Introduction
Fire – one of widespread accidents on our planet. This uncontrollable burning out of the special centre, putting a material damage. It is characterized: formation of open fire and sparks; in the raised temperature of air, subjects, etc., toxic products of burning and a smoke; the lowered concentration of oxygen; damage of buildings, constructions and installations; occurrence of explosions. All it concerns the dangerous and harmful factors influencing people [1].
Providing of fire safety of industrial objects, including coal mines, in accordance with the legislation of Ukraine about a labour protection, is obligatory government activity. The decline of mining does not lead, in obedience to statistical information, to diminishing of amount of fires. n Ukraine from 50 to 80 underground fires of exogenous origin originate annually, from them 36,7% from the currents of short circuit in cable networks which inflict economic losses coal enterprises in a size from 18,35 to 29,36 million grn. in a year.
Analysis of statistical data about the cases of fires in the coal mines of Ukraine for period with 1992-2002 has shown that exogenous fires had a steady tendency of growth, and the amount of human victims grows continuously, that makes 4 men in a year on one million tons of coal [1].
Most exogenous underground fires on mines take place as a result of damage of electrical equipment and cables, here most dangerous in a fire relation, in relation to other electrical equipment, there are mine cable networks. Therefore a task, related to prognostication of possibility of self-ignition of mine cable networks from the currents of short circuit and protective shutdown, which fire strength which is rationed security is provided at, is too actual and its decision coincides with interests of economy of Ukraine.
In networks 6 kV the most dangerous are short circuits of one phase on earth in cables. The fire hazard of cables is characterized the followings properties of their isolation:
a) by ability of self-ignition and burning at presence of source of heat, tricked into from the site of damage (combustibility of cable);
b) ability to support the independent burning after stopping of action of outsourcing of heat (ability to diffuse burning).
The burned completely of outward armour of cable at shorting of one phase is presented serious danger from point of self-ignition of objects, located near-by a cable, under act of sparks, being burning hot particles of metal and conflagrant isolation [2].
Purpose of work
Theoretical generalization and development of method of estimation of fire safety of the underground system of power supply 6 kV coal mine for prevention of self-ignition of cable networks in mines.
Idea of work
To present probability of self-ignition of cable from the monophase currents of earth-fault as a casual process of coincidence in space and time of row of casual factors (frequencies of appearance of earth-faults, presences of combustible material in the place of gasket of cable, reliability of facilities of defense and terms of their prophylaxis).
For achievement of the put purpose the followings tasks of research are certain:
- to conduct the statistical analysis of time domains between contiguous fires in mine cable networks from earth-faults, on the basis of which to ground possibility of application of theory of markovskih processes for the estimation of reasons of self-ignition of cable;
- to set dependence of current in the site of damage (current of loss) from the size of resistance in the site of damage at different length of feed-in cable for the static and dynamic modes;
- to define dependences of probability of origin of fire on frequency by chance appearing in a cable 6 kV earth-faults, presence of combustible material in the place of gasket of cable, reliability of defense of loss of current on earth and terms of its prophylaxis.
A research object is the isolated system of power supply 6 kV area of coal mine.
The article of research is factors which influence on reason of self-ignition of mine cable networks during their exploitation.
Research methods. For achievement of the put purpose analytical methods and methods, which are based on experimental researches which are based on the basic concepts of theory of chances and reliability.
The first section of work is devoted research of dependence of current in the site of damage from the size of resistance and different length of feed-in cable.
The estimation of fire safety of area of coal mine is described in the second section.
As a result, research in this paper has developed a mathematical model and proposed a method that can predict the probability of occurrence of fires from the operation of asynchronous motors, develop organizational and technical measures to ensure standardized GOST 12.1.004-91 level of fire safety. For case, the program for accounting, analysis and experimental data, developed at the Department «Electricity companies and towns» has been used.
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