Problems of Electrical Safety in Depots and Workshops for Servicing Electric Traction Vehicles
Last modified: 2017-02-28
Electric rolling stock workshops and depots are to be prepared for service of modern rolling stock, typically equipped with power electronic converters and in a case of railway vehicles with a multi-system as well. Presence of catenary, which is supplied by DC or AC voltage, and need to supply wagons by different voltages and use of typical low-voltage 230/400 V 50 Hz installations pose some obstacles due to different requirements towards electric shock protection in AC and DC systems. For DC systems in a catenary/pantograph zone bonding as a protection measure is applied and rails are not to be straight-line grounded due to a stray currents flow, while for AC catenary and in-door electric installations earthing is required. The safety of personnel during normal and emergency operation cases is a pre-requisite of any type of solution, which is to be applied in that kind of areas. So the allowed level of touch voltage is reduced both during a long-term (permanent voltage drops) and short-term (overvoltage, short-circuits) period, furthermore the presence of mix AC and DC components is to be taken into consideration acc. to the EN 50122-3 standards. The technical infrastructure spread-out in depots could cause an unexpected current flow through hidden elements as well as appearance of dangerous potential. In order to reduce possible occurrence of such cases during exploitation it is required, at a design level to undertake a detailed study of methods to assure safety. Additionally tests upon completion of the installation are to be performed as well. The paper presents safety measures implemented in a newly build depot of electric rolling stock in Poland. The paper discusses the problems of electric shock-protection coordination in depots and workshops of electric traction vehicles. Furthermore, the results of analysis of electric shock voltage under normal and different fault conditions of operation are described. A multi-track model of a return network was applied in the analysis, which allowed assessing values of maximum voltages which could appear during fault conditions. A study-case of a protection system for devices and installation requiring grounding or bonding, whilst maintaining isolation of rails from earth has been presented as well.
tram; electric shock-protection; catenary; depots; earthing