Thomas Dalton, Abe Boughner, C. David Mako and Cdr. Norbert Doerry, USN

LHD 8: A Step Toward the All Electric Warship

ABSTRACT (Figure 1) are designed to support Marine Corps air and amphibious assaults against The recently commissioned Iwo Jima defended positions ashore. The propulsion (LHD 7) is the last ship with plant for the first seven ships of the Wasp conventional steam propulsion that class consists of two independent steam the U.S. Navy plans to build. The boilers and two 35,000 hp steam turbine LHD 8 is the next ship of the class engines capable of driving the ship at over and will be built as a modified repeat 20 knots. This basic steam propulsion design of the LHD 7. The key approach was adopted from the earlier, circa modifications are steam propulsion 1960’s, steam propulsion plant of the being replaced with a hybrid Tarawa (LHA 1) class. In the early 1990s propulsion system of main gas turbine the U.S. Navy made a general decision to engines augmented with auxiliary phase out conventionally powered steam propulsion motors and electric ships due to the high cost of maintenance powered auxiliaries replacing those and manning. During construction of the powered by steam. The LHD 8 will LHD 5, 6 & 7, the Navy conducted a global also be the first USN surface ship to search to replace the steam plant with implement a 4160 VAC Zonal alternative power systems. At that time a Electrical Distribution System (AC General Electric LM2500 gas turbine engine ZEDS) as well as the integrated (25,000 hp) was the only gas turbine engine power system concept for electrical qualified for propulsion of U.S. Navy ships power generation, distribution and and inadequate by itself to replace a 35,000 propulsion. These modifications hp steam turbine plant. embody the intent of the all electric warship concept for the future U.S. Navy. This paper presents the constraints and issues involved in the design process by addressing major design impacts and significant design concerns. This text explores the design options within the available trade space and illustrates specifically how the fleet / mission requirements, LHD 7 hull design and propulsion shafting constraints, schedule and funding drove the propulsion system design. FIGURE 1 - Amphibious Assault Ship (LHD 2 – Essex) INTRODUCTION Because gas turbine engine ducting must be routed through the island structure, gas The 40,500 ton 844 ft ships of the Wasp turbine propulsion for an LHD requires a (LHD 1) class of amphibious assault ships tremendous amount of internal volume that manufacturing lead time needed to support may displace equipment in many existing the ship construction schedule spaces. Studies have shown that although - No Marine Corps missions could be two gas turbine engines per shaft would degraded provide ample power, they would not fit in - Minimize the impact to adjacent non- the existing machinery spaces without major machinery spaces impacts to the surrounding spaces and the - Allow only reasonable machinery engine ducting would severely impact the arrangement changes ship arrangements. With commercial development of the General Electric The amphibious assault ship operating LM2500+ gas turbine engine (35,000 hp), it profile is such that over 75 % of the became conceivable to fit a single gas underway time the ship requires less than turbine engine into a LHD at power levels 10,000 hp for propulsion to travel at speeds comparable to the steam turbine plant it up to twelve knots. Because a single 35,000 would replace. Although conceptual studies hp gas turbine engine is lightly loaded at this were conducted to fit LHD 7 with one power level, the specific fuel consumption LM2500+ gas turbine engine per shaft, the of a gas turbine plant is very unattractive ship was too far into construction to make and well off its most fuel-efficient design such a major change. Accordingly, Iwo point over much of the ship's operating Jima (LHD 7) is the last ship in the U.S. profile. Although these feasibility studies Navy to be built with a conventional steam were not predicated on supplementing the plant and LHD 8 will be the first ship in the gas turbine engines with an electric U.S. Navy to use an LM2500+ gas turbine. propulsion system, their analysis did indicate that significant fuel savings could PROPULSION PLANT be realized by augmenting the gas turbine DESIGN HISTORY propulsion with electric propulsion. As a result, propulsion motors were integrated with the gas turbine engines at a relatively In preparation for the design and modest 1600 hp per shaft, which is capable construction of LHD 8, the U.S. Navy of driving the ship to roughly six knots initiated a series of feasibility studies under ideal wind and sea conditions. (References 1 and 2) aimed at developing a Another recommendation from these studies gas turbine propulsion concept and reducing was to retain a small auxiliary boiler for Total Ownership Costs (TOC) over the heating and hotel services. This design expected 40 year service life of the ship. feature ensured that the 450 VAC electric Early results of this study showed that TOC plant would essentially be maintained at could be drastically reduced simply through roughly the same size as previous ships in the predicted reduction in crew size of at the class by simply replacing the same least 80 personnel and decreased number of steam turbine generators with maintenance requirements associated with diesel generators of comparable power level the removal of steam turbine engines and and density. Although the TOC savings boilers. To minimize design and were sufficient to justify the conversion to construction costs, a number of constraints gas turbine propulsion in manpower and were placed on the design: maintenance reductions alone without - Maintain the existing shaft line rake and electric propulsion, the addition of an skew of the steam propulsion plant to retain electric propulsion system enhanced those the same Wasp (LHD 1) class hull savings. hydrodynamic characteristics - Limit design changes to the second stage The design concept for the LHD 8 was of the reduction gear to maintain the further refined to totally eliminate all shipboard steam heating for spaces, laundry, cooking and other hotel services, resulting in PROPULSION PLANT a greatly increased electric plant capacity. DESIGN Consequently, the generation and distribution system voltage was increased to The propulsion system for each of the two 4160 VAC to meet the additional load shafts of the LHD 8 consists of a single demand for electric heating on a cold day. main gas turbine engine (LM2500+ at With the removal of the steam auxiliaries, 35,000 hp) and an auxiliary propulsion the worst case load demand changed from a 0 motor (5000 hp) driving a two-stage mission scenario of debarking on a 90 F 0 reduction gear into a controllable pitch day to a cruise condition on a 10 F day. It propeller (CPP) (Figures 3 and 4). The gas was then realized that the ship had as much turbine engines drive the reduction gear as 8 MW of excess generating capacity 0 through an overrunning self-synchronizing under typical climatic conditions of a 70 F clutch. The first stage reduction gear casing day (Figure 2). is modified from the LHD 7 design to accept the single gas turbine engine and propulsion All Conditions Total Load Composite motor input, in lieu of the high and low

