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Survey of Electric Machines

by: Mrs. Maud Gutkowski

Survey of Electric Machines ECET 3500

Mrs. Maud Gutkowski

GPA 3.57

Andrew Lyke

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Andrew Lyke
Class Notes
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This 29 page Class Notes was uploaded by Mrs. Maud Gutkowski on Tuesday October 20, 2015. The Class Notes belongs to ECET 3500 at Southern Polytechnic State University taught by Andrew Lyke in Fall. Since its upload, it has received 60 views. For similar materials see /class/225429/ecet-3500-southern-polytechnic-state-university in ELECTRICAL AND COMPUTER ENGINEERING at Southern Polytechnic State University.

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Date Created: 10/20/15
ECET 3500 Magnetism Andy Lyke SPSU ECET 3500 Magnetic fields Eectric current I creates Magneto Motive Force MMF symbol is H units are Ampereturnsmeter 5 H Andy Lyke SPSU ECET 3500 Magnetic Fields MMF Ampere turnsmtr induces magnetic flux density B Tesla o ouo is the permeability of just about everything vacuum wood air you me u04ngtlt10 7Hmrr therefore 1 Atrntr generates 47Tgtlt107 T in free space Andy Lyke SPSU ECET 3500 Magnetic Fields Earth39s magnetic field ranges between 30 amp 60 T on Earth39s surface Ferromagnetic materials enhance magnetic flux but proceed with caution Andy Lyke SPSU ECET 3500 Practical Electromagnets 1 Andy Lyke SPSU ECET 3500 Practical Electromagnets Andy Lyke SPSU ECET 3500 Practical Electromagnets Andy Lyke SPSU ECET 3500 Flux Density B Tesla Stylized BH Curve Low H region exaggerated Saturation Magnetic field Intensity H Atm Andy Lyke SPSU ECET 3500 BH Curves Sheet Steel Cast Iron ree B Tesla 4Tr X 10 7 X2500 A tmtr0003 14 T H Atmtr Andy Lyke SPSU ECET 3500 Flux Density B T Magnetic Field Intensity H oersteds Oersteds X 79577 Atm From HubertElectric Machines 1 1000 l 0000 9000 8000 7000 6000 5000 Relative Permeability 4000 3000 2000 I 000 Andy Lyke SPSU Magnetic Induction dd Eg dt 432 e For reasonable geometries 9PBAcos 39 I I I l VF quotquot 39 r39quot ECET 3500 Magnetic Induction Therefore we can induce a potential difference by changing B A or G Another view is the speed Voltage EBlv E is the generated potential difference along a straight wire of length 1 moving with velocity v through a magnetic field of flux density B And v is the velocity component normal to B Andy Lyke SPSU 12 ECET 3500 Hysteresis Not only is the 8H curve for ferromagnetic material non linear It also shows hysteresis Aligning the domains offers the benefit of dramatically increasing the magnetic flux for a given excitation but changing the domain alignment absorbs energy giving rise to hysteresis loss Andy Lyke SPSU 13 ECET 3500 Hysteresis The loss per cycle is proportional to the area of the hysteresis loop B The farther into saturation the larger theloop Andy Lyke SPSU ECET 3500 Hysteresis For each cycle around the 8H loop there is energy loss proportional to the area of the loop the loss per cycle increases as the peak value of B therefore H increases resulting in more area within the loop Empirically it is found that the energy lost per cycle is proportional to a power of B which is 16 for steel used in machinery P ocBl396 Hysteresis peak Since the energy lost is a function of the area of the loop the power loss is proportional to frequency peak P Hysteresis Andy Lyke SPSU 15 ECET3500 Driving a Core into Saturation Flux Density vs MMFBH curve Flux Density 06 08 1 12 14 16 Magneto Motive Force MMF 0 02 04 Andy Lyke SPSU ECET 3500 Driving a Core into Saturation Up to about BO8 the B vs H curve is somewhat Hnear Above BO1 very much more H is required to achieve small increases in B so the magnetizing current must increase disproportionately to achieve further incremental changes in B Andy Lyke SPSU 17 ECET 3500 Core Below Saturation B vs Magnetizing Current linear range ApSinT H Time Magnetizing current H is nearly sinusoidal Andy Lyke SPSU ECET 3500 Driving a Core into Saturation B vs Magnetizing Current core beginning to saturate 1 02 08 ApSinT 015 06 H 01 04 02 005 m 0 O 3902 005 o4 OI6 O1 O8 O15 1 o2 Time Higher harmonics are showing up in MMF wave Andy Lyke SPSU 19 ECET 3500 Driving a Core into Saturation B vs Magnetizing Current core saturating 0 7 05 1 V 1 ApSinT H Time oMMF is clearly not sinusoidal High order harmonics abound as incremental magnetizing current increases Andy Lyke SPSU 20 ECET 3500 Electromagnetic Force Force on a charge moving in a magnetic field q XE Cathode ray tube qaGa Andy Lyke SPSU 21 ECET 3500 Force on Current Carrying Conductor JKLJ XXXXXXXXXXXXXXXXXXXX XXXXXXXX XXXXXXXXXXX XXXXXXXX iXXXXXXXXXXX XXXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXXXXXX V I gtltgtltgtltgtltgtltgtlt Andy Lyke SPSU 22 ECET 3500 Eddy Current Loss dCD dB A V dt dt 2 P0werv R dividing the block into lamina diminishes V amp R for each sub element the net effect being to lower the loss due to induced eddy currents circulating in the iron Andy Lyke SPSU 23 ECET 3500 A simple motor Shaft Endtum a r b Andy Lyke SPSU 24 ECET 3500 Speed Voltage X X 25 Andy Lyke SPSU ECET 3500 Magnetic Circuit Battery drives current limited by the wire39s resistance oMMFfFnI current times turns H T Ampere turnsmeter i l f meEllength mgers Andy Lyke SPSU 26 ECET 3500 Isotropic Core of Constant Cross Section 19 I 915BgtltA A core cross section sotropic LL is everywhere the same in all directions r Jfaamealagtm Jm ersl i l Andy Lyke SPSU 27 ECET 3500 Reality sets in In a real structure cross sections will vary as will it permeability Reluctance is the magnetic analog of electrical resistance ogglmA compare RplA Inaego Andy Lyke SPSU 28 ECET 3500 A Practical Example lfl the core39s mean length and g the gap width then newline then EAuIg Artog Where pthe permeability of the core More precisely the A in the gap would be slightly larger than A the core cross section due to fringing v Andy Lyke SPSU 29


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