Automatic fast calculation and verification method for transformer overcurrent protection settings

Protection coordination studies are complex and involve multiple steps with interaction times between consulting companies, utilities, and operators. Incorrect settings are an important source of misoperations that cause blackouts. This paper presents a new, fast, and simplified method for automatic calculation and verification of power transformer overcurrent protection settings. The method is based on a new concept of a metadata short-circuit matrix for obtaining the boundary of the short-circuit in every bay of the transformer. The evolution of simulators and object-oriented programming has been used to design an integrated method that significantly reduces the time involved in protection coordination processes by calculating pickups, time dials, operating times, and margin times of all overcurrent functions used in power transformers (ANSI 50, 50N, 51, 51N). A simplified approach to computing inverse curve operating times is used, considering in-code equations to avoid the use of complex relay models. Expert programmable rules are used to verify the settings automatically, including input user settings. The method was implemented in Power Factory DIgSILENT, and it has been used by the Colombian power system operator for more than two years in the coordination protection process with successful results. Two real-world applications of the method are presented.