17000.0 pressure steam turbine engines. The single

15000.0 gas turbine engine input pinion splits into two locked power train drives. The 13000.0 Anchor propulsion motor drives through a self- Cruise 11000.0 Debark synchronizing clutch into one of the two

kW Shore 9000.0 locked train first stage reduction gears. The

7000.0 existing shaft rake and skew were retained and modifications to the second stage 5000.0 reduction gear have been minimized to only 3000.0 that necessary to fit the CPP hydraulic oil 90 Degree 78 Degree 65 Degree 40 Degree 10 Degree distribution box. The length of the gas Temperature turbine engine module in the machinery rooms required moving the reduction gear FIGURE 2 - Predicted LHD 8 ship service several feet aft from the prior ship design power demand loading curves location. This was beneficial since it without anticipated service life load growth eliminated one section of line shafting. margin While the reduction gear ratios for the gas This excess capacity could support electric turbine engines and propulsion motors are propulsion considerably larger than the 1600 identical, the maximum shaft speed of 180 hp propulsion motors originally planned rpm from the gas turbine engine is twice that anytime it was warmer than the extreme from the propulsion motor at 90 rpm. design condition of a 100 F day. Since the Propulsion is provided from either the gas propulsion motors are not mission essential turbine engine or the propulsion motor, but (the ship can fulfill all mission requirements not both simultaneously. Transitioning from using the gas turbine engines alone), larger propulsion motor to gas turbine engine drive propulsion motors could be incorporated and back is allowed over the entire speed / without requiring an increase in the total power range of the propulsion motor. electric plant generating capacity. Accordingly, follow-on study determined the optimal propulsion motor rating to be 5000 hp per shaft, which was subsequently incorporated into the final design. Propulsion Brakes Line Shafting MRG

Propulsion Gas Turbine

Motor Main Thrust Bearing

Propulsion Turning Clutches Gear

FIGURE 3 - Conceptual diagram of shaft propulsion power train arrangement for LHD 8

summary (Table 1) for each design condition, the worst case scenario was during a cruise condition on a 100 F day when approximately 19 MW of power was required to operate the ship. In comparison, a 900 F day cruise condition requires only 11 MW of power.

Table 1 - Predicted electrical load analysis summary with anticipated service life growth margin

FIGURE 4 - Sketch of shaft propulsion DAY ANCHOR CRUISE DEBARK power train design concept for LHD 8 TEMP 0 F MW MW MW ELECTRIC PLANT DESIGN 10 16.6 18.6 17.4 HISTORY 90 10.0 11.5 11.0

