Electric Generators for Direct Coupled High Speed Turbo Generators in Distributed Power Systems

Abstract

This article addresses various technical challenges in developing
high speed, lightweight electric generators for applications in direct
coupled high speed generators for distributed power systems. These
challenges involve the technologies of electromagnetics, thermodynam-
ics, rotor dynamics, and engineering assembly practices. How those chal-
lenges are being addressed and the results of activities to date relating to
generators from several hundred kilowatts to a few megawatts will be
discussed. Current status and the test data relating to these generators
will be presented.
While the requirements of power and voltage levels as well as the
duty cycle vary, the applicable generator technology is mainly impacted
by the power level. The electric generator is typically driven by a high
speed turbine. The operating speeds of the turbine and the mechanical
and thermal interfaces with the generator have a substantial impact on
the design details of the generator.
The best approach in interfacing the high speed turbine to the gen-
erator is to directly couple the two by means of a mechanical coupling
and exclude the need for gear, belt or other mechanical transmission
systems. The high speed turbine operates most ef ficiently at their rated
speed, which varies with rated power output. Thus while a typical 200
kW turbine may operate at 60000 rpm, a MW class turbine may oper-
ate in the range of 15000 rpm to 30000 rpm. It is often details such as
the coupling and mounting arrangement and the suitability of coolants
and lubricants that affect the generator design and impact the weight

and size of the final product. Selection of the appropriate generator
technology is highly dependent on the operating speed requirements.
Examples of speci fic power and speed ratings as well as suitability of
generator technologies such as permanent magnet (PM), wound rotor
synchronous, switched reluctance (SR) and induction will be discussed.
Current development programs for 30 kW to 2.5 MW power generators
will be presented