Feature 6 | PROPULSION IPS for DDG 1000 tested to full load
Working in partnership with the US Navy, power conversion specialist Converteam has successfully tested the DDG 1000 destroyer’s high-voltage Integrated Power System (IPS) to full power at a land-based test site in Philadelphia, Pennsylvania. An IPS generates the total ship electric power requirements, then distributes and converts it for all ship loads, including electric propulsion, combat systems and ship services. This unique architecture provides improvements in ship survivability, design flexibility, reduced signatures, and the potential of reduced life cycle and operational costs. DDG 1000 is the first US Navy surface combatant to use this technology – an all-electric architecture providing electric power for both propulsion and ship services. As the integrated power systems provider, Converteam is responsible for the entire programme’s high-voltage system design, commissioning and testing at the land-based site. The tests demonstrated full power operations of the IPS, which is a major milestone prior to delivery of equipment to the ship. The technology tested included one of two shipboard shaft lines; one main and one auxiliary gas turbine generator set, all four high-voltage switchboards, harmonic filters, two of four shipboard electrical zones of the Integrated Fight Through Power (IFTP) conversion equipment, and one of the two propulsion tandem advanced induction motors with their associated variable speed drives.
Of this, Converteam supplied systems integration know-how and hardware which includes the propulsion motors, variable speed drives, high-voltage switchboards and harmonic filters for the main and auxiliary turbine-generators. More recently, Converteam has been selected as the supplier of the complete electric power, propulsion and vessel automation system for the Mobile Landing Platform (MLP) programme. The MLP adds to Converteam’s experience with the US Navy’s IPS fleet, which includes DDG 1000, T-AKE, LHD 8 and LHA 6.
The MLPs are a new type of auxiliary support ship intended to serve as a transfer station or floating pier at sea, improving the US military’s ability to deliver equipment and cargo from ship-to-shore when friendly bases not available. Under contract, General Dynamics NASSCO has commissioned Converteam to provide a highly capable and flexible IPS including the tandem propulsion motor powered by variable frequency drives, as well as the harmonic filters, generators, high-voltage switchboards, transformers, automation, azimuthing thruster with dynamic positioning capability, and associated thruster drive and motor. Currently, three classes of MLP are planned, and are due to be delivered between May 2013 and December 2014.
gas to water phase and the resulting forces in nozzle flows. Tangren et al (1949) modelled homogenous mixed flows, and Witte (1969) developed solutions for mixed flows with separate phases, allowing unequal velocities, pressures and temperatures. Recently, Gowing et al (2010) measured
the efficiency of the energy exchange from two phase flows in different nozzles and showed efficiencies up to 70%. Te one- dimensional
flow equations were
used by Amos et al (1973) to predict the performance of air-augmented waterjets, and Stansell et al (1976) extended the analysis to include a gas turbine powerplant and the effect of extracting compressed gas from various turbine stages.
Predicted thrust augmentation Trust augmentation was predicted to be higher for higher craft speeds and higher pump flow rates. Tsai et al (2005) presented an experimental evaluation of a waterjet ski with an added air injection system. Te maximum thrust
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augmentation was about 10% for a bollard condition, but close to 100% for the highest speed and void fraction (0.5). Gany et al (2008) showed thrust increases of 25-50% with an air-augmented waterjet ski, and the results matched predictions assuming energy transfer efficiencies of about 70%. Tese thrust benefits were measured in a bollard condition and the nozzles were adjusted for the different engine speeds tested. In these jet ski tests, the effects of the air injection on the performance of the primary pump, shaſt power, and overall energy budget were not measured. Gowing explained that the study was
intended to explore those effects as well as measure thrust augmentation and took the form of a small boat tow which was attached a waterjet pump. Te boat was tested in a bollard condition, attached to a fixture through a force gage. Te boat (Ron Chapman Shipwrights, LA) had a flat bottom and transom to accommodate a mixed-flow sizing the nozzles, two criteria were used.
Mr Gowing’s full paper can be found at:
http://www.marinepropulsors.com/smp/files/ downloads/smp11/Paper/
index.htm; but his study concluded that it is possible to increase the thrust of a waterjet by air injection but that the injection process can strongly affect the primary pump performance.
Affect on pump performance Te injection process can reduce the pump flow, increase its headrise, and affect the pump efficiency. “Tese pump interactions can have as much effect on the thrust as the air augmentation process itself,” he explained. “Te sensitivity of the pump to injection may depend on the pump design, however.” “The nozzle size must be increased
from its water-only design point to allow thrust augmentation by injection. Using injection, the thrust can be increased using less rotor shaſt power than can be achieved by higher pump speed alone. But the power required for the injected air is significant and the total power required for thrust augmentation is more than if the rotor speed is simply increased.” WT
Warship Technology October 2011
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