NEW RAILWAY AUXILIARY CONVERTERS: MAIN TECHNICAL CHARACTERISTICS
1- These new converters are modular, as all the previous ones projected and made by Seira. Their mechanical configuration with removable conversion modules makes easier, safer and faster the after-sales assistance and the reparation of the converter. The mechanical structure is realized with anodized aluminum.
2- For these converters of new generation, the HV Switching use only the IGBT with voltage of 1,7KV. These conversion modules operate with 12kHz PWM frequency at High Efficiency. In particular the HV Switching removable module, with a power from 20KW to 140kW, has a VAC core transformer, englobed in epoxy resin.
3- The converters, with power up to 100KW, can have an only transformer with VAC core. In this case the transformer has a secondary that feeds the 3-phase inverter and a tertiary that feeds the Battery Charger. Obviously, the rigidity test up to 11KVca 60” is made between the primary and the secondary, tertiary and ground. Between the secondary, tertiary and ground, the rigidity test is made up to 4KVca 60”.
4- The purpose of this technological choice is to greatly reduce the weight of the converters and also, compatibly with the modular configuration, to reduce the dimensions. The result is that the weight of the converter, with power up to 140KW, is lower even than 30% compared with the product of the better competition.
5- To reach this aim we used the most recent electronic components on the market; for ex. the new ultrafast diodes with reduced commutation losses, the good quality VAC cores and the new IGBT with junction temperature up to 175°C.
6- The efficiency of the 140KW converter is better than 90%.
NEW HIGH FREQUENCY TRANSFORMER WITH VAC CORE FOR POWERS UP TO 140KW
This transformer operating at high frequency (12kHz) has been developed to be applied on all the converters of new generation, fed by 3KVdc catenaries (with voltage variable from 1,8KVdc to 4,5KVdc). Consequently it has an high galvanic isolation among the windings and a very reduced weight. Obviously this transformer is fed by an H.V. Switching conversion stage that use the IGBTs 1,7kV, opportunely disposed in series, in order to obtain a max block voltage of 13.6KVp. The windings of the transformer are realized with Litz wires with a small diameter. The secondaries of the transformer are two in order to obtain an output voltage stabilized at 800Vdc ( ± 400V ), suitable to feed a three-phase inverter with three-phase output voltage at 400Vrms. The rated power of 140kW at the output 800Vdc is obtained on all the voltage range 3kVdc of catenary and therefore on the range included between 1.8kVdc and 4.5kVdc. The weight of this 140kW transformer is lower than 16kg. The performance of the transformer is really high because the over-temperature is low (<25°C). Volume and weigh, in fact, are reduced in comparison with the supplied power. In order to transmit toward the outside the heat generated by the transformer, the cylindrical holder (in anodized aluminum – matt black) is filled with an alumina dust that is a good electric insulator, a good heat conductor and above all has very good fire resistance characteristics. The litz wires have an isolation cover in H class, following the smoke-fire norms EN 50264-3-1 table 2.