621.319 water treeing водные триинги система линейных алгебраических уравнений absorption characteristics amplitude of pulses of partial discharges coaxial cables computing experiment constructive and technological defects cooling bath length cooling mode diameter deviation dielectric loss tangent dielectric permeability deviation discrete resistive equivalent circuit method eccentricity electric field strength electrostatic axisymmetric field electrostatic field ellipticity of insulation equivalent circuit glass-mica paper tape impedance insulation resistance linear algebraic equations linear voltage location of the defect moisturizing cables nodal potentials method numerical solution accuracy