Direct Buried Cable Research Articles

Rapid calculation model for transient temperature rise of complex direct buried cable cores

Actual direct buried cable is a complex model that contains backfill sand and external soil. To improve dynamic load level and utilization of buried power cables, it is crucial to quickly calculate power cable core temperature under sudden changes in load. The complex buried cable structure is decomposed into three parts so as to improve the accuracy of calculation. These three parts are the cable body, the backfill sand and the external soil, which temporary temperature rise can be solved by respect transient thermal circuit models separately and then add them up to obtain the cable core temperature. In actual project, the values of the transient thermal circuit model elements can be solved in advance and made into a table, and the relevant parameters can be obtained by checking the table in use. The backfill sand is only related to its heat conductivity, the external soil is related to its heat conductivity and burial depth. There transient thermal circuit model elements values can be fitted by an expression with the environment parameters, which can improve application scope of the transient thermal circuit model. The experimental results of the simulation show that, after knowing cable type and environment parameters, the transient thermal circuit model elements can be obtained by looking up the table and calculating by expressions, thus enabling fast calculation of the value for the cable core temperature variation while ensuring the accuracy of the results, and can meet the requirements in engineering.

Full-scale test of Direct-buried Cable in Sand under Repetitive Loading

Direct-buried cable construction can minimize cumbersome processes, thereby decreasing construction time and cost. However, there is no regulation on burial depth that consider the long-term performance of backfilling soil for direct-buried cables. This study examines the mechanical response of direct-buried cables subjected to repetitive loads. This experimental study uses a full-scale chamber to replicate field construction. The stress on the cable, vertical displacement on the surface, and shear wave velocity between loading plate and cable are continuously monitored during 10,000 repetitive loading cycles. A miniature electrical cone is used to indirectly quantify the initial relative compaction. Repetitive loading densifies the soil around the cable, increasing stress on the cable and accumulating vertical strain. The trends are more pronounced with lower initial relative compaction. The shear wave velocity increases during repetitive loading, suggesting a change in the earth pressure coefficient. Applied stress – vertical strain allows the estimation of resilient modulus. These observations will provide a better understanding of the mechanical response of backfilling soil. Additionally, the uniaxial compression test of the underground power cable made for direct burial is conducted to measure the displacement of the cable insulator under the field condition obtained from the full-scale test. Then mechanical stability of the cable is investigated based on the axial displacement of the cable insulator.

Experimental Study on the Cyclic Ampacity and Its Factor of 10 kV XLPE Cable

The load varies periodically, but the peak current of power cable is controlled by its continuous ampacity in China, resulting in the highest conductor temperature is much lower than90℃, the permitted long-term working temperature of XLPE. If the cable load is controlled by its cyclic ampacity, the cable transmission capacity could be used sufficiently. To study the 10 kV XLPE cable cyclic ampacity and its factor, a three-core cable cyclic ampacity calculation software is developed and the cyclic ampacity experiments of direct buried cable are undertaken in this paper. Experiments and research shows that the software calculation is correct and the circuit numbers and daily load factor have an important impact on the cyclic ampacity factor. The cyclic ampacity factor of 0.7 daily load factor is 1.20, which means the peak current is the 1.2 times of continuous ampacity. If the continuous ampacity is instead by the cyclic ampacity to control the cable load, the transmission capacity of the cable can be improved greatly without additional investment.

Molecular thermodynamics of water in direct-buried power cables

The balance of this article examines what actually happens to water within a direct-buried cable throughout the day and year as the cable temperature, the soil temperature, the water content of the soil vary. Water, which is almost present at 100% relative humidity at the typical 1 meter burial depth of direct-buried power cables, moves very quickly through any polymeric layers

Practical Aspects of Applying Soil Thermal Stability Measurements to the Rating of Underground Power Cables

Due to the increased interest in the operating reliability of high ampacity underground cable systems, more concern is placed on heat transfer in soils and the necessity to properly rate direct buried cables.

Choices of Jacketed or Bare Concentric Neutral Cable for Effective Grounding and Corrosion Control

New types of underground corrosion have been experienced following widespread use of direct-buried cables for electric power distribution at 7.2/12.47 and 14.4/24.9kV. Alternatives that should be considered in selecting types of cable and corrosion control measures for underground electric facilities are discussed. The choices are examined in light of the permanence of other buried metal connected to the electric neutral wires, as well as possible corrosion of the copper neutral wires.

A Positive Approach to Corrosion Control of Submersible Vault Type Urd Systems

This presentation establishes corrosion controls for submersible vault type electric systems and includes a computerized analysis of galvanic and electrolytic conditions. Separate tests of anode configuration and of cathodic protection interference with the copper concentric neutral of a direct buried cable are discussed.

Insulated sodium conductorsߞa future trend

Polyethylene-insulated sodium conductors, having economic advantages over conventional conductors, have been developed. The sodium conductors are light in weight and can be manufactured on standard cable-fabricating equipment. The light weight and the usual flexibility of the sodium cable should afford greater ease of installation in direct-buried and overhead power cable applications. Extensive tests indicate that this system is tough and resilient, and can withstand considerable abuse. Sodium's electrical conductivity ranks just below copper and aluminum. A useful service life of 40 years, under normal ambient conditions, is predicted for direct-buried cable.