An engineer's diary

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  1. [No. 24] Synchronous torques in induction motors

    Fig. 1 shows two types of irregularity in the speed/torque characteristic of an induction motor — the asynchronous torque dip and the synchronous torque dip. These are sometimes c…

  2. [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 …

  3. [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.

  4. [No. 21] What is a space-vector?

    A space-vector — let us say, a space-vector of current — is a single complex number representing the combined effect of all three phase currents in an AC machine at a particular i…

  5. [No. 20] Equipotentials

    Sometimes I wonder why we don’t see equipotentials in finite-element flux-plots. Strictly speaking, at least in 2D flux-plots, we generally do see them because the flux-lines are …

  6. [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…

  7. [No. 18] Is it time to celebrate?

    In Finite Elements in Electrical and Magnetic Field Problems, edited by M.V.K. Chari and P.P. Silvester, (Wiley, 1980, ISBN 0 471 27578 6), A.L. Frisiani, G. Molinari and A. Vivia…

  8. [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…

  9. [No. 16] Four rules of saliency

    We often hear the terms "salient-pole" or "non-salient-pole" in relation to electric machines. "Saliency" is the idea of "projecting beyond the general outline", and it refers to…

  10. [No. 15] Reading a winding diagram

    Winding diagrams come in many different formats. There is no universal standard, but several common conventions can be found in the winding diagrams used by different manufacturin…

  11. [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 …

  12. [No. 13] Winding diagram for an AC motor

    Here we see a winding diagram for a 3-phase AC induction motor or brushless PM motor (IPM), having 4 poles and 36 slots. This winding could in fact be used with any AC machine, i…

  13. [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…

  14. [No. 11] What is the finite-element method?

    The idea in the finite-element method is to divide a difficult problem into a number of simpler problems which can be solved simultaneously; the solution to the difficult problem…

  15. [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…

  16. [No. 9] Can a magnetic circuit work without air ?

    Recently the U.K. Magnetics Society sent a list of 10 questions for their magazine MagNews, in which the first question was “What is your favourite magnetic material?” In a hurry…

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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.

Column: “An engineer’s diary”