Long Cable

With the development of national economy, petroleum plays a more and more important role as a strategy resource. During the exploitation of petroleum, various data should be gathered using many metrical instruments, and data should be transferred by the cable to the ground. In this condition, different methods will be taken according to different situations in order to control the under-well instruments. The length of common cable is 4000～7000m, so the attenuation of the signal is very large, and the elevation of transfer speed is very difficult. At present, the development of under-well instruments is very fast, but the speed of cable transmission becomes the block of speed elevation, so how to transfer data with high speed through long-cable is very significant.In this thesis, the author establishes a long-cable transmission model through the simulation methods, and compares the data with the measured data to validate the correctness and efficiency of the model. Then the author simulates the long-cable transmission system existed, and looks for the methods of improving the transmission capability, in this way, the author provides checking data and validating model for our long-cable transmission system.In chapter one, the author briefly presents the domestic and overseas status of long-cable transmission system.In chapter two, finite element method(FEM) and the process of calculating the distributing parameters of cable resistance, inductance, capacitance and conductance by FEM are presented. First, the author explains the change of parameters going with frequency, medium, distance etc. via electromagnetic field theory. Then the author simulates the changing disciplines of various parameters in the working frequency of long-cable transmission. At the same time, the author analyzes the impact of temperature on various parameters, taking the nonuniform temperature field of the real long-cable transmission system into consideration.In chapter three, the author introduces the theory of multi-conductor transmission lines(MTLs) and finite-difference time-domain(FDTD) method, and establishes MTLs simulating model using the distributing parameters, which is simulated by way of FDTD. Especially, the author analyzes the impact of the cable armor as the nonideal reference ground on the transmission capacity. At the end of this chapter, the author analyzes the adjusted method of FDTD, when parameters change with frequency.In chapter four, the author puts forward multi-mode methods of improving transmission speed on the base of simulating the transmission capacity of armored cable in different working modes, and comparing advantages and disadvantages of these modes. Also, the author simulates the impact of temperature in reality on the transmission capacity concretely in this part.On the base of the analyses of simulating modes mentioned above, the author simulates two overseas systems, namely base-band transmission method of manchester coding and AMI coding and modulated transmission method of QAM. At the same time, the author presents the methods of improving data transmission frequency, and provides parameter data for designing transmission system.In chapter six, the author introduces analog cable simulator and hardware cable simulator which is based on FFT and IFFT, and puts forward the method of realizing FDTD through FPGA.