Characterization of Power Quality transient phenomena of DC railway traction supply

DC railways are considered as an example of a complex distribution network, featuring distributed supply and moving loads. The Power Quality phenomena affecting traction voltage are many, steady and transient, depending on the converter operations at substations and on-board vehicles. A classification is proposed and a discussion follows of the correct methods for their quantification, with reference to related standards and to the vast background related to ac networks. The characterization of PQ is related on one side to ripple and fluctuation of the pantograph variables for supply purposes, and on the other side to the appearance of specific components relevant for interference to signalling on the track. Considerations and conclusions are based on a large amount of measured waveforms, recorded on the Italian railway networks, and are aimed at contributing to the forthcoming standards on traction supply quality.