Figure 6.1 Basic wind generator design
From the generator illustrated above it is clear that the following materials will be required in the construction of the generator:
· Magnets
· Stator and rotor
· Rotor mounted on a rotating structure
· Structure mound
In the following sections the author will outline steps taken and the challenges faced in collecting these materials.
6.2.1 Magnets used in the generator
In the investigation of the performance of the generator, the author was to begin by designing the generator using standard commercial magnets, which were to be later substituted with recyclable magnets. The recyclable magnets are picked randomly in the dumpsites of Ga-Rampuru village.
Finding commercial magnets for this investigation was a major challenge since for this two-pole generator the author needed to purchase two NdFeb32 magnets, two Alnico5 magnets and two ceramic8 magnets.
6.2.2 Stator and rotor
The rotor rotates with the structure mount while the stator is fixed and mounted to a support structure. Since all these investigations were to be carried out under controlled laboratory conditions a drive and a frequency inverter which are readily available in the laboratory will be used to rotate the rotor at the desired speeds.
The drive will rotate the rotor and the induced voltage from the coils on the stator will be monitored by a voltmeter in the laboratory. Figure 6.2 illustrated this type of drive.
The size of the rotor in this thesis was constrained by the diameter of the recyclable speaker magnets. Therefore steel with this shape had to be found or cut to this shape. After finding the relevant steel, the cylindrical steel has to be drilled at the center.
6.3 Converting an induction motor into a PM generator
Due to the challenges faced in gathering the materials needed to assemble the generator the author then decided to find an alternative method to investigate the performance of the generator using recyclable magnets. A company called Magnetag that supplies motors and generators was approached and after some negotiations the company was willing to donate an AC induction motor to the author.
The idea was to convert this AC induction motor into a permanent magnet generator. This was going to be done by stripping the motor down and replacing the wound rotor with recyclable magnets. This looked like an attractive option since recyclable magnets with any shape can be used in the generator to explore its performance
The author was unable to complete investigating this option in detail. This is strongly recommended for further work most probably at MSc level.
6.4 Challenges faced during the construction of the PM generator
The main challenge in the construction of this wind generator was cost. For the laboratory investigation of the PM generator, a lot of materials, like the magnets and coils on the stator were found to be very expensive. This inadvertently gives more support for the use of recycled materials.
There was a lot of machining needed for this project, the rotor and the stator needed to be cut and shaped to the desired diameter and drilled in the centre to fit on the mount structure. Time was the major constrained since a lot of things were required to be done in the limited time given for this thesis.
However the framework of how to proceed in constructing and assembling the wind generator is already well laid out in this thesis.
Chapter 7. Conclusions
Based on the findings of the report, the following analyses and conclusions were drawn:
7.1 There is an urgent need of electricity
Due to the number of people living without electricity in rural South Africa it is clear that alternative means of supplying these areas is essential. According to ESKOM, all house holds will eventually be electrified, but the problem is, what is happening in the meantime? Where are children’s medicines being stored? Therefore this makes the electrification process extremely urgent.
7.2 Resource assessment
7.2.1Recyclable materials in the village
An extensive assessment on the rural village of Ga-Rampuru was conducted. There are plenty of recyclable materials including old milling machines that are not in use. These materials can be recycled to clean Ga-Rampuru village.
7.2.2 Rural artisans who can assemble the wind turbine
Since there are many local artisans who fix cars, electrical appliances and do some mechanical work in this village, manpower should not a problem. An engineer from the government or Non-governmental organization could educate these local artisans on assembling the wind generator. This will have a positive impact on Ga-Rampuru village as it will encourage people to work and be creative. There are many old wind mills used for pumping water in Ga-Rampuru village, most of these wind mills are working perfectly well supplying sufficient water. This is a clear indication that there is a reliable supply of wind in the village.
7.3 Simulation results
It has been shown that a reasonable amount of power can be realised from a generator using recycled magnets from the dumpsites
7.4 Cost involved in the design
The overall cost of assembling this wind generator system will be very cost effective since all the materials are recycled from the village, and the entire system will be assembled by local artisans.
