INVESTIGATING SWITCHING OVERVOLTAGES IN THE ELECTRIC EQUIPMENT OF THE OXYGEN-CONVERTER MANUFACTURES WITH THE HELP OF SIMULATION MODELS

Lipetsk state technical University

SHPIGANOVICH A.N., Prof., Dr. Sci. (Tech.), SHPIGANOVICH A.A, Assoc. Prof., Cand. Sci. (Tech.), Pushnitsa K.A, Asst., Cand. Sci. (Tech.)

For investigation of switching overvoltages in the electric power supply system of the oxygen-converter manufactures requires adequate simulation model, which reflects the major processes that occur when triggering the switching device. Consider the main features of this model. The main receivers of oxygen-converter manufactures are induction motors of different power and complete transformer substation (CTS) which feed on smaller receivers. Typical scheme will be power supplied through intermediate distribution substations (DS), that is, the scheme: transformer-line-DS-line-receiver, where the receiver performs an asynchronous motor or CTS. Because the asynchronous motor has a much smaller margin of dielectric strength of insulation than the transformer, then later it was he who served as the research object. To build the models of elements we used Matlab package. The package allows to model complex electric power systems, combining methods of simulation and structural modeling. In constructing models of system elements into account their active, inductive and capacitive resistance. For cable lines taken of their distribution along the length of the line, and the dependence of the active resistance of the frequency - the so-called skin effect. For the motor is additionally taken into account the capacity between phases and between phase and earth, the attenuation in steel at a frequency of free oscillations.The attenuation in the cable line and the motor at high frequencies modeled connection in the appropriate mode resistor whose value is chosen in proportion to the attenuation at the frequency of free oscillations. General view of the model of the investigated system in Matlab package is shown in fig.1. Waveform processes, obtained on the model, are shown in fig.2,3.

Fig.2. The voltage on the switch (motor P = 100kW, cable L =25 m)

Fig.3. The current through the switch (motor P=100kW, cable L=25 m)

In the simulation of the vacuum breaker take into account the following main provisions:

- dielectric strength of a contact interval described by a linear dependence, and according to [1] is 20-80 kV/ms;

- the growth of dielectric strength up to the limit values occurs within 6 ms at a speed of 1 mm/ms [1];

- first current interruption is possible in the case of instantaneous current value of not more than i_c (cutoff current, which depends on the contact material, for modern switches is 2 - 5 A [1]);

- in case of the first and subsequent breakdowns of contact interval is considered possible damping of the high-frequency current in its passage through the "zero" at a rate not higher than the set (in the range of 50150A/ms [1,2]);

- arc resistance is taken into account and simulated constant resistance.

Taking into account the above provisions was built to simulate the model to investigate the switching overvoltages in the electric equipment of the oxygen-converter manufacture. Using the model it was investigating the influence of different factors on the process of overvoltages and offered protection schemes to reduce the multiplicity of overvoltages, that allows you to build a rational system of power supply in relation to protection against switching overvoltages.

REFERENCES

1. Evdokunin G.A, Tyler G. Modern vacuum switching technology for medium voltage electric circuit (technical advantages and performance characteristics). St. Petersburg.: Publishing Sizov M.P, 2002. 148 p.

2. Kachesov V.E., Shevchenko S.S., Borisov S.A. Overvoltages vacuum circuit breaker switching of motor loads and monitoring // Overvoltages limitation and neutral grounding electric circuit 6-35 kV: Proceedings of the Third All-Russian Scientific and Technical Conference. Novosibirsk, 2004. P. 90 - 96.