During the LHD 8 feasibility studies several Although a traditional U.S. Navy 450 VAC options for the electric plant were explored electrical power distribution system was that were based on ship construction cost, initially considered for LHD 8, the operating life cycle cost, survivability, maintainability configuration of such an electric plant was and feasibility of the design to support the much too awkward to be practical. In a 450 load increase from the removal of steam and VAC power distribution system no more incorporation of electric heaters and than two 2.5 MW generators can be auxiliaries. As shown in the load analysis paralleled due to the maximum interruptible fault current capacity of standard 450 VAC U.S. Navy circuit breakers. This limitation survivable and recoverable from battle would require ship’s force to operate too damage faults. many separate electric plants (at least three) to support the maximum power demand. ELECTRIC PLANT DESIGN This added complexity was deemed unacceptable. The configuration of the AC ZEDS architecture is a 4160 VAC power The only practical alternative to a 450 VAC generation and primary power distribution power system was to increase the power system for zone to zone power distribution generation and distribution system voltage as well as 450 VAC secondary power to reduce the operating and fault currents to distribution for supplying power to loads a level which existing switcher could within each of the fire / electrical zones handle. Because the U.S. Navy has design (Figure 5). The 4160 VAC primary power and operational experience with 4160 VAC distribution consists of two longitudinal power systems and U.S. Navy qualified buses located port and starboard in a high 4160 VAC circuit breakers exist, this and low orientation in the ship to enhance voltage level was selected as the low risk survivability. Each of the longitudinal buses choice. A 4160 VAC electric plant design consists of four switchboards and the allowed six 4 MW diesel generators, associated interconnecting cable. Eight sufficient to power all margined loads, to fit transformers are used to connect the primary into the proposed engineering spaces within power distribution switchboards to the 450 the LHD 8. Also, the electric plant offered VAC secondary power distribution systems. maximum operational flexibility by being The six diesel generators are installed with able to parallel up to five generators, or all two located in each forward and aft main but the standby generator, without exceeding machinery room (MMR) space and one the maximum interruptible fault current located in each forward and aft generator capacity of the 4160 VAC U.S. Navy circuit room. Each generator has an associated breakers. switchboard capable of feeding power to switchboards on either the port or starboard Since most loads on the ship are derived longitudinal bus. This permits independent from 450 VAC, a power distribution system operation of 4160 VAC generation and architecture was needed for routing the 4160 power distribution system as port and VAC power, converting the 4160 VAC starboard electric plants. This electric plant power to 450 VAC, and distributing the 450 configuration establishes two sources of VAC power. After reviewing several power throughout the ship and provides the previous U.S. Navy electric plant designs as flexibility to align generators as required for well as looking at current and future electric each electric plant. It should be noted that plant designs, an AC Zonal Electrical each section of the electric plant is isolated Distribution System (AC ZEDS) was by circuit breakers to ensure maximum selected. This application of AC ZEDS is protection and survivability to isolate any based on partial and full system designs damaged sections of the bus and reconfigure implemented on DDG 51 Flight IIA class the electric plant to maintain or restore destroyers and LPD 17 class amphibious power as quickly as possible. The electric assault ships, respectively and includes propulsion system may be powered from a using multifunction monitors (MFM III) to dedicated generator in each MMR or from enhance the response to multiple faults from either longitudinal bus. battle damage weapon effect scenarios. When compared to radial distribution Each switchboard on the port and starboard system architectures of previous classes of buses connects to a 3.5 MVA, 4160 VAC / ships, AC ZEDS provides an electric plant 450 VAC ship service step down that weighs less and is both highly transformer located within that electrical - The piers likely to be used by zone to power ship service loads in the local LHD 8 in her eventual home port are not zones via the 450 VAC secondary power capable of providing 13 MW of 450 VAC distribution system. Each of these ship power to a single ship. Piers in LHD 8’s service transformers has an associated 450 eventual home port will have to be upgraded VAC ship service distribution switchboard regardless of the shore power voltage. that feeds multiple ship service load centers Installing a shore power connection to to power ship service loads in the local provide 13 MW of shore power would be zones. These load centers are either in the considerably cheaper at 4160 VAC than at same electrical zone or in the adjacent 450 VAC. electrical zones as the ship service transformer and associated switchboard. AUXILIARY PROPULSION Each load center then feeds the ship service SYSTEM (APS) DESIGN HISTORY loads within its respective electrical zone. Vital loads are provided normal and As previously indicated the initial alternate power sources via automatic bus feasibility studies introduced the auxiliary transfer (ABT) devices that are provided propulsion motor design concept for ship power from load centers connected to loitering capability with a relatively modest switchboards fed from the port and starboard 1,600 hp per shaft. This was accomplished buses. by fitting two 800 hp propulsion motors at 450 VAC atop the second stage reduction Forward and aft 4160 VAC shore power gear and driving into pinions meshing with receptacles are provided from three of the the first stage reduction gear train. When 4160 VAC switchboards, two amidships and the generation and distribution of the electric one aft. The shore power distribution plant was increased from 450 VAC to 4160 system is centerline oriented to support VAC, the propulsion motor size was either port or the starboard connections to increased from 1,600 hp to 2,000 hp. This the ship from the pier. Shore power occurred because a propulsion motor with a connections at 4160 VAC were chosen over higher voltage rating could fit in the same the traditional 450 VAC shore power machinery space footprint and the increased connections for the following reasons: size of the electric plant could provide more - Supplying 13 MW of shore power power. Further study on the type and size of on a 10º F day at 4160 VAC would only propulsion motor recommended the use of a require three versus over fifty shore power single speed AC induction motor since an cables, connection boxes and switchboard AC synchronous motor, a DC motor or any circuit breakers at the 450 VAC design. two speed motor would be significantly ` - Shore power at 450 VAC would larger as shown in Table 2 (Reference 3). have required either large, heavy AC permanent magnet and super conductive transformers to convert the 450 VAC to motors were also considered as propulsion 4160 VAC for compatibility with the port motors, but were deemed far too and starboard longitudinal busses, or developmental in terms of risk, cost and extensive cabling to each of the eight 450 schedule impact at the power level required. VAC distribution system zonal load centers and an awkward power transfer procedure 4160V SWBD 4160V SWBD 4160V SWBD 4160V SWBD 7HB 5HB 4HB 1HB 800A 800A 1000A 1000A 800A 800A 2T400 3T400 2T400 800A 600A 800A 800A 600A 600A 800A 800A 600A 800A AUXILIARY PROPULSION MOTOR 3.5 MVA 3.5 MVA 3.5 MVA 4160/450V 3.5 MVA 4160/450V 4160/450V M TRANSFORMER TRANSFORMER 4160/450V TRANSFORMER HTF7B HTF5B TRANSFORMER HTF1B 4HMC HTF4B 450V SWBD 450V SWBD 450V SWBD 7LB 5LB 1LB 450V SWBD 4LB