7.5 Validity of this thesis
Small power that can turn on small lamps will really be appreciated in this village as children will be able to study after sunset. This will clearly have a wide range of positive developmental benefits on this community.
Chapter 8. Recommendations
Based on the above conclusions, the following recommendations were drawn:
1. For a more accurate recyclable wind turbine design, all its components such as the drum, the tower, rotor disk and cables must be explored in depth. The following must be considered:
· Investigate how to extract maximum power from the wind using the drum, and how to prevent the drum from over spinning.
· How to use other irregular recyclable magnets in the village in the generator design.
2. Investigate how a permanent magnet generator topology can be changed or re-designed to accommodate the design of a generator with the shape of the loudspeaker magnets.
3. Look in to how the magnets can be removed from the speakers, since very strong clue is used to mount them, how this can be done in a cost effective way.
4. The axial flux permanent magnet topology should also be looked into to compare it to the radial flux type.
5. The exact costs of assembling and maintaining the recycled wind turbine should also be incorporated in the design procedure.
6. With the little output power generated in this thesis, this project must definitely be taken further to alleviate the electricity problems in South Africa.
References
1. Socio-economic rights project, “The right to affordable electricity” copyright @ community law centre 2002
2. IDASA, <#"1.files/image027.gif">
b) Alnico FLux_RMS =0.0168
EMF_RMS = 5.1619
c)
NdFeB FLux_RMS = 0.0459
EMF_RMS = 9.4262
2. Loud Speaker Magnet
FLux_RMS = 0.0171
EMF_RMS = 3.4987
Appendix B
Matlab code for sketching the output emf and flux of the generators
% EMF calculation from FEMM
%By Maribini Manyage
clc
clear all; close all;
P = 2;
w = 1912; %mechanical speed in rpm
freq = (w*pi/30)*P/(4*pi); %frequency
XA = load('flux_link_A.txt');
XB = load('flux_link_B.txt');
XC = load('flux_link_C.txt');
beta = XA(:,1); % angle between Is_r and d-axis [elec degrees]
alpha = beta - beta(1,1); % Rotor position in [elec degrees] from Zero
time = alpha*(pi/180)/(2*pi*freq);%*1000; %time
flux_link_A = 2*XA(:,2);
flux_link_B = 2*XB(:,2);
flux_link_C = 2*XC(:,2);
% Perform spline in order to differentiate flux linkage vs time
pp_flux_A = spline(time,flux_link_A);
pp_flux_B = spline(time,flux_link_B);
pp_flux_C = spline(time,flux_link_C);
% extracting piecewise polynomial coefficients and derivation
[hgt,wdth] = size(pp_flux_A.coefs);
clear AA;
for k = 1:hgt
AA(k,:) = polyder(pp_flux_A.coefs(k,:));
end
dpp_flux_A = MKPP(time,AA)
[hgt,wdth] = size(pp_flux_B.coefs);
clear AA;
for k = 1:hgt
AA(k,:) = polyder(pp_flux_B.coefs(k,:));
end
dpp_flux_B = MKPP(time,AA);
[hgt,wdth] = size(pp_flux_C.coefs);
clear AA;
for k = 1:hgt
AA(k,:) = polyder(pp_flux_C.coefs(k,:));
end
dpp_flux_C = MKPP(time,AA);
%back emf
emf_A = ppval(time,dpp_flux_A);
emf_B = ppval(time,dpp_flux_B);
emf_C = ppval(time,dpp_flux_C);
figure(1);
plot(time*1000,flux_link_A,'r-');
hold on;
plot(time*1000, flux_link_B,'b-');
plot(time*1000, flux_link_C,'g-');
title('Flux linkage - under noload');
xlabel('Time [ms]'),ylabel('Flux linkage [WbT]')
grid;
figure(2);
plot(time*1000,emf_A,'r-');
hold on;
plot(time*1000, emf_B,'b-');
plot(time*1000, emf_C,'g-');
title('Back Emf - under noload');
xlabel('Time [ms]'),ylabel('Back EMF [V]')
grid;
x = length(flux_link_A);
FLux_RMS = norm(flux_link_A)/sqrt(x)
y = length(emf_A);
EMF_RMS = norm(emf_A)/sqrt(y)
