G, S & AG LS LMAGS AAG ALMM & H -S MALS by
Leonard R. row EDUCATIONAL SPECIAIST In evlopmnt of Elrica sruco
DIRECTOR OF REEARCH AND DEVEOMENT Usl Snic Compy, Inc.
THE SCENC BOOK PBLSNG CO V 95
Disaimer
Operation of he magnet descbed heein equies the use o 15 vos AC (Aeating uen) The votages and cuens used ae letha The epinte of his book Benjamin Fleming as we as he varos disrbtos of this pblication incding bt not limed o Lindsay Pbicaions Inc have not bui s poject no do hey endose the mehods heein descbed. he said eming as we as the distibuos assme no iabiliy fo in o pesons o popey hat may esu whie bilding, testing o opeaions in any way o the descrbe magne The intent of this pbication is fo educaiona puoe oy. .•
PREFACE
Back n 1935 I gave a pulc lecture demonstraon at he physics department of Dlnos Unversty In whch I used an eecrca trag id of my own de sgn and consructon o show tha an elecromgne coud be used o arac non erromagnec metas of good elecrcal conductvy. I the foowng fve years I devoted much thought, tme and fort to makng varous types styes nd szes of eectromagnets wth whch I could produce attracton of non ferros-metals eectvey
Foowng s a descrpon o and asc fundamental operatng prncpes peraing to the type of elec tromagnet hat I have f ond mos efecve for the attracon of non ferrousmetals
NOICE
Repinter.s ote I am ve nteested n communcatng wth ndivdas and o companies that hae in in the past, o ae cuenty usng ths magnet technoogy Shoud you know of addtional aceooks ec. or ndduas that have knowedge elating to ths subjt matte pease contact me at: Benjamn eming 1734 Vewpont D Fayettelle Akansas 72701 Akansas 72701 o e-ma bnenguaked
Some of e devices and consrucons lusraed and described hs book are covered by eers pae Desgners ad mafacrers ae wared o ceck he pae siuaion horougly, before coporag any o e embodimens descrbed herewih io heir own designs or consrucos lusrao or descrpio s boo mus no be consrued to Impy ha a device sysem o con sucio shown herein Is commo propery avaiabe for pubc use by anyoe. Accordgy, erefore, te publishers or auor wl o assume ay responsbiy for damages arsing ou of ligaio inolvg Irgeme sus relave o ay sysem consruco or apparas descrbed erei
NOICE
Repinter.s ote I am ve nteested n communcatng wth ndivdas and o companies that hae in in the past, o ae cuenty usng ths magnet technoogy Shoud you know of addtional aceooks ec. or ndduas that have knowedge elating to ths subjt matte pease contact me at: Benjamn eming 1734 Vewpont D Fayettelle Akansas 72701 Akansas 72701
Some of e devices and consrucons lusraed and described hs book are covered by eers pae Desgners ad mafacrers ae wared o ceck he pae siuaion horougly, before coporag any o e embodimens descrbed herewih io heir own designs or consrucos lusrao or descrpio s boo mus no be consrued to Impy ha a device sysem o con sucio shown herein Is commo propery avaiabe for pubc use by anyoe. Accordgy, erefore, te publishers or auor wl o assume ay responsbiy for damages arsing ou of ligaio inolvg Irgeme sus relave o ay sysem consruco or apparas descrbed erei
o e-ma bnenguaked
TOMAGNTS O SA ONSTTON OR T ATTAON O NON-OMAGNT MTAS Magnetism is one of the most interesting and mysteious as wel as one of the most impo impotant tant phys physical ical phenomena kno known wn Though its action we generae and utiize the enormous qan tities of eectrical we which make possibe moder modern n industry and moder modern n iving. Many impo importan rtantt principles of electomag netism can undestd fom the study of an electomagnet, invented ad designed by the autho, which aacts non-ferro magnetic metals Everyone hs eeimented with magnets and observed thei araction aractio n fo ion filigs naiS nd othe smal aticles of ion and steel ome of you ill have seen lage electomag nets attached to cnes pick p tons of scap stee steell and move it
TOMAGNTS O SA ONSTTON OR T ATTAON O NON-OMAGNT MTAS Magnetism is one of the most interesting and mysteious as wel as one of the most impo impotant tant phys physical ical phenomena kno known wn Though its action we generae and utiize the enormous qan tities of eectrical we which make possibe moder modern n industry and moder modern n iving. Many impo importan rtantt principles of electomag netism can undestd fom the study of an electomagnet, invented ad designed by the autho, which aacts non-ferro magnetic metals Everyone hs eeimented with magnets and observed thei araction aractio n fo ion filigs naiS nd othe smal aticles of ion and steel ome of you ill have seen lage electomag nets attached to cnes pick p tons of scap stee steell and move it fimly y to the magnet aut with ease. Tons of iro ae hed fiml with an invisible foce and are released by the fip of a switch atracted ted with such You have also obseved that hie ion is atrac ae e foce othe metls such as auminum coppe and sive a uaffected uaffecte d h his is pincipe is often us used ed to sepaate iro iron n fo fom m non-ferous mels No dou doutt you hav have e use used d a mag magnet net to dete dete mine whethe a ckel plated scew had an iron or bass se You may aso have noticed tht aternting curent is appIed
ELCTROMAGNES
2
DESIGN CONSTRCTION
A
OPERTG PRCES
3
igur 2
to an ordinary electomagnet, non-magnetc meals of good eecrica coductivty wl acuay acuay repeled. n view o a a of e ave wil be mos interestng o learn how magetsm can be used o atract nonferromagneic meals In 1934 he author desgned equpment with whch was pos sible to demonstrate princpes whereby non-erromagneic metals migh be atraced by by a special magne magne In 940 he eec ec auhor completed the deveopmen ad construcion o o an e romagnet wh would actualy aract meals sch as alumi num, copper and slver. In act the magnet would atract any ea o air or go electrica conductvity owa owadd the end of 1947 the author completed he desgn and consructon of a much mproved eecromagne or he aacton nonerrous meas he detas and descrpion of which ae ncluded n this arce The special special electromagne electromagne s iusrated n Fgure . In Fgure 2 he magnet magnet wih ts a horionta s shown pieces o supporting a heavy pece o copper I Fgure 3 tw twoo pieces auminum have en added to he original pece o coper Figure 4 shows te magne magne suprtng wo sUver dollars dollars The sze of he magnet ustraed by comparison wh he siver dolars a the maget may aso be used used to attrac ron ron is idicated cleary n Figure 5. consruction and prncples Beore considerng the detas detas o consruction o operaion of the speca elecromagnet et us revew some of he sc pricpes o magnetism and elecomagnesm
LETROMAGNTS
ire 3
metas can We wl not ony observe tha nonferromagneic nonferromagneic metas agnet t w also gan the peasure o attracted to an eecrom eecromagnet ndersanding its prncpes o action Oersed in 189 was the fs to show tha a current carrying wre was surounded surounded by a magnetic !eld He dscovered ha a compass neede algns tse a righ ages o a wre carryig
Fie"
DSIGN, CONSTUTION,
A OPATG PRCS 5
wih h vta xplaa tha urr lw fr pi v av a pa pad abv th wir wl pt h d ri hw I Fur 7A pit at rht a h ur r arryi dur h pa d wl pt th dri ta h lux li ar vi H th urrt r vr d a I Fur 7-B h pa wll p h ppt drti a hw ad w w th ux li hav rvrd h dit
Fgure
a ltr urrt hu it i w at a ru lar t a Fiu 6, thr wi a a Id aut h wir drt hw. hw . h urr drt arda
Fgue
w pa a ubr ati d r pa aut a urr arryi dutr I h ar hw i Fur 8 h pa dl w pIt drU lurad
'
CEl A Figure
6
Fig
LETROMAGNTS
DSIGN, CONSTUTION,
A OPATG PRCS 5
wih h vta xplaa tha urr lw fr pi v av a pa pad abv th wir wl pt h d ri hw I Fur 7A pit at rht a h ur r arryi dur h pa d wl pt th dri ta h lux li ar vi H th urrt r vr d a I Fur 7-B h pa wll p h ppt drti a hw ad w w th ux li hav rvrd h dit
Fgure
a ltr urrt hu it i w at a ru lar t a Fiu 6, thr wi a a Id aut h wir drt hw. hw . h urr drt arda
Fgue
w pa a ubr ati d r pa aut a urr arryi dutr I h ar hw i Fur 8 h pa dl w pIt drU lurad
'
CEl A Figure
6
Fig
EECTROMAET
DE, COTRCO A OERAT PRCL 7
s ndates vey eay a te magne ines o oe ae deted in a ia pat aond te ondto and tat ei deion eveses wit a evesa o ent in e odo o deemine e detion o e !ux ines we gasp te ondto n e ig and wt te tmb Jinng in e die tion o e ent ent en e inges ene e wie in in te detion o te x nes (see ige 9 is i nown nown as e Rig and Re
-1
PINTED RCO FUR£
iu 10
cn; G
to p e wies togee togee oe a e x nes between between te wies ae opse n dietion We may aso say tat tat n a e gion s te spae between te wies wee e ines o x ae in oppose dieions, tee s aation etween te on tos ow e e two ae wies ay ents in opposie di etions as n ge 12 Te [x ines a o ondo
lX
F e 9
ow et two ae wies aying ent i e same di etion be paed n ea ote as n igue 10 Te omass wi poin in te deion sown n igue A pa ave eite we a wi aso point n e same dieion sted o any stion ave ave e two wies oweve, w1 evese s dieion wen paed ndeneat eite o t o te wies (ige 10-B). T we onde tat x ines nie ea wie and aso tat ee ae ines extending ao o eniing t wies We an now dede two impoan popeies x ines is o e oseved by expeiment expeiment tat paae paae ies s as ose stated n ige 11 ae atated by te magneti a ion o e two ens ens owing n te same dieton dieton is a ation an expained by saying tat te ines o x ae de ension ie steed be nds ta s, tey tend t soten ose ines wi enie t wies i, en, end
