An engineer’s diary

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  1. [No. 46] Harmonic poles

    The number of poles is perhaps the most basic parameter in the design of an electric machine. When we speak of this parameter, we usually mean the number of working poles. Fig. 1 …

    • [No. 45] Gaps

      Fig. 1 shows a 2-pole IPM (interior permanent-magnet motor) that nobody would want to build. It has so many ‘departures from the ideal’, yet all of its imperfections can arise in …

      • [No. 44] Frequency

        The figure shows a sketch of the Epstein square that is used for the measurement of BH data of laminated core-plate in the form of strips arranged in a square with overlapping end…

        • [No. 43] Exponential function and complex numbers in electrical engineering

          Euler [1707-1783] is closely associated with this equation which has been described as the most beautiful equation in mathematics. It is sometimes regarded as having mystical sign…

          • [No. 42] Diameter

            D is for diameter! — surely the most fundamental of all engineering dimensions, at least in electric machine design. It is so important, we might ask ourselves why computer monito…

            • [No. 41] Coils and Conductors

              The two previous Engineer’s Diaries were titled A and B: A for vector potential and B for flux-density. This is C, for coils and conductors — and maybe for “crocodile clips” (croc…

              • [No. 40] Flux density

                The six images are listed below in the wrong order. Please, before you read this, try to decide what the Bees are showing. The answer is given at the end.

                • [No. 39] The magnetic vector potential

                  A is commonly used as the symbol for magnetic vector potential, just as B is used for flux-density or "induction", and H for mag…

                  • [No. 38] What has the automobile ever done for the electric motor?

                    From the provocative tone of the question, we might be led to expect an even more provocative answer : “nothing much”. Let’s see how wrong this is, and why.

                    • [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. 36] Some essential features of the induction motor – 1

                        In Column 34 we deduced several inherent features of the synchronous reluctance motor merely by inspecting its cross-section and considering the main flux-paths, and here we will …

                        • [No. 35] The position of wires in the slot

                          In the armature of a permanent-magnet DC motor, the wires usually occupy a rather untidy pattern in the slot — not because there is anything wrong, but simply as a result of the w…

                          • [No. 34] Some essential features of the synchronous reluctance motor

                            In Column 31 we deduced several inherent features of the switched reluctance motor merely by inspecting its cross-section and considering the main flux-paths, and here we will do …

                            • [No. 33] Transformations; and passing thoughts about rigour

                              It is probably fair to say that most of us do not have much to do with the mathematics of transformation theory, yet much of what we do relies on the theory of one or more transfo…

                              • [No. 32] Work of detent

                                Torque ripple is the variation in the torque of an electric machine as the rotor rotates. It depends on many factors including the current waveform, but in permanent-magnet motors…

                                • [No. 31] Some essential features of the switched reluctance motor

                                  Every type of electric motor has certain essential features. One way to begin to understand them is to make a drawing, and at the same time make a list of observed features and ch…

                                  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”