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Electrical Machines

ENERGY CONVERSION Takes place between well known pairs of forms of energy

FORMS OF ENERGY

FORMS OF ENERGY

FORMS OF ENERGY

FORMS OF ENERGY

FORMS OF ENERGY

FORMS OF ENERGY

FORMS OF ENERGY

Energy Conversion

Energy Conversion Matrix

Machine a tool containing one or more parts that uses energy toperform an intended action.

Dynamo a rotating machine for converting mechanical energy intoelectrical energy, or the reverse process, electrical energyinto mechanical energy.MechanicalElectricalGeneratorEnergyEnergy

DynamoElectricalMechanicalMotorEnergyEnergy

Construction andOperation of DCGenerator

Faraday’s Law ofElectro Magnetic InductionFirst Law:Whenever a conductor cuts magnetic flux an E.M.F isinduced in that conductor.

Faraday’s Law ofElectro Magnetic InductionSecond Law:The magnitude of the induced e.m.f. is equal to the rate ofchange of flux linkage.

Faraday’s Law ofElectro Magnetic Induction

Generated EMF

Electromechanical Energy Conversion

DC Generator

Two Major Parts of a Dynamo Stator That portion which is stationary The most important part of which is the field winding

Two Major Parts of a Dynamo Rotor That portion which rotates The most important part of which is the armaturewinding

Types of Armature Windings Lap winding It forms a loop as itexpands around thearmature core

Types of Armature Windings Wave winding It forms a wave as itexpands around thearmature core

Lap Winding In this winding the finishingend of one coil is connectedto one commutator segmentand the starting end of thenext coil situated under thesame pole and connectedwith same commutatorsegment.

Lap WindingA winding in which thenumber of parallel pathbetween the brushes isequal to the number ofpoles

Lap WindingEquations:Number of parallel paths multiplicity x Poles𝒂 𝒎𝑷Where:m multiplicity factor 1, for simplex winding 2, for duplex winding etc. A winding in which the number ofparallel path between the brushesis twice the number of poles

Wave WindingEquations:Number of parallel paths multiplicity x 2𝒂 𝒎𝟐Where:m multiplicity factor 1, for simplex winding two ends of each coil areconnected to commutatorsegments separated by thedistance between poles 2, for duplex winding etc.

Principle of Generator Action The principle of generator action requires1. The presence of magnetic lines of force2. Motion of conductors cutting the flux3. Voltage is generated

Principle of Generator Action When a conductor moves at a constant speed acrossa uniformly dense magnetic field,1 volt is generated for every 100,000,000 (108)lines cut per second

Principle of Generator ActionIf the flux density is not constant, the average generatedvoltage will be𝐸𝑎𝑣𝑒 𝑡 e generated voltage in a conductorVolts Total flux cutLines𝑡time, during which cutting takes placeseconds

# of Conductors vs # of Parallel Paths NOTE: the generated voltage isdetermined only by the “string ofconductors joined in series andnot by the number pf parallelpaths through the current maypass. The situation existing in agenerator with regards tovoltage and current is analogousto dry-cell connections.

# of Conductors vs # of Parallel PathsExample: If voltage and current ratings of 1.5 volts and 5amperes are assured per cell, determine the relativeratings of 120 cells connected when the number ofparallel paths is a.) 2 b.) 4 c.) 6 d.) 8The power rating is independent of the manner in whichthe cells or conductors are connected.

Problems1. A four-pole DC generator has an armature windingcontaining a total of 648 conductors connected in twoparallel paths. If the flux per pole is 0.321 106 maxwellsand the speed of rotation of the armature is 1800 rpm,calculate the average generated voltage.Answer: 125 V

Problems2. In Problem 1, calculate the rated current in eachconductor if the power delivered by the armature is 5kW.Answer: 20 A

General Voltage Equation for DCGenerator 𝐸𝑔 𝑃 𝑁 𝑍𝑎 60 10 8𝑣𝑜𝑙𝑡𝑠Where𝐸𝑔Total generated voltageVolts Flux per polemaxwells𝑃Number of poles, an even numberUnitless𝑁Speed of armaturerpm𝑍Total number of armature conductors effectively usedto add to resulting voltageUnitless𝑎Number of armature paths connected in parallel(determined by the type of armature winding)unitless

Problems1. A four-pole generator, having wave-wound armaturewinding has 51 slots, each slot containing 20conductors. What will be the voltage generated in themachine when driven at 1500 rpm assuming the fluxper pole to be 7.0 mWb ? Answer: 357 V

Problems2. An 8-pole d.c. generator has 500 armatureconductors, and a useful flux of 0.05 Wb per pole.What will be the e.m.f. generated if it is lap-connectedand runs at 1200 rpm ? What must be the speed atwhich it is to be driven to produce the same e.m.f. if itis wave-wound?Answer: 𝐸𝑔 500𝑉, 𝑁𝑤𝑎𝑣𝑒 300𝑟𝑝𝑚

Problems3. The armature of a four-pole shunt generator is lapwound and generates 216 volts when running at 600rpm. The armature has 144 slots, with six conductorsper slot. If this armature is rewound, wave connected,find the emf generated at the same speed and fluxper pole.Answer: 𝐸𝑔 432𝑉

Aug 01, 2018 · electrical energy, or the reverse process, electrical energy into mechanical energy. Energy Energy Mechanical Electrical Generator. Dynamo Energy Energy Electrical Mechanical Motor. Construction and Operation of DC .