LC54 LC52 LC48 LC46 LC44 LC42 800A PORT 800A 800A LC72 LC64 LC62 TO SHORE PWR STA @ LC34 LC32 LC24 LC22 LC12 800A 4.0MW, 4160V STBD 800A SWBD SWBD G D D G 3SG 5SG 4160V 4160V 800A 4.0MW, 4160V 800A 800A 800A GEN GEN

800A SWBD 6SG 4160V SWBD GEN 4.0MW, 4160V 800A 800A TO AFT 800A 4.0MW, 4160V

D G SHORE 800A 800A 800A 1SG G D 800A POWER STA 800A 4.0MW, 4160V 800A

800A 4160V GEN D G SWBD G D SWBD 4SG 2SG 4160V 800A 4.0MW, 4160V 800A 800A 4160V GEN

PORT GEN TO SHORE PWR STA v STBD LC71 LC63 LC61 LC33 LC31 LC23 LC21 LC11

LC53 LC51 LC47 LC45 LC43 LC41

450V SWBD 6LA

450V SWBD 5HMC 450V SWBD 450V SWBD 5LA 3.5 MVA 4LA 2LA 3.5 MVA 3.5 MVA M 4160/450V 4160/450V 4160/450V TRANSFORMER 3.5 MVA TRANSFORMER TRANSFORMER AUXILIARY HTF4A 4160/450V HTF6A HTF5A PROPULSION TRANSFORMER MOTOR HTF2A 600A 800A 800A 800A 600A 1000A 600A 800A 800A 800A 600A 800A 2T400 2T400 3T400 2T400 800A 800A 1000A 800A 4160V SWBD 4160V SWBD 4160V SWBD 4160V SWBD 6HA 5HA 4HA 2HA

