Magnetism, Transformers and Motor/Generators Scenario: As an electrical engineering apprentice working in the maintenance department of your company. Your employer is looking to introduce a wind generator mounted to the roof of the factory to reduce electricity costs. The supervisor has devised a number of activities that will evaluate the performance of a motor and a generator Task 1 Electric motors use the forces produced by magnetic fields to produce a turning motion. To understand the theory behind this, your supervisor has asked to research the characteristics of a magnetic field and produce a technical report in a professional format including the following information: a) Define magnetism. Draw a fully labelled bar magnet and the pattern of magnetic field around it (such as would be illustrated by iron filings). b) Draw a coil carrying a current. Show the direction of the current. Show the pattern of magnetic field around it (such as would be illustrated by iron filings). Identify the north and south poles. Explain the reason behind shaping a conductor into a coil. Describe the relationship between flux density (B) and field strength (H) to support your research further. You supervisor has provided with BH curves for cast iron and 3% silicon steel, included as Appendix A. 0) Explain what magnetic saturation is d) Identify saturation point for cast iron and 3% silicon steel from the curves. Compare the results e) Estimate the relative permeability of cast iron and 3% silicon steel at a flux of 0.3T. Compare the results f) Estimate the relative permeability of cast iron and 3% silicon steel at a flux of 0.7T. Compare the results. Task 2 To understand the working principles of motors, generators and transformers, your supervisor asked to produce a report on the application of electromagnetic induction. Your report should include relevant diagrams and brief explanation. Page 4 of 7 a) Describe the principles and applications of electromagnetic induction with relevant theory. Highlight the role induction process plays in transformer operation. Use illustrations to aid your explanations. b) Explain the application of electromagnetic induction in motors and generators. For each, briefly describe and explain the magnetic circuit inside each device with supporting theory of Faradays and Lenz's law and fully labelled diagrams. Task 3 To analyse the performance of a motor and a generator, you have been asked to produce a technical report in a professional format including the following information: A fully annotated, neatly drawn, sketch of the major parts of a simple, single coil DC generator. Ensure that the drawing includes connection to a DC load. Given the location of the parts of the DC generator in your illustration, indicate both the direction of current in the load and the direction of rotation of the coil. Produce a fully annotated, full page diagram of the Voltage output waveform of the generator. Determine the maximum induced emf (Electromotive Force) in the coil if the length of each magnet is 95mm, there are 350 turns in the coil, the coil diameter is 65mm, is rotating at 103 revolutions per minute (rpm) and the flux density is 1.75T. List all parts in your report by identifying the parts of a DC motor identified in the diagram and writing a short description of their function. f) 9) h) Figure 'l - DC Motor From the illustration, determine the direction of rotation. Explain what would happen to the direction of rotation if the wires to the battery terminals are swapped over? Determine the force of the conductor if the length of each magnet is 63mm, the current flowing is 3.75A, the coil has 312 turns and the flux density is 4.17T. What effect on the performance of the motor would doubling the current in the windings in part 3 have? Support your explanation with full (mathematical) working out. What effect on the performance of the motor would halving the current in the windings in part 3 have? Support your explanation with full (mathematical) working out. What effect on the performance of the motor would doubling the number of turns in the windings in part 3 have? Support your explanation with full (mathematical) working out. Page 5 of 7 What effect on the performance of the motor would halving the number of turns in the windings in part 3 have? Support your explanation with full (mathematical) working out. Appendix A B-H Properties - - - Cast Iron - 3% Silicon Steel 1.8 1.6 1.4 1.2 1 Flux Density, B (T) 0.8 0.6 0.4 0.2 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 Magnetic field strength, H (A/m) Magnetic Field Strength, H (a/m) 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 Cast Iron, B (T) 0 0.12 0.25 0.38 0.49 0.58 0.64 0.68 0.71 0.73 0.74 0.75 0.76 0.77 0.78 0.79 0.8 3% Silicon Steel, B (T) 0 1.3 1.48 1.52 1.55 1.58 1.59 1.6 1.61 1.62 1.63 1.64 1.65 1.66 1.67 1.68 1.69