Alternator

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Alternator

• Electrical Machines Electronics
• Lalji Katariya
• Electrical Electronics Department
• Indus Institute of Technology Engineering

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EMF Generation

• In 1930,Farady discovered,
• EMF df/dt

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EMF Generation

• But applicable only when Magnetic circuit is same
  at all points.
• So not possible to apply in rotating machines.
• Can be express as constant magnetic
  field(Density) B relative velocity v of field
  and conductor of length l moving through it for
• EMF Blv

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EMF Generation

• In one conductor
• Generated EMF Blvsin? volts
• In coil
• Generated EMF 2Blvsin? volts
• In N number of coil
• Generated EMF 2NBlvsin? volts

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EMF Generation
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Direction of Induced EMF

• Direction of Induced EMF by
• Flemings right hand rule.

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Generation of EMF

• Conductor / Coil

• Flux / magnetic field

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Making of Coil / Armature
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Coil / Armature
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Development of Field

• Magnetic field developed by magnetic coil.

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Main Parts

• Stator Armature

• Rotor Field

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Stator

• Stationary armature
• Coils is placed in slots of stator core.
• Stator is made of laminates.
• Whole stator is fixed in the frame.

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Rotor

• Field winding
• External D.C.supply of 120-600 volt
• Supply by Brush Slip ring
• N pole S pole developed alternatively

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Rotor

• Cylindrical Type
• Small diameter
• Large axial length
• High speed
• Used at Steam turbine motors.

• Salient Pole Type
• Large diameter
• Small axial length
• Low speed
• Used at water turbines IC engines.

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Excitation system

• Flux distribution
• Recently, Brushless excitation system used.

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Difference between A.C. D.C. Generator

• In D.C. Generator
• Armature--Rotating
• Field -- Stationary

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Difference between A.C. D.C. Generator

• In A.C. Generator
• Armature--Stationary
• Field -- Rotating

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Advantages of Alternator over D.C.Generator

• Generation of power at High level.
• Easy to collect High current.
• No commutation.
• Easy to provide Insulation Cooling in
  stationary armature.
• Low voltage level in field so less insulation
  required.

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Electrical Mechanical Degree




360 mechanical
360 mechanical
For 2 pole 1 electrical cycle1 mechanical cycle
For 4 pole 2 electrical cycle1 mechanical cycle
360 mechanical 360 x (P/2) electrical 1
mechanical cycle (P/2) electrical cycle
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Induce EMF Frequency

• 1 Mechanical Revolution P/2 cycle of EMF
• P/2 cycles/revolution
• For N rpm, (N/60) revolutions/sec
• Frequency cycles/sec f
• f (cycles/revolution)x (revolution/sec)
• ( P/2) x (N/60) Hz
• (PN/120) Hz
• For 50 Hz

P 2 4 8 12
N 3000 1500 750 500
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EMF Equation

• For one conductor
• Induced EMF/revolution dø/dt volt
• (P x ø)/ (60/N) volt
• 2fø volt
• For Coil, EMF/revolution 4fø volt
• Average EMF/phase (Turn/phase)x 4fø volt
• 4føTPH volt
• R.M.S. value of EMF Form Factor x Avg EMF
• 1.11 x 4føTPH volt

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Types of Windings

• Single layer Double Layer
• Full pitch Short pitch winding

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Types of windings

• Concentrated Distributed winging.
• In Concentrated Winding
• all the conductor of coil in 1 slot
• In Distributed winding
• all the conductor of coil in more than 1 slots

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Pitch Factor/ Coil Span Factor Kc

• Kc factor by which EMF get reduced due to
  short pitch
• a short pitch angle
• Coil is shorted by angle a
• Kc COS(a/2)

1800
a
1800 -a
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Distribution Factor Kd

• Kd factor by which EMF get reduced dut to
  distributed winding.
• n slots / pole
• m slot / pole / phese
• Slot angle ß 180/ n
• Kd sin(mß/2)
• m sin(ß/2)

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Generalized EMF equation

• For full pitch concentrated winding
• EPH 4.44 føTPH volt
• For short pitch distributed winding
• EPH 4.44 Kc Kd f ø TPH volt

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Voltage drop in Induced EMF

• Due to following resistance
• 1.Armature resistance Ra
• 2.Armature leakage reactance Xl
• 3.Armature reaction Xa

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Voltage drop in Induced EMF

• 1.Armature resistance Ra
• Resistance offered by the armature winding
• In star connection, In delta connection

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Voltage drop in Induced EMF

• 2.Armature leakage reactance Xl
• Armature flux develop by current carrying
  conductor
• Armature Flux not cross air-gap but takes
  different paths and makes the winding inductive.

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Voltage drop in Induced EMF

• 3.Armature reaction Xa

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Voltage drop in Induced EMF

• 3.Armature reaction Xa
• Effect of armature flux on the main field flux on
  loading condition.
• For Unity p.f.
• cross magnetizing effect
• For zero p.f. lagging
• demagnetizing effect
• For zero p.f. leading
• magnetizing effect

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Synchronous reactance

• Xs Xl Xa
• Total voltage drop
• IRa jIXs
• I (Ra jXs )
• I Zs
• Zs Synchronous
• Impedance
• Due to Zs , No load voltage E0 reduced to
  terminal voltage V for lagging p.f.

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Voltage Regulation

• regulation E0 - V x 100
• V

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Parallel operation

• To full fill new increased load ,
• two alternators connected in parallel with bus
  bar.
• In this process, new running alternator is
  connected to bus bar by matching frequency V by
  synchroscope.
• This process called Synchronization.
• Another methods- 1. Dark Lamp Method
• 2. Bright Lamp Method.

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Condition for Synchronization

• following parameter should be same for incoming
  alternator bus bar
• Terminal voltage
• Frequency
• Phase sequence

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Any Question? Thanks