NOTES: 1) ALL LOAD CENTERS ARE 2000A 2) “*”,“u”,“@” ,“v” = INTERLOCKED 3) ALL 4160V CABLE TO BE TYPE LS5KV

FIGURE 5 - Electric plant one line diagram design concept

TABLE 2 COMPARISON OF PROPULSION MOTOR TYPE OPTIONS

MOTOR RELATIVE RELATIVE RELATIVE TYPES SIZE COST RISK

DC max dia near min min

AC SYNC near max dia near min min

AC INDUC near min dia min min

AC PM near min dia near max near max

AC SUPER-C min dia max max

Additional analysis (Reference 4) confirmed reduction gear design and having a power that the optimal propulsion motor size was demand within the capacity of one diesel between 3000 hp to 5000 hp and indicated a generator. With 75% of the ship’s operating slight improvement in investment return profile and a ship speed of over 12 knots with a 5000 hp propulsion motor. A 5,000 possible with the 5,000 hp propulsion hp propulsion motor was also the motors, the loiter motor title was no longer appropriate size based on the largest frame appropriate. Once the decision was made to size AC induction motor that would go forward with the 5,000 hp design, the physically fit without major impacts to the propulsion motor and associated drive was renamed more appropriately as the auxiliary shaft and thereby allows the APS to operate propulsion system. To accommodate the independently from the gas turbine engine. larger size of the 5000 hp propulsion motor, While adding this capability would not a separate foundation was added adjacent to reduce operating costs, this feature was the gas turbine engine foundation. In this highly desired by the ship operators during arrangement the size of the propulsion motor the fleet review of the APS design and its became restricted to that which would fit operation. The near proximity of the between the edge of the gas turbine engine propulsion motor to the gas turbine engine module enclosure and input shaft centerline meant a larger propulsion motor frame size of the reduction gear. beyond the 5000 hp for an AC induction motor was not possible. This ruled out The initial APS design concept required the using 5000 hp DC motors, even though DC shaft to be spinning before energizing the motors could more easily develop the propulsion motor because the limited requisite starting torque. starting torque of a relatively small single speed induction motor was not sufficient to Other design approaches of moving the start a stopped shaft. Normally this would propulsion motor foundation farther from entail the gas turbine engine powering the the gas turbine engine to accommodate a shaft, but the shaft could spin without shaft larger AC induction motor frame to develop input power if the ship happened to have more starting torque would increase the sufficient speed to cause water windmilling propulsion motor pinion size. The of the propeller. associated loss of mechanical advantage from such a change would offset any The single speed aspect of the propulsion increase in propulsion motor starting torque. motor also caused a concern for CPP blade Of course, changing the gear ratio (smaller cavitation. Since the propulsion motor pinion) to provide more mechanical would only operate at a nominal rated speed advantage at startup would lower the full of 1800 RPM, altering the blade pitch angle rated shaft speed. However, a gear ratio of the propeller controlled ship speed. At change would not be acceptable since the lower ship speeds and minimal thrust there propulsion motor would be unable to reach was a risk of cavitation on the suction side its full rated load capacity at full or even of the propeller blades. Also, since maximum propeller blade pitch angle. A transitions were required “on-the-fly” from torque assist motor option using a hydraulic gas turbine engine to propulsion motor, motor to break the static friction of the speed matching and synchronization had to bearings to reduce the starting torque be accomplished by manipulating gas requirement for the propulsion motor was turbine engine speed only since the also considered. This unconventional propulsion motor speed was fixed. concept would also require soft motor starting for the torque assist motor and an To minimize propulsion motor inrush additional clutched drive interface with the currents and avoid having to dedicate up to reduction gear. The torque assist motor three generators to provide start-up torque approach was not considered practical since for even an unloaded propulsion motor, a it would require more design lead time for reduced voltage (soft) start concept was additional gear redesign than was available. incorporated into the original design. All of these design issues were considered If the 5000 hp AC induction motor were manageable, except for the inability of the capable of developing rated torque at zero propulsion motor to start a stopped shaft. speed, it would be able to start a stopped shaft. The design option of full voltage The next design iteration provided the APS starting was quickly dismissed because the with the capability to “pick-up” a stopped high inrush currents dictated that at least four of the six ship service generators need developing the required propulsion motor to be dedicated to the propulsion motor for torque and maintaining acceptable power starting. Low voltage starting was not quality from the primary power distribution feasible either since it could not develop the system or powering from a single dedicated required starting torque. A variable speed generator. The VSD solution was also drive (VSD), provided the capability of chosen to help solve the potential propeller developing full rated torque at start-up cavitation problem by providing the within the power capability of a single capability of lowering the propeller speed as generator. However, VSD power power is decreased, which was not possible electronics cabinets are relatively large and from a single speed propulsion motor. The difficult to locate in an existing ship design capability to vary shaft speed also allowed with limited space available. Moreover, in flexibility in controlling the transitions order to maintain the power quality between the gas turbine engine and APS to requirements for the ship service bus, VSDs include the propulsion motor as well gas typically require large phase shifting turbine engine. transformers and perhaps large passive filters. AUXILIARY PROPULSION SYSTEM DESIGN OPTIONS After considerable study, as indicated by Tables 3 and 4, the VSD design option was Once VSDs were chosen as the propulsion chosen as the method to achieve the required motor drive, a final study was undertaken to propulsion motor start-up torque because it determine the range of design solutions is affordable and an acceptable machinery possible as depicted in Table 5 (Reference arrangement was identified. Despite the 6). With regard to the VSD size, significant impact of VSD on ship arrangements, it is the best means of

TABLE 3 PERFORMANCE COMPARISON OF PROPULSION MOTOR STARTING OPTIONS

MOTOR MOTOR MOTOR QTY OF MIL SPEC STARTING DESIGN DIAMTR 4 MW PWR QUAL OPTIONS BASIS IN FIT AT GEN W/2 GEN SETS CURRENT 5000 HP SETS 50% LOADED

Full Voltage 6 x probably six yes Starting rated

Low Voltage not applicable since unable to develop required torque to turn a stopped shaft Starting (r, xfmr or soft)*

Variable Speed 1 x yes one yes Control (PWM) rated

Torque Assist 2 - 3 x probably at least yes Motor With Low rated two Voltage Starting

* indicates resistance, transformer and power electronics soft starting methods TABLE 4 IMPACT COMPARISON OF PROPULSION MOTOR STARTING OPTIONS

MOTOR SYS SYS SYS SYS STARTING SIZE WT COST RISK OPTIONS

Full Voltage 1 x 1 x 1 x none Starting

Low Voltage 2 – 3 x 2 – 3 x 2 – 3 x not feasible Starting (r, xfmr or soft)*

Variable Speed 3 – 4 x 3 – 4 x 4 – 5 x minimal Control (PWM)

