Analysis of the operation stability of measuring engines of backup protection of electrical networks

Abstract

Electrical distribution networks in Russia with a voltage of 6 – 110 kV are characterized by the widespread use of multi-terminal overhead lines with branch substations with relatively low power transformers of 2.5-25 MVA, to which consumers and distributed generation sources are connected. One of the problems of the backup protection system for these substations is insufficient sensitivity due to the comparability of short circuit currents with the flow currents between supply substations in normal load mode and load currents. The purpose of the article is to consider the possibility of using adaptive measuring elements that monitor the emergency components of arguments and current and resistance modules from the standpoint of the stability of the monitored parameters under various influencing factors: load modes, transient resistance at the site of damage. The initial data for consideration are the results on the above topic, carried out by domestic and foreign researchers, as well as previous work by the authors of this article. The research methods are mathematical modeling of the modes of electrical networks with branch substations, algorithms for the functioning of current and resistance measuring devices. The result of the research was the identification of measuring elements that have the most stable characteristics, which are recommended for use in multi-parameter long-range backup relay protection devices. It is proposed to use the stability (instability) indicator as a criterion for the stability of controlled parameters. The instability coefficients of the IO that control the parameters of current and resistance alarm signals are in the range of (2-12)% when load currents change up to 130% of the short-circuit current of the lowest power transformer, which is quite acceptable for backup protection. An additional effect of achieving stability of the monitored parameters of the measuring elements can be achieved through the use of correction signals, depending on the parameters of the protected electrical network and its previous load mode.