HTS Utility Generators

Utility generators are a class of generators -- either merchant or utility owned -- designed to supply power directly to the transmission grid. These machines usually are 100 MVA or larger in size.

By incorporating HTS wire into utility generators, designers can reduce operating costs, lower up-front costs and improve reactive power compensation. Significant advantages of these machines center on their:

Greater Efficiency Conventional 100 MVA generators operate at approximately 98.5 percent efficiency at full load. The net efficiency improvement of HTS generators, including refrigeration, is about 0.3-0.5 percent. In continuous operation, annual savings can exceed $100,000/year -- with returns even greater as the size of the generator increases.  This allows greater flexibility to adjust the output of a generation plant without shutting down generators or losing efficiency.

Longer Life Thermal cycling is a major factor in the breakdown of the coils in conventional copper rotors.  This is eliminated with HTS rotor designs, which are operated at constant temperature.  The reduction of thermal expansion and contraction in the field winding coils eliminates shear stresses to the electrical insulation and prevents premature insulation failure due to mechanical fretting.

Size and Weight The high current density of HTS wires in the field windings generates high magnetic fields in the stator. This enables designs that are one half to two thirds smaller than conventional generators.

Lower Up-front Costs Currently, HTS wire is more expensive than copper and the incorporation of HTS technology into a generator requires the addition of refrigeration equipment. Savings in the following areas, however, can offset these costs:

Significant reductions in the size of the generator reduces the material requirements of the non-superconducting portions of the generator.

• Simplicity of the HTS rotor design, and the reduced size and weight of the machine, translates into a less costly manufacturing process.
• Smaller size makes transport of the generator to customer sites easier. Generators with high power ratings can be shipped fully assembled, reducing transportation costs and eliminating onsite assembly. With smaller generators, shipment may be possible by truck instead of by rail.
• Lower direct and indirect installation costs. The diminished weight and size of an HTS generator, reduces the floor space and the required support architecture surrounding it, making them less expensive to install than conventional systems.

Improved Reactive Power Compensation HTS generators operate at a much lower power factor than conventional generators, permitting them to supply leading or lagging VARs up to their rated load. Since HTS generators have very low synchronous reactance (~0.35 pu), it is much simpler to achieve required voltage regulation without a need for fast exciters. Their transient and sub-transient reactances are similar to conventional machines, which permit use of existing monitoring and protection equipment.

General Electric is currently developing an HTS utility generator under the USDOE Superconductivity Partnership Initiative.  The first 100 MVA prototype, Powered by AMSC wire,  is planned for operation in 2007.