D.C MOTORS

D.C MOTORS

PRINCIPLE of D.C MOTORAn Electric motor is a machine which converts electric energy into mechanical energy Its action is based on the principle that when a current carrying conductor is place in magnetic field , it experiences a mechanical force whose direction is given by FLEMINGs left hand rule (F=Bil sin) & LORENTZ force

Lorentz force The force which is exerted by a magnetic field on a moving electric charge is called lorentz force dF = dq(E+vB) for the operation of D.C motor ,consider E=0 dF=dq*v*B w.k.t v=dL / dt Where dL is length of Conductor carrying charge q i.e., dF=dq*dL/dt*B dF=I*dL*B F=BIL sin

Significance of back EMFWhat is Back EMF ?When the armature of a d.c. motor rotates under the influence of the driving torque, the armature conductors move through the magnetic field and hence e.m.f. is induced in them as in a generator.The induced e.m.f. acts in opposite direction to the applied voltage V (Lenzs law) and in known asback or counter e.m.f. Eb.Theback emfEb(= PZN/60 A) isalways less than the applied voltage V, although this difference is small when the motor is running under normal conditions.

INTERNAL WORKING

HISTORY of MOTORS With the invention of the battery (Allessandro Volta, 1800; produces a continuous electrical power as opposed to a spark or static electricity, from a stack of silver and zinc plates ).

The generation of a magnetic field from electric current (Hans Christian Oersted, 1820 finds the generation of a magnetic field by electric currents by observation of the deflection of a compass needle. This was the first time a time a mechanical movement was caused by an electric current.)

ALLESSANDRO VOLTAORESTED

HISTORY of MOTORS

In 1821, MichaelFaraday(British) creates two experiments for the demonstration of electromagnetic rotation. A vertically suspended wire moves in a circular orbit around a magnet.

Later in 1825, WilliamSturgeon(British) invents the electromagnet, a coil of wires with an iron core to enhance the magnetic field.This foundation for building electricmotors was laid.

FARADAYSTURGEON

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HISTORY of MOTORSThe first rotating device driven by electromagnetism was built by the Englishman Peter Barlow in 1822(Barlow's Wheel).

1834 - Thomas Davenport of Vermont developed the first real electricmotor('real' meaning powerful enough to do a task) although Joseph Henry and Michael Faraday created early motion devices using electromagnetic fields.

CONTRUCTION OF D.C MOTOR

Main classification of D.C MotorsBrushless D.C motorsA DC Brushless Motor uses a permanent magnetexternalrotor, three phases of driving coils, one or moreHall effect devicesto sense the position of the rotor, and the associated drive electronics HALL EFFECT: the production of a potential difference across an electrical conductor when a magnetic field is applied in a direction perpendicular to that of the flow of current.Brushed D.C motorsA Brushed Motor has a rotating set of wound wire coils called an armature which acts as an electromagnet with two poles.

Pros & cons of Brushless D.C motor BLDC Motor ProsElectronic commutation based on Hall position sensorsLess required maintenance due to absence of brushesSpeed/Torque- flat, enables operation at all speeds with rated loadHigh efficiency, no voltage drop across brushesHigh output power/frame size.Reduced size due to superior thermal characteristics. Because BLDC has the windings on the stator, which is connected to the case, the heat disipation is betterHigher speed range - no mechanical limitation imposed by brushes/commutatorLow electric noise generation

BLDC Motor ConsHigher cost of constructionControl is complex and expensiveElectric Controller is required to keep the motor running. It offers double the price of the motor

BRUSHLESS MOTOR

Pros & cons of Brushed D.C motorBrushed Motor ProsTwo wire controlReplaceable brushes for extended lifeLow cost of constructionSimple and inexpensive controlNo controller is required for fixed speedsOperates in extreme environments due to lack of electronics

Brushed Motor ConsPeriodic maintenance is requiredSpeed/torque is moderately flat. At higher speeds, brush friction increases, thus reducing useful torquePoor heat dissipation due to internal rotor constructionHigher rotor inertia which limits the dynamic characteristicsLower speed range due to mechanical limitations on the brushesBrush Arcing will generate noise causing EMI

Function of each part of DC Motor

Yoke: It is outer cover of dc motor also called as frame. It provides protection to the rotating and other part of the machine from moisture, dust etc. Yoke is an iron body which provides the path for the flux to complete the magnetic circuit. It provides the mechanical support for the poles. Material Used: low reluctance material such as cast iron, silicon steel, rolled steel, cast steel etc

Function of each part of DC Motor field coil wound on pole

Field winding :The coil wound on the pole core are called field coils. Field coils are connected in series to form field winding. Current is passed through the field winding in a specific direction, to magnetize the poles and pole shoes. Thus magnetic flux is produce in the air gap between the pole shoe and armature. Field winding is also called as Exciting winding. Material Used for copper conductor is copper. Due to the current flowing through the field winding alternate N and S poles are produced.

Classification of electric motors

Classification of electric motors

Types of Brushed D.C Motor

Applications of separately excited motors Electric traction( in train)

servomotor

load carrying vehicles like e-rickshaw

Application of D.C series MotorTraction system

Cranes

Air compressors.

Applications of DC Shunt MotorLathe Machines (used to rotate work piece) Centrifugal PumpsFansBlowersConveyorsLiftsWeaving MachineSpinning machines, etc.

Lathe machineconveyorsSpinning machine

Applications of DC Compound MotorsPressesShearsConveyorsElevatorsRolling MillsHeavy Planners, etc.

presseselevatorsRolling mills

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