Features Identification of Emergency Situation of Line Transmission

Abstract

The results of research of the currents of three-phase short circuit and start-up of induction motors electric network 10 kV are presented in the article. The traditional ways of protecting the transmission lines of networks 6–35 kV are investigated. For the recognition of the transition modes of three-phase short circuits and the start-up of induction motors there has been proposed the difference-integral method, which is based on the continuous formation of the difference-integral characteristics of the phases as a function of ΔНS(t) by calculating the difference between the integrals НS(t), НS(t – Т) of the quadratic functions of the instantaneous values of the phase currents is(t), is(t – Т), shifted in time, usually for the period T of the oscillations of the alternating current of the main frequency. The interphase coefficient of the difference-integral characteristics of the phases is calculated and its reduction to the reference interphase coefficients has been calculated. It is established that during 3,3 ms from the moment of perturbation the character of the recognition coefficient is similar and smaller than 1 for both the three-phase short circuit and for the start-up of induction motors, which does not allow recognizing the mode. During the next 11...12 ms, the character of the recognition coefficients varies and differs for each of these modes. At the same time, the recognition coefficients for three-phase short circuits increase monotonically and practically become equal to the unit for 5...6 ms. And the character of the growth of the recognition coefficients at the start of the induction motors depends on the moment of start-up and in all cases their values are several times greater than the unit in 11...12 ms. The analysis of the results of the study showed that for the considered network the values of the proposed criteria for recognition of the three-phase short-circuit mode do not depend on the location of the circuit, since the value of the recognition factor kр(t) becomes close to 1 due to the recognition time Тр 14...15 ms from the moment of perturbation. The use of the difference-integral method allows clearly distinguishing the mode of three-phase short circuit from the mode of starting induction motors in 15 ms from the moment of the short circuit.