ie 1
EECTROMAET
DE, COTRCO A OERAT PRCL 7
s ndates vey eay a te magne ines o oe ae deted in a ia pat aond te ondto and tat ei deion eveses wit a evesa o ent in e odo o deemine e detion o e !ux ines we gasp te ondto n e ig and wt te tmb Jinng in e die tion o e ent ent en e inges ene e wie in in te detion o te x nes (see ige 9 is i nown nown as e Rig and Re
-1
PINTED RCO FUR£
iu 10
cn; G
to p e wies togee togee oe a e x nes between between te wies ae opse n dietion We may aso say tat tat n a e gion s te spae between te wies wee e ines o x ae in oppose dieions, tee s aation etween te on tos ow e e two ae wies ay ents in opposie di etions as n ge 12 Te [x ines a o ondo
lX
F e 9
ow et two ae wies aying ent i e same di etion be paed n ea ote as n igue 10 Te omass wi poin in te deion sown n igue A pa ave eite we a wi aso point n e same dieion sted o any stion ave ave e two wies oweve, w1 evese s dieion wen paed ndeneat eite o t o te wies (ige 10-B). T we onde tat x ines nie ea wie and aso tat ee ae ines extending ao o eniing t wies We an now dede two impoan popeies x ines is o e oseved by expeiment expeiment tat paae paae ies s as ose stated n ige 11 ae atated by te magneti a ion o e two ens ens owing n te same dieton dieton is a ation an expained by saying tat te ines o x ae de ension ie steed be nds ta s, tey tend t soten ose ines wi enie t wies i, en, end
8
ELECTROMAGNETS
ie 1
DESIN CONSTRUCTION AND OPERAT RCLES 9
ATRACION Figure 13
Figure 1
rrent. I is ing crre rrying tors carry ductors conduc en e con etween and etwe gnets and magnets there ated that ther nstr strate demon sily be demo can easily awing and can the drawi own i the shown tors rs d cto c c ond on u s) r rou ro n -fer -fe (non (no p er op two copp the two tween the tion btwee traction is attrac s ; i ons on ecti direct dir s ite p pos po n o r e i a them th em e n t wee we bet be n es x lin li flx fl the h en w eel eces o f steel two piece the two tween the ction tion betwe ttra rac here att ise, there likew ikewise
he are in etween the ines et flux lines nets when the flux nent agnet (per (peranent
s. tions irection osite dire opposi
will be opsite to the flux lines at No. 2 conductor and there are no flux lines encircli encircli th conductors The two conductors conductors will repel each other other Thus we see that flux lines lines which travel in the same direction, direction, as in the space between the wires wires ' produce repulsion From the foregoing we see that such non-ferromagnetic metals as copper condctors can be moved about in magnetic fields becaus of the magnetic lines of force that are proded by currents currents flowing in the conductors conductors (metals) themselves This does not necssarily, indicate that it is possible to magnetize non-ferromagnetic metals (such as copper or aluminum) in the manner that we do a piece of steel or other ferromagnetic metal, however it is quite interesting to note the striking similiarity of araction nd eplsion as shown by Figres and . In Figure , by the se of conventional symbols, two con dctors are are shown carrying current The circles with with a pls (+) at their centers represent the cross section of two condc tors carrying crrent crrent away from the observer observer The direction direction of the magnetic flux aut the conductors is also shown in rela tion to the direction of crrent flow Jst low the two condc tors are two ermanent magnets with an indication of the direc tion of flux lies of each magnet in relation to its ' polarity Note the imiarity i n the direction of the flx lines between th
tors ductor conduc same two con tion is made of the sam stratio ill stra igre 4, ill In igre
and ight hand the righ rent in the crren here the cr xcept her nets exce nent magnet permanen and per ver, such server the oser ard the toward ing tow flowing sented as flow presen ctor is repre ndcto cond
or). uctor) onduct rcle (cond the circle ter o f the center ( at the cen dot ( eing a dot tion being gnatio deS eSgna
agnet has ent magnet rmane hand perman ght han the right that the o, it is t o be noted that Als Also netic the magnet Here the gre 13. Her that o f Figr sed to tha versed rity rever olarity its pola rece direcs ame am h e i n t re r s a c tor to n duc du o con co two tw t he tween rce etwe lin lines o f force per copper the two cop tween the sion between plsion ducing repl produc by pro thereby tion there
EPULSO Figure 14
ELECTROMAGNETS
8
DESIN CONSTRUCTION AND OPERAT RCLES 9
ATRACION Figure 13
Figure 1
rrent. I is ing crre rrying tors carry ductors conduc en e con etween and etwe gnets and magnets there ated that ther nstr strate demon sily be demo can easily awing and can the drawi own i the shown tors rs d cto c c ond on u s) r rou ro n -fer -fe (non (no p er c opp op two tw o the th e e n twee twe n b tio traction is attrac ons; directiions posite direct them are in oppos ween them betwee lines bet flx lin when the flx eel eces o f steel two piece the two tween the ction tion betwe ttra rac here att ise, there likew ikewise
he are in etween the ines et flux lines nets when the flux nent agnet (per (peranent
s. tions irection osite dire opposi
will be opsite to the flux lines at No. 2 conductor and there are no flux lines encircli encircli th conductors The two conductors conductors will repel each other other Thus we see that flux lines lines which travel in the same direction, direction, as in the space between the wires wires ' produce repulsion From the foregoing we see that such non-ferromagnetic metals as copper condctors can be moved about in magnetic fields becaus of the magnetic lines of force that are proded by currents currents flowing in the conductors conductors (metals) themselves This does not necssarily, indicate that it is possible to magnetize non-ferromagnetic metals (such as copper or aluminum) in the manner that we do a piece of steel or other ferromagnetic metal, however it is quite interesting to note the striking similiarity of araction nd eplsion as shown by Figres and . In Figure , by the se of conventional symbols, two con dctors are are shown carrying current The circles with with a pls (+) at their centers represent the cross section of two condc tors carrying crrent crrent away from the observer observer The direction direction of the magnetic flux aut the conductors is also shown in rela tion to the direction of crrent flow Jst low the two condc tors are two ermanent magnets with an indication of the direc tion of flux lies of each magnet in relation to its ' polarity Note the imiarity i n the direction of the flx lines between th
tors ductor conduc same two con tion is made of the sam stratio ill stra igre 4, ill In igre
and ight hand the righ rent in the crren here the cr xcept her nets exce nent magnet permanen and per ver, such server the oser ard the toward ing tow flowing sented as flow presen ctor is repre ndcto cond
or). uctor) onduct rcle (cond the circle ter o f the center ( at the cen dot ( eing a dot tion being gnatio deS eSgna
agnet has ent magnet rmane hand perman ght han the right that the o, it is t o be noted that Als Also netic the magnet Here the gre 13. Her that o f Figr sed to tha versed rity rever olarity its pola rece direcs ame am h e i n t re r s a c tor to n duc du o con co two tw t he e en e twe tw e o rce rc o f f n es lin li per copper the two cop tween the sion between plsion ducing repl produc by pro thereby tion there
EPULSO Figure 14
ELETROMAETS
DESG, COSTRTON, AD OPERA PRCPES 1
non-feos conductos. kewse the magnetic ines of foce beween he two pemanent magnets ae in the same diecon ad eplsion is puced tween te two (feous steel mag nets om the foegoing ilustatons we see that magetic lnes of foce fowing in opse decions tween cuent caying conducos o between magnes (ween non-feos o beween feous metas pduce ataction And that magneic lnes of foce fowing n the same diection beween cent caying conductos o beween magnets (beween nonfeous o between feos meals puce eplsion. The magnetc foce aut a cuen caying condcto Is quie smaU uness a vey age cuent is se p in i. ode o podce quie sikng demonsations to fhe illusate sic aws of magneism and the elaion to and associaon wih electca cuents we sal utize a conveniently aanged elecical tainig aid as an effcient and Inexpensive means of spplying a vey a e cuent to a single conducto a a ow volage and low we consmption Tis device sown n igue is a specially designed ds secible ansfome. ansfome. The wo tn seconday povides a cu en soce of moe han ampees a less than 3 vols po entia and wen sot ciced by the single coppe oop ( con dco) povides e conduco wih an extemely heavy cuen.
