Planning of mobile complete set for a rural wind generator (стр. 4 из 4)
5.3 Factors that may have affected the recycled generator outputs
There are many factors that should be taken in consideration with regards to the induced voltage from the recycled generator. Some magnetic deterioration may have occurred after the magnets were thrown into the dump. But, due to the magnet’s magnetic permanent properties, these magnets are expected to still have some surface flux density when found in the dumpsites.
This is evidence that any permanent magnet that is found in the dumpsites can be reused in a generator design to induce some voltage, of course depending on their B-H properties.
The estimated properties of the speaker magnets that were used in this thesis were found from the loudspeaker manufacture, clearly these properties will not be the same as the properties of recycled magnets that were found in the rural area of Ga-Rampuru. These recycled magnets have been affected by different conditions such as temperatures, climates, etc.
The exact properties of the recycled magnets can only be found by testing these magnets in the laboratory. For this thesis the author was unable to take the loudspeaker magnets found in the rural area of Ga-Rampuru to the laboratory.
5.4 Applications of voltage from the wind turbine
The induced voltage of the generator will vary with the wind speeds experienced in this village. The generator can be connected to a battery to store the power which can be utilized when there is little or no wind.
If more power is required, the voltage can be boosted by using any economical booster that can convert the output of the recycled generator to at least a minimum of 12V. The voltage from the booster can then be put through a cheap electronic regulator that will only charge the battery if the boosted voltage from the wind generator is sufficient to produce at least 12V direct current.
To power the refrigerator in chapter 1, the store owner in the village will have to purchase an inverter that will convert the DC voltage to AC voltage. The inverter will convert the low-voltage from the battery (12V) into mains-type 230V alternating current.
5.5 Design using speaker magnets
Finally, the author investigated how speaker magnets can be used in the generator design, if they have to be smashed or used as they are.
As already investigated, loudspeaker magnets are commonly from the ferrite magnets family. Ferrite and rare-earth magnets are by nature very hard and brittle. Although they can be cut, drilled and machined this should only be done by individuals who are experienced with ceramics. If the magnets get over about 300 deg F, they will lose their magnetism permanently [17].
Therefore, it will be very difficult for rural artisans to cut these magnets and use them. Due to limited time the author could not investigate if these magnets can be used as they are in the machine.
In the next chapter the author attempts to assemble the wind generator in the laboratory.
Chapter 6. Practical comparison of the generators
6.1 Introduction
The following chapter outlines the steps that were taken in order to assemble the permanent magnet generator discussed in the previous chapters. This is done in order to compare the practical outputs of the generator with the simulated ones. The other reason is to investigate the performance of recyclable magnets with irregular shapes.
This investigation will only concentrate on assembling the generator part of the wind turbine system.
For the construction of the PM generator in this thesis two options were considered, the first was to collect readily available off-shelf materials to assemble a small generator. And the second was to convert an AC induction motor to a PM generator. Both options are discussed in this chapter.
6.2 Materials required to assemble a PM generator
The main idea is to build a portable generator that is easily assembled and constructed in the laboratory. The author first begins with highlighting all the materials that are needed in the construction of this generator. Figure 6.1 gives the schematic of how the generator will look like.
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, http://www.idasa.org.za
3. Department of Minerals and Energy, White Paper on the Renewable Energy Policy of the Republic of South Africa. August 2002
5. Sathyajith Mathew, “Wind Energy-Fundamentals, Resource Analysis and Economics ” © Springer- Verlag Berlin Heidelberg 2006
6. Smail Khennas, Simon Dunnett and Hugh Piggott, “Small wind systems for rural energy services”. ITDG Publishing 2003
7. Kevin Reeves, “The design and Implementation of a 6kW wind turbine simulator” University Of Cape Town, South Africa, Oct 2004
8. FrequentlyAskedQuestions http://www.magnetsales.com/Design/FAQs_frames/FAQs_2.htm © 2000 Magnet Sales & Manufacturing Company, Inc
9. R.C. Bansal, T.S. Bhatti, D.P. Kothari, “On some of the design aspect of wind energy conversion systems” Birla Institute of technology and science, Pilani, September 2002
10. Jacek F. Gieras, Mitchell Wing, “Permanent magnet motor technology-Design and Applications” 1st edition. Marcei Dekker, Inc. 1997
11. Prof E. J. Odendal, “Design, construction and testing of a small wind generator with electronic controller for domestic use”. University of Natal, Durban
12. Jacek F. Gieras, Mitchell Wing, “Permanent magnet motor technology-Design and Applications” 2nd edition. Marcei Dekker, Inc. 1997
13. P.C. Sen, “Principles of electric machines and power electronics” 2nd edition. John Wiley & Sons
14. Bhag S. Guru, Huseyin R. Hiziroglu, “Electric Machinery and Transformers” 3rd edition. Oxford University Press, Inc. 2001
15. Dr. James Livingston, “Magnetic Materials Overview”
16. E. Muljadi, C.P. Butterfield, Yih-Huei Wan, “Axial flux, Modulator, Permanent-Magnet with a Toroidal winding for wind turbine applications”. Cole Boulevard, Nov 1998
17. Magfag, 2003 by Force Field
18. M.A. Khan, P. Pillay, “Design of a PM wind generator, optimised for energy capture over a wide operating range”
19. Joe Naylor, “Speakers with Alnico magnets vs. speakers with ceramic magnets”
20. Hybrid (Wind/Solar/LP Gas) Systems for Rural Community Development, “Electrifying South Africa for prosperity and development”. Upper Maphaphethe by Mike Wintherden
21. Danish Wind Industry Association, ‘Guided Tour’ online htt://windpower.org/en/tour/wres/betz.htm
22. Lysen, E.H., ‘Introduction to Wind Energy’ CWD,2nd edition, p.p 51-73
23. Ripinga Nonkululeko, “Comparison of grid and off-grid rural electrification, based on the actual installation in Limpopo Province”. University of Cape Town, Oct. 2005
24. Alfred Still & Charles S. Siskind, “Elements of electrical machine design”. 3rd edition. McGraw-Hill Book company,inc. 1954
Appendix A
Graphs of output rms induced voltage and flux of the generator
1. Commercial Standard Magnets
a) Ceramic FLux_RMS = 0.0175
EMF_RMS = 3.6075
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)