Project Napier sees twin-track plan adopted to resolve Type 45 problems
Warship Technology: May 2016
Commissioned into service between July 2009 and September 2013, the six Type 45 destroyers are the first front-line warships in the world to introduce an Integrated Electric Propulsion (IEP) system. The decision to adopt IEP at the heart of which is the Rolls-Royce WR-21 marine gas turbine and its associated recuperation system was taken in the expectation that it would realise multiple operating benefits including improved fuel efficiency, reduced maintenance and manpower requirements, and lower environmental impact.
However, early operating experience has revealed a wide range of problems with regard to both reliability and performance. Numerous instances of total electrical failure have occurred during underway operations, and it has become evident that the marine engineering issues affecting the power and propulsion system are deep-seated and systemic in nature. Reflecting this, last year’s Strategic Defence and Security Review (SDSR) included a specific commitment to improve the Type 45 IEP system: this work is being advanced under an activity known as Project Napier.
The original decision to select IEP for Type 45 was taken back in 2000. The judgement to adopt what was an innovative but, in a warship application, still unproven power and propulsion architecture reflected the strong thrust prevailing within the Ministry of Defence (MoD) and the Royal Navy’s marine engineering community towards the adoption of an ‘Electric Ship’ architecture for future warships on the grounds of improved survivability, improved operating efficiency, reduced costs of ownership, and an ability to meet the needs of future pulsed power weapon systems. The extant Marine Engineering Development Strategy also espoused the adoption of high-efficiency, complex cycle gas turbine technology on the basis of the through-life benefits accruing from significantly improved fuel efficiency at part load.
IEP is fundamentally different from conventional mechanically driven machinery arrangements in that it uses a common set of prime movers to provide power to both propulsion and ship service ‘consumers’. However, while IEP is well proven in the commercial marine sector, it remains novel in a warship application given the requirement for much higher power densities and shock standards compared to existing commercial designs.
One factor that strongly influenced the choice of IEP for Type 45 was the encouraging news from the US Navy’s Integrated Power System (IPS) land-based testbed in Philadelphia, where testing had demonstrated the performance of a 20 megawatt (MW) Advanced Induction Motor of sufficient compactness and weight to fit inside the Type 45 hull. Confidence in the technology had in January 2000 seen the decision taken by the US Navy to endorse the use of the IPS architecture for the next-generation DD-21 land attack destroyer (later to become the DDG-1000 Zumwalt class). A second factor was the impending award of a contract for an Electric Ship Technology Demonstrator (ESTD) to de-risk the full electric solution for the future. The ESTD subsequently built up at a facility at Whetstone in Leicestershire was conceived to allow system-wide integration and testing in support of future surface ship and submarine electric ship architectures.
Taking the progress of the IPS test programme into account, and the UK’s planned investment in technology de-risking through the ESTD, BAE Systems and the MoD in early 2000 reviewed the selection of Combined Gas and Electric (COGAL) machinery arrangement baselined for the Type 45 programme in late 1999. After a detailed study a decision conference assessing 14 different solutions concluded that IEP represented the optimum solution when assessed on a whole-life cost basis. As a result, the decision was taken to drop the COGAL baseline and instead pursue direct drive IEP with fixed-pitch propellers on the basis it represented the best option in terms of through-life costs, performance and risk. The IEP system would leverage the Advanced Induction Motor and associated converter tested at the IPS shore-based test site in Philadelphia.
There was an acknowledgement at the outset that the decision to proceed with IEP carried a greater degree of risk than a more traditional solution. However, the judgement at the time was that these risks would be outweighed by the long-term benefits of a propulsion system using a reduced number of prime movers acting in a more integrated fashion. As well as improved fuel efficiency, IEP was seen to provide through-life savings in maintenance and personnel costs, along with lower environmental impacts.
As regards the supply of gas turbines for Type 45, this requirement was initially competed by BAE Systems (as prime contractor). GE offered the proven and widely used simple-cycle LM2500, while Rolls-Royce proposed the complex cycle WR-21, then still completing development. Unlike simple-cycle gas turbines, which are inefficient at part load, the complex cycle WR-21 has been designed to deliver more efficient power generation over a wide range of demand. This is achieved by using an intercooler to cool the air that flows through the engine before combustion occurs, and a recuperator to recover waste energy from the exhaust so as to improve the overall cycle efficiency.
BAE Systems’ evaluation of the two rival bids concluded that while both engines met requirements, the LM2500 was both cheaper to acquire and presented lower technical risk. However, in November 2000 the MoD announced its decision to set aside the competition and negotiate a sole-source contract with Rolls-Royce for the supply of WR-21. While acknowledging that WR-21 carried a greater degree of risk, the MoD justified its decision in part on the basis of factors falling outside the Type 45 programme, including commonality of support with existing Rolls-Royce engines, the suitability of WR-21 for specific Royal Navy operating profiles, and the through-life cost savings accruing from WR-21’s low fuel consumption across the power range. There were also significant industrial and political considerations.
Each Type 45 has an IEP system operating through twin shafts, each driven by a 20MW Advanced Induction Motor. Pulse Width Modulated (PWM) converters provide variable frequency power supplies for the two 20MW Advanced Induction Motors directly coupled to the propeller shafts. Unlike all other vessels of this power, these motors are direct fed from the high-voltage bus without drive transformers, given increased gravimetric and volumetric density. The drive arrangement of a PWM converter with an Advanced Induction Motor offers the normal benefits of electric propulsion, but additionally brings the shock withstand, low noise and vibration, and fallback/failure modes needed for a full warship.
