth on
promotion in 1978. On completion of his degree at RNEC
Manadon and initial training as a marine engineer he served as the
Deputy Marine Engineer Officer in HMS Sirius. He subsequently
took a MSc in electrical marine engineering and served in the MoD
as the project officer for pollution control equipment. He then
served as the Marine Engineer Officer in HMS Boxer before
undertaking the French Staff Course in Paris. On return to the UK
he spent 15 months with the Joint Planning Staff precursor to the
Permanent Joint Headquarters (PJHQ) before becoming one of
the appointers. He was promoted to Commander in 1997 and
was appointed as the head of the Electrical Power Distribution
and Propulsion Systems specialist group within the Ship Support
Agency in March 1998. Commander Newell joined HMS Albion
as Senior Naval Officer and Marine Engineer Officer in January
2001.
INTRODUCTION
I
n recent years a variety of papers, seminars and conferences
have sought to provide detail and promote discussion on
the diverse range of issues that make up the electric warship
concept. The same period has also seen a huge amount of
progress in enabling technologies that have made integrated
electric propulsion the system of choice for many new naval
ships. This paper looks to review the MoD’s Marine Engineering
Development Strategy (MEDS), examining its role within the
framework of the Equipment Pillar of the Royal Naval Strategic
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Plan and the Smart Acquisition Initiative. Recent progress and
successes will be reviewed along with a look at the enabling
technologies and the ‘road map’ for managing the successful
introduction of such technologies. The aim of the paper is to
provide the wider naval marine community with clarity of the
MoD’s programme and to invite debate for marine systems of the
future.
Perhaps by way of an overview it is worth reviewing the trends
in power and propulsion systems in recent years, noting that the
reality of electric propulsion was successfully introduced in 1920
in HMS Adventure and has seen widespread use in the submarine
community.
In the last decade of the 20th century, the Type 23 frigate
demonstrated the benefits that an electric architecture can bring
to bear with the hybrid power distribution and propulsion system
known as Combined Diesel Electric and Gas (CODLAG).
Building on the success of the Type 23 and the step change in
technology driven by the commercial sector, electric propulsion is
the reality as we enter the 21st century, with two Auxiliary Oilers
(AO) and two Landing Platform Docks (LPD) shortly to enter
service. Both classes have integrated electric propulsion and bring
turnkey commercial solutions to satisfy a naval application. An
artist’s impression of the LPD(R) is at Fig 1 together with an outline
schematic 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, all
embracing electric propulsion. The Type 45 solution is driven by
the requirement for a power dense system with reduced whole
life costs and challenging signature targets. The goal has been
met by exploiting the commercial market and incorporating the
United States’ integrated power system (IPS)-derived advanced
induction motor (AIM) development and the WR21 ICR gas
turbine.
WHY ELECTRIC PROPULSION AND
WHAT IS IT?
Electric propulsion brings together efficiency, flexibility,
survivability and, perhaps most importantly, reductions in cost
of ownership. Captured simply, reduced numbers of prime
movers, integrated systems, flexibility in layout and proven
commercial precedent make it a credible solution to the requirement.
Electric propulsion systems fall into three broad categories,
namely hybrid, integrated (IEP) and integrated full (IFEP). The
terms electric ship and electric warship are also used. They can be
defined 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 propulsion
being purely electric. T45, AO and LPD(R) are examples.
●
IFEP - takes the IEP concept further by incorporating
advanced power electronics and energy storage into the
architecture to give further cost and operational benefits.
●
Electric ship - incorporates advanced prime movers and
widespread electrification of auxiliaries into the IFEP
architecture.
●
Electric warship - where novel high-power weapons and
sensors are incorporated to take advantage of the high
system powers available.
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Fig 3 looks to put the various system configurations into
context.
THE MARINE ENGINEERING
DEVELOPMENT STRATEGY
The current strategy
The first Marine Engineering Development Strategy was
endorsed in 1996. It aimed to achieve significant life cycle cost
reductions, whilst meeting naval requirements, by exploiting
world-wide industrial and commercial developments. Only if
naval requirements could not be met would development of
specific equipment be funded. It envisaged achieving this through
the development and introduction of advanced-cycle gas turbines within an integrated full electric propulsion architecture
and the electrification of auxiliaries. Development of industry
partnering and international co-operation opportunities was
encouraged.
Much has been achieved. Since 1996 every major ship
ordered for the Royal Navy has had an integrated electric
propulsion system. The selection of IEP for the T45 means that
life cycle cost benefits will now be achieved earlier than envisaged in 1996. The electric ship technology demonstrator is
expected to start testing in spring 2002. This builds on the T45
concept and introduces new power conversion systems and
advanced energy storage concepts to accrue further LCC benefits with high system integrity, particularly under damage or
fault conditions.
The Marine Engineering Development Programme (MEDP) is
more than just electric ship, it covers all marine engineering
technologies where MoD-funded work is needed to ensure that
new technologies meet the requirements of future ships. Work
either 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 diesel exhausts.
●
Fuel cross-flow micro-filtration.
●
Electrical actuation of hydrodynamic control surfaces.
