Synopsis: The present paper presents an extensive theoretical investigation of the impedance of the “sea return” of various types of submarine cables. In the case of the cables used for submarine telegraphy the impedance of the sea return has been practically negligible because of the low frequencies involved. For these low frequencies the cross‐section of the return path is very large and its resistance low, even though the specific resistance of sea water is of the order of ten million times that of copper. As the frequency of the cable current is raised, however, the return currents crowd in nearer the cable and the resistance of the return path is increased. For frequencies in and above the telephone range, the return currents are forced into the steel armor wires around the cable and into the water just outside of the insulation. The small cross‐section of the water involved and the loss in the armor wires cause the resistance of the return path to become a very large part of the total resistance of the circuit. The present investigation led to the conclusion that the resistance of the return path could be greatly diminished by winding a low resistance conductor in the form of a copper tape immediately around the gutta percha insulation applied to the core of the cable. The concentric, cylindrical conductor thus formed lies within the armor wires but is not insulated from them and the sea water. Estimates of the sea return which would have been obtained in the Key West‐Havana cable if no copper tape had been provided give values of 4, 6.5, and 8 ohms per nautical mile at 1,000, 3,000 and 5,000 cycles. The resistance actually obtained with the copper tape does not exceed 1.7 ohms at 5,000 cycles. The greater values would have increased the attenuation by approximately 30% at 1,000 cycles and by 50% at the two higher frequencies. The present cable permits of the operation of a carrier telegraph channel at 3,800 cycles, this lying above the range of telephone frequencies. The paper gives a comparison of the theoretical conclusions with experimental data and the agreement is so satisfactory as to indicate that the theory is a reliable guide in the design of such a cable.—Editor.
SYNOPSIS: The use of permalloy for continuous loading has introduced a number of new factors of importance in the study of transmission of signals over long submarine telegraph cables. Data to check the theoretical assumptions that are used in the design of permalloy loaded cables can be obtained by measuring on such cables the attenuation and time of propagation of sinusoidal currents of various frequencies in the telegraph range. By combining the results of these measurements with data obtained on the cable during process of manufacture, the resistance, inductance, capacity and leakance of the cables can be determined.This paper describes the experiments that were performed on three laid cables and discusses in a general way the methods of computing the cable parameters.
~3~3 d X 3S,LN V NO dFU3 SLE I-X-3XN SECTION I INTRODUCTIONThis report is a compilation of two previous sets of pretest calculations, references 1 and 2 and the grounding and shielding report, reference 3. The calculations performed in reference 1 were made for the baseline system, with the instrumentation trailers not isolated from ground, and wider ranges of ground conductivity were considered. This was used to develop the grounding and shielding plan included in the appendix. The final pretest calculations of reference 2 were performed for the modified system with isolated trailers, and with a better knowledge of the ground conductivity.The basic driving mechanism for currents in the model is the motion of Compton electrons, driven by gamma rays, in the air gaps and soil. Most of the Compton current is balanced by conduction current which returns directly along the path of the Compton electron, but a small fraction will return by circuitous paths involving current flow on conductors, including the uphole cables.The calculation of the currents is done in a two step process -first the voltages in the ground near the conducting metallic structures is calculated without considering the presence of the structures. These are then used as open circuit drivers for an electrical model of the conductors which is obtained from loop integrals of Maxwell's equations. The model which is used is a transmission line model, similar to those which have been used to calculate EMP currents on buried and overhead cables in other situations, including previous underground tests, although on much shorter distance and time scales, and with more controlled geometries. The behavior of air gaps between the conducting structure and the walls of the drift is calculated using an air chemistry model which determines the electron and ion densities and uses them to calculate the air conductivity across the gap.Section II of this report discusses the EMP driver terms, and basic physical parameters of the air and soil models. Section HI discusses the basis of the transmission line electrical model, including the special models which had to be developed to account for the air gaps, rockbolts and isolated trailers. In section IV, the calculational results are presented, including both the scoping calculations of reference 1 and the pretest calculations of reference 2. In this section, the pretest predictions are also compared with the experimental data. DISCLAIMERThis report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thmeof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not ...
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