Ths conducto wen caying a cuent of appomately 400 ampees can be sed to podce (with small powe consmption some sting eJeimens to illstate mpoan basic mag neic phenomena. ge ilsates hw a cuen of ampees will po dce a vey stong magnetc field abou a conduco fact, the magec fed abut the condco in this nsance is so geat at a ayman mgt easily misae the condco fo a magnet. Alhogh t does actally actally look ie e coppe conducto as become a magne we kow, of couse, tat the small nails ae mageed by te song magneic field podced as a e sl of he lage cuen flow hough the copper ( we.
Fir 16 Fir
ELETROMAETS
DESG, COSTRTON, AD OPERA PRCPES 1
non-feos conductos. kewse the magnetic ines of foce beween he two pemanent magnets ae in the same diecon ad eplsion is puced tween te two (feous steel mag nets om the foegoing ilustatons we see that magetic lnes of foce fowing in opse decions tween cuent caying conducos o between magnes (ween non-feos o beween feous metas pduce ataction And that magneic lnes of foce fowing n the same diection beween cent caying conductos o beween magnets (beween nonfeous o between feos meals puce eplsion. The magnetc foce aut a cuen caying condcto Is quie smaU uness a vey age cuent is se p in i. ode o podce quie sikng demonsations to fhe illusate sic aws of magneism and the elaion to and associaon wih electca cuents we sal utize a conveniently aanged elecical tainig aid as an effcient and Inexpensive means of spplying a vey a e cuent to a single conducto a a ow volage and low we consmption Tis device sown n igue is a specially designed ds secible ansfome. ansfome. The wo tn seconday povides a cu en soce of moe han ampees a less than 3 vols po entia and wen sot ciced by the single coppe oop ( con dco) povides e conduco wih an extemely heavy cuen.
Ths conducto wen caying a cuent of appomately 400 ampees can be sed to podce (with small powe consmption some sting eJeimens to illstate mpoan basic mag neic phenomena. ge ilsates hw a cuen of ampees will po dce a vey stong magnetc field abou a conduco fact, the magec fed abut the condco in this nsance is so geat at a ayman mgt easily misae the condco fo a magnet. Alhogh t does actally actally look ie e coppe conducto as become a magne we kow, of couse, tat the small nails ae mageed by te song magneic field podced as a e sl of he lage cuen flow hough the copper ( we.
Fir 16 Fir
12
EECTROMAGNETS
T uhe usate he efect f the magneic field puced by the current fw hugh this p cnduc Figure 6 shws a lge l suspended withi ad a he cete f the lp The age curet flw thugh he p cnducr prduces a magnetic field aut he p whch magetizes the large nai Visul p that he lge ai is magneized is shwn by the fact that it attracts ad hds i suspesin a lage numbe smal nals T pceed a step furthe, we sha nw sudy igue 7. ee a few arge nails are shw whi the op cpper we
DSGN,, CONSTRCT DSGN CONSTRCTON, ON, AND ORATN ORATN PRCPL
3
As he magneic ux circles aut the cducr it wil lw upwad n the uside uside the lp Theer e, a nai placed n the utside the lp wil hve he ppsite plaity t e n the iside ad attracti will result between a nail n the utside ad ne he iside since uike ples attract attract igure 8 shws ths very clealy whee several ails n the Inside f the lp cing t the aUs the uside the p.
gre 18
Figue 7
and it is be ned ha al these ails have cme magnezed by the mageic ield abut the curent caying cnduct cnduct Each f the ails has cme a maget ad they al epe each her because ike les o a magnet magnet epel These nail magnets have he same laiy cause they ae all the same side f he cnducr and ae subject ies rce that are lwing In the same directi Alhug Alhugh h he cuent lwing lwing hugh the the cpper lp is aleatig t neveheless prduces a magnetic lux that a any insant is the same diectin thugh all the ais As he ield segh segh ad plarity plarity ay ay ne ni chages, chages, it likewise changes changes thrugh thrugh all he thes Cnsequently, the ais have like rities at all times wch esuls i epulsin betwee them since like ples epel Let us assume hat the mageic lux f a give aenatin is flwing dwwad n the iside f the cppe lp cnducr
As has previusly en stated the magnetic fce aut a curret carryig cductr s quite small unless a very large curret is made made flw thrugh It de t cceate cceate he actin and incease the fce, the wie may fmed in several ts as shwn in igre 9, Here thee ae three turns rming he cl (helix) theeby ccentratig the magneti c ines fce alng sevea inches the cnduct it a sma space, which shws hw the magetic stength pduced by a given curen fw ca be cncenated. t is a wel esablished act tha he mageic rce (stegh) a ci Is diectly prptina t the ampee turs f the ci T find the ampere turns a ci it is ecessay ecessay t mu iply the num turns i the cil by he current lW, i am peres, thugh the cil cil emple, a c uns caryIng 1 amperes is equivalen t a cil 10 turns carying 0 ampees, assumig f crse hat all her actrs culd made equa in each cil The magetic frce betwee tw paralel cnducs may
12
EECTROMAGNETS
T uhe usate he efect f the magneic field puced by the current fw hugh this p cnduc Figure 6 shws a lge l suspended withi ad a he cete f the lp The age curet flw thugh he p cnducr prduces a magnetic field aut he p whch magetizes the large nai Visul p that he lge ai is magneized is shwn by the fact that it attracts ad hds i suspesin a lage numbe smal nals T pceed a step furthe, we sha nw sudy igue 7. ee a few arge nails are shw whi the op cpper we
DSGN,, CONSTRCT DSGN CONSTRCTON, ON, AND ORATN ORATN PRCPL
3
As he magneic ux circles aut the cducr it wil lw upwad n the uside uside the lp Theer e, a nai placed n the utside the lp wil hve he ppsite plaity t e n the iside ad attracti will result between a nail n the utside ad ne he iside since uike ples attract attract igure 8 shws ths very clealy whee several ails n the Inside f the lp cing t the aUs the uside the p.
gre 18
Figue 7
and it is be ned ha al these ails have cme magnezed by the mageic ield abut the curent caying cnduct cnduct Each f the ails has cme a maget ad they al epe each her because ike les o a magnet magnet epel These nail magnets have he same laiy cause they ae all the same side f he cnducr and ae subject ies rce that are lwing In the same directi Alhug Alhugh h he cuent lwing lwing hugh the the cpper lp is aleatig t neveheless prduces a magnetic lux that a any insant is the same diectin thugh all the ais As he ield segh segh ad plarity plarity ay ay ne ni chages, chages, it likewise changes changes thrugh thrugh all he thes Cnsequently, the ais have like rities at all times wch esuls i epulsin betwee them since like ples epel Let us assume hat the mageic lux f a give aenatin is flwing dwwad n the iside f the cppe lp cnducr
4
ELECTROMAGNS
As has previusly en stated the magnetic fce aut a curret carryig cductr s quite small unless a very large curret is made made flw thrugh It de t cceate cceate he actin and incease the fce, the wie may fmed in several ts as shwn in igre 9, Here thee ae three turns rming he cl (helix) theeby ccentratig the magneti c ines fce alng sevea inches the cnduct it a sma space, which shws hw the magetic stength pduced by a given curen fw ca be cncenated. t is a wel esablished act tha he mageic rce (stegh) a ci Is diectly prptina t the ampee turs f the ci T find the ampere turns a ci it is ecessay ecessay t mu iply the num turns i the cil by he current lW, i am peres, thugh the cil cil emple, a c uns caryIng 1 amperes is equivalen t a cil 10 turns carying 0 ampees, assumig f crse hat all her actrs culd made equa in each cil The magetic frce betwee tw paralel cnducs may
DSIGN, CNSUCTN, A PEATG CS 5 very strkng demonstraton of te attractve ad repulsve fOrces pruced y the magnetc feds of two cols s ustrated 22.. n gure 21- two cois are shown sus by gures 2 and 22 pended and separted a cosderable dstance before current was
Figure 19 augmented by concentra1ng the magnetc feld and thereby increasng the force by formng the conductors nto cos as shw in Figure . Here there would many fux nes nkng h coUs ad tus pul tem together so long as the currens
gure
Fge 20 though th cos were In the same drection the eads to one of te cois were reversed therey reversng the dectio of current flow trough that col the two cos woud repel eah other.
