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Changing the fields: An electromagnetic design perspective

Electromagnetic design is right at the core of the product design stage in alternators and can mean the difference between releasing a good product and a great product. The expertise we have at Cummins Generator Technologies allows us to tip the scales into consistently releasing great products which either meet or exceed our customers' demands and requirements in relation to, for example, size and performance.

We at Cummins Generator Technologies not only perform extensive computer simulations and validation processes to guarantee our generator quality, but continue to improve our alternators with various optimisations of the electromagnetic design through a computer simulation method called Finite Element Analysis (FEA), to ensure our products are the of the highest quality and best performing in the market.

FEA is an expert tool to perform a multitude of analyses on alternators and is used from the principle stages of design, all the way to finishing touches to bring out that extra few percent of performance. The electromagnetic FEA software specialises in looking into the electrical side of the design and allows us to create a very wide range of tests, for example the losses in the stator iron of the machine.

Our efforts are not however solely focused on using FEA, we also use a few other tools which have varying degrees of ability. One of those other tools was developed in house and is instantaneous at producing results rather than consuming a number of hours to yield a result. However this tool is much more limited and understandably less accurate than the FEA software. This fast tool was built based on classical theory and the magnetic reluctance circuit, so naturally there are no massively iterative, time consuming, calculations to be performed here.

The next piece of software we have at our disposal is a step up from the prior but still not as good as our FEA methods. This tool uses design templates which are modifiable by inputting the various machine dimensions, again this is based on the magnetic reluctance circuit theory but this time within a more in depth software package that allows for a much broader analysis more akin to that capable in our FEA software. It is slower than our instant results tool but generally more accurate and still a lot faster than finite element analysis.

Another option is multi-physics software which performs' beyond the scope of our electromagnetic FEA software and allows for the inspection of other performances such as mechanical stresses and temperature in various places inside the generator along with continuing to be able to simulate the electromagnetic fields inside the machine at the same time. Being able to use multi-physics software allows a more complete observation of how small changes and optimisations for the electromagnetics affect the rest of the generator and so can help ensure the excellence of our machine design.

When designing a generator from an electromagnetics point of view, there is much more to consider than simply the size and how much power we want to get out of the machine. Not only do we have a number of steps from hand calculations to computationally heavy finite element analysis, but there is a multitude of different ways in which we can alter the geometry inside the rotor and stator to manipulate the magnetic field in order to, for example, reduce the percentage of total harmonic distortion in the output voltage at the terminals, and also to improve the electrical efficiency; both of which when kept to a high standard contribute to a higher quality machine.