GB734298A - Improvements in means for locating a leak in the sheath of an electric cable - Google Patents

Abstract

734,298. Locating leaks in cables. SOUTHERN UNITED TELEPHONE CABLES, Ltd. Nov. 25, 1953 [Nov. 26, 1952], No. 29955/52. Class 99 (2). A leak in the sheath of a dry core telephone cable 5 is located by charging the cable from both ends simultaneously with gas until the rate of flow of gas into each end remains constant and the pressure at both ends of the cable is the same, and then measuring the rate of inflow at each end of the cable by cutting off the gas supply to the cable and maintaining a pressure equal to the supply pressure and in a gas container 7 connected to the cable end by reducing the effective volume of that container. The' approximate distance of the leak from the ends of the cable can then be calculated, e.g. the distance from one end A of the cable is given by the formula L.VB/(VA + VB) where VA, VB represent the volume of gas flowing in unit time into the respective ends A, B of the cable, and L is the length of the cable. The apparatus may comprise a reservoir 1, provided with a pressure gauge 3, connected through a valve 2 to a supply of gas under pressure and through a valve 4 to the end of the cable 5, a manometer 6 being connected across the valve 4. The container 7 which may be in the form of a graduated glass tube and serve as a measuring device is disposed between the valve 4 and the cable, and the volume of the container is varied by raising or lowering a funnel 9 filled with mercury and connected to the lower end of the container by a flexible tube 8 ; alternatively, a bellows filled with mercury or other liquid is attached to the bottom of the container, the volume of the bellows being varied to change the level of the mercury in the container. In operation, the reservoir 1 and the gas supply serve initially for charging the cable and after a steady state of gas flow has been reached the valve 2 is closed so that the reservoir serves as a reference standard for the pressure in the tube connecting the reservoir to the cable. At that state the valve 4 also is closed and the rate of flow of gas from the container 7 to the cable is noted for the condition that the manometer shows. no difference of pressure between the reservoir 1 and the container. A number of readings of the rate of flow of gas, separated by intervals of time, are taken to ascertain that the steady state has been established, and the position of the leak is calculated when such readings cease to vary.