http://ieeexplore.ieee.org/iel5/57/17476/00806380.pdf

Outdoor insulators

This paper deals with the use of corona ring at the HV end fitting for improving the electric field and potential distributions and then for minimizing the corona discharges on 230 kV AC transmission line composite insulator. A single corona ring is installed at the energized end side. Three-dimensional finite element method (FEM) software is employed to compute the electric field. As the performance of high voltage insulator strings closely depends on designs and locations of corona ring, the effects of the corona ring radius, the ring tube radius and the ring vertical position are examined. The minimization of the electric field necessitates the optimization of corona ring. For this purpose, new nonlinear mathematical objective function linking the electric field strength to the corona ring structure parameters is established. The optimization problem is achieved by minimizing the objective function using a modified particles swarm optimization (PSO) algorithm with a dynamic population size. The algorithm adjusts the size of population for each iteration. Based on the average value and the best solution of the objective function, we propose a new mathematical model to update the population size. This algorithm enables the population size reduction leading to computing time decrease. According to the results, FEM-PSO hybridization technique could be very helpful in optimization of corona ring design.

Optimal design of corona ring on HV composite insulator using PSO approach with dynamic population size

An insulated composite power cable having a wire core defining a common longitudinal axis, a multiplicity of composite wires around the wire core, and an insulative sheath surrounding the composite wires. In some embodiments, a first multiplicity of composite wires is helically stranded around the wire core in a first lay direction at a first lay angle defined relative to a center longitudinal axis over a first lay length, and a second multiplicity of composite wires is helically stranded around the first multiplicity of composite wires in the first lay direction at a second lay angle over a second lay length, the relative difference between the first lay angle and the second lay angle being no greater than about 4°. The insulated composite cables may be used for underground or underwater electrical power transmission. Methods of making and using the insulated composite cables are also described.

Insulated composite power cable and method of making and using same

With the increase of transmission power in China, the heating problem of converter transformer resin impregnated paper (RIP) bushings is increasingly serious. In this paper, applying the computational fluid dynamics (CFD), using a 3D electromagnetic-fluid-thermal analysis method, and considering the heat conduction, convection, and radiation effects, the temperature field distribution of the converter transformer RIP bushing has been simulated; according to the simulation results, the max-imum temperature of epoxy impregnated paper is above the heat distortion temperature 120 °C. Then, to verify the accuracy of the simulation method, temperature rising experiment has been car-ried out. Through the comparison, the temperature difference percentage between the simulation results and the experimental results is within 9 % proving the rationality of the simulation method. Finally eight optimization schemes for the 400 kV con-verter transformer RIP bushing were proposed which include the heat conductors with different diameters and numbers and the thermal conductive oil inside the inner conductor. Through the simulation of the eight optimization schemes, it can be proven that the heat conductors and the thermal conductive oil inside the inner conductor can effectively decrease the temperature distri-bution of converter transformer RIP bushings and improve the stable operation of transmission line.

A novel dissipating heat structure of converter transformer RIP bushings based on 3-D electromagnetic-fluid-thermal analysis

The overhead transmission line system is one of the methods of transmitting electrical energy at a high voltage from one point to another, especially over long distances The demand for electrical energy is increasing due to the increase in the world population, the evolution of transport technology, and economic expansion, thereby resulting in overloading to the overhead line (OHL) system In building new infrastructure for transmission lines, several issues need to be addressed Thus, optimizing existing power by increasing the ampacity of power line is a practical solution to meet energy demand issues During long-term operation, the temperature of OHL conductors may increase beyond their rated temperature, which is typically 75 °C for conventional conductors such as aluminum-conductor steel-reinforced cable This condition is defined as thermal stress, which results in lower sag vertical clearance, tensile loss, elongation and creep, and reduced life span of the conductors This condition must be avoided to ensure that the line is not permanently elongated, which can disrupt the vertical ground clearance, and to expand the conductor’s life Other factors such as lightning, wildfire, aging, and degradation of the conductor can also cause thermal stress on the conductors and have thermal effects on the conductor’s performance Therefore, unwanted thermal stress needs to be examined and identified by monitoring the thermal effect and behavior of the lines This paper presents the state of the art in monitoring technologies that can be used to identify thermal stress on OHL conductors, including the issues and challenges in monitoring At the end of this paper, a few suggestions are included to address the occurrence and assessment of thermal stress in lines Ultimately, this work may provide complete information to researchers and maintenance engineers to enable them to make better decisions on condition monitoring, operation, and maintenance of the system

/pdf/review-of-thermal-stress-and-condition-monitoring-48g4ahy87n.pdf

Review of Thermal Stress and Condition Monitoring Technologies for Overhead Transmission Lines: Issues and Challenges

Satisfactory operation of composite insulators is intimately related to the surface electric field (stress) distribution. This paper presents results of calculation of the electric field distribution for composite insulators up to 1200 kV, using a 3D software package based on the Boundary Element Method. The impact of corona and grading rings, single and bundled conductors, insulator orientation (dead-end and suspension), single and double units, and surface condition (dry and wet) on the electric field distribution has been analyzed. For UHV systems (higher than 750 kV ac) the use of dual insulators with individual corona rings at the line and ground end and a common grading ring at the line end is beneficial. The existence of optimal dimensions of corona and grading arrangement has been illustrated on a 1000 kV insulator string. It was found that the dead end insulators experience higher electric stress when compared to their suspension counterparts and this difference gets more prominent as the system voltage increases.

Electric field computation of composite line insulators up to 1200 kV AC

This paper presents an overview of important aspects regarding the use of overhead conductors employing composite materials. These issues must be addressed for them to be accepted as viable replacement of traditional overhead conductors employing a steel core. It also elucidates the lessons learned from the use of composite insulators that can be applied to composite conductors. Preliminary experimental and theoretical results performed on two types of composite cores technologies presently available are presented.

J. Hunt

Papers

Electric field computation of composite line insulators up to 1200 kV AC

Mechanical and electrical issues concerning the use of composite materials for the supporting core in transmission line conductors