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	DonNTU Master's port
E-mail:alexandra_maslova@gorizont.dn.ua E-mail:alexandra_22_85@mail.ru	Alexandra Maslova Faculty: Ectrotechnical Speciality: Power plants Theme of master's work: The researen of transitive process in energy power engineering on the computor. Leader of work : T.S.D., professor – Sivokobilenko V. F.
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Abstract

Substantiation of the actuality

Distributive networks 6-10 kV occupy the significant part in the infrastructure of transfer and distribution of the electric power; the total of their uninterrupted operation of delivery of the electric power to the consumer and the costs of its transfer in the big degree determine reliability of their work.
Now electric networks 6-10 kV work with the isolated neutral or with the neutral, which earthed through the arc-suppressing reactor. However operating experience shows, that significant internal the overvoltage arise at single-phase arc short circuits on the ground, which result to breakdowns of isolation of cables and electric motors in the points of the network, i.e. many-placed damages occurrence and pass in the short multiphase circuits. Last years the introduction in practice of operation of grounding of the neutral of the specified networks through the current-limiting the resistor attempts, which results to the reduction in the level overvoltage and to the increase of the reliability of the functioning of protection against short circuits of the phase at the ground.

The purposes and tasks of work

The purpose of work: is the creation of the mathematical model, which allows to analyze the phenomenon at the indistinct and arc short circuits on the ground in system 6 kV  electric system.
Research problems:
- the choice of the mathematical model and parameters of the basic elements of the electric system;
- the development of the basic algorithm of transitional of transients;
- the writing of the subroutine for the analysis of transitional of transients with the help of software package of MathCAD;                                                 
- the analysis of the overvoltage, arise of at single-phase short circuits on the ground;
- the definition of character a current of short circuit on the ground at indistinct and arc short circuits on the ground;
- the estimation of serviceability of various types of protection against short circuits on the ground. 

The basic maintenance of work

In the master’s work the mathematical model is submitted and allows to analyze the transitional transients at short circuit of a phase on the ground in networks of 6-10 kV. On the fig. 1 the equivalent circuit of the network is resulted. In this circuit the power supply is submitted by the phase inductance of dispersion L and resistance R. The network is reflected of the concentrated phase C and interphose См in capacities. The isolation is submitted of the active phase by Rи and междуфазными Rм resistance. The connections of the equivalent circuit are submitted as resistance Rpr and capacities Срr. Arresters are established as a terminators of the overvoltage. On the fig. 2 the columns of the network is resulted, where branches of the tree and a chords are designated. At the research of the transitional transients at short circuit of the phase on the ground in networks 6-10 kV the formalized topological methods of the analysis of electric circuits, such as the method of contour currents and Euler's implicit method are used. The values of the surge voltuge are resulted in the table 1. On the fig. 3 results of calculation of short circuit of the phase on the ground are resulted.

Conclusions

Master’s work is not finished yet, but, it is possible to do the following conclusions, proceeding from the received results:

• as a result of work the subroutine for the analysis of software with the help of software package MathCAD is written;
• the overvoltage are analysed, which arise at single-phase short circuits on the ground;
• the offered circuit of the restriction of overvoltage by translation of a network of own needs in a mode of indistinct the short circuit of a phase on the ground excludes long arc short circuits and raises reliability of the network’s work;
• the serially equipment is used for the realization of the offered circuit of the restriction of overvoltage and additional installation of connecting transformers and bulky resistors is excluded.

 

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