Presentation on theme: "Lesson 6: Electromagnetic Induction and Magnetic Forces"— Presentation transcript:
1 Lesson 6: Electromagnetic Induction and Magnetic Forces ET 332aDc Motors, Generators and Energy Conversion Devices
2 Learning Objectives After this presentation you will be able to: Explain how voltage is induced in dc generators and motorsExplain how generators and motors develop magnetic forcesExplain the electromechanical operation of generator and motor systems
3 Electromagnetic Induction Moving a conductor through a magnetic field induces a voltage across the conductorMathematicallyWhere e = induced voltageB = flux density of the magnetic fieldv = velocity of the conductor in the fieldl = active length of conductor
4 Electromagnetic Induction The maximum voltage is induced when B and v are at 90 degreesCurrent into slidevNSxBVoltage induced whenconductor cuts flux linesPolarity: Right-hand RuleThumb = v -velocityFirst Finger = B – flux densityMiddle Finger = I directionNo voltage induced when velocity , v, isparallel to flux, B. Conductor must cutB for induction
5 No induction here. l || to B Induced Voltage in Rotating ConductorsConsider a loop of conductor rotating in a magnetic fluxConductor loopNo induction here. l || to BvNSe = induced voltageB = flux densityl = conductor l in fieldq = angle between B and v (B reference)v = conductor velocityabdcB
6 Induced Voltage in Rotating Conductors Rotating conductors produce sine wave voltagesNSabdcB9018027036021eq()bacaAll voltage induced by a rotating conductor is sinusoidal.dq
7 Electromagnetic Force Induced voltage causes an induced current to flow when the wire loop forms a circuit.Induced current causes flux field around conductorvFFlux fields follow the rules of magnetic attraction.Direction of force on conductor depends on:1.) magnetic polarity of stationary magnetic field2.) direction of induced current in conductor.
8 Electromagnetic Force Mathematical definition of electromagnetic forceBIFWhere: F = forceB = flux densityI = current in conductorl= length of conductor in field
9 Induced Voltage & Electromagnetic Force in Generators Generator ActionNvSFx1. External force moves conductor at velocity v, induces emf2. Induced emf produces flux around conductor3. Conductor field interacts with stationary field to produce opposing force.Force producing velocity must work against F
10 Magnetic Force follows Left-hand Rule Induced Voltage & Electromagnetic Force in MotorsMotor ActionMagnetic Force follows Left-hand RuleFirst Finger = field, BMiddle Finger = Current, IThumb = Force directionNSxFvCEMF+1. Applied voltage produces flux around conductor2. Field interaction causes force (torque)3. Motion causes induced voltage of opposite polarity in conductor
11 Summary of Generator and Motor Electromagnetic Actions F opposes driving torque that produces emfMotorInput I produces force. Force produces v (rpm) v produces CEMFAll generators develop an opposing force (torque) when generating a voltageAll motors generate an internal voltage (counter emf) when producing a force (torque)Motor and generator action occur simultaneously in rotating machines. Therefore they can be operated as either.
12 Motor /Generator Systems Torque and speed act oppositeMechanical drive call prime moverGenerator SystemT and w act in same direction
13 END Lesson 6: Electromagnetic Induction and Magnetic Forces ET 332aDc Motors, Generators and Energy Conversion DevicesEND Lesson 6: Electromagnetic Induction and Magnetic Forces