METHOD OF THE CABLE QUALITY EVALUATION Russian patent published in 2018 - IPC G01R31/11 

FIELD: electrical engineering.

SUBSTANCE: invention relates to pulse equipment and electrical measurements and can be used to assess the coaxial cables quality, in particular copper power cables with cross-linked polyethylene insulation or with paper impregnated insulation. To obtain the cable quality estimate with an inhomogeneity in the cable quality assessing method, including the cable probing with short voltage pulses, producing of a reflectogram with probing and reflected pulses, separation the reflectogram fragment for determining of the distance to the inhomogeneity and its equivalent circuit, elimination of the "ski effect", "zero-line" offset, and the estimated inhomogeneity coefficient calculation from the reflectogram fragment, according to the invention, the conductor diameter is preliminary measured and determining the cable insulation type, and as the inhomogeneity estimated coefficient from the reflectogram fragment, the reflected pulse shapes from the inhomogeneity and the probe pulse areas ratio is used, then the inhomogeneity active resistance value for the "longitudinal inhomogeneity" equivalent circuit is calculated according to the formula: , where a₁, a₂, a₃, a₄ – empirical coefficients for a cable with cross-linked polyethylene insulation: a₁=8.678497; a₂=2.182438; a₃=0.775739; a₄=-0.736041; for cable with impregnated paper insulation: a₁=8.251717; a₂=2.232208; a₃=1.036615; a₄=-0.794184; OK is the heterogeneity estimated coefficient, which is determined by the formula: , where 0 is the cable beginning coordinate, m; x_z is the probing pulse on the reflectogram final coordinate, m; u_z is the probing pulse voltage function, V; dx is the integration step, m; x_D0 is the reflected pulse on the reflectogram initial coordinate, m; x_D1 is the reflected pulse on the reflectogram final coordinate, m; u_D is the reflected pulse voltage function, V; x is the distance to the inhomogeneity on the reflectogram, m; d is the cable conductor diameter, mm; after that checking the condition: ,

where P is the energy receiver active electrical power, kW; l is cable length, m; U_nom is the cable rated voltage, kV; r₀ is the cable specific resistance, Ω/km; x₀ is the cable specific inductive resistance, Ω/km; ϕ is the angle between the energy receiver voltage and current vectors; R is the inhomogeneity active resistance, Ω; 0.1 is the permissible voltage deviation; if the condition is satisfied, then the cable is of high quality; for the "transverse inhomogeneity" equivalent circuit is calculated by the formula: , where a₁, a₂, a₃, a₄ – empirical coefficients for a cable with cross-linked polyethylene insulation: a₁=2.76876; a₂=-1.40164; a₃=-0.49824; a₄=-0.68309; for cable with impregnated paper insulation: a₁=2.83903; a₂=-1.32283; a₃=-0.61436; a₄=-0.62646; OK is the estimated inhomogeneity coefficient; x is the distance to the inhomogeneity on the reflectogram, m; d is the cable conductor diameter, mm; after that checking the condition:

where – cable rated voltage, V; – cable impedance until heterogeneity, Ω; – cable impedance after inhomogeneity, Ω; – energy receiver impedance, Ω; R is the inhomogeneity active resistance, Ω; I_ad is the long-time admissible current in the cable, A; if the condition is satisfied, then the cable is of high quality.

EFFECT: enabling the possibility of obtaining of the cable with heterogeneity quality assessment.

1 cl, 2 dwg