SCIENCE REVIEW. – 2012. -№2 (10). – P.17-21 DETERMINING CAPACITIVE SUSCEPTANCE OF NETWORK WITH INSULATED NEUTRAL OF UNDER 1000 V VOLTAGE Utegulov В.B.,Utegulov A.B., Uakhitova A.B. ________________________________________________________________ Abstract The present work develops the method of determining capacitive susceptance of an electrical network with insulated neutral of under 1000 V voltage for delfts, based on the measurement of values of phase-to-ground voltage, line-to-line voltage and the measurement of the phase shift angle between the vectors of line-to-line voltage and phase-to-ground voltage, as well as consideration of the length of air-cable lines and coefficients that characterize the capacitive susceptance of the line. Keywords: state of insulation, capacitive susceptance, insulated neutral, reliability, security, electrical network. 1. Introduction Delfts pay great attention to the state of electrical installation insulation during their exploitation, because the state of insulation is a most important aspect that characterizes the electrical safety of delfts. Deterioration of the state of insulation may be caused by hard usage of electrical installations: the unfavorable effect of the environment (in underground operations – aggressive and dangerously explosive), the uneven regime of using machines and mechanisms, presence of current-conducting dust and so on, which, in its turn, leads to the aggravation of the level of electrical safety, as well as the reduction of electrical supply systems reliability [1]. As a result of this, to raise the electrical safety of delfts, it is necessary to pay still greater attention to the study of the state of insulation at the exploiting electrical installations. 2. Capacitive susceptance characteristics When considering the parameters of insulation, it is necessary to analyze the overall, active, capacitance and ohmic resistance of the insulation. The value of the overall resistance of insulation Z ins characterizes the value of total leakage current, the value of the active R ins and ohmic R ohm resistances of insulation are used in constructing protection devices against the leakage current, and the value of the capacitance resistance X ins is necessary for the solution of the problem of compensating the electrical networks in relation to the ground [2]. To the parameters, characterizing the electrical safety of electrical networks also belong the admittance, conductance, and capacitive susceptance of insulation. The conductance is in direct dependence on the insulation properties of the materials, of which it is composed, and the capacitive susceptance corresponds to the quantitative indices of the connected electrical installations and the length of air-cable lines. The electrical installations exploitation practice at delfts shows that as different from open-cast mine electrical networks, in underground electrical networks the value of insulation conductance is determined mainly by the capacitive susceptance constituent [2]: y b. (1) In this case the value of the current in single-phase ground short circuit is described by the capacitive susceptance, because the conductance constituent is very small: I 0 I 0C U ph b . (2) 3. Method of determining capacitive susceptance To determine the capacitive susceptance in a three-phase electrical network with insulated neutral under a damage of one of the phases of the network they use the value of the current of single-phase ground short circuit, which is expressed through the mathematical dependence [3]: I0 U l U ph0 U0 g0 , (3) where U l is the line voltage, V; U ph 0 is the phase-to-ground voltage under the phase-to-ground connection of additional conductance, V; U 0 is the zero string voltage, V; g 0 is the additional conductance. The value of single phase ground short circuit current, which takes into consideration the extent of air-cable lines, is established through the expression [2]: L L I 0 U l A C , KA KC (4) where L A , L C are extent of the air and cable lines, km; K A , K C are coefficients for the air and cable line, kOhmkm. Handling the equations (3) and (4) together, let’s establish the value of the additional conductance: g0 U 0 L A K C L C K A . K C K A U ph0 (5) The value of the voltage in a zero string is expressed through the mathematical dependence: U0 1,73U ph0 (U l2 + 3U 2ph0 - 3,46U l U ph0Sin α) U l (U l - 1,73U ph0Sin α) , (6) where α is the phase-shift angle between the vectors of line voltage and phase-to-ground voltage. The value of capacitive susceptance of the network insulation is established on the basis of the expression [3]: b Ul g 0 Cosα . U0 (7) Solving the equations (5), (6) and (7) together, we find the value of capacitive susceptance of the network: b U l (L A K C L C K A )Cos . K A K C U ph0 (8) When inserting expression (8) in the equation (2), the value of the current of single-phase ground short circuit will have the following form: U l2 (L A K C L C K A )Cos I0 . 1,73K A K C U ph0 (9) The expression (8) is a random relative root-mean-square error of determining the network insulation capacitive susceptance, where the values U l , U ph0 , Cosα have been obtained by direct measurement. The relative root-mean-square error of the method in the determination of capacitive susceptance of the electrical network phase-to-ground insulation is found through the expression [4]: 1 b 2 b 2 b 2 2 2 b U l U ph 0 Cos 2 , 2 2 2 b U l U ph 0 Cos (10) b b b , , are partial derivative functions of U l U ph 0 Cos b f U l , U ph 0 , Cos . where Here U l , U ph 0 , Cos are absolute errors of direct measurement of the values U l , U ph0 , Cosα , which are established through the following expressions: U l U l U l ; U ph 0 U ph 0 U ph 0 ; (11) Cos CosCos . To establish the errors of measuring instruments, let’s assume that: U l U ph 0 U , where U is the relative error of the metering circuits of voltage; Cos is the relative error of the instrument for measuring the phase-shift between the vector of phase-to-ground voltage and the vector of the line voltage [4]. We determine the partial derivative functions b f U l , U ph 0 , Cos by the variables U l , U ph0 , Cosα : L K L C K A Cosα b A C ; U l K A K C U ph0 U l L A K C L C K A Cos b ; U ph 0 K A K C U 2ph 0 (12) U L K L C K A b l A C . Cos K A K C U ph 0 We solve the equation (10), substituting in it the values of partial of equation (12) and the values of partial absolute errors (11), assuming here that U Cos , then we obtain [5]: b 3 U l CosL A K C L C K A . b K A K C U ph 0 (13) To establish the root-mean-square relative error of capacitive susceptance of the network insulation, we divide equation (13) by equation (8), and after the transformation we obtain: b b 3. (14) The value of relative root-mean-square error of establishing b does not exceed 1,73 %, under the use of a measuring instrument of 0,1 precision. The developed method of determining capacitive susceptance of insulation in electrical networks with insulated neutral of under 1000 V voltage is based on the measurement of phase-to-ground voltage modules values, the line voltage, and the measurement of the phase-shift angle between the vectors of the line voltage and the phase-to-ground voltage, as well as considers the extent of air-cable lines and coefficients, characterizing the line capacitive susceptance. 4. Conclusion On the basis of the above-stated, it follows that the developed method makes it possible to determine the capacitive susceptance in an electrical network with insulated neutral under the damage of one of net phases in relation to the ground with adequate accuracy and ease. The developed method provides for the reliability of the determination of capacitive susceptance, on the basis of which the technical-organizational measures are proposed, to raise the reliability of the internal electrical power supply system of delft, as well as to ensure the rise of electrical safety under the exploitation of electrical installations of the voltage of under 1000 V. References 1 Tsapenko E. F., Sychev L. I., Kuleshov P. N. Mine flexible cables and electrical networks. – Moscow: Nedra, 1988. 2 Gladilin L. V., Shchutskiy V. I., Batsezhev YU. G., Chebotaryov N. I. Electrical safety in mining industry. – Moscow: Nedra, 1977. 3 Utegulov A. B. Development of phase-sensitive methods of raising the level of electrical safety and exploitation reliability of under and higher than 1000 V voltage electrical network with insulated neutral. – Pavlodar, 2003 4 Zaidel A. N. Measurement errors elementary estimation. – Leningrad: Nauka, 1968. 5 Gladilin L. V., Utegulov B. B. 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