High-power synchronous alternators (part 1)

This article deals with the sizing of large synchronous alternators for power generation. The original article, written in 1982, represented the capitalization of the know-how of several generations of engineers, who in the space of a few decades had been able to boost alternator power from around ten megawatts to almost two gigawatts. This value could have been exceeded by using superconducting conductors, as the tests carried out by Alstom Belfort in 1986 had led us to hope. But as no steam turbine was capable of delivering such power economically, the race for power came to a halt in the 1980s. Another limiting factor was the fear of concentrating a significant proportion of power in a single piece of equipment. Suppose, for example, that a 10 GW generating unit were to be decommissioned. It would represent 14% of France's installed electrical capacity. Two or three simultaneous failures on similar equipment would immediately plunge the country into darkness.

The consequence of this end to the race for raw performance was, as early as 1985, the search for standardization of alternators, in order to reduce costs and lead times. The growing market for gas-turbine power plants led to the application of the know-how acquired during the French nuclear power program to alternators rated at less than 300 MW. The result was the concept of a ready-to-use standard product, deliverable within a very short time (18 months). It is presented in the form of a container ready for installation on site, with all its accessories for regulation, control, cooling, etc. With the decline in nuclear programs, this type of product now accounts for the bulk of the market for high-speed alternators (1,500 to 3,000 rpm). To these must be added hydraulic alternators, the variety of which remains linked to that of turbines.

The design of a rotating electrical machine always involves an initial optimization phase, using analytical models. This leads to an initial dimensioning that can be very realistic. In a second stage, finite element simulations are used to refine the calculations and validate the results. But they never replace the first step. We have therefore retained this original article, whose author is now deceased, with only minor modifications, induced by the evolution of technology. Based on real-life experience, it provides all the information needed for correct alternator sizing. It contains previously unpublished information, corresponding to know-how that has now disappeared and cannot be found in books. The formulas and methods proposed are applicable to smaller machines, whether operating in motor or alternator mode....