The Equipment Pillar
The Marine Engineering Development Strategy does not
exist in isolation and its pursuit over the next two to three years
is a key element of the Equipment Pillar of the Royal Naval
Strategic Plan. The Equipment Pillar outlines the Navy’s concerns regarding reliability, manning levels and through-life
costs of current equipment and indicates how these could be
improved by:
●
Exploiting the concept of smart acquisition, closely aligning needs of through-life fighting power with specifiers
and designers of equipment, focusing on ease of operation, maintenance, reliability and longevity, efficient manning and operating costs.
●
Seeking innovative ways of monitoring and employing
trends in technology, especially encouraging potential for
non-warfighting technology to improve conduct of routine business.
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THE DRIVERS FOR CHANGE
Technology
Technical progress over the last five years has been far more
rapid than envisaged in 1996. The step change to integrated
power architectures, with all the ensuing benefits, has now been
taken. Future development will be more evolutionary rather than
revolutionary, and the benefits will be obtained through equipment, rather than system development.
Development of the first ICR gas turbine (the WR21) has
been completed and the engine system selected as the primary
power source in the T45. Propulsion motor technology has
allowed a power-dense advanced induction motor to be selected
for the T45. Many manufacturers around the world are now
developing permanent magnet motors of various topologies,
and major breakthroughs have recently been achieved in superconducting motor technology. Semiconductor development
continues unabated, as predicted, and further major advances
are expected over the next few years. In many areas, commercial
shipping has embraced future technologies earlier than navies;
podded drives are an excellent example of an equipment now in
widespread commercial use whilst still under assessment by the
major navies. Fuel cell development, driven by automotive
requirements, is progressing rapidly and to the extent that offthe-shelf solutions may be available within the foreseeable
future. The choice of fuel, and its production, transportation
and storage remains a major issue.
As a result, further MoD-funded development — except to
address shock or signature issues and other specific naval issues
— is probably unnecessary but technology assessment in order to
ascertain suitability is very important. This assessment is best
conducted through the medium of the proposed Ministry-led
Marine Engineering Centre of Excellence, utilising the available
expertise to make strategic decisions that have the full backing of
both MoD and industry. These achievements and a re-assessment
of trends need to be reflected in any revised development strategy.
Smart Acquisition - The new environment
Smart Acquisition was introduced within the Ministry of
Defence in 1999 and adds clarity to the acquisition process which
was not available to the original strategy in 1996. It refined the
concept of capability-led requirements and defined a new acquisition cycle, with clear decision points and therefore clear windows in which technologies needed to be sufficiently mature in
order to be selected as candidate solutions. It defined incremental
acquisition and technology insertion. More investment during
the early project stages is encouraged is order to reduce risk, and
close liaison with industry is regarded as essential. Although the
original strategy anticipated many aspects of smart acquisition,
the revised strategy needs to stress further how marine engineering development fits into the smart acquisition framework.
Risk
Risk management is a key tool in the acquisition process. In
the assessment phase the user’s requirements will be developed
into the more detailed system requirements. At each stage the risk
associated with attaining the requirements will be assessed. The
technology development and demonstration within the MEDP is
a primary means of mitigating this risk. In addition the technology
specialists within the proposed Marine Engineering Centre of
Excellence (primarily the Marine Equipment Integrated Projects
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teams within the UK’s Warship Support Agency) can advise on
the risks associated with attaining the required capability. Thus a
dialogue needs to be established between all the relevant
stakeholders.
Environmental
Royal 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 must
anticipate future requirements. Commercial waste treatment
technologies may be applicable to the naval requirement but
would need to be made significantly more compact to facilitate
installation on a surface warship or submarine. Furthermore,
warships are required to stay at sea for far longer periods and shore
support facilities for disposal of waste stored onboard may not be
available. The goal of achieving a zero-emission warship, across
the operational profile, remains.
The environmental impact of ships throughout their life cycle
must also be assessed and minimised. This requires examination
of environmental impact during build, in-service maintenance
and on disposal. Within the automotive industry the manufacturer’s responsibilities are clear cut and increasing. Similar trends can
be 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 years
or more. However, cost will increase through this time frame and
at some point it will become more cost-effective to use an
alternative. The Royal Navy will be governed by commercial
trends in this respect but needs to monitor trends closely and
initiate development to ensure that warships can operate within
the wider future fuel economy.
Operational
The operational capabilities required from future warships
continue to develop. Specific capabilities of future power and
auxiliary systems will, of course, vary but there will be a number
of 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 CENTURY
Taking these factors into account, the following strategy for
marine engineering development in support of the Royal Navy’s
future capability requirements is proposed:
●
Maintain awareness of technology and its capabilities by
monitoring and assessing technology innovation and
industrial capabilities and trends whilst maintaining the
Electric Ship Programme Office as a focal point for the
monitoring of industrial and commercial technology trends
and utilising the Marine Engineering Centre of Excellence
for the dissemination and assessment of applicable technologies.
●
Identify the warship acquisition risks which can be mitigated through marine engineering system solutions.
●
Develop mitigation strategies that satisfy the prime contractor (or potential prime contractor), satisfy the DEC
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and Warship IPT and are within our ability to fund and
manage to completion within required time-scales.
Build on success of original MEDS and the electric ship
concept, with emphasis on facilitation of incremental
acquisition and technology insertion through the use of
open systems.
