Transient analysis of auxiliary DC installations in power plants and substations

The goal of this work is to present a developed adequate model that will allow analyzing, dimensioning and control of auxiliary DC installations in power plants, first of all from the protection device point of view. This paper deals with risk of power system blackout caused by auxiliary DC installation failure. In the past, failure of auxiliary DC installation has been caused by wrong selectivity of protection devices. However correct selectivity calculation is based on short-circuit current calculation. For this reasons it has to be made a general mathematical model of auxiliary DC installations in power plants and substations that correspond with laboratory results of short-circuit current test. It was concluded that the transient state during short circuit has to be taken into account and mathematical model of auxiliary DC installations in power plants and substations should include not only resistances, but inductances and capacities of auxiliary DC elements as well as the active network in front of the rectifier. The essence of this work is to suggest changing of present IEC standard 61660 - "short circuit currents in DC auxiliary installations in power plants and substations" that does not correspond with present technology used in auxiliary DC installations. Based on that hypothesis an original program package was developed and used for analyzing and dimensioning auxiliary DC installations in power system. The results obtained by means of the program package are relevant for dimensioning all elements of auxiliary DC installations, particularly when protection devices are considered.