made to flow through them current flow through the two coBs n the same drecton caused the attractive force to be so great that the coils jumped together tough seera nches as show n gure 21-B By suspending the two cos so tat they touched each other fore ssg current though them, they were as show n gure A. ut as soon as current was made to fow though the two cols n opste drectons they repeled each other n the maer shown n gre 22B. n order to concentrate and utilze effectvely the magnetc ines of force that ae pruced y a current flow through a conductor for most appcations it s advsale to use ferro magnetc metals such as steel to conduct the flu ecause ar s a very or conductor of magnetism and ferromagnetc metals such as steel steel are eceptonaly go magnetc magnetc conductors. conductors. That s, a offers a gh reluctance whe ferromagnetc metas offer
4
ELECTROMAGNS
DSIGN, CNSUCTN, A PEATG CS 5 very strkng demonstraton of te attractve ad repulsve fOrces pruced y the magnetc feds of two cols s ustrated 22.. n gure 21- two cois are shown sus by gures 2 and 22 pended and separted a cosderable dstance before current was
Figure 19 augmented by concentra1ng the magnetc feld and thereby increasng the force by formng the conductors nto cos as shw in Figure . Here there would many fux nes nkng h coUs ad tus pul tem together so long as the currens
gure
Fge 20 though th cos were In the same drection the eads to one of te cois were reversed therey reversng the dectio of current flow trough that col the two cos woud repel eah other.
6
ECTROGNS
made to flow through them current flow through the two coBs n the same drecton caused the attractive force to be so great that the coils jumped together tough seera nches as show n gure 21-B By suspending the two cos so tat they touched each other fore ssg current though them, they were as show n gure A. ut as soon as current was made to fow though the two cols n opste drectons they repeled each other n the maer shown n gre 22B. n order to concentrate and utilze effectvely the magnetc ines of force that ae pruced y a current flow through a conductor for most appcations it s advsale to use ferro magnetc metals such as steel to conduct the flu ecause ar s a very or conductor of magnetism and ferromagnetc metals such as steel steel are eceptonaly go magnetc magnetc conductors. conductors. That s, a offers a gh reluctance whe ferromagnetc metas offer
DSGN, CONSTRUCON, CONSTRUCON, ND OPRTG RNCES
A
22
low rectance . How a ferromagnet c met my used to il strate this fact 1s clearly shown y the se of the soft steel cores shown n Fgres 23 and 2. he foregoing eerments shoud sucent to gve a very clear pictUre of how mgnetc fux Is pruced y current Clow iue
e
23
a someing e reation of the lux to the current he discssion s far has en concerned wth the me ' cncal force prduced y magnetism We must also study he eect of magnetsm n nducing a voltage or current we are to understand the attraction of non-magnetc etas by the spe cal eectromagnet. After Oersted dscovered the magnetc feld at a con ductor carryng crrent 8, many expermenters attempte to prouce the nverse effect. That s, they tred to produce a crent y means of a magnetc magnetc feld. Al were nsccessful untl FaradayS hstoric experments n 83 araday showed that a current, or more correctly an electromotve force, was nduced when the amount of fux threadng a col was changng,
6
ECTROGNS
DSGN, CONSTRUCON, CONSTRUCON, ND OPRTG RNCES
A
22
low rectance . How a ferromagnet c met my used to il strate this fact 1s clearly shown y the se of the soft steel cores shown n Fgres 23 and 2. he foregoing eerments shoud sucent to gve a very clear pictUre of how mgnetc fux Is pruced y current Clow iue
e
18
23
ELECTROMAGNETS
but that no voltage was induced by a steady magnetic field re gardless of how strong it might b made. Let us consider a few simple experiments concerning induced electromotive force. Let the bar magnet of Figure 25 be thrust quickly into the coil. The d-c voltmeter with with a zero center scale will deflect
Figre 25
momentarily either to the right or left depending upon the po larity of the connections. connections. Let us say it deflects deflects to the right. Next, the magnet is withdrawn quickly the voltmeter will de flect momentarily to the left. Now let the bar magnet be replaced by a coil r solenoid and a battery as in Figure 26 Upon closing closing the battery circuit circuit the
Fgre 26
a someing e reation of the lux to the current he discssion s far has en concerned wth the me ' cncal force prduced y magnetism We must also study he eect of magnetsm n nducing a voltage or current we are to understand the attraction of non-magnetc etas by the spe cal eectromagnet. After Oersted dscovered the magnetc feld at a con ductor carryng crrent 8, many expermenters attempte to prouce the nverse effect. That s, they tred to produce a crent y means of a magnetc magnetc feld. Al were nsccessful untl FaradayS hstoric experments n 83 araday showed that a current, or more correctly an electromotve force, was nduced when the amount of fux threadng a col was changng,
DESIGN CONSTRUCTION AND OPERATING PRINCIPLES 19 voltmeter will show a deflection and will deflect in the opposite direction upon opening the circuit. The magnitude of the voltage induced with the arrangement of Figure 26 would be quite small. However the magnitude of the induced voltage can be greatly increased by inserting a laminated iron core in the solenoid as in Figure 27 The introduction introduction of an airon core causes a great
Fgure 27
deal more flux t be set up in coil B for a given current in the coil A thus increasing increasing the induced voltage. We say the iron carries flx more readily than air because it has a higher per mebility Let us consider the direction of te induced electromotive force in Figure 27. Un closing the switch current will flow in the diection of the arrows on the solenoid winding and thus produce a north pole pole at the right hand end of the iron core. Now we must use a law discovered by Lenz in 1834 which is called Lenz' Law. The law may be stated as follows: follows: Any induced electromotive force tends to set up a current in such a direction as to oppose the action which produced the electromotive force. Thus upon closing the switch n Figue 27 a current would be induced in coil B in the direction indicated because such a cur rent would set up a magnetic flux which opposes the flux set up by a north pole at the right hand end of the electromagnet core. Figure 28 shows that coil B will be repelled since flux lines in the same direction repel. We might also consider that the cur rent in coil A is prucing a north pole at the left side of coil B which is repelled by the the adjacent north pole of coil A. Upon opening the switch the urrent in coil A would be reversed
18
ELECTROMAGNETS
but that no voltage was induced by a steady magnetic field re gardless of how strong it might b made. Let us consider a few simple experiments concerning induced electromotive force. Let the bar magnet of Figure 25 be thrust quickly into the coil. The d-c voltmeter with with a zero center scale will deflect
DESIGN CONSTRUCTION AND OPERATING PRINCIPLES 19 voltmeter will show a deflection and will deflect in the opposite direction upon opening the circuit. The magnitude of the voltage induced with the arrangement of Figure 26 would be quite small. However the magnitude of the induced voltage can be greatly increased by inserting a laminated iron core in the solenoid as in Figure 27 The introduction introduction of an airon core causes a great
Fgure 27
Figre 25
momentarily either to the right or left depending upon the po larity of the connections. connections. Let us say it deflects deflects to the right. Next, the magnet is withdrawn quickly the voltmeter will de flect momentarily to the left. Now let the bar magnet be replaced by a coil r solenoid and a battery as in Figure 26 Upon closing closing the battery circuit circuit the
deal more flux t be set up in coil B for a given current in the coil A thus increasing increasing the induced voltage. We say the iron carries flx more readily than air because it has a higher per mebility Let us consider the direction of te induced electromotive force in Figure 27. Un closing the switch current will flow in the diection of the arrows on the solenoid winding and thus produce a north pole pole at the right hand end of the iron core. Now we must use a law discovered by Lenz in 1834 which is called Lenz' Law. The law may be stated as follows: follows: Any induced electromotive force tends to set up a current in such a direction as to oppose the action which produced the electromotive force. Thus upon closing the switch n Figue 27 a current would be induced in coil B in the direction indicated because such a cur rent would set up a magnetic flux which opposes the flux set up by a north pole at the right hand end of the electromagnet core. Figure 28 shows that coil B will be repelled since flux lines in the same direction repel. We might also consider that the cur rent in coil A is prucing a north pole at the left side of coil B which is repelled by the the adjacent north pole of coil A. Upon opening the switch the urrent in coil A would be reversed
Fgre 26
2
CA
DG, CRC, A PRG PRC 2
•
'
, /
/
"
e