Maintain focus on LCC reductions through equipment
development within the IFEP architecture, technology
trends, including fuel cells, podded drives and smart
systems, and integration of high-power weapons and
sensors.
Take into account external influences, including increasing environmental legislation and trends in future fuels.
Gain effective pull-through into service by ensuring that
sufficient de-risking is undertaken, results of de-risking are
available for those who need it (whilst protecting IPR) and
industrial capability to deliver solutions is maintained,
particularly through competition.
Maximise value-for-money through international
co-operation.
●
●
●
●
●
Thus the aim of the Marine Engineering Development Strategy
is:
To achieve the required capability whilst generating ongoing reductions in life-cycle costs, through the leveraging of
technology to mitigate the associated warship acquisition
risks.
THE ELECTRIC WARSHIP - EXPOSED
As discussed previously, the all-electric ship embodies the
IFEP concept with the additional enablers of advanced-cycle gas
turbines and wider electrification of auxiliaries.
It is however the IFEP architecture and possible solutions
which offer the most exciting possibilities; in terms of operability, capability and reduced cost of ownership. The framework that is IFEP is founded on a number of enabling subsystems; high power generation, high power distribution,
energy storage and conversion, low power distribution, automation systems and propulsion systems. Within these baseline sub-systems a bespoke architecture can be produced, an
example of which is at Fig 4.
The overall concept for the baseline architecture is one
of flexibility of design solution with a range of technologies
able to meet the demands of the system. It is these technologies which have been the focus of MEDP and the
marine engineering community and will form the basis of
the next section. Before reviewing the technologies it is
worth highlighting the importance of a generic baseline
solution in the context of understanding and maximising
the synergy between various platform architectures; a key
theme in realising the potential of IFEP. Given a generic
baseline allows system level design assessments to be made
together with supporting a technology development focus.
It must, however, be remembered that at the system and
sub-system level a number of themes need to be understood
if the system is to be optimised effectively, these include:
hullform; power system architecture; energy storage; operability; user demands; and, field effects.
Hullform. The hullform solution drives the IFEP solution,
primarily from a power density perspective but with support-
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Electric warship new
ing considerations of signature, survivability and shock. The
spectrum of hullforms is bounded by the larger carrier-based
hullform (steel is cheap and air is free solution - although this
is not an entirely valid statement) and the exacting requirements of a submarine platform. The middle ground occupied
by the destroyer and frigate, whether multi- or monohull,
completes the picture. This is not the entire picture as IFEP is
also relevant to smaller vessels, but the requirements that set
the main contenders apart is installed power which is significantly greater than those anticipated for minor war vessels. The
huge benefit of the IFEP solution is that premised on the
currently-accepted range of hullforms possible for warships
driven by naval architecture and weapon and sensor solutions,
the IFEP concept can be designed to fit. This will not go
unchallenged as the required bounds of power density from
both gravimetric and volumetric perspectives are placed under
considerable pressure and the demands for increases in both
are made.
Power system architecture. At the heart of the ‘power
station’ is the system architecture, on which the solution
will hang; in the case of IFEP a number of options are still
presented as viable. The traditional architecture of a ring
distribution with centralised switchboards and electrical
distribution centres (EDCs) offers, in most part, a good
baseline solution against which other ‘more novel’ solutions can be gauged. Novel approaches to EDC architectures
provide inherent flexibility and system redundancy with
further enhancement possible using change-over switches
and uninterruptible power supplies (UPS). Looking at a
slightly more novel approach leads us to the much courted
‘zonal concept’, whereby the distribution system, together
with all the supporting systems, is zoned with at least two
methods of supplying energy within a zone. Central to this
architecture is a zonal power supply unit (ZPSU) and zonal
energy storage unit (ZESU). Extremely attractive, the zonal
concept infers increased survivability and operability but
not without an element of technology and integration risk;
a decision that will be informed by the MoD’s energy
storage philosophy.
Energy storage. A wide range of technologies exist to support
a profusion of possible requirements; indeed it is this that
supports the need for a platform, if not pan-platform, energy
storage philosophy. The requirements range from the equipmentbased UPS, commonly found in weapons and sensors, through
sub-system requirements such as steering, to the most onerous
demands 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, this
needs a much broader focus. Assessment of technologies will be
based on demonstration in the ESTD and the MoD’s energy
storage strategy.
Operability. Often described as the panacea for the platform
systems, IFEP and its variants, provides a huge step forward in
flexibility of operation and system survivability, to name but two.
However, a note of caution - realising the full potential of the plant
can only be achieved if it is fully understood and not, as some
protagonists suggest, left to ‘come out in the wash’ as more is
understood and experience gained. Operability is a key strand and
must be understood at the earliest point in the design process.
Central to the operability debate is the issue of single generator
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operation (SGO), a subject which has attracted a huge amount of
interest, notably from the operating community. The technical
community has not helped themselves on this one as the term
SGO conjures up all sorts of issues in the minds of the operators.
However they have now been articulated clearly and it has been
demonstrated, with some clarity, that SGO does not result in
reduced system availability when balanced against the ship handling constraints, operational state and provision of energy storage. The concept of minimum generator operation (MGO) embraces SGO fully and is perhaps a far more relevant description of
the operating procedures.
