INFLUENCE OF CURRENT-TRANSFORMER'S INTERACTION ON TRANSIENT PROCESSES IN CURRENT CIRCUITS OF HIGH-VOLTAGE TRANSMISON LINES' HIGH-SPEED PROTECION

Current transformers (CT) of different phases and grouper in three-phase circuits interact intensively, therefore, if one of the transformers is saturated, input currents of the high-speed protection of high-voltage transmission lines can be seriously distorted. It can provoke non-selecting switching or delay in switching of protection. In the paper there are discussed transient processes of CT interaction, are found the most angerous regimes of the high-speed protection of high-voltage transmission lines, if there non-symmetrical short-currents, are realized conditions of such regimes. It is show, that, if there is the two-phased short-current to the ground, as the result. of the CT interaction there appear rather big distortions of the high-speed protection input currents, which pricipally differ from distortions of a single CT saturation. The same distortions appear, if the high-speed protection is connected to two groups of CT with phase shift of .those two groups primary currents, it there is short-cur- rent, even in one phare. The main reason of that current. distorsions is shifting in time CT magnetization and they primary current therefore magnetizating aperiodic CT core component can cousiderably exceed primary current aperiodic component. As a rule, modern high-speed protection (HSP) of high-voltage transmission lines (HVL) gives mainly active load on the current. transformers (CT), this allows to perform anal i t.i cal research of the qualit.ive side of transient. processes in the current circuits comparatively easy (called the method "helping functions") [1,2,3], counting after that, the main quantitive characteristics of protecting regimes under consideration, using computer. This method is rather fruitful because the problem is manyfactoral and gives no opportunity to find the most dangerous regimes by sorting out many parameters of; short-circuit currents and protecting outputs. [he method allows to solve the problem of non-simultnneus short-circuits and three-phase short.-currents [4], but it. would not.. be treated ii) the paper because of the space limitations.