FAQ

HTS Motors

How do motors work?

Motors are machines that convert electrical energy into mechanical energy using magnetic forces. When current is passed through a wire loop that lies in a magnetic field, a turning force, or torque, is created that causes the loop to rotate. In motors, this rotating motion is transmitted to a shaft. This rotational energy is then utilized for useful work in the form of mechanical power. Industrial motors are used for running pumps, fans, and compressors as well as in equipment involved in the handling and processing of manufactured materials. Marine propulsion motors are used to propel commercial vessels and warships.

The basic features of modern conventional AC (alternating current) and DC (direct current) electric motors were first designed in the 1890s, and the underlying technology has not changed significantly in the past fifty years. Despite the lengthy period of time in which motors have been in development, motors are still far from being perfectly efficient converters of electrical to mechanical energy. The principal causes of lost power in motors come from the electrical resistance of the wire and from mechanical friction.

According to the U.S. Department of Energy, motors account for 70% of all energy consumed by the domestic manufacturing sector and use over 55% of the total electric energy generated in this country. Large electric motors, those greater than 1000 horsepower, consume over 25% of the total generated electric energy. With some minor exceptions, nearly all cruise ships today are being built with electrical propulsion, and many other types of commercial vessels and warships are now also adopting marine motors as their primary source of motive power.

How do superconducting motors differ from conventional motors?

Superconducting motors are AC synchronous motors that employ HTS (high temperature superconductor) windings in place of conventional copper coils in their rotors. Because HTS wire can carry significantly larger currents than can copper wire, these windings are capable of generating much more powerful magnetic fields in a given volume of space. Advances in coil design make it possible for a superconducting machine to match the power output of an equally rated conventional motor with as little as one-third the size and one-half the weight. The smaller size and compact nature of superconducting motors allows them to be manufactured at lower cost than equivalent conventional motors.

Additionally, the replacement of conventional copper rotor windings with non-resistant HTS coils results in sharply reduced electrical losses in the rotor. The increased electrical current in the motor's rotor results ultimately in the increased power density (and hence smaller size). The HTS motor's smaller size means it is significantly lighter and therefore can be utilized in new and innovative ways. In addition, the motor's increased efficiency results in lower operating costs than conventional motors.

HTS AC synchronous motors may have no iron teeth in the stator windings, not only contributing to their smaller size and lighter weight, but also removing a significant source of motor noise.

Where and how will superconducting motors be used?

An important and rapidly growing use for HTS motors will be in transportation applications, particularly naval and commercial ship propulsion, where size and weight savings will provide a key benefit by increasing design flexibility and opening up limited space for other uses. A marine engineering "revolution" is taking place today in the maritime industry, and more and more ships are being built with electrical motors as their primary means of propulsion as the benefits of electric propulsion are being verified and new types of innovative ship designs incorporating electric propulsion are introduced.

What is the market potential?

It is estimated that the worldwide addressable market for large synchronous motors is over $1.2 billion annually. HTS motors will offer an attractive economic alternative to synchronous motors by virtue of their lower first (acquisition) cost and their reduced ongoing (operating) cost. Electric marine propulsion and electric power generation is a market of approximately $250 million that is growing strongly. Some studies indicate that this market will quadruple over the next decade. Superconducting specialty motors will be particularly attractive for niche applications in which size and weight considerations come into play.

What are the benefits?

• High Power Density: The HTS field winding produces magnetic fields higher than those conventional machines resulting in smaller size and weight.

• High Partial Load Efficiency:  HTS motors have higher efficiency at part load (down to 5% of full speed) that results in savings in fuel use and operating cost.  The advantage in efficiency can be over 10% at low speed.

• Low Noise:  HTS motors have lower sound emissions than conventional machines.

• Low Synchronous Reactance: HTS air-core motors are characterized by a low synchronous reactance which results in operation at very small load angles.  Operating at a small load angle provides greater stiffness during the transient and hunting oscillations.

• Harmonics:  HTS motors tolerate power grids with high harmonic content.

• Cyclic load insensitivity:  HTS motor field windings operate at nearly constant temperature unlike conventional motors and, therefore, are not subject to thermal fatigue.

• Maintenance:  HTS motors compared to conventional motors will not require the common overhaul, rewinding or re-insulation.

HTS Generators

What is an HTS Generator?

An AC synchronous generator converts rotational mechanical input energy, such as that from a steam or gas turbine, diesel engine or wind turbine into electricity. It does this by rotating a field (the rotor), which produces voltage in stationary CU stator conductors. The generator field can be produced with copper windings or permanent magnets--and now with HTS superconductors for significant advantages. In large machines, mechanical considerations and the desire to vary the level of field produced typically favor the use of copper windings over permanent magnets.

Where and how are they used?

The primary applications are wherever power is generated:  utility, hydro, wind and particularly marine propulsion where, similar to the motors above, size, weight and efficiency are operating and partial load conditions with reduced noise and enhanced shock capability are very important.

What are the benefits?

• High Power Density: The HTS field winding produces magnetic fields higher than those conventional machines resulting in smaller size and weight.
  
• High Partial Load Efficiency:  HTS generators have higher efficiency at part load (down to 10% of full load), that results in savings in fuel use and operating cost.  The advantage in efficiency can be over 10% at light load.
  
• Low Noise:  HTS motors have lower sound emissions than conventional machines.
  
• Low Synchronous Reactance: HTS air-core motors are characterized by a low synchronous reactance which results in operation at very small load angles.  Operating at a small load angle provides greater stiffness during the transient and hunting oscillations.
  
• Harmonics:  HTS generators produce power with very low harmonics.
  
• Cyclic load insensitivity:  HTS field windings operate at nearly constant temperature unlike conventional motors and, therefore, are not subject to thermal fatigue.
   
• Maintenance:  HTS generators compared to conventional generators will not require the common overhaul, rewinding or re-insulation.