User demands. As wider electrification becomes a reality the
demands on the power system increase, this is best illustrated as
we focus on the possible next generation of weapons and sensors,
or indeed those of aircraft launch and recovery. The user demands
need to be understood from the outset if the design solution is to
be flexible enough to accommodate technology insertion and,
indeed, the capacity to support demands from the outset. Not just
confined to weapon systems and sensors, the implication of
increased electrification of auxiliary systems needs to be understood and quantified.
Field effects. Subject to much recent focus for both inservice and newbuild projects, the effects of electromagnetic
fields have been raised as an area of concern for hybrid and IEP
installations, from signature and safety perspectives. Whilst
the issue cannot be dismissed out of hand it equally must not
be made too much of, and a number of approaches are in hand
to manage this effectively. From a safety perspective, measurements are being taken on current classes and it is planned to
carry out similar trials onboard LPD(R) and AO as they enter
service. Any potential further problems can be reduced significantly by up front design and focus on shielding and installation. The issue of signatures is being assessed but cannot be
discussed in this paper.
The generic baseline and system framework allows for a more
holistic approach to system and platform design, primarily from
a technology insertion perspective - an important point as the
platform visions of the future begin to move into and out of focus!
Outwith these system design issues, it must be recognised that a
range of enabling technologies are central to IFEP, a number of
which, together with the review of risks are outlined in the next
section.
Framing the technology
As mentioned previously, the key thread must be understanding and managing the risk, both from equipment and
platform perspectives. To articulate the technical risk requires
a formal risk review across the enabling technologies, the
outcome of which will provide generic and platform-specific
risk assessments across the technology, thereby framing the
technology issues and underpinning future development. Fig
5 captures the high-level technology enablers within which the
analysis will be undertaken.
Before reviewing the technologies it is worth reiterating the
central themes for MEDS and AES; power density, risk, whole-life
costs, efficiency, environment and survivability. These criteria
frame the focus on technology of power generation, high power
distribution, energy storage and distribution, and low power
distribution.
Power generation, Gas turbines are established as the
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power-dense, efficient and environmentally-sound solution to
the problem of installed power. Coupled with conventional
generator technologies, the high power generation capability,
vested currently in the WR21 GTA and the ACL GTA looks to
provide the surface platforms with the bulk of their power well
into the late part of the 21st century. Technology focus for the
future is reliant on established construction techniques with
possible trends to super-conducting and permanent magnet
technology. Before moving away from generation it is worthy
of note to raise the issue of fuel cells. The jury is still out and
the MoD focus has, at best, until recently been uncoordinated.
Whilst the short term possibilities are limited, advances in fuel
storage and cell technology will undoubtedly make fuel cells a
future attractive low power energy source. Industry is developing the fuel cell as a clean and efficient source of energy. Future
work may concentrate on the use of alternative fuels (eg
methanol or hydrogen) and its safe storage and handling in a
shipboard environment. This work will be driven by the need
to identify an alternative to conventional fossil fuels by the
middle of the 21st century.
High power distribution, The ac/dc debate is still far
from resolved, indeed which way we fall will primarily be
driven by the industrial focus and the level of risk. The ac/dc
subject is as emotive as ever and the decision point is fast
approaching. Switchgear and cables cannot be readily divorced from this debate and will play a key role in the
solution. Switchgear rated for the perceived IFEP architectures
is on the limits of its capability and a number of options such
as the hybrid switch and novel breakers are being assessed for
their applicability to marine systems. Related to this are the
issues of switchboard design and a possible trend away from
centralised 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 exacting
protection and switching requirements increase. The last
issue within this area is that of cables, and whilst we are
confident that the issues of EM fields, buildability and shock
can be managed with existing technology, we need to look at
how we might embrace busbars or more novel systems for the
future. At present all such systems are prohibitively expensive for the gains in ease of build and similar.
Energy storage and conversion, Noting the profusion of
possible solutions to meet the varied demands on energy storage,
it is difficult to progress any one technology without having
articulated the architecture and energy storage philosophy. In
general terms, the industrial base is making the enabling technology available, it is how we grasp this technology for the naval
marine environment that presents the greatest challenge. Returning briefly to ESTD, flywheel technology and a regenerative fuel
cell are being assessed for power system suitability at the zonal and
bulk levels of power.
Low power distribution, Not wishing to open the ac/dc
debate or indeed repeat the high-power discussion, this section is
best left looked at from a system perspective. System issues are
very much architecture-dependent and we must be aware of the
importance of the transversal issue with the high-power system.
Current solutions include transformed supplies but the technology is ‘here and now’ for bi-directional static power converters and
perhaps presents a viable solution for platform incremental acquisition.
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SWITCHGEAR - THE DC CHALLENGE - A
FOCUS
Not a focus for previous electric warship papers, switchgear is
however worthy of mention as a key enabling technology, particularly for a potential dc distribution system where the interruption
of fault currents is more onerous than for comparable ac systems.
