Comparison between traction electrical motors based on the working of a ten years old light rail transit

Twenty years ago the Transit Company of Turin decided to renew the light rail transportation vehicles. They decided to buy two groups of cars: the former, about fifty vehicles, was composed of three-bogies cars with inverter controlled AC induction motors. Controls present two kinds of inverters: current inverter and PWM voltage inverter. Both of them are equipped with thyristors; and the latter, about fifty vehicles, was composed of three-bogies cars with chopper-controlled DC motors; the DC chopper control is equipped with GTO which are cooled with freon (contained in sealed tanks). These vehicles show a low floor which makes passengers boarding easier (directly from street level). The management of three different kinds of vehicles, with different electric controls, has involved maintenance, spare parts, and diagnostic equipment complications. Further, maintenance personnel training had to achieve a very high preparation level. The effort they made has been very important, from a cultural point of view: now, good elements are available to make a scientific comparison among the different developments. This paper shows the data which have been collected for ten years. Data refer to the three different kinds of cars and they are pertinent to the electric control. From an electric and maintenance point of view, GTO chopper-controlled DC motor cars are the most reliable one