The electrical power for the propulsion and ships service load is provided by the two 21MW-rated WR-21 gas turbines (each driving a two-pole cylindrical rotor generator at up to 3,600rpm) and two anchor-load Wärtsilä 12V200 diesel generator sets rated at 2MW each. Two main high-voltage switchboards distribute power to consumers, either at 4,160V AC to the VDM25000 propulsion converters, or via transformers at 440V and 115V AC to weapons and ship services.
The Type 45 IEP system was shore-tested using the ESTD at Whetstone. These de-risking trials tested a subset of the Type 45 power and propulsion plant in a variety of regimes and modes. However, while the ESTD de-risked the functional integration of the IEP design, in retrospect it appears that it did not achieve sufficient running hours to provide adequate equipment reliability assurance.
At the outset, the design intent was that the IEP system would typically run on a single WR-21 gas turbine alternator (GTA) in a single-island mode, with the second GTA brought on line only in ‘high risk’ operating regimes; the two 2MW diesel alternators were to provide power for harbour services and ‘blackout’ recovery, and not foreseen to perform as true backup generators in the event of GTA failure. In actual fact, current operating practice tends towards one WR-21 and one auxiliary diesel in single-island mode.
However, operating experience has revealed significant shortcomings in the IEP system, both with specific equipments and fragility in the overall system architecture. These issues have collectively resulted in numerous ship-wide power outages.
The most complete overview of the problems, and their root causes, became public towards the end of March 2016 with the release of a letter from Secretary of State for Defence Michael Fallon to Dr Julian Lewis MP, chair of the House of Commons Defence Committee (HCDC).
According to Fallon, the first evidence of performance and reliability shortfalls had in fact emerged during ESTD shore testing in 2005, though by the end of that year “the level of performance was deemed sufficient to proceed to the next stage [sea trials] of the programme”.
First-of-class HMS Daring commenced sea trials in July 2007. A large number of defects quickly became evident in the IEP system, with industry required to identify and implement improvements in system configuration, tuning and reliability. Between the first Type 45 launch in February 2006 and the sixth and final Type 45 launch in October 2010, approximately 50 design changes were introduced.
Yet the truth was that the interrelated nature of the defects associated with the IEP system architecture masked the real extent of the shortcomings inherent in the design. In 2011 an independent study commissioned by the MoD found that there was “no single root cause underlying the low reliability”, pointing instead to a “large group of unconnected individual causes.” The report concluded that IEP remained a sound choice for Type 45, while at the same time noting that “acceptable reliability will [only] be achieved once the issues identified in this report have been satisfactorily resolved”.
Referring specifically to the power and propulsion system design, the report concluded that poor performance was attributable to a combination of both design shortfall and reliability problems. A total of 16 specific recommendations were made, all of which were approved and taken forward into design, testing and implementation.
Fallon’s letter to the HCDC notes that the process for the design, integration, trials and acceptance of these design modifications “is necessarily rigorous and time consuming”, and so the majority of IEP system alterations were not embodied into the Type 45 ships until after the sea trials of the sixth and final ship (HMS Duncan) in 2012. “The ships were therefore accepted into service based on the performance and reliability improvements anticipated,” he continued. “Key to this was the clear conclusion of the 2011 independent report that acceptable reliability would be achieved when all its recommendations were implemented.”
All of the various recommendations contained in the 2011 report had been realised by 2013. However, while reliability did continue to increase, the rate of improvement began to slow. Additionally, in-service experience accrued through the deployment of ships to the most demanding operational environments revealed that the original design intent of operating the ship while running WR-21 alone was flawed. “Only the addition of extra prime movers, in effect changing the design architecture, would allow these shortfalls to be addressed,” acknowledged Fallon in his letter to the HCDC.
Project Napier was established in 2014 with two core work strands. The first of these, known as the Equipment Improvement Plan (EIP), is continuing efforts to enhance system reliability and to meet the original design intent in the near term. The second component of Project Napier is a longer term Power Improvement Plan (PIP), intended to improve overall system resilience by adding upgraded diesel generators to provide the electrical generation capacity required to meet the overwhelming majority of propulsion and ship power requirements without reliance on WR-21.
Various measures and modifications to the existing power and propulsion system have already been embodied, or are in the process of being introduced incrementally, under the EIP. These include improvements to system integration aspects, and modifications to converters and converter cabinets. In addition, the training, doctrine and operating guidance provided to ships’ crews has been revised and refreshed to take account of initial operating experience.
Further ahead, the PIP project plans to deliver a diesel generator upgrade that will be embodied towards the end of the decade so as to add greater resilience to the power and propulsion system. Feasibility studies for this work, co-funded by BAE Systems and the MoD, concluded at the end of March 2015.
The PIP is now into its assessment phase, with three alternative options and a variety of delivery models currently being investigated with a number of industrial partners. The objective is to provide sufficient additional electrical generation capacity such that the IEP system can make cruise speeds (covering the major part of the Type 45 operating profile) on diesels alone. The WR-21 GTAs will remain to provide boost power as necessary, but will be used much less often.
It is expected that a down-selection to a preferred PIP technical solution will occur in mid-2016 which will form the basis of a final recommendation to the MoD’s Investment Approvals Committee. The total cost and timetable of embodying the diesel generator upgrade will be determined at the main investment decision point, and will be conditioned to a large part by the final design solution selected. In advance of the long-term solution promised by the PIP, the MoD insists that it is already seeing significant improvements in the general reliability of the Type 45 power and propulsion system, including the WR-21 GTA.