The reason for this is simply that an ac circuit breaker can interrupt
at or around current zero whereas a dc breaker must create a
current zero either by forcing the current to zero by controlling the
arc voltage or, creating a current zero by commutating the current
around an opening contact. In addition the dc circuit breaker
design is driven by the arc energy that can be dissipated, mindful
that a dc breaker will be much larger than its equivalent rated ac
counterpart, and the need to minimise the rise of fault current.
The technology solutions to these problems are high-speed air
circuit breakers and hybrid breakers.
Air circuit breakers. The mechanism during a fault is the
control of the arc within the arc chute whereby an increased
resistance of an established arc reduces the circuit current so that
the arc cannot be maintained by the circuit voltage and the current
is reduced to zero. The control of the arc is achieved by natural
electromagnetic and thermal forces assisted by a magnetic field;
technology which is well established. Currently available at up to
3kV, 8kA with a breaking capacity of 60kA, the move to voltages
in excess of 5.6kV for the electric warship application will need
development, but the more onerous rating is containable within
current technology.
Hybrid circuit breakers. Combining a fast mechanical switch
and power electronics, hybrid circuit breakers utilise either zero
current or zero voltage switching, both of which are illustrated at
Fig 6 and described below.
Zero current switching. The mechanical switch carries the
load current until a short circuit is detected whereby the switch
opens, the power electronic switch is then triggered and a
resonant current is established in the L-C network with a reverse
current flow at the mechanical switch. The voltage across the
capacitor rises and the varistor begins to conduct, which dissipates the inductive energy within the circuit and the current drops
to zero.
Zero voltage switching. The mechanical and power electronic
switches are triggered simultaneously but the time constants of
the mechanical switch allows a parallel conducting path to be
established within the power electronics. As the mechanical
switch opens, the arc voltage shifts the current flow fully to the
parallel power electronics path. The commutation provided by
the power electronics then extinguishes the arc and with the
electronic switch turned off with the mechanical switch open, the
remaining energy is dissipated within the varistor.
Issues. The hybrid breakers provide improved current limiting overfast-acting air circuit breakers with a significant reduction,
almost elimination, of arcing. The hybrid variants are very similar
but the trade-off is between the bulky resonant circuit required in
the zero current switch compared to the need for switchgear
development. The technology has been implemented in prototype designs but no production arrangements have been taken
forward. In a marine application the constraints are the mechanical and power electronic switches, with current limiting only
achievable at the planned ratings if the mechanical opening force
and time to open are in the order of 35kN and 1.6 milliseconds1.
Propulsion systems. A huge subject area, broadly captured
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by the propulsion motor (PM) system and the transmission/
propulsor system. Comprising a drive and motor, power density
and signature direct these technologies which have seen a huge
amount of industrial and government effort in recent years. The
advanced induction motor (AIM) is currently the preferred solution, and is shown at Fig 7, but the industry pack of chasing
technologies is focused on taking PM system developments to
meet the demands of pods, low displacement and novel hullform
applications. Whether it will be a derivative of the AIM, a
permanent magnet machine or indeed a super-conducting machine, is a long way from being resolved, indeed the MoD is
actively pursuing a PM strategy to assess where best to focus its
efforts and, perhaps more importantly, its money! Again industry
is actively pursuing and solving the technical issues surrounding
the novel PM technologies and this looks to be an area of
significant industry-led work in the near term. In support of this,
power electronic devices and system developments continue
apace and a number of maturing PM system combinations now
feature advanced pulsed width modulated (PWM) converters.
The three technology areas - conventional, permanent magnet
and superconducting - all offer high power density (volumetric
and gravimetric) efficient solutions. Whilst the technologies are
all at varying stages of maturity, the key is that they would all seem
to have a role to play in the next generation of warships, albeit not
all technologies are suited to all applications. Fig 8 looks to
provide a snapshot of motor technology to put each of the
contender technologies into perspective.
Of course Fig 8 is only half of the story, particularly the power
densities, and the motor technologies cannot be compared in
isolation; any longer term assessment will need to include the
converter and auxiliaries and this is the subject of the MoD’s
propulsion motor strategy.
Platform management systems (PMS). These have long
been the key to achieving manpower savings, and work is underway
on how to specify systems, in performance requirements terms,
which support the operating and manning philosophies of the
future navy. This work will be further enhanced by developments
in smart systems, which will be able to identify failures and
damage, and reconfigure themselves automatically without operator intervention.
DELIVERING CAPABILITY
Returning to the theme of strategy and how this and the
technology can be embraced and engaged as platform system
solutions, Fig 9 puts forward a roadmap for technology within the
framework of capability, requirement and timescales. These bounds
are extremely pertinent to the longer term focus of the electric
warship concept and system design and technology integration
for future platforms. The key thread throughout is risk and how
it is identified, owned and managed by the various stakeholders;
notably the MoD, the prime contractors’ offices (PCOs), system
integrators and equipment suppliers the balance of which needs
to be developed if the capability is to be delivered.
Mindful of the common thread of risk, the roadmap looks to
capture the main themes and how the stakeholders need to be
integrated and relevant to ensure that the obvious synergy is
exploited. Within the bounds of the roadmap, here are a few
thoughts. Procurement of future platforms is now focused on
delivering capability by the most cost-effective means, with the
key themes being that of ‘requirements engineering’ and risk
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aversion - basically PCOs are tasked to deliver a capability to time
and cost, and they are not paid enough to embrace additional risk.
