An engineer’s diary

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  1. [No. 25] Constructing and reading the flux-weakening phasor diagram

    This article concerns the permanent-magnet brushless AC motor. We’re going to review the phasor diagram, which has been the basis of AC motor theory for about 120 years. We will c…

    • [No. 37] Some essential features of the induction motor – 2

      In Column 36 we studied the cross-section of an induction motor with 36 slots, 30 rotor bars, and a 4-pole distributed winding. Just by looking at the features of the winding, we …

      • [No. 30] Rotational EMF

        In electrical machine theory we often hear the term rotational EMF. What exactly does it mean?“EMF” means “electro-motive force”. In electrical machine theory it is a voltage indu…

        • [No. 28] Notional equations in engineering

          On the telephone recently my 8-year-old grandson asked if I knew the equation E = mc^2. When I said I’d heard of it, he proceeded to explain: E is energy, m is mass, and c is the …

          • [No. 22] What can we do when we can’t go to work?

            Many engineers are at home because of the pandemic, unable to go to work. Although many can work “from home” by internet links, it’s not the same.

            • [No. 19] The number of poles in a rotary electrical machine

              The figure shows the some of the effects of pole-number on the magnetic field in a rotary electrical machine. It is a highly idealised figure: the winding is a current-sheet in th…

              • [No. 5] Formulas and Equations

                What’s the difference between a formula and an equation? Take the examples,

                • [No. 23] The complexity of the single-phase induction motor in your refrigerator

                  The single-phase induction motor is one of the most common electric motors. For many years the annual production levels world-wide have been 100,000,000 in round numbers. You can …

                  • [No. 17] Classification of electric machines

                    The diagram shows most of the electric machines in common use, together with the two reluctance machines which are rare but interesting. Classification is much more than an acade…

                    • [No. 10] RW

                      All electric machines use wire — usually of copper, but sometimes of aluminium. The electrical resistance R determines the I2Rloss (Joule loss) in each winding when the RMS curre…

                      • [No. 12] The IPM

                        The IPM or interior permanent-magnet motor started its history as a line-start motor in the 1950s. At that time Alnico magnets were the best available, but their low coercivity me…

                        • [No. 6] The Periodic Table of Electric Machines

                          When the archaeologists dig us up in 5,000 years’ time, they will find a large number of electric motors and generators. Who knows if they will understand what they find? They w…

                          • [No. 14] Synthesis of AC motor windings

                            How should we synthesize a suitable winding layout for an AC brushless PM motor? While the properties of existing windings can easily be analysed using a spreadsheet program, it …

                            • [No. 7] Peripheral, marginal, second-order, inexact . . . and IMPORTANT!

                              The finite-element method is very rarely exactly correct. Now surely that is an outrageous thing to say on the JMAG website! But what do we mean by exactly? The finite-element met…

                              • [No. 58] Maxwell

                                Almost exactly 10 years ago I made a ‘pilgrimage’ to visit the grave of James Clerk Maxwell at Parton Kirk in Dumfries and Galloway in the south-west of Scotland.

                                • [No. 47] Harmonic poles again — this time produced by the stator!

                                  In Engineer’s Diary No. 46 we discussed the harmonic poles of a 2-pole rotary machine. ‘Harmonic poles’ refers to the space-harmonics of the flux distribution around the air-gap. …

                                  PROFILE

                                  Prof. Miller was educated at the universities of Glasgow and Leeds, U.K., and served an industrial apprenticeship with Tube Investments Ltd. He worked for G.E.C. in the U.K. and General Electric in the United States. From 1986-2011 he was professor of electric power engineering at the university of Glasgow, where he founded the Scottish Power Electronics and Electric Drives Consortium. He has published more than 200 papers and 10 books and 10 patents, and he has given many training courses. He has consulted for several industrial companies in Europe, Japan and the United States. He is a Life Fellow of I.E.E.E. and in 2008 he was awarded the Nikola Tesla award.

                                  The Green Book: “Design of Brushless Permanent-Magnet Machines”

                                  The Blue Book: “Design Studies in Electric Machines” (June 30, 2022)