Magnet
Type
Flux (Rms)
EMF (Rms)
Rare-Earth
NdFeb32
0.0459
9.4262
Alnico
Alnoco6
0.0186
5.1619
Ceramic
Ceramic8
0.0175
3.6075
For speaker applications, the amount of permanent magnet required is directly proportional to the rated output power of the speaker. In other words high power speakers are often made using the high-grade magnetic types like the rare-earth. But since the speakers found in the dumpsite were from low power appliances their typical magnets are normally from the ceramic group type. In addition unlike Alnico magnets, ferrite or ceramic magnets are not easily demagnetised magnetized and hence find wide application in such appliances.
4.4.2 Properties of the loudspeaker magnet
According to its nameplate the speaker that used the magnet in figure 4.3 had a 0.5W rms and an impedance of 8 ohm. The magnet type on the loudspeaker is a ferrite [Refer to appendix D1]. The manufacturer of the magnet on the speaker is traced in order to find the B-H properties of the magnet on the speaker.
Appendix D2 indicates TDK datasheet for ferrite magnets FB series. These notes were used to find the magnetic, physical and mechanical characteristics of the magnet. The properties of the loudspeaker are summarized in table 4.3.
Br (T)
Hc (kA/m)
Ferrite
FB5N
0.43
214.9
Table 4.3 Summarized properties of the magnet speaker
Loudspeaker Magnet
0.0171
3.4987
Output Power
28.3W
Alnoco5
15.5W
10.8W
Speaker magnet
10.5W
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
4. Department of Minerals and Energy, White Paper on the Renewable Energy Policy of the Republic of South Africa. November 2003
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);
AA(k,:) = polyder(pp_flux_B.coefs(k,:));
dpp_flux_B = MKPP(time,AA);
[hgt,wdth] = size(pp_flux_C.coefs);
AA(k,:) = polyder(pp_flux_C.coefs(k,:));
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-');
plot(time*1000, emf_B,'b-');
plot(time*1000, emf_C,'g-');
title('Back Emf - under noload');
xlabel('Time [ms]'),ylabel('Back EMF [V]')
x = length(flux_link_A);
FLux_RMS = norm(flux_link_A)/sqrt(x)
y = length(emf_A);
EMF_RMS = norm(emf_A)/sqrt(y)
Страницы: 1, 2, 3