Family Hydro - a propeller type micro turbine with directly coupled generator

Thomas Staubli Fluidmechanics and Hydromachines
Alfred Koch, Energy Technologies
HTA Lucerne, Technikumstrasse 21, CH 6048 Horw
wufrey@hta.fhz.ch

Project
The Swiss company ENTEC, St.Gallen, involved in projects with developing countries asked the HTA Lucerne to have a look at the design of a series of micro turbines produced in very large numbers in Vietnam. "swisscontact" supported the analyses on the power generation unit and in the following the design of a new electric generator.
These turbines with types of 200W up to 2000W are used in rural regions to satisfy family needs for electricity. The week points of these turbines are the much too short life cycle duration, not constant frequency, and safety risks. The life cycle problems arises from demagnetization of generator magnets and from bearing wear. Voltage increase is coupled with too high revolution speeds during operation. Goal should be for this reason to have the turbines design point with 50Hz not in the best efficiency point of the hill chart but in an over speed range making sure that hydraulic losses will limit the maximum speed. A new electric generator design should solve the problem of demagnetization the permanent magnets, avoid overvoltage and increase the rotor speed and efficiency.

Results of two student's projects
With the aim to check the design the student Antonio DiMiele performed a numerical study of the flow within the turbine. The flow through the turbine is modeled with the commercially available CFD code, CFX-Tascflow. It is shown on the basis of these flow simulations, confirmed by experiments, that the original design point is far off the best efficiency point and that the generator should be equipped with six poles instead of 4 poles.
An improved electric generator was designed by the students Adrian Ambord and Daniel Blaser in course of their diploma thesis. A 3-phase and a 1-phase machine was calculated and physically defined. For each version a prototype with a power generation of about 500W was built. The measurements showed an efficiency of 90% for the 3-phase version and 84% for the 1-phase version. In this new design the lifetime of the permanent magnets is not limited. On top, a protection circuit cuts the overvoltage in case of low power consumption.