It is in the management of the dichotomy of risk aversion and the
introduction of technology in which the MoD can be most
effective with the combination of MEDP, partnerships with
industry and collaboration. It is the MoD’s informed customer
status and ability to identify and mitigate risk that underpins
much of the Smart Procurement Initiative - notably the balance of
COTs, development of commercial solutions and bespoke naval
development. How then against such a background can it be
ensured that the work being undertaken within the MEDP
programme is not nugatory and that our future ships fully
embrace IFEP? The answer is, in principle, easy to identify; in
practice it is much harder to implement. Fundamentally it is
imperative that the risks are captured from technical, programme
and platform perspectives so that a coherent risk register is
maintained - this functionality is vested with the Electric Ship
Programme Office, thereafter the key is how to translate the risk
process into design, development and technology insertion. In
making this transition it is essential that PCOs and the wider
industrial base are ‘onboard’. The drivers here, in addition to
those of risk management, are the need to reduce cost of ownership with effective support packages, the emphasis towards
commercial off the shelf equipments, and the trend away from
naval standards towards best practice, wherever that may be
vested. The AO, LPD(R) and Type 45 have been provided as
almost turnkey solutions, thereby minimising risk and therefore
cost. As system and equipment trends move away from the
commercial sector, the overriding issue must be ‘partnership’ and
this is the area in which the MoD can bring a huge amount of
experience and knowledge to bear. A key focus for technology
insertion and de-risking is the Electric Ship Technology Demonstrator (ESTD).
ELECTRIC SHIP TECHNOLOGY
DEMONSTRATOR
The ESTD is a joint programme between the UK and France
which looks to de-risk IFEP technology so that it becomes an
attractive option for future ship propulsion system prime contractors. The schematic of ESTD is at Fig 10. Broadly speaking it
includes a half ship set of equipment with representative power
generation and distribution systems linked by two static power
converters. The 20 MW propulsion motor drives a dynamic fourquadrant load, enabling the system to be demonstrated throughout the complete operating envelope. The zonal distribution
system, and inclusion of both zonal and bulk energy storage
complete the picture. The supporting aims of ESTD are:
●
To identify and de-risk IFEP system integration issues,
including system stability, fault identification and protection and harmonic distortion levels.
●
To validate equipment and system software models to
reduce or eliminate need for shore testing of future war
ship 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
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the facility to be used for shore integration testing (SIT) for
Type 45 systems once the majority of ESTD testing has
been completed.
One of the key issues for ESTD is how it will be utilised beyond
the current testing programme to manage technology insertion
and incremental system design; this presents a unique opportunity for the wider naval power system stakeholders to be engaged
in this important programme.
THE REALITY - AN INSIDE VIEW
This section will look at the all electric warship from the reality
of a practitioner’s perspective with the emphasis on operating
challenges related in the most part to LPD(R) experiences but
equally applicable to the wider concept. The single line diagram
at Fig 2 should be used to support references to the LPD(R)
system.
There are several key features that will make electrical propulsion a success or a failure in warships. We must of course adopt
a safe system of work but with many examples available from
industry, the merchant marine and of course the Royal Fleet
Auxiliary (RFA), this is a well-trodden path. More crucially we
must differentiate between an all electric ship and an all electric
warship in that we take these latter platforms into operational
theatres where we can expect some damage, even if minor, and we
cannot afford to take away propulsion or electrical services from
the command. This leads to a focus on operation, fire-fighting and
damage control, equipment design, onboard organisation and
training, all of which are discussed below:
Safe system of work and compartment access
A safe system of work to include Health and Safety and other
statutory requirements is essential if the system is to be operated
safely, noting the requirement to have established procedures for
maintenance and operation by naval and civilian personnel.
Wherever possible standard RN practice has been adopted but
high voltage requires additional precautions including hazard
markings for compartments, hazard signage, restricted access
procedures and CCTV monitoring of all compartments designated HV. Routines are required both by contractors and visitors
with restricted access regulations controlled by either a ‘day pass’
or ‘contractors pass’. Contractors requiring access to HV compartments will need to be briefed on the hazards and will require
a limitation of access prior to unescorted access/work in these
spaces. None of these issues is insurmountable but they need to
feature in the baseline design for an IFEP solution as the presence
of HV will limit access and require control procedures.
System operation and manning of HV spaces
The HV system will be operated via the platform management
system (PMS). For the LPD(R) system, the normal practice will be
to run continuously in parallel, de-isolated with the minimum
number of generators required (minimum generator operation
(MGO) leading to single generator operation (SGO)) at State 3. At
State 1, all generators may be required but the system will remain
de-isolated.
Because of the late change to electric propulsion during the
design phase of the LPD contract, some HV equipment built to
IP23 is located in main machinery spaces. This means that the
spaces concerned need to be disconnected from the live system
before any water-based extinguishers can be used to tackle a fire
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or before any attempt is made to control a flood. System disconnection procedures for the isolation of the HV system in the event
of fire/floods need careful consideration to ensure that the appropriate action is taken without endangering personnel and maximising availability of the propulsion system to the command.
