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Dmitriy Severin

Faculty: electrotechnical

Department: electricity industry and cities

Speciality: electrotechnical systems of power supply

Theme of master's work:

Estimation and prediction of electric spark safety circuits with capacitive elements and the nonlinear inductance

 Scientific adviser: Ph.D. Berchadskyi Iliy

Summary of research and developments

     Intrinsically safe electrical circuit is defined as a chain, in which the level or the thermal effects arising in the normal and abnormal operating electrical equipment does not cause ignition of methano-air mixture. Despite the large amount of experimental work, a generalized design methodology to take into account the influence of capacitive elements of intrinsically safe systems (cables, capacitors, inductors coils own capacity), has not yet been determined, that in some cases difficult to design and test of intrinsically safe apparatus [1].

Figure 1 - Schematic diagram iskrobezropasnyh chains

     The most characteristic elements of intrinsically safe circuits are shown in Figure 1. In most cases encountered in practice they can be kept to a circuit consisting of series connected DC or AC, ohmic resistance R, inductance L and the spark of contact mechanism K (Fig. 1.a). Latest ekvivalentiruetsya mathematical (computer) models that reflect the characteristics of discharge with follow-up assessment of the risk of electrical arcing in explosive gas environments.

     The chain may also contain a capacitor C or cable shunting inductance L with the resistance R (Fig. 1.b), or the bit period (Fig. 1.B).

     For different classes of intrinsically safe circuits are characterized by different kinds of sparking. The article [3] provides the methodology for assessing the risk of ignition of inductively-active chains with single extension. In spark safety are also considered single-circuit and intermittent arcing. These two kinds of sparks are used to test circuits with capacitors charged in the inductive-capacitive circuits, as for the most aggression against ignition of explosive gas mixtures. This is because, unlike single breaking sparkover with discontinuous sincere possible if the condition is:

U_max<U_заж,                                                                                         (1)

where U_max - maximum voltage at the contact, V;

          U_заж - self-ignition voltage discharge in a gas, V.

     The reason for this phenomenon is that when the closure of an electrical discharge can occur due to avtoelektronnoy emissions [2]. Based on the characteristics proboynoy level circuit for the function of the distance between the copper electrodes U_pr=f(l), from the table. 1.

Table 1 - Punching voltage discharges circuit for copper electrodes

l, mm	0,02	0,026	0,047	0,096	0,178
Uпр	85,5	313,5	513	969	1425

     Thus, when the approximation of electrodes connected to a charged capacitor, there odnoproboyny sparkover. The same type of discharge occurs when interrupted sincere in inductive-capacitive circuits, as well as breaking the single inductive-capacitive circuit in the near bezyskrovoy switching [2].

     Accurate calculation of parameters in circuit level, with storage capacity, can be obtained only with the known patterns change over time instant resistance bit interval r. However, for such low-voltage pulse discharge capacitor bank such patterns in the general case has not yet been found.

     With the known parameters of the chain C, U₀, L, α, k₁, k₂, p, m can be obtained from the curves change the current level of resistance and ip r bit interval of time (Fig. 2, Fig. 3 built in the L_p≈ 10^-8H) where k_1,2=-R/2L±α, . The parameter m selected by successive approximations. As a result, produced a decline until the current and the voltage level does not fade at the same time, ie, simulated aperiodic discharge the capacitor for a spark resistance r.

Figure 2 - Dependence of the current bit interval oskrobezopastnoy capacitive circuit, with the closure of contacts: R=15Ом, U₀ =314В

Figure 3 - The dependence of the resistance r of the bit period of time t: 1 - U₀=200V, C = 1mkF, R_p = 5,6 Ohms (calculation), 2 - U₀ = 200V, C = 2mkF, R_p = 0,18 Ohms (experiment); 3 - U₀ = 200V, C = 2mkF, R_p = 0,18 Ohms (calculation)

     Then, using the method outlined in [3] evaluated the risk of electrical arcing in the circuit diagram of Fig. 1.v. The results of the calculations and their comparison with data GOST [5] presented in the table. 2.

Table 2 - Results of the calculation of the risk of electrical arcing chains with a charged capacity C, and additional active resistance in the circuit level R_p

Rр, Ohms	U0, V	С, mkFr		Wразр, mJ	Tразр, mks	Рразр, W t=1×10-6s
		Calculation	GOST
0,01	314	0,04	0,095	1,7	5,9	198
5,6		0,3	0,4	9,9	17,8	2922
15		0,6	0,7	15,7	59,7	1476
0,01	85	0,8	0,95	2,5	6,2	292
5,6		4,2	3,5	9	150	301
15		5	6	10	390	114
0,01	50	2,8	3	3,2	9,26	467
5,6		7	10	5,2	22,8	105
15		18	20	12,4	1251	39,7

Conclusions

     1. For the computer evaluation of intrinsically safe inductive-capacitive electrical circuit is proposed to test the developed mathematical simulation model for the 3 rd type of discharge:

     odnoproboyny-level circuit capacitive element circuit;

     -limit breaking odnoproboyny level (bezyskrovaya switching) in the circuit containing the capacitor element;

     -spark (arc) level breaking in the active-inductive circuit without considering the impact of capacity.

     As a criterion of ignition was adopted by the most dangerous type of discharge.

     2. In the electrical circuit with a capacity close to its own tank systems, the most dangerous is the spark (arc) level breaking the active-inductive circuit.

     3. Defining the risk of electrical arcing on the grade in the capacitive circuit and the active-capacitive circuits in the first approximation can be made on the basis of the methodology [4] with the proposed pre-selection of a continuous time damping aperiodic transition process in the circuit containing a variable amount of active resistance bit of spark.

REFERENCES

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    2. Петренко Б.А. Электрический разряд в искробезопасных цепях / В сборнике статей «Механизация и автоматизация  в горной промышленности.», вып. 3, М.: Госгортехиздат, 1963, с. 300 – 317.

    3. Иохельсон З.М. Бершадский И.А. Влияние параметров искры на воспламенение метано-воздушной смеси. – Уголь Украины, 2007, №3.

    4. Намитоков К.К.Электроэрозионные явления. – М.: Энергия, 1978. -456с.

    5. Электрооборудование взрывозащищенное, ГОСТ P51330.10 – 99      (МЭК 60079 – 11 – 99). Госстандарт России от 09.12.1999 г. – М.: Изд-во стандартов, 1999. - Ч.11. – Искробезопасная электрическая цепь.

    6. Фурманов Б.М. Научные основы, методы оценки и обеспечения искробезопасности горного слаботочного электрооборудования. М.: Недра, 1970. – 150 с

    7. P.H. Schavemaker and L. Van der Sluis . The arc model blockset//Proceedings of the Second IASTED International Conference POWER and energy systems (EuroPES) June 25-28, 2002, Crete, Greece. pp. 644-648.

    8. Иохельсон З.М., Бершадский И.А., Неледва А.В. Расчетная модель воспламенения метано-воздушной смеси электрической искрой цилиндрической формы // Наукові праці Донецького національного технічного університету. Серія: «Електротехніка і енергетіка», вип. 7 (128), с.215-220. – Донецьк: ДВНЗ «ДонНТУ», 2007.

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    10. Коган А.Г. Электроизмерительная и расчетная оценка искробезопасности индуктивных электрических цепей на основе математической модели очагового зажигания рудничных газов: Автореф. дис. … канд. техн. наук: 05.26.01, Макеевка, 1988.

Autobiography