Torque Assist Motor 1.5 x 1.5 x 2 – 3 x high With Low Voltage Starting

* indicates resistance, transformer and power electronics soft starting methods

TABLE 5* COMPARISON OF APS DESIGN OPTIONS+

APS COST SIZE IHD - IN-RUSH RISK TOTAL OPTIONS THD CURRENT VOLTS CONCERN

6 pulse w/filters 4 3 < 1 - < 1 no 1 8

12 pulse w/o filters 3 2 1.6 - 2.5 yes 3 8

24 pulse w/o filters 2 1 0.7 – 1.3 yes 2 5

Active rectifier 1 4 na no unsat na

* a rating of greater value means better performance + the MIL spec power quality requirement is individual and total harmonic distortion in terms of voltage of 3 % IHD and 5 % THD transformerless designs are expected to would also require development. For VSD result in lower converter size, but need designs incorporating transformers, twelve, further evaluation to ensure that the motor eighteen and twenty-four pulse rectifier insulation system will not be stressed. A designs could provide adequate power six-pulse rectifier requires substantial quality performance without filters. filtering to achieve the level of power Unfortunately, a very large single propulsion quality required on a naval ship. Passive transformer would be difficult to arrange filtering is space intensive and active within the limited height of the machinery filtering would require development. A spaces. Although a split design option pulse width modulated (PWM) rectifier or consisting of two propulsion transformers active front end converter is feasible, but equal to the rating of the required single transformer is possible, this option may be essential, all of the APS equipment, except just as difficult to locate within the the propulsion motor, was preliminarily machinery spaces due to the additional located in the adjacent AMR as indicated in switchgear necessary for two transformer the notional machinery arrangements connections. The actual selection of VSD (Figures 6 and 7). topology and technology will be left to the shipbuilder / vendor team during the detail PROPULSION SYSTEM CONCEPT design. OF OPERATIONS

By functioning as a non-mission essential The propulsion system concept of operations propulsion system, the APS can be (CONOPS) was developed by the ship commercial-off-the-shelf (COTS) based and design team (Reference 7) ahead of the obviate some demanding military system specifications as guidelines for requirements, such as Grade A shock defining the overall propulsion system qualification. This requirement to remain performance and APS system design, fully operational after a shock event has interface and control requirements. This been one of the key reasons preventing the was a necessary starting point since there application of modern COTS power were no mission requirements and TOC electronics based AC electric propulsion reduction goals are not firm performance systems in naval ships. However, the APS requirements. The propulsion system still requires Grade B shock qualification of CONOPS was also used to develop APS not injuring or being a safety hazard to purchase specifications and factory, personnel or causing other damage that dockside and sea trails requirements. The results in the failure of any Grade A shock propulsion system CONOPS will likely qualified equipment. Similarly, the APS has continue to be used as a basis for developing no acoustic or other survivability Machinery Control System (MCS) hardware performance requirements since it is and software requirements as well as designated as non-mission essential. Engineering Operating Station (EOS) operating procedures and technical Typically, the U.S. Navy requires that a instruction manuals. propulsion system for each shaft be located within a single machinery room to minimize The basic propulsion system CONOPS to its vulnerability. This ensures that damage describe the overall propulsion system outside a machinery compartment, other performance is as follows: than to the shafts or their bearings, does not · Power quality criteria disable an entire propulsion system. In the Integrated Generation and Propulsion Mode case of the APS, no such requirement limits - MIL-STD-1399 power quality must be its arrangement to within a single machinery retained under worst case conditions of two space. As previously mentioned, generators operating to support ship service incorporation of the VSD required a lot of loads equal to the rating of one generator space to locate equipment enclosures for during APS ship propulsion loading power electronic cabinets and perhaps (evaluated in terms of harmonic content and transformers and filters. The existing hull frequency and voltage response to ramp design did not allow locating all the required loading to rated propulsion power and step APS equipment in the forward MMR. unloading from rated propulsion power) Normally this would be an unacceptable design, but since the APS is not mission FIGURE 6 - Notional forward APS machinery arrangement in AMR for LHD 8

o Dedicated Generator Mode has to be invoked or - no specific power quality additional generators have requirements, except that to be placed on-line to the generator must be provide more power for ship compatible with APS ship propulsion propulsion loading in regard o Dedicated Generator Mode to not causing excessive - No restrictions on power heating of the generator usage rotor due to harmonic · Gas turbine engine and APS currents present capabilities and response characteristics · Power management philosophy o Each shaft may be powered o Integrated Generation and by either gas turbine engine Propulsion Mode - Ship or APS, but not both service power has priority simultaneously over ship propulsion power so manual load shedding DRIVE TRANSFORMER