Likewise, careful thought must be given when operating in SGO
mode to ensure that a total electrical failure (TLF) does not occur
if the affected compartment contains the only running prime
mover. It is also possible to lose main motor excitation if isolations
are carried out in the incorrect sequence. A series of hard-wired
trips allow rapid disconnection of the HV system.
The PMS system consists of a Pentium-based PC system
communicating via a dual redundant ethernet with batterybacked power supplies. This reversionary power source is located
in the forward switchboard and could perhaps be split into zoned
power supplies to make the system more resilient to action
damage in upgrades or future platforms.
Manning of machinery spaces at State 1 should not be unduly
affected by the possible hazards of exposure to HV (we have for a
long time manned magazines), but should be primarily driven by
the operational gains of manning secondary or local machinery
control positions as well as the ability to carry out immediate first
aid action. This approach must also be balanced against the
availability of manpower and the increased risk of exposure to
injury from action damage within a large machinery space. Hence
HV compartments will not be manned at State 3 but will be at
State 1. The mobile party (the cavalry!) needs to be best located
to cover all main machinery spaces; particularly any unmanned at
State 1. They need good communications and a high degree of
individual protection.
Fire-fighting and damage control
The recommended fire-fighting approach is to always
maintain a continuous aggressive attack using appropriate
first aid fire-fighting appliances. Should high voltage equipment within the compartment be correctly protected by
correctly IP-rated enclosures, then AFFF and HPSW hoses
may be used without restriction, although the inherent
dangers of unprotected lower voltage systems must also be
taken into account. Should the compartment become untenable it should be evacuated and closed down prior to using
the fixed suppression system. The process of closing down
and isolating the compartment should be initiated as early as
reasonably possible with the available manpower.
How then to first aid fire-fight in HV compartments? The
suggested solution is to replace AFFF extinguishers and hose reels
with portable CO2 and dry powder extinguishers to maintain the
aggressive attack without isolating equipment, although compartment isolation prior to initial attack on the fire could also be
considered. Kill Cards will indicate HV compartments and also
compartments through which HV cables pass, and how to isolate
power to these cables. There is however no need to isolate spaces
prior to CO2 drench although direct injection of CO2 onto HV
equipment is not supported.
Electrical isolations for fire-fighting and the use of foam blankets
will depend on the IP rating of high voltage equipment which
should be a minimum of IP55 for a compartment below the
waterline and/or with fluid systems running through it (low voltage
systems must also be considered). The ability to isolate equipment
from outside the compartment is essential and there should be a
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Electric warship new
clear indication at the compartment entrance, and possibly on the
equipment, as to whether high voltage equipment is still live.
Normal re-entry into any space requires the fire-fighting team
to be protected behind a water wall. Whilst this may remain
sensible during peacetime operations, it probably is not if we wish
to protect the HV system from water ingress and maintain
propulsion to the command at State 1.
Fig 11 summarises the range of fire and flood scenarios.
Equipment design
The selection of IP ratings for equipment must take into due
consideration the siting and possible consequences of fire-fighting and flooding taking place in the immediate vicinity. We
cannot afford to evacuate a space and abandon the prime movers
or other equipment contained within. The number of systems
adjacent to HV equipment should be minimised and, where
unavoidable, pipework should be continuous. CO2 injection
ports on HV equipment will not be fitted; rather compartment or
equipment fire suppression systems should be installed.
Onboard organisation and qualifications
The organisation to be employed for the ‘day to day’ operation/maintenance of the HV system is shown at Fig 12.
Training
There is the requirement for the provision of a training/joining
video for the education of the ship’s company not involved in the
day-to-day working of HV equipment. This video may also have
to be made available to potential contractors to also make them
aware of the potential hazards. Training organisations such as
FOST will be required to input proposed training scenarios and
also they will have to be informed of any limitations that HV may
place on proposed training (eg charged hoses, training smoke,
etc). FOST currently use exercise smoke during operational sea
training and this may have an impact on HV installations.
High voltage policy
The preceding paragraphs highlight a number of themes for
high voltage systems, all of which will be captured in the MLS1sponsored HV Policy Document. The document looks to provide
the wider naval marine power system community with guidance
on the specification, design, installation, test and operation of HV
power systems in warships together with the wider issues of
training and infrastructure. In the longer term it is hoped to
incorporate the policy guidelines within the requirements documentation for future platforms, notably on all safety-related issues
but in the near term the plan is to issue the document for ‘buy in’
from the wider naval power system community.
THE CHALLENGES
Notwithstanding the specific technical issues mentioned, a
number of other challenges also face the effective implementation
of IFEP. Whilst not exhaustive, the Top ‘X’ challenges includes
integration, electrical standards, equipment strategies, maintaining innovation whilst minimising risk, embracing automation and
system analysis. The following takes each of these issues in turn.
Integration. The integration of the complex IFEP architecture
is a significant challenge to system and equipment designers and
an area which needs the requisite focus at all stages of the design
process. Integration issues include system stability, operability,
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compatibility - notably EMC, physical issues and system transversals. Experience has shown that the transversals issue is the most
difficult to manage as boundaries are established between systems
and sub-systems; the management of which needs system level
co-ordination. On the theme of integration, the physical integration and buildability of solutions is extremely important and must
be a significant focus during the design process.
