Modeling of Inverse Time Overcurrent Relay Protection in Distribution Network

The reliable operation of the electric power system depends largely on the operation of relay protection and automation facilities. The primary equipment in electrical power systems, including generators, transformers, power transmission lines, and motors, relies on various types of protective relays, with overcurrent protection (OCP) being the most commonly used. Overcurrent protection can be divided into two main categories: definite time overcurrent protection and inverse time overcurrent protection. In our study, we focus on the relay protection systems used in the Baganuur branch of the Baganuur South-East Region Electricity Distribution Network (WESRDN), where most systems utilize definite time overcurrent protection. This type operates with a fixed time characteristic regardless of the magnitude of the fault current or the length of the line. However, it has the drawback that the protection time increases as it approaches the generator in series-connected lines and equipment. In contrast, inverse time overcurrent protection can adjust its timing characteristics based on the size of the fault current, which helps to overcome the earlier mentioned problem when applied to line equipment protection. Therefore, based on the example of the Baganuur branch's distribution network, we modeled the primary circuit and inverse time overcurrent protection using DigSILENT PowerFactory 15.1 software, and an analysis of the experiment results was conducted.