Electrical Machines Module SE3231

1. 20/01/03 Lecture 1 Electrical MachinesModule SE3231 Lecturer: Dr Vesna Brujic-Okretic Ext: 9676 and 9681 Email: mes1vb@surrey.ac.uk

2. 20/01/03 Lecture 1 Course Organisation Students on the following courses: Aerospace Engineering and Biomedical Engineering will not do Electrical Machines - only Transducers Tutorials arrangement: 1 hour/week Alternates with Transducers Assessment: 3 hours written joint examination (75%) The paper will have 2 sections; The Aero..and Bio…students will do just 1/2 of the exam (the Transducers section) Mid-module test and tutorial assessment (25%)

3. 20/01/03 Lecture 1 Tutorials scheduling Tutorial sheets + Questions for assessment are released once in a fortnight RELEASE weeks: 2, 4, 6, 9, 11 Questions for assessment are due for submission at the subsequent tutorial session The assessed answers are due back 1 week later Note: usually, week 7 is allocated to the mid-semester test. If there are any changes to the schedule you'll be informed

4. 20/01/03 Lecture 1 Course notes In the Week 12, the Course Manual will be delivered to students. It contains the core elements of the lectures. In addition to the Manual, the lecture notes (generally with some more material), in the form of PowerPoint presentations will be uploaded on the School's intranet, every week. Go to the School of Engineering home page; click InfoPoint; go to Learning&Teaching section and click On-line courses; it is self-explanatory from then on. The URL is: http://www.surrey.ac.uk/eng/InfoPoint/online/emc/El_Machines/

5. 20/01/03 Lecture 1 Recommended Literature G. Rizzoni: Principles and Applications of Electrical Engineering, International Student Edition, Richard Irwin, Inc., 1993; ISBN 0-256-12969-X A. Hughes, Electric Motors & Drives - fundamentals, types & applications, Heinemann Newnes, 1990, ISBN 0-434-90795-2 T. Kenjo, Electric Motors and their Control, Oxford University Press, 1991 (re-printed: 1993, 1994, 1996, 1998); ISBN 0 19 856240 3 P.C. Sen, Principles of Electric Machines and Power Electronics, John Wiley & Sons, 1989

6. 20/01/03 Lecture 1 Syllabus Application of electrical machines. Classification DC mahines: Basic principles of operation Steady-state characteristics of DC motors: series, shunt, permanent magnet types Dynamic regime - loading/unloading Mechanical power and developed torque. Losses & efficiency Application, performance & classification of AC machines

7. 20/01/03 Lecture 1 Syllabus AC machines: Induction motors. Principles of operation Rotating field, slip & torque Electrical machines with special application: Stepper motor; Linear motor Electrical machines in the info society State-of-the-art technology & applications Revision & examples

8. 20/01/03 Lecture 1 Introduction before we start with the principles of operation we shall try to summarise and classify the everyday use of motors motors are used in: households industry & manufacture automobiles information technology medicine transport etc. etc.

9. 20/01/03 Lecture 1 Motors in a household How many motors are typically used in a household??? virtually countless!!! They are found in: refrigerator coffee mill dishwasher, washing machine food processor vacuum cleaner ventilator gardening machines video recorder CD player computer etc. etc.

10. 20/01/03 Lecture 1 Motors in automobiles starter motor fuel pump windscreen wiper air-conditioning actuator oil cooling fan sun roof variable shock absorber etc. etc.

11. 20/01/03 Lecture 1 Motors in information equipment floppy and hard disc drives printer plotter fax machines ventilators in computers and other electronic devices etc. etc.

12. 20/01/03 Lecture 1 Miscellaneous various motors on a robot (e.g. for arm & finger motions) automatic vending machines transportation toys amusement machines vision and sound equipment (e.g. moving tapes, focusing & positioning in the camera, shutter, film winding etc.) medical and healthcare equipment (e.g. dentist’s drill, artificial heart motors etc.) etc. etc.

13. 20/01/03 Lecture 1 Broad classification An electric machine is a device that can convert either mechanical energy to electric energy (generators) or electric energy to mechanical energy (motors). In this course, we will be dealing with motors only without going into details at this moment - we shall classify motors very broadly into three main categories: Conventional DC motors AC motors Electronically controlled precision motors we shall talk about their applications & the principles of operation

14. 20/01/03 Lecture 1 Typical requirements of a DC motor DC motor is an obvious choice where: speed or torque control is called for (in spite of a growing challenge from induction inverter-fed motors) Application range: steel rolling mill railway traction wide range of industrial drives robotics printers precision servos etc. etc.

