Resumen
All types of relay protection are based on comparing the values for certain attributes under a system's normal and emergency operational modes. A new attribute for defining the emergency mode in a direct current traction electricity supply system has been proposed, namely, the speed of voltage drop in the feeder of a traction substation. It is known that at a short circuit in the traction network, its voltage is reduced. Its sharpest, almost linear, decrease is observed, first, at the first moment of the emergency transition process, and, second, at a short circuit site and at points near it. Therefore, the steepness of the front of such a reduction in a feeder voltage could become an attribute of short circuit. A given attribute makes it possible to determine the type of short circuit based on a distance from the power source. In addition, we have proposed the circuit solutions for implementing a system of protection based on this attribute. Three options for building such protection systems have been considered. A first option implies using a RC filter. A second variant employs a pulse transformer. A third option is to use a bridge scheme. Each scheme has its advantages and disadvantages; however, modern electronics and digital technology make it possible to implement any of them. In the future, this would facilitate the construction of a selective protection (in terms of distance) from short circuit. To this end, one needs to use as many protection kits as how many points along a traction line must be monitored. Such a system is also easily implemented by software using microprocessor equipment.The practical results from our study at a section of traction power supply of the Dnieper Railroad make it possible to assert that the proposed technique for determining short circuits is rather effective. It could be used as an additional (backup) system in general relay-protective hardware. That would improve the reliability of power supply systems for traction networks. Overall, the considered technique for determining short circuits could be used in any DC power system