Zumwalt-class destroyer DDG 1000, a new class of multi-mission US Navy surface combatant ship designed to operate as part of a joint maritime fleet, assisting Marine strike forces ashore as well as performing littoral, air and sub-surface warfare.
The DDG 1000 will be powered by Rolls-Royce MT30 gas turbines, which is based upon the Rolls-Royce “Trent” engine that powers the Boeing 777 airliner. The aviation version of the engine has a demonstrated reliability of 99.98%. The ‘marinized’ version of the MT30 has 80% commonality with the Trent 800 but is shock-mounted and has different blade coatings for operation in a saltwater environment. This engine is also serving today aboard the new Littoral Combat Ship USS Freedom (LCS 1). Zumwalt will also have a smaller gas turbine, the Rolls-Royce 4500. DDG 1000 power generators produce 4,160 volts alternating current (AC), which is rectified to direct current (DC) that allows ship service power distribution to be tailored to the ship’s needs. There are three primary advantages to DC. First, DC uses solid state power conversion that supplies loads which are con- verted back to AC and is a cleaner way to supply power. Secondly, many of the combat systems’ loads are DC. Finally, it enables power to be shared and auctioned. DC enables uninter- rupted power even in the occurrence of a casualty. The DDG 1000 will employ fixed pitch propellers. Controllable pitch propellers and their associated complex hydraulics are not required since the motor, and thus the shaft, can be electrically reversed. But novel approaches to propulsion are being considered for future combatants. Other new naval ships are also adopting integrated electric power systems. The next-generation CVN 21 aircraft carrier, the USS Gerald Ford , will have a newly designed nuclear power plant and all-electric systems and propulsion. The next amphibious assault ship, the USS Makin Island (LHA 6), will feature a combined gas turbine and electric propulsion system. The surface combatant IPS propulsion engineering develop- ment model (EDM) for DDG 1000 is being tested at the Land- Based Test Site (LBTS) at the Ships Systems Engineering Station in Philadelphia. The test site has been used to evaluate different configurations and motors. The test program validates key system metrics such as torque, speed and power output, and specific fuel consumption for the various configurations. The Navy has tested the 18-megawatt (MW) advanced induc- tion motor (AIM), which will be the baseline for DDG 1000, produced by Alstom at the LBTS. This is essentially the same system installed on the Royal Navy’s new Type 45 destroyer, the HMS Daring, which has just been commissioned. The IPS features Integrated Fight through Power (IFTP), a fully automated DC Zonal Electric Distribution System (DC ZEDS) that provides flexible, reliable, high quality power to all shipboard loads. Other configurations are also being tested. The IPS system is fully automated with little operator intrusion.
The DDG 1000 engineering plant layout is relatively conventional because of the air intake, exhaust, and drive arrangement. DRS Technologies and General Atomics Electromagnetic Systems are developing a hybrid electric drive which permits a smaller service gas turbine to power a permanent magnet motor that can power the ship at slow or “loiter” speeds. Using a small- er turbine can result in significant fuel savings. Furthermore, the motor can be reversed to function as a generator when propul- sion gas turbines are online. Overall, integrated electric drive offers ship designers and operators a plant flexibility that does not exist with mechanical drive systems.
However, trade studies must be used to select the appropriate power and propulsion system for each ship. There are some ships with partial electric drive or hybrid elec- tric drive mechanical drive systems. These include the opera- tional Type 23 frigates; the European Multi-Mission Frigates (FREMM), a joint program between France and Italy, which are now in construction for France, Italy, Morocco and Greece; and the amphibious assault ship USS Makin Island (LHD 8), now undergoing trials. Despite the advantages, there are not a lot of electric drive warships in service.
The new generation of electric ships has yet to prove themselves. The DDG 1000, Royal Navy Type 45, and T-AKE propositioning ships are examples of all-electric warships, but they are still in the design phase, under construction, or just entering service. Even though there is significant interest in electric drive systems, there are only a relatively small number of ships actually under construction and in operation.
Thursday, August 13, 2009