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Induced emf Developed torque Magnetization curve

SEE 3433 ELECTRICAL MACHINES. Induced emf Developed torque Magnetization curve. + e a . v. Induced emf. Regardless of operation, emf is always induced in armature circuit when there is rotation.

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Induced emf Developed torque Magnetization curve

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  1. SEE 3433 ELECTRICAL MACHINES Induced emf Developed torque Magnetization curve

  2. + ea  v Induced emf Regardless of operation, emf is always induced in armature circuit when there is rotation For a conductor of length l, moving at a speed v in magnetic field intensity B, the induced voltage is given by: X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X ea= B v l Induced emf ea= Bv l

  3. Induced emf

  4. Induced emf l

  5. _ + + _ + ea + ea ea= 2 B m r l In terms of flux per pole, where  = B A and Induced emf l

  6. Induced emf where  = B A and which gives This is an induced voltage for a single turn. If there are N turns with a parallel path,

  7. F i Developed torque For a conductor of length l, carrying current i in magnetic field intensity B, the torque developed is given by: Fc= B i l X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X Force produced, F = Bl i

  8. Developed torque

  9. x l i i Developed torque

  10. Tc = B l Ia r x Tc = B l Ia r In terms of flux per pole, where  = B A and Developed torque T = F r l Ia Ia T2c = 2 B l Ia r

  11. Developed torque This is torque for a single turn. If there are N turns with a parallel path, Similar to the constant obtained in induced emf !

  12. + Ea  If Field current  (flux per pole) depends on field (stator) current and hence MMF of the stator circuit  - angular speed of the rotor K is a constant – depends on physical construction of the machine Magnetization curve Is a plot of the induced emf vs If on an open armature circuit, at a given rotor speed Armature circuit Field circuit Induced emf Ea= K  At a given speed and K, the emf induced depends on 

  13. If Magnetization curve How does  vary with the field current? Flux will increase with field current - but not necessarily linear! Flux path produced by field: stator core  air gap  rotor core  airgap  stator core At low , core reluctance is small – most of MMF drop appear across air gap – consequently relation between  and field current is almost linear (due to the airgap)

  14. If Magnetization curve How does  vary with the field current? As field current increases, so too  - some part of the core (especially the rotor teeth) will saturate  Relation between  and Ifield is no longer linear

  15. Ea 2 Reduced speed 3 Ifield Magnetization curve 1 1 > 2 > 3 Since for constant speed Ea   the curve can be represented by Ea vs If

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