(dcasn). Accodn to nz' law, th ndcd cnt cnt n co B wod st p a mantc whch wod nd to pvnt th dcas of h xstn fx. nd s condton th fx n co B wod vsd, and co B wod b attactd to wad th ctomant ctomant A s 26 and 27 show tns of w havn voas cd n thm cas of a chann c nt n th sonod s vdnt hat a coctn non-fo mantc wash wd hav n a sma mn. Yo ca that fo dct cn, ndcd voas and c ntss aa oy dn swtchn opatons nt opatons and that th s no dcd vota dn stady cnt fow adss o how sto th fds may . Howv J h atho' spca cto mant ts atnatn cnt, and w a t dstan th opaton o th ctomat w mst consd a fw o th chaactstcs o atnatn cnt As yo alady ow atatn cnt h th popty of vsn ts dcton o !ow many tms a sco o th sa 6 cyc cnt t fows n on dcton fo 1/12thof a scond an thn n th opst dcton fo th nxt 1/2th scond Howv t dos not chan abpty fom say 1 am ps n on dctn to 1 amps n th oh dcton hs wod q a vy apd chan n cnt at th v sas and consqnty ndc hh voas nstad t chans chans n th ada mann lstatd lstatd n 29. hs cv s cad a sn wav and psnts many nata motons as w as atnatn cnt. o amp, psnts h vocty vocty tm aton of a wht sspnd fom a spn a st nto oscaton Consdn atatn cnt, h pont A
igu 2 psnts zo cnt, bt h cnt s ncasn. fact, s ncasn most apdy at ths pont of th wav h pont B psnts maxmm cnt, bt th cnt has stoppd n casn Byod nt B th cnt dcass At pnt C th cnt s zo and dcasn most apdy apdy om C to D a th th ffct s ad bt n th oppost dcton hs w s that wth atan cnts, th cnt s chan contnosy cpt at h paks of th wa, that s, cp at ponts k B and D D nc chann cnt cnt pcs chan f ad chann f podcs ndcd voas ad cnt n condctos nd by th chann f thn atnatn c nts podc sma atnatn ndcd ctomotv focs ow t s consd an on co sonod connctd to an atnatn cnt soc wth a non-fomantc condctn wash (shot cctd sconday) sspndd fo as n ncan 3 At som nstant th sonod cnt s ncan n th dcton ndcatd ndcatd h dcton of th th dcd cnt n h wash w as ndcatd bcas an ndcd vota s aways n th opst dcton to th cn vota. vota. hs th wash w d fom h ctomant bcas th f ns podcd y th cnt fow n th ash podcs a noth po adjacnt th nd of th ctomant nast th wash, a th cnt ow toh th ctomant po dcs a noth p adjacnt th fac of th wash nast th ctomant h psv foc td btwn th fd of an ac
2
DG, CRC, A PRG PRC 2
CA
•
'
, /
/
"
e
(dcasn). Accodn to nz' law, th ndcd cnt cnt n co B wod st p a mantc whch wod nd to pvnt th dcas of h xstn fx. nd s condton th fx n co B wod vsd, and co B wod b attactd to wad th ctomant ctomant A s 26 and 27 show tns of w havn voas cd n thm cas of a chann c nt n th sonod s vdnt hat a coctn non-fo mantc wash wd hav n a sma mn. Yo ca that fo dct cn, ndcd voas and c ntss aa oy dn swtchn opatons nt opatons and that th s no dcd vota dn stady cnt fow adss o how sto th fds may . Howv J h atho' spca cto mant ts atnatn cnt, and w a t dstan th opaton o th ctomat w mst consd a fw o th chaactstcs o atnatn cnt As yo alady ow atatn cnt h th popty of vsn ts dcton o !ow many tms a sco o th sa 6 cyc cnt t fows n on dcton fo 1/12thof a scond an thn n th opst dcton fo th nxt 1/2th scond Howv t dos not chan abpty fom say 1 am ps n on dctn to 1 amps n th oh dcton hs wod q a vy apd chan n cnt at th v sas and consqnty ndc hh voas nstad t chans chans n th ada mann lstatd lstatd n 29. hs cv s cad a sn wav and psnts many nata motons as w as atnatn cnt. o amp, psnts h vocty vocty tm aton of a wht sspnd fom a spn a st nto oscaton Consdn atatn cnt, h pont A
22
Let two wahes placed nea the end of the electomaget as in igue 33 ome of the fux fom the eectomaget w thead o ct thogh th of the washes, and at a paticula insant cents in the two washes and in the electomagnet winding will have the diections diections indicated indicated ee we have one of the most impotat opeating pincipes of the special electo magnet fo atactig n-magnetic metas
,
psnts zo cnt, bt h cnt s ncasn. fact, s ncasn most apdy at ths pont of th wav h pont B psnts maxmm cnt, bt th cnt has stoppd n casn Byod nt B th cnt dcass At pnt C th cnt s zo and dcasn most apdy apdy om C to D a th th ffct s ad bt n th oppost dcton hs w s that wth atan cnts, th cnt s chan contnosy cpt at h paks of th wa, that s, cp at ponts k B and D D nc chann cnt cnt pcs chan f ad chann f podcs ndcd voas ad cnt n condctos nd by th chann f thn atnatn c nts podc sma atnatn ndcd ctomotv focs ow t s consd an on co sonod connctd to an atnatn cnt soc wth a non-fomantc condctn wash (shot cctd sconday) sspndd fo as n ncan 3 At som nstant th sonod cnt s ncan n th dcton ndcatd ndcatd h dcton of th th dcd cnt n h wash w as ndcatd bcas an ndcd vota s aways n th opst dcton to th cn vota. vota. hs th wash w d fom h ctomant bcas th f ns podcd y th cnt fow n th ash podcs a noth po adjacnt th nd of th ctomant nast th wash, a th cnt ow toh th ctomant po dcs a noth p adjacnt th fac of th wash nast th ctomant h psv foc td btwn th fd of an ac
DESN ONSTRUC ONSTRUCTON TON A OPERATG PRLES 23
ELECTROMAGNETS
,
igu 2
I : .
\'
I \ Fire 30 elecomaget ad the Held of a shot cicuited seconday (washe) is stikngy shown by a study of igues 31 and 32. igue 31 shows an electomagnet and with a means povided fo connecting it t o a soce of alteating cuent. The electo electo maget has an ee coe ove which ae placed thee almi nm wahes esting on the end of the magnet coil pimay windig. When the mnet winding is enegized enegized by the ate nag cuent the magetic field podced by the coi wding ad hat set up by the (seconday auminm washe cuent poduce epulion and the washes ae thown violently ito he ai, as shown in ige 32. COND U TI TIVE VE
WASHER R£PlLf
TO . OURC
ie 31
F 32
F 33 ompae the situation of the cuents in the two washes ige 33 with the cents in the two cois of iges 2 and 21 The cen ae fowing in the same diection and as i cated in igue 33 thee wil flx lines inkng the two washes which will tend to hem oweve since the foce of epulsion beween the ac electomagnet and h washes is vey stong is dfict to show by the aangement of ige 33 hat thee is an attaction between the two washes the cen in the ' two washes wee suficienty age the washes wold ped ogethe with consideable consideable foce foce The hoe in eithe washe i immateia since fu passes though non-feomagetic mateias just as does though ai With thi fndamnta pinciple mid that thee Is at taction between the two washes igue 33), let s now con side the constuction and fields of the special electomaget which wi atact ofeos ofeos mateias mateias The elecomaget is show diaamacaly In ige 34 The few tns show epesent the ente ente winding of the electomagnet ige 35 s a coss section of the inne and oute laminated ion coes which eend the entie aa length the electomagnet. g e 36 shows the inne coe and he goup of coppe washes which tiay fl the anna space between the inne and ote coes These coppe washes occupy this space in only the face e the maget maget The top washe washe shows cealy in the phoogaph of igue 1. The complete eectomagnet is
22
DESN ONSTRUC ONSTRUCTON TON A OPERATG PRLES 23
ELECTROMAGNETS
Let two wahes placed nea the end of the electomaget as in igue 33 ome of the fux fom the eectomaget w thead o ct thogh th of the washes, and at a paticula insant cents in the two washes and in the electomagnet winding will have the diections diections indicated indicated ee we have one of the most impotat opeating pincipes of the special electo magnet fo atactig n-magnetic metas
,
,
I : .
\'
I \ Fire 30 elecomaget ad the Held of a shot cicuited seconday (washe) is stikngy shown by a study of igues 31 and 32. igue 31 shows an electomagnet and with a means povided fo connecting it t o a soce of alteating cuent. The electo electo maget has an ee coe ove which ae placed thee almi nm wahes esting on the end of the magnet coil pimay windig. When the mnet winding is enegized enegized by the ate nag cuent the magetic field podced by the coi wding ad hat set up by the (seconday auminm washe cuent poduce epulion and the washes ae thown violently ito he ai, as shown in ige 32. COND U TI TIVE VE
WASHER R£PlLf
TO . OURC
ie 31
24
F 32
ELECTROMAGNETS
F 33 ompae the situation of the cuents in the two washes ige 33 with the cents in the two cois of iges 2 and 21 The cen ae fowing in the same diection and as i cated in igue 33 thee wil flx lines inkng the two washes which will tend to hem oweve since the foce of epulsion beween the ac electomagnet and h washes is vey stong is dfict to show by the aangement of ige 33 hat thee is an attaction between the two washes the cen in the ' two washes wee suficienty age the washes wold ped ogethe with consideable consideable foce foce The hoe in eithe washe i immateia since fu passes though non-feomagetic mateias just as does though ai With thi fndamnta pinciple mid that thee Is at taction between the two washes igue 33), let s now con side the constuction and fields of the special electomaget which wi atact ofeos ofeos mateias mateias The elecomaget is show diaamacaly In ige 34 The few tns show epesent the ente ente winding of the electomagnet ige 35 s a coss section of the inne and oute laminated ion coes which eend the entie aa length the electomagnet. g e 36 shows the inne coe and he goup of coppe washes which tiay fl the anna space between the inne and ote coes These coppe washes occupy this space in only the face e the maget maget The top washe washe shows cealy in the phoogaph of igue 1. The complete eectomagnet is
DESIGN, CONSTRUON AND OPERATG PRCLES 25 AMINAD CNR
AC W"'NG
ig 34 g
mouted o a suortig stand for coveience i demostratig its qe ability to attract o-ferromgetic metals. We ow know the costrctio of the eletomaget ad ave studied the essential magetic theory volve i ts operatio.
