..the introduction of the electric motor would eliminate the need for a reduction gear. Electric drive also would eliminate the need for a lengthy shaft that couples the prime mover to the propeller, he said. This is important for combat purposes, because the shaft creates a direct path for engine noise into the water, increasing the ship's acoustic signature.
For electric drive, the prime movers-which now are installed amidships-can be linked to generators and then to the motors by a flexible cable, permitting them to be positioned elsewhere in the ship, creating extra capacity for fuel and ordnance.
The demand for power for ship's propulsion "has reached a plateau," Carnavale said, "but the need for power for ships' systems continues to increase geometrically, with no end in sight.
"In today's warships," he added, "half of the propulsion power is used to get the last 10 percent of speed-a ship traveling at 30 knots could go 27 knots on half the power, potentially freeing up that power for other needs."
Numerous Operational Advantages
An IED [integrated electric drive system], Carnavale said, would power both the propulsion motors and the ship systems through a powerconversion system that would regulate and transfer power at the levels required throughout the ship to power weapons, sensors, and other systems.
Discussing the impact of electric drive on a ship's warfighting capabilities, Mullen said that the move to IED will "revolutionize the way we do business." The reduction in a ship's acoustic signature afforded by electric drive, he said, will permit the ship to remain in hostile waters longer without being detected and to operate in a more vigorous manner. Because the quieter ship will be more difficult to detect, it will be more survivable and more effective in carrying out combat operations.
The freedom to position elements of an lED power system throughout the ship, Mullen said, will dramatically improve survivability if the ship takes a hit from enemy fire. The integration of the propulsion system and the ship's "hotel" power will enable the commander to reroute power in the event of damage, permitting the ship to continue to fight.
The efficiency of space arrangements will require fewer personnel to carry out damage control; therefore, fewer lives will be placed at risk. The introduction of computer-based power-conversion and damage-control systems also will reduce the need for auxiliary mechanical- and hydraulics-based damage control systems. .. Electro Dynamic has designed a 6,000 horsepower PMM motor that is being built at WEMD for the Navy's LSV-2 demonstration submarine. .."This first in what we are confident will be a series of contracts from the US Navy, will enable us to continue optimizing HTS motors and power electronic drives for use in future surface combatants as well as other classes of naval vessels. It will also strengthen the foundation for adoption of these revolutionary advanced motors in a broad set of commercial ship types," said Greg Yurek, chief executive officer and founder of American Superconductor.
About American Superconductor's HTS Motors
The 36.5-MW HTS motor undergoing factory testing in Philadelphia has the potential to change the way naval warships fight due to the dramatic reductions in size and weight it offers. The motor weighs approximately 75 metric tons and is about one-third the weight and one-half the size of conventional copper-based propulsion motors of the same power and torque rating. This enables Navy ships to carry more fuel and war fighting capabilities as well as expanded crew's quarters. The HTS motor offers a significant reduction in noise, and thus a smaller acoustic signature, compared to current motors In addition, HTS motors operate with higher fuel efficiency over the entire mission profile of a warship. American Superconductor expects the motor to have lower maintenance costs than their conventional copper and permanent magnet motor counterparts. The substantial advantages offered by HTS ship propulsion motors are expected to be provided at a price equivalent to conventional motors of the same power and torque rating. ..
In general, the same line of reasoning that applies to surface ship power and propulsion systems also applies to submarines. Optimization of submarine systems will be driven by stealth, safety, power density, and other requirements that differentiate surface and undersea vehicles. Submarine power and propulsion system technologies of the future will include the following:
Very low harmonic motor controllers;
High-power-density and high-performance solid-state inverters and converters and the components thereof;
Electrical substitutes for systems and components that now rely on fluid transport for energy and actuation, e.g., electric actuators, electromagnetic launchers, and thermoelectric coolers;
Motors and generators with very low acoustic and magnetic signatures, including versions that can operate submerged in seawater at high pressure; and
New technologies for motors and generators such as superconducting magnets, cryogenic coolers, current collectors, high-field permanent magnets, liquid cooling, and active noise control.
A HTS high-torque drive motor can be one-fourth the size of a permanent magnet motor, and its efficiency can be high enough to compete with existing reduction gear/steam turbine systems. HTS motors and generators can also be quieter because the high-density magnetic fields produced allow elimination of iron cores, simplification of armature designs, and elimination of other components that create noise. ..Future submarine power and propulsion technology will inevitably move toward increased reliance on electricity. Advanced dc power distribution using high-speed, turbine-driven rectified alternators feeding solid-state inverters through a dc distribution bus is already targeted to the new nuclear-powered submarine (SSN). Electric propulsion offers an affordable opportunity to enable new propulsor concepts that can improve signature. Studies over the past few years indicate that integration of the electric-propulsion and ship-service power-generation functions at the prime mover can result in reduced ship size and displacement because of fewer power plant components and improvements in their arrangement. Studies have also shown that eliminating centralized hydraulic systems and transporting energy electrically to the point of use will result in up to 70 tons of weight savings and potential cost reduction. In the future, this concept might be extended to other systems, such as heating, ventilation, and air conditioning.