Electrical standards. Existing power system standards are
not sufficiently robust to support IFEP and IEP architectures.
Fundamentally, standards reflect conventional systems and are
not sufficiently flexible to be adapted to suit novel systems. In
support of this a review is being undertaken to propose a policy
for IEP and IFEP systems covering issues as diverse as power
system standards, safety, Design constraints and working practices. This is even more relevant in view of the high voltage
implications. The MoD’s HV Policy Document will look to
provide the framework for naval marine power system standards.
Equipment strategies. Building on the themes of risk, the
overarching MEDS and its implementation through the centre of
marine engineering excellence, equipment and system strategies are essential to the electric warship aspirations. A number
of strategies are being written which look to draw together the
requirements, platform risks, timescales and industry focus to
produce the supporting justification for equipment development, the outcome of which will inform development and the
wider stakeholding community. Within DOpsE, a Directorate of
the Warship Support Agency, system strategies are being produced to support medium (10 year) and long (25 year) term
visions, which look to provide a coherent focus across the
marine engineering community embracing the MEDP and elements of both the Corporate (CRP) and Applied (ARP) Research
Programmes.
Innovation. Innovation will always be constrained by risk
and 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 future
Royal Navy will face increasing support costs and degrading
performance and capability compared to other, more adventurous, navies. A balance must therefore be struck. This can be
achieved through establishing a thorough appreciation of
future technologies and their assessment, through the MEDP
and the expert eye of the Marine Engineering Centre of
Excellence. The risks associated with innovation can then be
fully quantified, and effective, focused risk-mitigation put in
place. As a result the likelihood of the pull-through of innovative technologies into service by the warship prime contractor
will be enhanced.
Wider strategy. The marine engineering aspects are focused,
but the lack of coherent strategies or, in some cases, coherency
between strategies in the wider naval service creates difficulties.
Notably, the lack of a weapon engineering equivalent to MEDS
remains a concern and it is imperative that the future requirements of combat systems are identified as a priority to ensure that
the platform solution can meet the demands, primarily in terms
of power requirements and possible requirements for pulsed
energy. Manning, support and similar strategies do, however,
exist but it is essential that coherency is maintained between
them.
Automation. Central to the platform system solution, the
platform management system (PMS) and its derivatives provide
the operability and functionality of the system - the main concern
however is that of integration. PMS needs to be embraced at the
outset and become an integral part of the design solution. Often
seen as the ‘cure all’ for system functionality and integration, it is
important that it is not left to pick up the design deficiencies from
the system and equipment integration.
System analysis. As the focus moves away from platform
shore test facilities, a function of cost and time, the emphasis on
alternative mechanisms to assess system and equipment performance has come to the fore. The spectrum of activities in support
of the analysis is bounded by full scale test and simulation
balanced with prototyping and equipment tests. The trend towards simulation is worthy of note, with both MoD and industry
embracing it to balance equipment and system development. The
strength of this approach is flexibility and cost, and the ability to
model at component, equipment, sub-system and system levels.
Already naval marine power system modelling has produced a
modelling blockset to assess system and sub-system issues in a
‘fuel to thrust’ approach, the outline schematic for which is at Fig
13. The functionality of the models allows assessment of dynamic
performance, system transients, external impacts and bounds of
operation. Validation of models remains a key theme along with
the issue of models containing proprietary information, which
must be resolved if the goals are to be realised. The simulation
vision is to maintain a database of models for all power systems
and equipment, with all new systems and equipment being
delivered with a validated model - wishful thinking, perhaps, but
essential if we are to realise the full potential of simulation.
SUMMARY
The last year has seen a huge amount of activity in both the
electric ship and electric warship arenas, notably with the reality
of the electric warship and the coming of age of the integrated
electric propulsion concept in the guise of LPD(R) and Type 45.
In support of these vessels and within the framework of smart
acquisition, the marine engineering development plan has sought
to maintain momentum and relevance with a number of notable
successes, primarily that of ESTD. The emphasis is now, as ever,
on cost-effective capability for the marine engineering solution
and it is hoped that this paper has gone some way to demonstrate
how the MoD is looking to take this forward in partnership with
industry with the focus very much towards incremental acquisition and technology insertion.
REFERENCES
1.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.
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Fig 1: The reality of the electric ship
Fig 3: The usual suspects
Fig 4: Baseline architecture or marker in the sand
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Fig 2: LPD(R); the single line diagram
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Fig 5: Framing the technology
Fig 6: The hybrid switch schematic
Fig 7: The advanced induction motor
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Fig 8: Motor development compared
Fig 9: A technology roadmap
Fig 10: ESTD schematic
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Fig 11: Fire and flood scenarios and responses
PERSONNEL
TRAINING
Authorising Authority (FOSF ashore)
Authorising Engineer (MEO-May have nominated deputies)
Authorised Persons
Competent Person (CP)
HV Aware (Remainder of ship's company)
MEOOW1
HVA
MCQ +AP+local assessment
AP+local assessment
Video + detailed briefing
Video + briefing
As CP
Fig 12: Onboard organisation
Fig 13: IEP Model; the software realisation
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