LITED
g
35
36
With tis iormato it wil ot dfficlt to explai its performance Figre 37 is a cross sectio of the magnet wth the four copper washers removed The circles at the top ad ttom rereset the widig. widig. The dots ad crosses idcate tat cur ret is directed ot of the paper ave and ito the pper low at the ist istat at cosidered We ow from the right had rle tat
Fre
37
24
ELECTROMAGNETS
DESIGN, CONSTRUON AND OPERATG PRCLES 25 AMINAD CNR
AC W"'NG
ig 34 g
mouted o a suortig stand for coveience i demostratig its qe ability to attract o-ferromgetic metals. We ow know the costrctio of the eletomaget ad ave studied the essential magetic theory volve i ts operatio.
LITED
g
35
36
With tis iormato it wil ot dfficlt to explai its performance Figre 37 is a cross sectio of the magnet wth the four copper washers removed The circles at the top ad ttom rereset the widig. widig. The dots ad crosses idcate tat cur ret is directed ot of the paper ave and ito the pper low at the ist istat at cosidered We ow from the right had rle tat
Fre
37
28
ELECTRMAGNETS
DESGN CONSTRCTON N PERATG RCLES 29
principle The shadd le provdes the roating field requied to start the rotor of he he sngle-phae nduction moor To ex pan wt is mant a ·shad le let us us study te eectro magnet of Figre 40
�
pole face from the uhaded rton toward the saded por tion Fige 1 a schematic drawing of a shaded e motor Here we see te decton of he shifting flux and the dection of rotaon of the rotor Note that the fl sfts in a decton ·SHlfTING
:
SHDG COL ",
WX
RO A ION O OTO
.�
,
-O A. SOUE�
Fre 40 Here Her e w e ha have ve a m nat nat ed ed core elec electom tom agn agn et et in wh ch ch a sor ort t ci ci cuI t ted d cop e op r ri I emb mbdd dd ed n n h e e ace Th e ortio rtion n of the pol pole e fa fac ce in d d e t e sh ort cic icu uite ited d tU tUr rn 1 sa saiid t o b w hle hle tha thatt rtio rtion n ex ernal ernal t o it i us ush h ad ad ed. S
the po poe e itse tseU U i c cle led d a t urn (co (condu nducto ctor r) is kn ow ow
a the short cicuit
Wih alternating current n he here Is an alternatin magnetic field in the rton o the pole which 1s in tim phse wth te aternaing curent rucing t The magnetic field n the shade rtion of the le las the ave mentoned fied due to the actio o the shading coU" et us assume tt at a given nstant, the fl the unshaded portion s a certain value and increasng The fl in te shadd porton due to he prmary coil is that same value, t in te sded porton te ux set up y he curent nduced in the shadi co s n the opposte dection enz' aw) so the net fux s some smaler vaue Ths would mean that given vaues of fux would occur first in the unsaded rtion of the pole and at a slghtly later time n the shaded porton o the pole Hence the appeance of a shting or moving magnetic fed results Te drection of te shiftng f s across the
Jl from e unshaded toward the shaded porton of eer motor poe s a wel establshed fact tt a conductor in a rotating magnetic field wl have a force exerted on t tendng to make the conductor folow the the rotating fied herefore, e force on the conductors n the otor face cause t to move from the un sadd towad the shaded e secton as llustrated in gure 41 From the foregoing eanatons it s ovious that the copr conductor (Y) of Fre 40 w have a force exerted on t that wil move t in th drecton ndicated toward the shaded poron of the le U a hree legged core as shown in Figure 2 s wound w a coi and exted y a source of alternatng current the three poe peces wl all ecome (N north poes at some insananeous vaue of e ipressed votage whch wU resut n repusion e tween the fux lnes as lustrated The fux of the the two outer poes wl tend to repe the fux lines of the center poe to crowd them toward e center and the flux from the center poe w tend to reel the f of the two outer les Here now we have ectly the conditon existing n the authors speca eectro magnet except tat n e eectromagnet the two outer poles are
28
ELECTRMAGNETS
DESGN CONSTRCTON N PERATG RCLES 29
principle The shadd le provdes the roating field requied to start the rotor of he he sngle-phae nduction moor To ex pan wt is mant a ·shad le let us us study te eectro magnet of Figre 40
pole face from the uhaded rton toward the saded por tion Fige 1 a schematic drawing of a shaded e motor Here we see te decton of he shifting flux and the dection of rotaon of the rotor Note that the fl sfts in a decton ·SHlfTING
�
WX
.� RO A ION : O OTO
SHDG COL ",
,
-O A. SOUE�
Fre 40 Her e w e ha Here have ve a m nat nat ed ed core elec electom tom agn agn et et in wh ch ch a sor ort t ci ci cuI t ted d cop e op r ri I emb mbdd dd ed n n h e e ace Th e ortio rtion n of the pol pole e fa fac ce in d d e t e sh ort cic icu uite ited d tU tUr rn 1 sa saiid t o b w hle hle tha thatt rtio rtion n ex ernal ernal t o it i us ush h ad ad ed. S
the po poe e itse tseU U i c cle led d a t urn (co (condu nducto ctor r) is kn ow ow
a the short cicuit
Wih alternating current n he here Is an alternatin magnetic field in the rton o the pole which 1s in tim phse wth te aternaing curent rucing t The magnetic field n the shade rtion of the le las the ave mentoned fied due to the actio o the shading coU" et us assume tt at a given nstant, the fl the unshaded portion s a certain value and increasng The fl in te shadd porton due to he prmary coil is that same value, t in te sded porton te ux set up y he curent nduced in the shadi co s n the opposte dection enz' aw) so the net fux s some smaler vaue Ths would mean that given vaues of fux would occur first in the unsaded rtion of the pole and at a slghtly later time n the shaded porton o the pole Hence the appeance of a shting or moving magnetic fed results Te drection of te shiftng f s across the
30
Jl from e unshaded toward the shaded porton of eer motor poe s a wel establshed fact tt a conductor in a rotating magnetic field wl have a force exerted on t tendng to make the conductor folow the the rotating fied herefore, e force on the conductors n the otor face cause t to move from the un sadd towad the shaded e secton as llustrated in gure 41 From the foregoing eanatons it s ovious that the copr conductor (Y) of Fre 40 w have a force exerted on t that wil move t in th drecton ndicated toward the shaded poron of the le U a hree legged core as shown in Figure 2 s wound w a coi and exted y a source of alternatng current the three poe peces wl all ecome (N north poes at some insananeous vaue of e ipressed votage whch wU resut n repusion e tween the fux lnes as lustrated The fux of the the two outer poes wl tend to repe the fux lines of the center poe to crowd them toward e center and the flux from the center poe w tend to reel the f of the two outer les Here now we have ectly the conditon existing n the authors speca eectro magnet except tat n e eectromagnet the two outer poles are
DSGN, CONSTRUC CONSTRUCTON, TON, AND OPERATG PCES
ELECTROMAGNETS
MGN FD K IY PL
N SRE
ad C Ts mes tt the tertary tertary Y wll hve forces eerted on it from poles A ad B wic wll case a strong ceterg acton of te tertary tertary over pole C Here aga we ve ve te same n te authrs speca eectromagnet ecept at poles codton codto A ad B are ormed to one contuos cydrical pe at te ceter pole A grap c lstraton of te estence of e travelling m agetc ed prced by the specal electromaget s illstrated by a actl potograp (igre 44) Here two almnm lls are placed upo te face o te electromagnet ad wh te pr turned on te amm bals rotate very rapdly mary crrent turned Te curved arrow aove eac all ndicates te drecton o ro tio of te l tatio ta Several interestg tings are to be noted abut te attractive propertes properte s of tis specal electroma electromaet et Te mass to be
Figue 2
formed Into oe contnuos cyldrical pole aut the iner poe. But addton te ceter pole o te ahors specal eectromaget as a sort cicted (copper waser) secodary surroundng te le ed U we mody the thee legged eectromagnet 01 igre 42 b addg a sort ccuted copper secodary o te center core leg e mied electromaget electromaget will lok le gure 43. Tis saded pole electro device will terefore come a magnet ts elecoagnet a second secodary tertiary tertiary piece of copper Y wll ave a rce exerted on it te drecton sown I t s paced over poes A ad C but wil ave a orce erted on it e opsite drecto i paced over poes B
OR
y
N SHET
TOAC.
