An engineer’s diary

  1. [No. 71] p.u.

    The first time I saw the expression “p.u.” was in an examination paper on electric power-systems, when I was a student-apprentice. Fortunately it was the previous year’s paper, no…

    • [No. 70] Don’t make your eddy-currents angry !

      Imagine a block of permanent magnet material in an IPM, Fig. 1. Our line of sight is parallel to the direction of magnetization, at right angles to the plane of the diagram.

      • [No. 69] Animation

        The educational and commercial importance of animation can hardly be overstated. We see it almost everywhere, and it now has a significant role in even the most traditional areas …

        • [No. 68] Torque waves (and the insane simplicity of the torque equation)

          Smooth torque. Isn’t that what we get from electric machines? They certainly appear to produce smooth torque. Unlike internal combustion engines, they have no flywheels or balanc…

          • [No. 67] Harmonic waves in AC machines

            The famous Park’s equations for the d- & q-axis voltages in synchronous machines were developed from the concept of sine-distributed armature ampere-conductors. The fundamental or…

            • [No. 66] Axial flux

              Axial-flux machines are currently in vogue. With an internet search we can quickly find numerous examples, including many videos of home-made machines and some notable products an…

              • [No. 65] Inductance

                Inductance may come as a shock to anyone who thinks that V = I × R. That delightfully simple expression of Ohm’s law is not the whole story. For sure, if we have a coil connected …

                • [No. 64] Eddy-currents

                  Eddy-currents flow in closed loops. It follows that for any physical device in which eddy-currents arise, only a three-dimensional analysis can be complete. Any two-dimensional an…

                  • [No. 63] Oh no! No magnets!

                    Scarcity is nothing new in human history, and in electrical products we hear about it all the time in relation to lithium or rare earths, or even copper. So the poem might seem li…

                    • [No. 62] OK — the laws of Ohm and Kirchhoff

                      OK — We’ve reached letter ‘O’ in the alphabetic sequence of Diary topics, and Ohm’s law immediately comes to mind. When I was a student, one of my room-mates (a medical student) h…

                      • [No. 61] Nervous about Neumann?

                        Continuing the more-or-less alphabetic sequence of initial letters for the titles of Engineer’s Diary, we arrive at the letter N. What topic could be more relevant in finite-eleme…

                        • [No. 60] Mystery, Magic and Mappings

                          Mystery is not confined to novels.We have it in abundance in engineering.I remember as an apprentice in the 1960s working alongside a service engineer on a new DC drive system, an…

                          • [No. 59] Mutual inductance

                            Mutual inductance M is one of the most common concepts in electromagnetic engineering. Indeed we can argue that it is also one of the most fundamental concepts.

                            • [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. 57] L and Linkage and Leakage

                                Readers may have noticed that Engineer’s Diary has been trying to follow the alphabet in selecting monthly topics, and some letters provide more ideas than others. This month, ‘L’…

                                • [No. 56] Lèse-Majesté

                                  It is easy to imagine the IPM (interior permanent-magnet motor) as the monarch of electric motors. Indeed to question its supremacy could be said to be lèse-majesté.


                                  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)