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DC power generation for MVDC grids is in the easiest way realized by a cascade connection of a synchronous generator and a diode rectifier. Due to large peak fault currents, including oscillating transient components, it is important to know in depth the short circuit behaviour of diode rectifiers, mainly during the first moments after the fault. This is helpful to be able to perform a suitable sizing of the system and its protections. In order to obtain an accurate estimation of the transient short circuit current, models for software simulation of 6-pulse and 12-pulse DC generator systems have been implemented. This paper shows the validation of such models by the comparison of simulation results with experimental tests.

Induction motors are presently the most widespread kind of electric machinery used in industrial applications. In the engineering practice, it frequently happens that designers or final users have to roughly estimate the size, weight and some basic performance data of an induction motor based on few specification requirements such as its rated speed and power. This paper describes homothety as an effective answer to this problem. The main principles of homothety as an induction motor sizing approach are discussed and quantitative formulas are derived based on theoretical considerations. The homotetic laws are finally assessed considering a set of sample built four-pole machines (whose data are fully available). The assessment confirms homothety as an actually powerful approach for a first-attempt estimation of many motor data including size, weight, utilization factor, current density, electric loading, etc.

In conventional three-phase electric machines, coil pitch ratio is usually selected around 5/6 so as to minimize the 5 th and 7 th flux linkage harmonics. In the electromagnetic deign of inverter-fed multi-phase motors different criteria should be adopted, depending on motor and inverter typology and possibly on the number of phases too. In this paper the main design issues involved in this choice are discussed showing that the final decision has to be the best compromise among various design needs and objectives.