15. 20/01/03 Lecture 1 Parameter value limits although it is possible to design a DC motor for any desired voltage supply usually rated voltages range from: 6[V] to about 700[V] small DC motors (say, up to hundreds of watts) can run at approx. 12000 rev/min majority of medium and large DC motors are usually designed for speeds below 3000 rev/min

16. 20/01/03 Lecture 1 DC motors classification Traditionally, DC motors are classified as: separately excited self-excited: shunt series compound the names reflect the way in which the armature and the field circuitry are interconnected first, we shall gain understanding of how the basic machine operates

17. 20/01/03 Lecture 1 Electromagnetism - fundamentals electric current produces magnetic field (Oersted) in its surroundings - this was further formulated by Ampere (Ampere’s Law); magnetic field is the fundamental mechanism through which energy is converted conversely, changing magnetic field generates voltage at the ends of a conductor placed in it; if there is a closed loop - an electric current will flow. This forms the essence of Faradey’s Law these Laws illustrate relationship between electric and magnetic fields

18. 20/01/03 Lecture 1 First Principles We are going to use, mainly, the following fundamental laws and principles: Faraday’s Law Ampere’s Law Electromagnetic Force (Lorentz force) Second Newton’s Law for Rotation

19. 20/01/03 Lecture 1 Relevant Quantities: Definition Magnetic field , H, Si unit: [A/m]; vector Magnetic permeability, m, - property of the medium;for vacuum, m0=4px10--7 [H/m]; for other media: m= mr m0 Magnetic Flux Density, B, SI unit: Tesla [T]; vector B is represented by so called magnetic lines of force magnetic lines of force are always CLOSED, however long they may be B is tangential to the line of force at any point

20. 20/01/03 Lecture 1 Relevant Quantities: Definition Magnetic flux, F, can be interpreted as a number of magnetic lines of force that cross certain given area - the greater the number of lines, the greater the flux and stronger the field Flux through a surface area is, mathematically, the integral of the dot product of a vector B and a vector ds representing the surface element: SI unit: Weber [Wb]; scalar

21. 20/01/03 Lecture 1 Magnetic Flux if B is perpendicular to the surface, then if B is UNIFORM (and perpendicular to A) then

22. 20/01/03 Lecture 1 Ampere’s Law the integral of the vector magnetic field intensity, H, around a closed path is equal to the total current linked by the closed path, I it is a scalar product (dot product) if vectors H and dl are co-linear (same direction) it will be a simple algebraic product the integral will strongly depend on the GEOMETRY

23. 20/01/03 Lecture 1 Typical Configurations The magnetic field around an infinitely long, straight conductor carrying a current, i is:

24. 20/01/03 Lecture 1 Right-hand Rule so, in this case: B~1/r as a vector, it lies in a plane perpendicular to the wire, it is a tangent to the circle of a radius r and its direction follows the right-hand rule

25. 20/01/03 Lecture 1 Solenoid (coil) the longer the coil - the straighter the lines of force where N is a number of turns at the centre of a long solenoid the magnetic field is: H=NI/L B=mH=mNI/L

26. 20/01/03 Lecture 1 magnetic lines of force around a permanent magnet rod

27. 20/01/03 Lecture 1 Faraday’s Law states that a changing magnetic field induces a voltage in the conductor, and consequently a current (if the circuit is closed) time varying flux causes an induced electromotive force (emf) to occur (e) F is the magnetic flux through the surface bounded by a conductor

28. 20/01/03 Lecture 1 Faraday’s Law - ‘Blu’ form

29. 20/01/03 Lecture 1 Principles of Electromechanics where there is a field there is a force, too the force is a mechanical quantity causing objects to move hence, electromechanical coupling through electromagnetic force and the transformation from electrostatic/magnetic energy to mechanical and vice versa

30. 20/01/03 Lecture 1 Electromagnetic Force F is perpendicular to the plane formed by v and B the right-hand rule applies to work out the direction of force

31. 20/01/03 Lecture 1 ‘Bli’ Law

32. 20/01/03 Lecture 1 ‘Bli’ Law (u’ is the velocity of + charge) If B and l are perpendicular then the intensity of F’ F’=Bli

33. 20/01/03 Lecture 1 Confirmation the presence of the current causes the occurrence of the F’ force pushing the bar to the LEFT we have to exert EXTERNAL force to move the bar to the RIGHT (overcome F’) this is the basis of electromechanical energy conversion the area crossed by a moving conductor in the time dt: confirming Faraday’s Law

34. 20/01/03 Lecture 1 Electromagnetic Force a conductor carrying a current, I is in a constant magnetic flux density, B as a result - there are forces, F, - F, acting upon it and forming a couple hence, torque T and a rotation

35. 20/01/03 Lecture 1 Electromagnetic Force dF=IdlxB force on the element dl of the segment L F=BLI magnitude of total force on segment L (if B & I are constant) F, B & dl are vectors, pointing as shown on the previous slide; they form a couple; hence, the torque T=RxF T (torque) is a vector = vector product of the radius vector R and the force vector F, with respect to a pre-defined reference point T=2RF is a magnitude of total torque where: L=AB and R=AC/2 (previous slide)