Scientific paper ID 2752 : 2025/3

The power supply of electric vehicles (EVs) of ground urban electric transport (NGET) in the city of Sofia is carried out through rectifier stations (TS). Their function is to convert alternating voltage, through rectifiers, into direct voltage for powering the traction consumers of the EVs. In order to avoid interruptions in the power supply, the main role is played by protective devices that limit the harmful consequences of accidents. The presence of a fault is detected by the relay protection, which, using an algorithm, decides whether or not it is necessary to turn off the protected facility. The main task is the analysis of possible emergency modes in a given unit of the power system and the correct adjustment of the facilities. Relay protection performs its tasks by continuously monitoring the state of the controlled object: current, voltage, power, temperature, etc. In the event of a fault or an abnormal mode, under the influence of the information received about the object, it reacts according to a specific, pre-set program. Optimally selected and set relay protection reduces the total time during which the power supply to consumers is interrupted and limits the damage to individual facilities caused by the fault. Faults and abnormal modes create unfavorable conditions for the operation of electrical facilities. The processes occur very quickly. Their detection and shutdown must occur in fractions of a second and can only be realized with the help of automatic devices, such as relay protection. In some cases, relay protection only signals the presence of an abnormal mode. In modern relay protection, implemented on the basis of digital electronic equipment, the received information about the objects is registered, processed, transmitted at the substation and dispatch center level, and the protection and control functions are implemented by the same technical means. The report examines the protection of traction units - rectifiers.