Newport News Pursues The Electric Drive
Newport News Shipbuilding (NNS), with its partner Kaman Electromagnetics Corporation, has developed and patented an Integrated Power System (IPS), an electric drive system technology NNS says offers multiple benefits for both commercial and military ships.
Among those touted benefits are significantly less total system weight and volume; flexible arrangement options; module commonality among ship classes; reduced spare requirements; improved construction efficiencies; standard machinery controls; zonal electrical distribution for ship services; heater machinery component reliability; simplified logistics support; and increased compliance with the environmental requirements for reduced emissions. All of this, according to NNS, leads to reduced acquisition and life-cycle costs.
The Navy estimates a 40,000-hp electric drive propulsion package is less than one-third the volume of the diesel equivalent. That greater flexibility of arrangement options is enhanced by the fact that the prime mover need not be directly attached to the propulsion shaft.
The Navy also says the 40,000-hp electric drive is less than one quarter the weight of a diesel with the same power.
According to NNS, engineering case studies comparing IPS to other propulsion systems estimate anywhere from $2 million (for an LNG carrier) to $29 million (for a military vessel) in acquisition cost savings from the new technology, and between $1 million and $4 million annually in life-cycle costs.
The System NNS's Integrated Power System is configured as follows: compact permanent magnet generators produce high-frequency AC power that is converted to DC power by modular rectifiers located at the generator.
That DC power is then distributed by bus duct to the propulsion motor inverters located on the motors.
DC power is also distributed to the ships service system by two bus ducts that run the length of the ship. Vital ships service loads are powered from both buses through electronic transfer devices. Inverters located at the load convert the DC power to whatever type and quality AC power is required. The rectifier and inverters also provide circuit protection, eliminating the need for mechanical circuit breakers at their locations.
When used to supply dedicated loads, the inverters incorporate the functions of variable speed motor controllers and circuit breakers, thereby eliminating these components.
One prime mover develops power for both ships service and ship pro- pulsion, using the same basic control and distribution system, reducing the number of prime power sources on a ship.
Making the pursuit of this technology feasible were certain recent advances in solid-state electronics and permanent magnet technology.
NNS says that by developing highperformance electrical hardware — high-power density motors, generators, inverters, rectifiers, controls and distribution systems — they are making the theoretical technology real. NNS has renamed these sets of hardware, now calling them power generation modules, propulsion motor modules and electric power transmission distribution conversion modules.
The modules are common across ship classes; specific ship service requirements are met by installing a varying number of given function modules — eliminating the need for separate ships service generators and auxiliary systems.
Permanent Magnet Generator Under contract to the U.S. Navy, the NNS/KEC team is developing an IPS permanent magnet generator which will be directly shafted to the prime mover using high-strength permanent magnets and high rotation speed. The generator is configured as a radial cup with the rotor outside the stator, and with the permanent magnets attached to the inside of the cup. Propulsion-derived ships service power is obtained from the common high frequency generator that also supplies electric drive propulsion.
Direct Current Zonal Power Distribution DC power distribution became feasible with the development of the Insulated Gate Bipolar Transistor (IGBT), which can switch high levels of power at high speed, permitting the use of pulse-width modulation to invert DC power to the type of high-quality AC power desired. The same inverter module can produce whatever type of power output is required, simply by changing the software.
Propulsion Motor The electric propulsion motor is an axial gap, permanent magnet design that employs pulse-width modulated inverters to control the wave shape of the stator current.
Both the generator and the propulsion motor use the same permanent magnet material — neodymiumiron- boron.
The Time Frame Tests have been conducted on 20, 100-, and 700-hpprototypes. A3,000- hp scaled prototype of a 25,000-hp motor is scheduled for testing this year. The final phase of the development project will be to build and test the full-scale motor.
NNS says that its current prototype development of the IPS system will allow full-scale installation in both military and commercial surface ships by 1998.
For more information on NNS Circle 78 on Reader Service Card
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