Cable Characteristic Impedance Research Articles

Design of distributed temperature-measuring system based on 1-wire bus for ultra-kilometre frozen deep well

The temperature field of artificial freezing curtain is a transient temperature field changing with time. In order to ensure the safety of the project, improve the timeliness and accuracy of temperature measurement, and ensure the safety strength and effective water sealing of the curtain, it is necessary to implement the information temperature monitoring control for the freezing process. According to the application environment of the freezing monitoring for the long distance and multi measuring points in the construction of the coal mine over a kilometre, a monitoring system of the frozen deep wells which is developed by the 1-wire bus technology is proposed. By using high-performance single chip microcomputer, designing pull-up and level detection driving circuit, matching cable characteristic impedance and distributing digital temperature measurement cable, the 1-wire bus network monitoring points can reach 55 and the transmission distance is over 1000 m, which meets the current monitoring requirements of frozen deep wells.

Embedded OMTDR Sensor for Small Soft Fault Location on Aging Aircraft Wiring Systems

Based on OMTDR technology, the first embedded Smart Connector (SmartCo) which could locate very small soft defects resulting from partial degradation of cables is introduced in this paper. To do so, the SmartCo injects the generated OMTDR signal at an extremity of the cable and then listens to the echoes created at each discontinuity of the cable characteristic impedance. Since soft defects result in faint reflected energy, they are hard to distinguish from the noise. Hence, the SmartCo uses an innovative approach based on advanced post-processing methods data fusion to eliminate false alarms and to determine the small soft fault position.

High Frequency Signal Propagation in Solid Dielectric Tape Shielded Power Cables

High frequency signal propagation in shielded power cable is important to many cable diagnostic techniques including time domain reflectometry, partial discharge location, etc. The signal propagation characteristics, including electromagnetic propagation velocity, cable characteristic impedance, and attenuation are well studied in power cables with concentric neutral wires or solid metallic shield. However, high frequency signal propagation in tape shielded cable is more complicated as conduction at the tape laps tends to decrease with cable aging, which forces more of shield current to spiral down the tape shield. The cable inductance increases with the fraction of the shield current in circumferential direction, which affects all the signal propagation characteristics. High frequency signal propagation characteristics of tape shielded power cable were studied using a custom manufactured 15 kV cable sample which has a PET tape intercalated with the copper tape shield to eliminate conduction at the overlap, which simulates the effects of corrosion in aged tape shielded cables. The inductance of the cable sample was computed as a function of fraction of shield current following a spiraling path along the cable, as were the signal propagation velocity, and the cable characteristic impedance, all of which are in reasonable agreements with measurements. Calculations and measurements of high frequency attenuation indicate that large eddy current and “transformer effect” losses in the ground shield semicon dominate once a substantial fraction of shield current spirals down the tape.

New Data Bus Interface Technique

Data bus systems as defined in MIL-STD-1553B are widely used in aerospace instrumentation systems for digital data transmissions between units on the bus. Although the bus is protected against a short circuit which may occur in the remote unit electronics or transformer, it has no protection against a cable termination failure. Open or short failure along main bus cable results in failure of the entire bus system. A new data bus interface technique is described which is insensitive to cable termination failure. The central feature of this new interface circuit is that communication between main unit and remote units is not affected by the cable termination failure. In applications such as multistage missiles, no provisions need be made for retermination in the cable characteristic impedance after stage separation. The key to this new technique is a directional coupling transformer which is only slightly more complicated than standard interface transformers. Design equations for directional coupling transformer and experimental results of new data bus systems are presented.

Wave Propagation Characteristics In Underground Power Cable

Calculations have been done to evaluate the effects of the semiconducting screens, the conductors, and the surrounding earth on the propagation constants of electromagnetic waves in concentric underground power cables. The theory, based on Maxwell's field equations, is reviewed. Results of calculations of both speed and attenuation are presented for a variety of practical configurations. Limited comparisons with experimental results are included. In addition to their direct application, the results can be employed to calculate the cable characteristic impedance from an algebraic expression which is presented.