查看“︁Goodness係數”︁的源代码

{{Expert needed|subject=物理|time=2012-11-15T15:30:55+00:00}}
'''Goodness係數'''是一個由英國电气工程师[[埃里克·莱思韦特]]所提出，有關[[馬達]]效率的[[無因次]][[度量]]<ref>
{{cite journal
 | author = ER Laithwaite
 | date = 1965
 | title = The Goodness of a Machine
 | journal = Electronics and Power
 | volume = 11 | issue = 3 | pages = 101–103
 | doi =10.1049/ep.1965.0071
}}</ref><ref>{{cite journal
 | author = DJ Patterson, CW Brice, RA Dougal, D Kovuri
 | date = 2003
 | title = The "Goodness" of Small Contemporary Permanent Magnet Electric Machines
 | url = http://vtb.engr.sc.edu/vtbwebsite/downloads/publications/IEMDCpaper.pdf
 | journal = Proceedings of the International Electric Machines and Drives Conference
 | volume = 2
 | issue = 
 | pages = 1195–1200
 | doi = 10.1109/IEMDC.2003.1210392
 | access-date = 2012-11-15
 | archive-date = 2010-06-13
 | archive-url = https://web.archive.org/web/20100613193529/http://vtb.engr.sc.edu/vtbwebsite/downloads/publications/IEMDCpaper.pdf
 | dead-url = no
 }}</ref>。他根據此公式開發了高效率的[[磁浮]][[感應馬達]]<ref>{{cite journal
 | author = ER Laithwaite
 | date = 1965
 | title = Electromagnetic levitation
 | url = http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5176480
 | journal = Electronics and Power
 | volume = 11
 | issue = 12
 | pages = 408–410
 | doi = 10.1049/ep.1965.0312
 | access-date = 2012-11-15
 | archive-date = 2019-10-17
 | archive-url = https://web.archive.org/web/20191017003938/https://ieeexplore.ieee.org/document/5176480/
 | dead-url = no
 }}</ref>：

:<math>G = \frac {\omega} {R \times \mathcal R} = \frac {\omega \mu \sigma A_\mathrm{m} A_\mathrm{e}} {l_\mathrm{m} l_\mathrm{e}}</math>

其中
:''G''為Goodness係數，超過1表示效率良好
:''R''為[[電路]]的電阻
:<math>\mathcal R</math>為[[磁路]]的磁阻
:''A''<sub>m</sub>及''A''<sub>e</sub>分別為磁路及電路的[[截面積]]
:''l''<sub>m</sub>, ''l''<sub>e</sub>分別為磁路及電路的長度
:''&mu;''為鐵芯的[[磁导率]]
:''&omega;''為馬達工作的[[角頻率]]
:''&sigma;'' 為電路的[[電導率]]

莱思韦特證明了最有效率的馬達，其Goodness係數也會比較大。不過Goodness係數只適用在沒有永久磁鐵的馬達。

對於簡單的[[感應馬達]]，以下的比例關係會成立：

:<math>G \propto \frac {\omega \mu_0 p^2} {\rho_\mathrm{r} g}</math>

其中
:''p''為極節距的[[弧長]]
:''&rho;''<sub>r</sub>為轉子表面的[[電阻率]]
:''g''為[[氣隙]]厚度

==參考資料==
{{reflist}}

[[Category:電動機]]
[[Category:无量纲]]
[[Category:磁学]]
[[Category:需要物理专家关注的页面]]