An engineer's diary

[No. 75] What finite-element analysis can and cannot do

Is FE Man telling the truth? Let’s pretend somebody has sued him for making false claims. We’re in the High Court, and the lawyers pose two carefully-worded questions: 1 Can the f…

[No. 74] Uncertainties in design calculations for electric machines

Although these are the words of a forlorn princess wringing her hands in a castle, concerned about uncertainties in her design space, they could surely have been expressed by any …

[No. 73] Butt joints and other gaps in electric machines

There are several gaps and joints (or interfaces) in any electric machine, and we can classify them as follows. A. Intended gaps. The air-gap between the stator and the rotor is t…

[No. 72] Properties of the dq-axis transform

In any system of calculations using dq-axis theory for synchronous machines, the question will arise, as to which transform should be used. The two transforms shown in Fig. 1 are …

[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…