Munir Aburumman

        The urgency of this development, the analysis of fires that occurred from damage to electrical equipment and failure in triggering appropriate remedies, testified as follows: in thermal power plants has occurred 52% in substations - 43% from hydropower - 5% of the total number of fires that have occurred for other reasons, not associated with electric shock. The number of fires that occurred through the fault of electrical machinery, 16% [1].
        Overheating of windings of electrical machines can cause inflammation of the wire insulation, which often leads to a fire in those cases where the enclosures of these machines are deposits of fire-dust, and remedies in this case are not in use, or do not respond to this mode of operation.
       The most frequently overheated windings BP appears locked rotor (jamming), the stator phase failure, voltage deviation from the normalized values, voltage unbalance [2].
       One of the common modes, causing an overload of blood pressure, is the asymmetry of the primary voltage. The coefficient of asymmetry in cliff line of wire on the side of the supply voltage, both at the precipice - 28,7%, and in nearby sites - 15 - 28,3%, significantly higher than those established by GOST 13109-97 [4]. The asymmetry of the supply voltage leads to negative sequence currents, which are superimposed on the currents of positive sequence and cause additional heating of the rotor and the stator, which leads to the rapid aging of the insulation.
       Currents in the phases of primary and secondary windings when the symmetry of the distortion voltage distributed unevenly, with a deep unbalance can grow to 2 or more times. The growth of current leads to overheating of the windings of AD. The most heated node AD is a frontal part of the stator windings, and its temperature increases with increasing asymmetry. Table 1 shows the distribution of the temperature front part of the stator windings at different values ??of the coefficient of asymmetry K2U.
        The temperature increase of windings affects the life of insulating materials. When working in BP nominal mode lifetime of insulating material is an average of 10 years. Using data from Table 1, was used to calculate the service life of blood pressure at different values of voltage unbalance [5]. At the level of asymmetry K2U = 4% of the life of the insulating material is reduced in 1,7 times in comparison with the nominal, while K2U = 10% - more than 15 times. When the engine with K2U = 20% residual insulation life was 3.2 hours.
        From the foregoing it follows that the appearance of the output voltage unbalance BP 20% and the refusal to triggering of relay protection, after about 3.2 hours of winding insulation breakdown occurs. Such a regime will exist as long as charred stator winding and will blow the bearings, the temperature of the motor housing will rise to the temperature at which it is possible ignition of combustible dust, randomly located on the body, causing a fire in the room [4].
       Consequently, the fire in the operation of blood pressure can occur when the coincidence in space and time following random events: Invalid overheating of the motor housing (eg, breakage of one phase, which feed blood pressure), denial of actuation of appropriate remedies, the presence of combustible material in the buildings under consideration of blood pressure.

        Scientific significance - an analytical dependence of the ignition fire-dust for a time t on the frequency of occurrence of cases of overheating of the windings induction motor, the duration of the existence of such a regime, the reliability of the remedies, the timing of its diagnosis, frequency of occurrence of fire-dust on the body of an induction motor and the timing of its discovery.

        The purpose of the work - to determine the time interval between checks the availability of combustible material (dust) on the hulls of induction motors, the probability of fire from their operation would be at the level recommended by GOST 12.1004-91, ie Q0 (8760)* 10-6.

        Practical value - derived methods of choosing the optimal from the standpoint of fire safety inspections timing of dust (combustible material) on the hulls of induction motors during their operation in the industry.

        State of the problem - One of the common modes, causing an overload of blood pressure, is the asymmetry of the primary voltage. The coefficient of asymmetry in cliff line of wire on the side of the supply voltage, both at the precipice - 28,7%, and in nearby sites - 15 - 28,3%, significantly higher than those established by GOST 13109-97. The asymmetry of the supply voltage leads to negative sequence currents, which are superimposed on the currents of positive sequence and cause additional heating of the rotor and the stator, which leads to the rapid aging of the insulation [3].

          Example 1. In the observation for T = 8760 h for one of the electrical fire departments received the following input data:

           h. – the average time interval between the appearances of phase failure in this network, the supply of blood pressure;

         d₁ = 5,6*10^-5 h. – average response time protection for phase failure of blood pressure;

         d₂ = 15400 ч. – the average time between failures of the automatic shutdown safety switching device;

          h. – the time interval between checks of the system off the protective switching device;

          h. – the average time interval between the appearances of a combustible fire-dust on the hulls of BP;

          h. – the time interval between checks the availability of combustible material on the hulls of AD.

          Determine the likelihood of fires within t = 8760 hours when operating in the BP shop and compare the result with the normalized GOST 12.1.004-91 value Q0 (8,760) = 1 * 10-6.

          Solution. Using the original sample data   and  .

,      ,    

,

,

,

.

          Substituting these data into the system of equations to first fire and the dispersion of time to first fire. Q (8,760) = 5.619 * 10-4.     for finding the average time , we define the mean time to first fire   and the variance of the time  . Got that . Then the probability of fire in the shop from the operation of blood pressure is determined from the approximate formula:

          Using a system of linear differential equations, computer-assisted find P8 (8,760) = Q (8,760) = 4.42 * 10-4. Results are compared with the rated value of Q0 (8,760) = 1 * 10-6 shows that in this case, the fire department in the operation is not guaranteed.

        Conclusions:
       1.Predlozhena method of assessing fire safety equipment shops (light industry, chemical production, etc.) during its operation.
       2.Predlozheny engineering formulas, through which, with sufficient accuracy for engineering calculations, you can choose the optimum from the standpoint of safety intervals between the diagnosis, as a means of protection, and check for flammable material on the equipment enclosure.

        References

1. Кашолкин Б.И., Мешалкин Е.А. Тушение пожаров в электроустановках. – М.: Энергоатомиздат, 1985. – 112 с.
2. Корогодский В.И., Кужеков С.Л., Паперно Л.Б. Релейная защита электродвигателей напряжением выше 1 кВ. – М.: Энергоатомиздат, 1987. –248 с.
3. Кузнецов В.Г., Николаенко В.Г., Висящев А.А. Математические модели и анализ неполнофазных режимов ЛЭП. – Техническая электродинамика, 1985, № 4. – с. 24 – 27.
4. Шевченко О.А., Якимишина В.В., Пинчук О.Г. О пожарной опасности асинхронных электродвигателей, эксплуатирующихся на промышленных предприятиях. Наукові праці ДонНТУ. Серія «Електротехніка і енергетика», випуск 67. Донецк: ДонНТУ, 2003. – с. 65 – 68.
5. Федоров М.М., Денник В.Ф., Корощенко А.В. Исследование температур узлов асинхронного двигателя при несимметрии питающих напряжений. – Электротехника, // Сб. тр. ДонГТУ. Сер. Электротехника и энергетика. – Донецк – 1999. – Вып. 4. – с. 138 – 141.
6. Ковалев А.П. О проблемах оценки безопасности электротехнических объектов. – Электричество. – 1991, № 8. с. 50 – 55.
7. Тихонов В.И., Миронов В.А. Марковские процессы. – М.: Советское радио, 1977. – 340 с.
8. Ковалев А.П. Оценка степени риска поражения человека электрическим током при эксплуатации оборудования в подземных выработках угольных шахт. – Промышленная энергетика.– 1992, № 2. - с.42-45.