x-
Fr 44
Fr 43
31
30
DSGN, CONSTRUC CONSTRUCTON, TON, AND OPERATG PCES
ELECTROMAGNETS
MGN FD K IY PL
N SRE
ad C Ts mes tt the tertary tertary Y wll hve forces eerted on it from poles A ad B wic wll case a strong ceterg acton of te tertary tertary over pole C Here aga we ve ve te same n te authrs speca eectromagnet ecept at poles codton codto A ad B are ormed to one contuos cydrical pe at te ceter pole A grap c lstraton of te estence of e travelling m agetc ed prced by the specal electromaget s illstrated by a actl potograp (igre 44) Here two almnm lls are placed upo te face o te electromagnet ad wh te pr turned on te amm bals rotate very rapdly mary crrent turned Te curved arrow aove eac all ndicates te drecton o ro tio of te l tatio ta Several interestg tings are to be noted abut te attractive propertes properte s of tis specal electroma electromaet et Te mass to be
Figue 2
formed Into oe contnuos cyldrical pole aut the iner poe. But addton te ceter pole o te ahors specal eectromaget as a sort cicted (copper waser) secodary surroundng te le ed U we mody the thee legged eectromagnet 01 igre 42 b addg a sort ccuted copper secodary o te center core leg e mied electromaget electromaget will lok le gure 43. Tis saded pole electro device will terefore come a magnet ts elecoagnet a second secodary tertiary tertiary piece of copper Y wll ave a rce exerted on it te drecton sown I t s paced over poes A ad C but wil ave a orce erted on it e opsite drecto i paced over poes B
OR
y
N SHET
TOAC.
x-
Fr 44
Fr 43
ELECTROMAGNES
DESGN ONSRUON OPERG PRNS 33
attracted may subec o a repulsive force from the primary Held an therefore should b of a size not larger han he space wihin the cylindrica e Since th e current in he pr imary wining Is g enerally oosie to th e current in the mass to araced, that mass shoud of a general size and shape o lie within he cylindrical le pe ce undary and should o exend over into the ifuence of he primary coi When he circumerence f the mass to atraced is larger than the cicumference of he cylindrca pole, he repusive force exered un it by he primary winding in creases very rapidy wih an increase n is size he non-ferrous mass s aso reled is approximately of he same periphera i mensions as he inside dmnsion of the cylindrica core bu is not closey adjacen hereo he obect to atracte shoul be adapted o he field and soud generaly be placed fairly close to the magne unless i is Quie a bit smaer tha the in side dimension of the cyndrica poe face. · is possibe to make the conductive mass to b attracte "ump a considerable dstance o affix se to the aractor b y havig he nofer rous mass of consierably smar dameter tha the cyinrica core By experimening wih armatures of eren sizes suspended a various disances from the atracor face i has en found hat a region or zone of atraction exss which is conical in shape. A coductive coductive obect ace ace with is principa conducting pah wthn ths cone is atrace he se of of this cone
substantiay coincides wih he face of the attractor and has is vertex on he axs a a distance from the attracor as illustrated n gre igre shows a siver half or suspended near he at ractor face. n his f gure the half do lar is suspeded so as o have ts pane perpen dicuar o the plane of the aractor face
32
Fr 45
31
re 46 bore he magnet s energized But the nstan nstan current flows though he primary winding of the eecromagne he ha oar urns so t ha is pane is paralel with h e pane of the attr actor ace as shown in igure 7 and is attrace with considerabe force his resu is exacly opposite o he resul t o be expected he silver doar were paced in he fiel o a ordinary al ternaing curren elecomagnet he atracor in t his special eecromaet were o prese to exercise ts iuence the coi wou hen urn with its pane perpendicuar to the pane of the electromanet face U a non-ferrous ring washer or isc with a pane dimesion consieraby in excess of the cyindrica poe face dmensio is paced near the face of this speca eecromagnet the the ob ect s ou in he inluence of the primary c an as the case of a conventional electromagne the obect woud be re pele.
ELECTROMAGNES
DESGN ONSRUON OPERG PRNS 33
attracted may subec o a repulsive force from the primary Held an therefore should b of a size not larger han he space wihin the cylindrica e Since th e current in he pr imary wining Is g enerally oosie to th e current in the mass to araced, that mass shoud of a general size and shape o lie within he cylindrical le pe ce undary and should o exend over into the ifuence of he primary coi When he circumerence f the mass to atraced is larger than the cicumference of he cylindrca pole, he repusive force exered un it by he primary winding in creases very rapidy wih an increase n is size he non-ferrous mass s aso reled is approximately of he same periphera i mensions as he inside dmnsion of the cylindrica core bu is not closey adjacen hereo he obect to atracte shoul be adapted o he field and soud generaly be placed fairly close to the magne unless i is Quie a bit smaer tha the in side dimension of the cyndrica poe face. · is possibe to make the conductive mass to b attracte "ump a considerable dstance o affix se to the aractor b y havig he nofer rous mass of consierably smar dameter tha the cyinrica core By experimening wih armatures of eren sizes suspended a various disances from the atracor face i has en found hat a region or zone of atraction exss which is conical in shape. A coductive coductive obect ace ace with is principa conducting pah wthn ths cone is atrace he se of of this cone
substantiay coincides wih he face of the attractor and has is vertex on he axs a a distance from the attracor as illustrated n gre igre shows a siver half or suspended near he at ractor face. n his f gure the half do lar is suspeded so as o have ts pane perpen dicuar o the plane of the aractor face
32
Fr 45
34
LECTROMAGNES
re 46 bore he magnet s energized But the nstan nstan current flows though he primary winding of the eecromagne he ha oar urns so t ha is pane is paralel with h e pane of the attr actor ace as shown in igure 7 and is attrace with considerabe force his resu is exacly opposite o he resul t o be expected he silver doar were paced in he fiel o a ordinary al ternaing curren elecomagnet he atracor in t his special eecromaet were o prese to exercise ts iuence the coi wou hen urn with its pane perpendicuar to the pane of the electromanet face U a non-ferrous ring washer or isc with a pane dimesion consieraby in excess of the cyindrica poe face dmensio is paced near the face of this speca eecromagnet the the ob ect s ou in he inluence of the primary c an as the case of a conventional electromagne the obect woud be re pele.
