221 april 7 - q'('- Vv E' -gB d+ = lJBoAtvr,'//$ bo,€, 'a...

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p F ECE221H1S - ELECTRIC AND MAGI{ETIC FIELDS Lncrunn #33: TRANsFoRMxns,c,ND Eonv CIIRRENTS Key ldeas: a) lf two coils are placed around a common magnetic core, the magnetic flux due to one coil will induce an emf in the other coil. This isa transformer. b) ln non-perfect conductors, the electric field induced by a changing magnetic field results in the formation of eddy currents (J = oE;,a) Suggested Readingz Demarest, pp. 283 - 285 9-2: Faraday's Law of lnduction + ltr',, i (,k) uob: fi,tll , x Q,ft) /,^ ,{-r1 ,zt*/c,,'/ 1- */Y/^*; ^- e-'/ il/9 *, + /, H) L/' 6fu- o. ;" h)6.2/ /.tl I , (, 'r(f) z" fu**/' vrat''/" Y t E'-'f' ' /vt' + {q ^;,L/' ,/* + fr"- frr^t10,', J- .) [/,t',t-N.i"' k{ " #8, a) .F Il "9- = /u[ar= a, /{ /r .t&r*orJ ,1" uF /'. =) t. l" y'2 il, r t-- /",^tt f ,//. -/,1/) vf v/ a-.-
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Eddy Currents LEcruRx #33: TRANSFORMERS AND EDDY CURRDNTS (CoN'r) 9-2: Faradat's Law of Induction (con'tl 679"rnrw+tu +1' " 'te1 6 v ,y' ' / "1L'su L'/* li Dt '! tltl +fn5laU w"{e-r.
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Unformatted text preview: q'('- Vv E' -gB d+ = lJBoAtvr,'//$ bo,€, 'a = i /'i tra/ - Llg. .5 in 72 { 4 *&u rfL, e"n-o? Ll ,t" ehr,;c, /o,'os _* /*+, p.lfe/trfu * 5,^n *lu,/*n,t ? ur {ror,n, 1,^ tr /, , ,,7n *) / Dr" fi^',"$/ co, ._+_/4* rA,^ ,lr, *'r;{, Kev Points 1. ln an ideal transformer, 14=@, so the reluctance of the core is zero, Rc= 0. 2. Through Faraday's Law, the changing magnetic flux from one coil, creates a changing magnetic flux in a secondary coil, For ideal transformers: a. The two currents are related through the turns ratio: L_N, tz Nr b. The two emfs are related bv: ur =N, u2 N2 3. Within a non-perfect conductor (0 < o < co), the electric field induced by a changing magnetic fiefd wiff create an eddy current (l = aE66l. a. This current can lead to significant losses within the cores oftransformers, motors and generators. b. We can use low-loss ferrites, or laminated cores to reduce the eddy current losses. 33-2...
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This note was uploaded on 04/17/2008 for the course ECE ECE221 taught by Professor Stickel during the Spring '08 term at University of Toronto- Toronto.

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221 april 7 - q'('- Vv E' -gB d+ = lJBoAtvr,'//$ bo,€, 'a...

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