FILTER

FIGURE 7 - Notional aft APS machinery arrangement in MMR 2 for LHD 8

FIGURE 7 - Notional aft APS machinery arrangement in MMR 2 for LHD 8

o The APS will be capable of or APS, but if one shaft is turning a dead shaft powered by the gas turbine o Gas turbine engine ship and the other shaft is propulsion capability is powered by the APS, the from a minimum shaft shaft powered by the gas speed corresponding to the turbine engine may not be gas turbine engine idle operated at shaft speeds speed to full rated shaft beyond the capability of the speed of 180 rpm APS to prevent o APS ship propulsion overspeeding the propulsion capability is from a minimal motor on the shaft powered shaft speed of 55 rpm, by the APS which matches the gas o Crashback by the gas turbine engine idle speed turbine engine or APS is (1050 rpm) and retains the performed by reversing the same propeller blade pitch propeller blade pitch angle, angle for both operational but the power of the APS is modes of propulsion, to a limited to the power maximum shaft speed available from that ship corresponding to the rated service bus if in the propulsion motor speed integrated generation and (1800 rpm) propulsion mode o Each shaft may be powered by either gas turbine engine · APS control, local and remote APS CONTROL o Control is normally remote from either the bridge or The present design provides for normal EOS control of the electric plant and APS (Figure o Local control always 8) from a Machinery Control System requires knowledge of the (MCS). The MCS will also provide remote propeller blade pitch angle monitoring and remote control of and, if in the integrated propulsion, auxiliary, fuel, fuel fill and generation and prolusion transfer, damage control, and ballast mode, the quantity of systems. The MCS includes multi-function generators operating workstations, data acquisition units and local · Recommended APS configurations operating panels, which communicate with for maximum propulsion capability each other via a fiber-optic MCS-LAN. The or maximum fuel economy MCS remotely controls and monitors all o Integrated generation and aspects of the electric plant and APS. The propulsion plant mode MCS also incorporates a power management provides the most system that prevents inadvertent ship service economical operation load shedding or overloading of diesel o Dedicated generator mode generators. This ensures optimum provides the maximum utilization of the power available from the maneuverability operation on-line diesel generators when an APS is · Propulsion plant transitions from connected into a ship service bus. The MCS gas turbine engine to APS and from monitors on-line generating capacity for APS to gas turbine engine each ship service bus, ship service loads per o Propulsion transition from ship service bus, APS load per ship service gas turbine engine to APS bus or dedicated generator and shaft must be made within the propulsion power control lever position. capability of the APS and When the shaft propulsion power control power transfer from the gas lever is moved to a position that would turbine engine to the APS require more power to the APS than the on- does not occur until the gas line generators are capable of delivering turbine engine is shutdown from a ship service bus, power to the ships since the APS is applied by service loads are maintained while the MCS an overrunning clutch automatically limits the APS power to the o Propulsion transition from highest level possible within the full rated APS to gas turbine engine capacity of the on-line generators. may be made at any shaft Similarly, when the power demand from the speed within the capability ships service loads increases and causes the of the APS and power total power demand (ships service and APS) transfer from the APS to the to exceed the capacity of the on-line gas turbine engine does not generators, the MCS automatically reduces occur until the propulsion the power delivered to the APS. Likewise, motor is commanded to a when the generating capacity decreases, the slower speed than the gas MCS automatically reduces the power turbine engine is providing available to the APS. Whenever MCS is since the gas turbine engine limiting the power demand of the APS, an is applied by an overrunning alarm is initiated to indicate that the MCS is clutch limiting power to the APS and that additional generators should be placed on- line or load shedding applied. When additional generating capacity is brought on- line, either manually or automatically, or command for shaft propulsion unless power load shedding is manually invoked; the limiting continues to occur. MCS automatically increases the power delivered to the APS to the ordered

MCS Interface MCS Interface, Modbus Hardwired Filter cooling fan control, seawater valve control, Transformer cooling fan PC interface temperature, over current, ground control, seawater valve control, Main Circuit Breaker monitoring Modem Control and Monitor temperature monitoring

Service Power 450 V Filter HEAT XFMR XCHGR VSD CONTROLS 120 Volt Main Lighting circuit breaker Turning Gear Interlock

R/G oil pressure Switch Motor Monitoring: Pressures Temperatures Speed Seawater Vibration

