IEEE Electrification Magazine - March 2015 - 73

Figure 8. The assembly of the generator consisting of two magnet
rotor disks and a stator. (Source: scoraigwind.co.uk.)

OSh Technology assessment
at the NTUa

Figure 9. The bench tests on a locally manufactured axial flux generator at the NTUA. (Source: rurerg.net.)

Table 1. The estimation of the total cost of connecting a locally
manufactured small wind turbine to the 48-Vdc bus of an existing
off-grid reS system. (Source: rurerg.net.)

The Rural Electrification Research
Group (RurERG), which is part of the
Rotor diameter (m)
Smart Grids Research Unit (Smart
RUE) of the NTUA, has been assessSmall wind
ing the technology of locally manuturbine cost (€)
factured small wind turbines since
12-m tower (€)
2009, as a part of a wider validation
Power cable and
process of OSH renewable energy
electronics (€)
technologies used for sustainable
rural electrification. The necessary
experimental infrastructure for testing this small wind turbine technology according to international standards has
been designed and implemented in the laboratories of the
NTUA and includes an axial flux generator bench testing
facility using a dc motor drive, an airfoil and rotor blade
testing facility using a wind tunnel, and an outdoor test site
located in the nearby windy coastal area of Rafina.
The Hugh Piggott (HP) small wind turbine has been
used as the reference design of the OSH small wind turbine community since the majority of existing locally
manufactured small wind turbines have been based on
this design. To date, three small wind turbines have been
manufactured in practical student workshops, two for battery charging and two for grid connection, with rotor diameters of 1.8, 2.4, and 4.3 m. The practical workshops are
organized as parts of undergraduate dissertation projects
and are open to all students of the NTUA. During these
workshops, the small wind turbines are constructed from
scratch by the participating students, a process that provides practical evidence of the ability of unqualified constructors to locally manufacture this small wind turbine
technology. The educational aspect of these workshops is
of significant value and provides a chance to experiment
with various learning processes.
The 2.4-m HP small wind turbine with neodymium
magnets has been assessed for performance and robustness in the laboratories of the NTUA, as it is the size of
wind turbine that is most frequently manufactured and
installed. This type of wind turbine was constructed in a

1.2

1.8

2.4

3.6

4.2

300

400

650

750

1,000

1,200

150

200

300

350

500

600

300

550

650

student workshop during the spring of 2009, following the
2005 design manual of Piggott for charging a 48-Vdc battery system.

Laboratory Experiments
Several bench tests have been conducted on the axial flux
generator of the small wind turbine in question using the
dc motor drive bench testing facility (Figure 9). Some of
the most important of these tests are mentioned, which
describe aspects of the performance of the generator as
well as the impact of the manufacturing techniques used
during its construction on its operation.

CH1
RMS
84 V
CH2
RMS
84.1 V
CH3
RMS
83.1 V
CH1
Phase
120
CH1
CH: Channel
Frequency
RMS: Root Mean Square 14.36 Hz
Figure 10. The voltage measurements under no load at a 2.4-m HP
axial flux generator. (Source: rurerg.net.)

IEEE Electrific ation Magazine / March 2 0 1 5

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

Table of Contents for the Digital Edition of IEEE Electrification Magazine - March 2015