DESIGN CONSRUCTON, AND OPRATG PCES 35
Fgue 47
In Fgure 48 a large alumium dsc s suspeded n fo o he eectromagne wh s pane paale wit te attraco face befoe the eectromagne wndng s eegzed wh curent Bu the insa hat curent flows toug the electomagne's prmary widng e large dsc s epelled wit geat foce and fally comes o est wt ts plane pepedcua to the face of te eectomagne (see Fue 9 9)) and emais tis posion as log as e cuent coiues to fow hough he primay Widng of the eectomagne I s altogete ssible o modfy e seconday atacto) elemen by substug a wdg n pace of the coppe washes. Such a aangemen s show y Fgure 50. Hee a means s povded fO shr ccung he secoday col by cosg e swch o poso A as ustaed By hs arangement the swtc may b cosed, causg he so c cr r cuted widng o ac ke the coppe washers washers poducng at raco of a non-ferous mass whe used conjuncto wt e prmay wding a cydca coe Ten te te swtch may may e opened causng e non-ferous mass o b epelled ice te only fx nes now poduced by he elecromage ae oe
Flgu.e 48
hs w hs show e sho geme ragem t e ara y. By te mary. primar d by e pri duce uced pod po g g nec ec y co con eeb eby he ito o B h osit d o pos ose sed tc c may e co e sw swt e th the fgure fgur t e ch ch o w rce e s orc o e n curr cu rre g g r a a a lter lte ame am e ding ng to te s ndi e wn
se op er so as o op nner ted d b b a mann Mec ecte cOM ng g s cO dn y y wd prm prm r on-fe -fer co o of te on ttra rac ans s att s mean s dng ng By y w d ma ay e p m te t en en gem m ra r age s s a d T lshe ls hed omp p a ccom cc so be also al ss ca ca s m a ou ous e pas ase ced d so a to e n p one ece co Is con ta aco y (a (at oda day e sec eco c h he w c form wch he or r to he for ife feo ay s i prm ma the e pr ton on o th ps st op
son n fo easo ced d I I. e rea ndu uce ret t nd urre cto o)) has cur ata act y (at oda day sec eco the e d n th duce ced n i idu urre ren te e cur ta a t fac c t he e fa ed o h u ued t s is to b at ts t mass o
b
ly y exac acl no ex tay y)) s no (er erta ted d ( tac acte at
e phas ase n ph
ctly y in exa actl re wl no be ex eefo efore he n and h cure ren ay y cu pim ima the e p to th pase wt he cue e secodary whee he secondary s fed in exact exact opposto o e prmay prmay e en n curre n n he secondary s nduce s more nearly exacty n pase wh aca um a xmu uls s In maxm esul re whch res a re e am ma he en n h cu en he cu he ton ) aco) atraco y (atr onday seconda ary and sec mary e e pm whee nce whe Instance In he he Insta
-
34
DESIGN CONSRUCTON, AND OPRATG PCES 35
LECTROMAGNES
Fgue 47
Flgu.e 48
In Fgure 48 a large alumium dsc s suspeded n fo o he eectromagne wh s pane paale wit te attraco face befoe the eectromagne wndng s eegzed wh curent Bu the insa hat curent flows toug the electomagne's prmary widng e large dsc s epelled wit geat foce and fally comes o est wt ts plane pepedcua to the face of te eectomagne (see Fue 9 9)) and emais tis posion as log as e cuent coiues to fow hough he primay Widng of the eectomagne I s altogete ssible o modfy e seconday atacto) elemen by substug a wdg n pace of the coppe washes. Such a aangemen s show y Fgure 50. Hee a means s povded fO shr ccung he secoday col by cosg e swch o poso A as ustaed By hs arangement the swtc may b cosed, causg he so c cr r cuted widng o ac ke the coppe washers washers poducng at raco of a non-ferous mass whe used conjuncto wt e prmay wding a cydca coe Ten te te swtch may may e opened causng e non-ferous mass o b epelled ice te only fx nes now poduced by he elecromage ae oe
36
ELECROMAGNE
hs w hs show e sho geme ragem t e ara y. By te mary. primar d by e pri uced poduce pod g g nec ec y con co eeb eby B he h ito o p osit os d o ose o sed e c m ay tc c e swt sw e th the fgur fg ure ch ch te rce e o w orc en so curr rre g g cu ra a lter ame e alte ding ng to te sam ndi e wn se op er so as o op nner ted d b b a mann Mec ecte cOM ng g s cO dn y y wd prm pr m r on-fe -fer co o of te on ttra rac ans s att s mean s dng ng By y w d ma ay e p m te t en gem men ra age s s ar d T lshe hed omp pls ccom so be acc al also ca s mass ca ou ous e pas ase ced d so a to e n p one ece co Is con ta aco y (a (at oda day e sec eco c h he w c rm wch he for or r to he fo ife feo ay s i prm ma the e pr ton on o th ps st op son n fo easo ced d I I. e rea ndu uce ret t nd urre cto o)) has cur ata act y (at oda day sec eco the e d n th duce ced n i idu urre ren te e cur ta a t fac c t he e fa ed o h u ued t s is to b at ts t e phas ase n ph ly y exac acl no ex tay y)) s no (er erta ted d ( tac acte mass o b at ctly y in exa actl re wl no be ex eefo efore he n and h cure ren ay y cu pim ima the e p to th pase wt he cue e secodary whee he secondary s fed in exact exact opposto o e prmay prmay e en n curre n n he secondary s nduce s more nearly exacty n pase wh aca um a xmu uls s In maxm esul re whch res a re e am ma he en n h cu en he h e cu ton ) aco) atraco y (atr onday seconda ary and sec mary e e pm whee nce whe Instance In he he Insta -
DEG CORU CORUCTO, CTO, AD OEAG RNC RNCE E
Figre
Figre 49 are connected n phase opposion o he sae alernaing cu ren source, he secondary (aractor) crcut may b modid afford d soe phase ag. An arrangement arrangement or ths odi 50 a� to affor fcaion s shown in Figure 5 where a ressor may b con nected I series wih he attracor wning y closng the swtch to posiion B. his circut can e conneced n paralel Ppos on with he priary and y adjustmen of he variale rheosa a fairly coparae phase lag may b produced How Howe eer er tis for o consrucion (even wth a reSstor) n whch he secod r � (atractor s connected n phase oppositon to the priay S neror o he orm n whch the secodary h current in duced n t he arrangemen shown n Fgure has soe advanages for educaona deonsraons een hough It s no as efcen as he copper copper washer ype The swichng syste allows a much greater lexility in ts use snce he equipmen ay b
I
37
used oh as a special electroagne for non-errous aeras and as a convenionl eectromagne ue o he fact ha hs eecroagne s an open core device power r factor is not not unty his resuls n raher large power power powe consupon and n heatng of he wnding although he heating ay e reduced consideray y usng very large wire. For lae electroagnes o ths kind I I ay e necessary o pro ve means or circuaing a coolng medium hrough h pr ary and secondary olow copper uing could e used in the consructon of exremely arge elecromagnes o his ype Generaly speaing capaciors ay e used n correctng the power facor of his ype eectroagnet therey reievng he power supply line o much of Its watess curren urden and hus helping to eep he electroagnet prary wndng coo Fgure 51 s a graph showing amount of power faco facor correc on ha was oaned wih static capacitors of 100 icrofarads used In conuclon with one of the auhors' elecroagnets for he atracion of non-ferrous meals. ae shows the change n current line voage, power factor, and phase angle obtained hrough he use o statc ca paciors in conuncion wth wth the eectroagnet he elecro magnet and capacitors were those used to otain he graph shown n Figure 1. n order to correc he power facor y use of sac capacors he capactors are of course, shunted across he Inpu erminals of he prmary winding of he eectro magne
36
ELECROMAGNE
DEG CORU CORUCTO, CTO, AD OEAG RNC RNCE E
Figre
Figre 49 are connected n phase opposion o he sae alernaing cu ren source, he secondary (aractor) crcut may b modid afford d soe phase ag. An arrangement arrangement or ths odi 50 a� to affor fcaion s shown in Figure 5 where a ressor may b con nected I series wih he attracor wning y closng the swtch to posiion B. his circut can e conneced n paralel Ppos on with he priary and y adjustmen of he variale rheosa a fairly coparae phase lag may b produced How Howe eer er tis for o consrucion (even wth a reSstor) n whch he secod r � (atractor s connected n phase oppositon to the priay S neror o he orm n whch the secodary h current in duced n t he arrangemen shown n Fgure has soe advanages for educaona deonsraons een hough It s no as efcen as he copper copper washer ype The swichng syste allows a much greater lexility in ts use snce he equipmen ay b
38
I
used oh as a special electroagne for non-errous aeras and as a convenionl eectromagne ue o he fact ha hs eecroagne s an open core device power r factor is not not unty his resuls n raher large power power powe consupon and n heatng of he wnding although he heating ay e reduced consideray y usng very large wire. For lae electroagnes o ths kind I I ay e necessary o pro ve means or circuaing a coolng medium hrough h pr ary and secondary olow copper uing could e used in the consructon of exremely arge elecromagnes o his ype Generaly speaing capaciors ay e used n correctng the power facor of his ype eectroagnet therey reievng he power supply line o much of Its watess curren urden and hus helping to eep he electroagnet prary wndng coo Fgure 51 s a graph showing amount of power faco facor correc on ha was oaned wih static capacitors of 100 icrofarads used In conuclon with one of the auhors' elecroagnets for he atracion of non-ferrous meals. ae shows the change n current line voage, power factor, and phase angle obtained hrough he use o statc ca paciors in conuncion wth wth the eectroagnet he elecro magnet and capacitors were those used to otain he graph shown n Figure 1. n order to correc he power facor y use of sac capacors he capactors are of course, shunted across he Inpu erminals of he prmary winding of he eectro magne
ELECTROMAGNTS ,350 .40 . 40
. 30 .320 .310
.30
20 1·28 �.270 260 250 240 230
37
� a
10CAPTAE 20 0IN MfARADS 0 0 Fie 51
'0 0 90
0
38
ELECTROMAGNTS ,350 .40 . 40
. 30 .320 .310
.30
20 1·28 �.270 260 250 240 230 � a
10CAPTAE 20 0IN MfARADS 0 0
'0 0 90
0
Fie 51 Table CAPACTORS USED FOR POWER FACTOR CRRECTIN Cpcne n d
Ln.
ine E
Powe Ft P E
0
16
0 0
• 3 3
".
50
8
289
7 8'
1
48
ego 42'
O O 1
0
Phase Ane
An eectromagnet for attracton of non-ferros metals such as has en descrd canot made effectve for the attrac ton of smll peces of nonferros metals when sed on a ow freqency freqen cy power sorce In order to use ths type eectroma eectromag g net for the atracton of smal particles or peces of nonferrous meals s necessary tht desgned and constructed for oraUon on a sppy of hgh freqency current The freqency requred wi deend on the sze of he peces or partcles to be attracted
