IEEE Electrification Magazine - March 2015 - 72

Figure 5. The coils cast in resin to produce the 2-D stator of the
axial flux generator. (Source: scoraigwind.co.uk.)

Figure 6. A hand-made coil winder with a coil ready to go in the stator. (Source: rurerg.net.)

Figure 7. The 2-D rotor of an axial flux generator with neodymium
magnets. (Source: otherpower.com.)

thickness and, after being cast in vinylester resin, can
produce the solid disk parts of the generator (Figure 5).
In addition, the air gap of the generator, which is the
distance between the two magnet rotor disks, can be

72

I E E E E l e c t r i f i c ati o n M agaz ine / March 2015

adjusted easily, which is important for the performance
and long-term operation of the small wind turbine. The
stator coils are wound by hand using enameled copper
wire and a simply constructed coil winder (Figure 6).
The steel rotor disks, on which the permanent magnets are placed and form part of the magnetic circuit of
the generator, are usually precut with laser, water jet, or
oxygen torch computer numerical control routers or can
also be cut with hand power tools (Figure 7).
The generator's rotor disks are mounted on a car or
trailer wheel hub, which can be new or recycled from an
old vehicle, that provides a robust bearing for the axis of
revolution of the turbine (Figure 8). The metal frame,
which supports the car hub axle, the yaw tube, and the
furling tail hinge, is constructed out of typical steel profiles and with the use of basic welding techniques and
tools such as an electric arc welder. Other tools used for
the construction of the generator are a jigsaw, a drill press,
an angle grinder, and a hand drill, which can all be found
in village workshops and are also used for a variety of
rural maintenance activities.
The small wind turbine's tail consists of a steel tube,
which provides the appropriate length of the tail, and a
vane made of plywood, with the appropriate area to effectively yaw the rotor blades toward the prevailing wind
direction. The total weight of the tail is important as it
specifies the furling operation of the turbine and, thus, its
power control mechanism in higher winds.
An estimation of the total cost for construction, installation, and connection of a typical battery-charging small
wind turbine of this type, with respect to rotor diameter, can
be seen in Table 1. The cost of a 12-m guyed tower could
amount to more than 50% of the total cost of the construction of the small wind turbine, depending on the anchoring
type and the materials used. The power cables, rectifier,
diversion load controller, and resistive load could amount to
30% of the total cost of the system, depending again on the
location of the installation, the system dc voltage used, and
the quality of the components. The cost estimations of
Table 1 refer only to the materials; the labor required for the
construction and the installation of the small wind turbine
are considered to be provided by the users. Typically, a
2.4-m-rotor-diameter small wind turbine will require 450
working hours to be completed, with 50% of the total time
allocated to carving the rotor blades. This is one of the main
reasons that manufacturing open-source small wind turbines is usually a group process. Smaller turbines will
require less time than larger ones, but this will not be directly proportional to the rotor diameter, as constructing a wind
turbine with double the rotor diameter of the one mentioned will not require twice the amount of working hours
but less. Finally, considerable amounts of labor are also
required for manufacturing the tower and installing the turbine, activities that may even require as many working
hours as for constructing the turbine itself, especially for
larger rotor diameters.


http://scoraigwind.co.uk http://www.rurerg.net http://www.otherpower.com

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https://www.nxtbook.com/nxtbooks/pes/electrification_september2020
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