Brake Heater Controller Motor

Heater

Cooling fan controller Cooling Fan

L/O L/O Return In

FIGURE 8 - APS control diagram design concept for LHD 8

Present day COTS variable speed drive CONCLUSIONS systems are designed for remote control through a data interface protocol. Most also Through the elimination of the steam plant include a local operating panel for control, and the incorporation of main gas turbine monitoring and troubleshooting. The APS propulsion with auxiliary electric will utilize this local operator interface as a propulsion, the LHD 8 will have significant secondary control station in the event the TOC savings as compared to earlier ships of MCS or data interface is inoperable. The the Wasp (LHD 1) class. These savings are VSD will also incorporate an interface port principally through the reduction of crew by for a portable computer (laptop) as a backup over 80 personnel and significant to the local operator panel. Except for improvements in propulsion plant propeller blade pitch angle and power efficiency. The incorporation of the APS available, either of these two local control enables fuel efficient diesel generator to methods will allow the operator to provide propulsion power at low speeds completely control the APS including such when gas turbine engines are least efficient. functions as breaker closure, cooling water Feedback from fleet operators led to valve sequencing, motor vibration incorporating a VSD to start a stopped shaft monitoring and component fault diagnosis. using the APS alone. LHD 8 also includes an AC ZEDS featuring a 4160 VAC power generation and primary distribution system 5. LHD-8 Loiter Motor Study, Alstom and a 450 VAC secondary distribution report, NAVSEA IPS Technical system. The AC ZEDS provides a more Instruction 004, 12 February 2000 survivable and reconfigurable power 6. LHD-8 Loiter Motor Study II, Alstom distribution system with less weight than a report, NAVSEA IPS Technical traditional radial distribution system. A Instruction 006, 24 May 2001 modern MCS will integrate control of the 7. Concept of Operations for LHD 8 APS and AC ZEDS and provide the LHD 8 Propulsion System, NAVSEA, May with significant capability to monitor and 2001 control the propulsion and electric plant. In summary, although eliminating steam and BIOGRAPHIES reducing TOC was the motivation for changing the propulsion and electrical plant Mr. Dalton (MSEE – University of Miami, on LHD 8, the resulting design, based on Florida – ’75) has been with NAVSEA for sound engineering and economic analysis, is over fourteen years of his past 28 years in a significant step toward the all electric ship the marine industry. He began his for the U.S. Navy. government service with the US Department of Transportation – Maritime Administration ACKNOWLEDGEMENTS and then worked for the commercial firms of Gibbs & Cox, Inc., Rosenblatt & Sons, Inc. The authors would like to acknowledge the and Advanced Marine Enterprises, Inc. and efforts of Northrop Grumman - Ship Frank E. Basil, Inc. before returning to Systems - Ingalls Operations and Computer government service with NAVSEA in 1987. Science Corporation (CSC) in the NAVSEA Mr. Dalton has been involved with typical sponsored development of the propulsion ship service electric plant design support as and electric plant designs. The authors well as various integrated electric plant ship would also like to recognize the support designs throughout his career. In particular, from General Electric Company in the he has been supporting the Integrated Power NAVSEA sponsored gas turbine engine System (IPS) developmental program over installation and reduction gear design effort the past seven years. His initial duties for and Alstom Power Systems in the NAVSEA IPS program office were technical review sponsored APS design effort. and oversight of the Full Scale Advanced Development (FSAD) testing phase of IPS REFERENCES at the land based test site (LBES) facility of Naval Surface Warface Center – Ship 1. Work Task Assignment WTA-2204- Systems Engineering Service (NSWC- 017, Northrop Grumman - Ship Systems SSES) in Philadelphia, PA. He presently - Ingalls Operations report, LHD7 serves in the IPS program office as the Alternative Propulsion System, 19 May Assistant Program Manager for Mission 1997 Interface Loads in an effort to provide the 2. Work Task Assignment WTA-2204- combat system with the type, quality, 024, Northrop Grumman - Ship Systems quantity and survivability of power required - Ingalls Operations report, LHD 7 Gas from the IPS architecture. Turbine Propulsion Installation, 4 September 1998 Mr. Boughner (EET - Penn State 3. Loiter Motor Study for LHD-8, CSC University, ‘91) is a retired Coast Guard report, October 2000 Engineering Duty Officer with 24 years of 4. Loiter Motor Study II for LHD 8, CSC marine service. Prior USCG assignments report, February 2001 included Manager, Gas Turbine Propulsion and Auxiliary Systems Life-Cycle Support and In-Service Engineering, Executive Officer and Ship Repair and Construction Officer. His present responsibility at the Propulsion and Power System Department, NAVSEA-Philadelphia, PA is USN integrated product team leader for the LHD 8 propulsion system.

Mr. Mako (BSEE - Pennsylvania State University - ‘86) has been an electrical engineer with the Naval Surface Warfare Center, Carderock Division – Ship Systems Engineering Station (NSWCCD-SSES) since April 1987. From 1987 to 1996, Mr. Mako was an in-service engineer for Navy shipboard 60 Hz power generation and distribution systems. He was promoted to a senior technical special position for Electric Power Systems in 1996. From 1998 to 2001, Mr. Mako served as the supervisor for the Diesel and Steam Turbine Electric Power Systems Section. Mr. Mako’s present duties as a senior engineer in the Electric Power System Branch of the Propulsion and Power Systems Department include the USN integrated product team lead for the LHD 8 electrical power generation and distribution system.

Dr. Doerry (Ph.D. - Naval Electrical Power Systems – MIT - '91) is currently a Commander in the U.S. Navy and the Assistant Acquisition Manager for LHDs in PMS 377. As an Engineering Duty Officer, he has recently served in the Naval Sea Systems Command as the Technical Director for IPS from 1991 to 1995 and Ship Design Manager for JCC(X) from 1998 to 2001. He also served as an Assistant Project Officer for Aircraft Carrier repair and new construction at SUPSHIP Newport News from 1995 to 1998.