MAOximr nKSTGx of relays 



40 



the nppioxiiu;!! inn jusl dcscriltcd. ('oiisidcr tlic idealized loiiii siiowii in 

 Fig. I(), where the magnetic path consists mainly ot two parallel cylinders 

 connected at ()n(> end, th(> armatiu'c and woiking gap being at the op|)()- 

 site end. 'I'he leakagt^ fhix in parallel with the main gap linx is delermined 

 l)y the relnctance of the patli l)etw(M'n these cylind(Ms. l''oi- that poi'lioii 

 of tlie two cylinders appeai'ing ontside the coil and therefore at appio.xi- 

 mately constant potential, the relnctance is fonnd fi'om the relations 

 given in Fig. 14. For the leakage relnctance over the length (Miclo.sed l)y 

 the (oil, the drop in potential along the core results in one-thii-d tlie 

 previous reluctance, as is sliown in S(M'tion 6. The variation in ])er- 

 meance pei' unit length for such cases may l)c found in Fig. 17. 



Leakage also occiu's between the end sections of many magnet forms, 

 and ma\- he estimated by a procedure similar to those above, assuming 

 the end surfaces to be eciui\'alent to two hemispheres having the same 

 diameter d as the eyhnders. The (luantity C->d in Fig. 17 is one half the 

 permeance between corresponding spheres, as determined from the re- 

 lations of Fig. 15. From this the net leakage permeance of leg and end 



D 



AREA S 



AREA S 



Exact: (R = 



' + '77 + 77' + 



(^y-©'-(^)' 



+ . . . 



1 - 



AiJpidxiiiiiito: 



w here 



(R = 



(R = 



D 



2-Kr ' 

 1 1 



S = surface area of one sphere. 



when I) > 6r 



wlieii /; » 



Latter apjiroximatioii ma\- Ix' used to estimate leakage r(>luctancc lietwceii 

 hack surfaces of pole ])ieces. 



Lig. 15 — Keluctance helween spherical surfaces. 



