Pressure and Oil Flow in Oil-filled Cables at Load Variations

Abstract

This paper presents a method for calculating pressure and oil flow in a section of an oil-filled cable at load variations with due regard to both the hydraulic resistance of the oil canals and the elasticity of the sheath and the pressure armor, if any, and the compressibility of the oil. The present article restricts itself to cable sections terminated with oil reservoirs in which the pressure is constant; in a forthcoming paper this restriction will be dropped. Formulas are given for pressure, oil current, and amount of oil which flows through a cross section of the cable for an arbitrarily prescribed oil expansion per unit length. These formulas are applied to the following oil expansion functions: S0·1, d/dt(N0·1), e−t/T·1, and 1/√t·1, which represent the oil expansion or terms occurring in the series giving the oil expansion in some important cases. Generalized functions are plotted for the pressure at the midpoint, the oil current at the endpoints, and the amount of oil which passes the endpoints for the above mentioned oil expansion functions. Using these generalized functions, the calculation of pressure and oil flow, with the simplifying assumptions made here, is reduced to elementary operations. Numerical examples illustrate the use of the given formulas and curves.