By Keith Henderson at October 17, 2010 15:25
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Earlier this month a new product called Amperium was announced by the American Superconductor Corp. (AMSC), of Devens, Massachusetts. It is the name they have given to a second generation (2G) high temperature superconductor (HTS) wire.

The wire is ribbon-shaped and comprises a core of 2G HTS material clad with thin strips of metal such as copper or stainless steel and has an approximate width of 4.8 mm and thickness of 0.2 mm ( 0.2 x 0.008 inch)

It has the remarkable ability to conduct more than 100 times the electrical current (amperage) of copper wire of the same dimensions. Electrical systems incorporating Amperium wire instead of copper are significantly more compact and lighter than their copper based equivalent. There are wide applications for Amperium in many industries but what is particularly interesting for the marine segment is its use in ship propulsion motors and generators and for naval ships degaussing systems.

Basically a superconductor is a substance that below a critical temperature, its electrical resistance falls away to zero making it in effect a perfect conductor. It is a physical fact although a theory to explain high-temperature superconductivity still eludes modern science!

The term “high temperature” is a relevant one and also needs some explanation. It refers to a high temperature on the Kelvin temperature scale and in this context means a temperature higher than that of the freely available coolant liquid nitrogen, which boils at 77 K or -196 deg C (-321 deg F).

Translating these features into tangible benefits, by using superconductors a new generation of AC synchronous machines can be made with significant advantages over conventional AC synchronous and induction machines.

In conventional AC synchronous motors the rotor current is continually varied. These constant changes create fatigue in the rotor windings ultimately causing failure. The nature of the low temperature controlled HTS systems is such that the machines operate at near constant temperature. This eliminates a primary cause of failure therefore offers greater reliability and longer MTBF.

AMSC has already delivered electric propulsion motors to the US Navy in sizes of 5MW at 230 rpm and 36.5MW at 120 rpm. The 36.5MW motor is less than half the size of the conventional motors used on the USS Zumwalt (DDG-1000) destroyer and is approximately 200 tonnes lighter.

The rapidly increasing use of diesel electric, hybrid and integrated electric propulsion systems for commercial and naval ships looks to benefit from this superconductor technology in the years ahead.

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