Electrical protection selectivity in auxiliary DC installations in power plants and substations

The goal of this work is to present an adequate model that will allow analysis, dimensioning and control of auxiliary DC installations in power plants, first of all from the protection device point of view. A general mathematical model of auxiliary DC installations in power plants was developed in order to be used for analyzing short circuit conditions. It was concluded that the transient state during the short circuit has to be taken into account. The essence of this new approach is the new mathematical model which takes into consideration not only resistances, but inductances and capacities of auxiliary DC elements as well as the active network in front of the rectifier. Based on this mathematical model, an original program package was developed and used for analyzing and dimensioning auxiliary DC installations in power plants. The results obtained are relevant for dimensioning all elements of auxiliary DC installations, particularly when protection devices are considered.