Bench-scale experimental study on the fire behavior of electric cable arrays by considering different layouts

The effect of different cable layouts on the fire behavior of electric cable arrays was experimentally studied. The influence of external heat flux on cable fire characteristics was investigated. Several parameters for electrical cables such as the post-burning morphology, ignition time, heat release rate, peak heat release rate and total heat release were obtained. The results show that cable layouts could affect cable charring degrees according to the post-burning morphology. A linear relationship was found in the transformed form of time to ignition and radiant heat flux, and the critical radiant heat flux value for the single cable array appeared smaller than that for the other two layouts. The peak heat release rate for Cables A–D with the single array presents the increasing trend with an increase in radiant heat flux, while the two parallel and intersectional cable arrays present the different trends. Moreover, the total heat release values of Cables A–D in the different cable layouts were analyzed. This work provides the basic data and preliminary investigation to fire engineering of cable arrays with the different layouts.

Development of digital twin model of underground electric cable: thermal part of the problem

Innovative technologies of generative design using the concept of digital twins of the designed objects play an important role in growing digitalization trend of project activities. The digital twin of an object is the object simulation model with high accuracy of mathematical description. It is used to solve the problems of regime and structural optimization of the object. Usually, generative design technologies are implemented using 3D models of physical fields. And specialized packages which have high requirements for computer resources and user skills are used. At the same time, quite often the object for which the digital twin model is developed consists of several subsystems that allow relatively independent modeling. A one-dimensional model of the thermal process cannot provide the required accuracy, but a 2D-model is quite sufficient for this purpose. The development of such a model that combines the required accuracy, and low cost of machine time is currently topical scientific and practical problem. The method of mathematical modeling is used to solve this problem. The model uses the mathematical apparatus of the Markov chain theory. The model is two-dimensional and is adapted to the multi-layer environment representing the soil, in a separate cell of which a non-stationary heat source may be found. Heat passage through the surrounding soil is described in terms of thermal conductivity, and the heat exchange with the environment is described in terms of heat transfer. The influence of the parameters on the process flow is studied by numerical methods. At this stage of the study, experimental verification of the model is not expected. A mathematical two-dimensional model of digital twin of underground electric cable has been developed. It allows us to predict the cable temperature and its distribution in the surrounding soil. The assessment of thermal state of the power transmission line is given according to the power and the depth of the heat source location. It is found that the results of simulation modeling are consistent with the physical concepts of the process. The results obtained are of scientific novelty, since they are based on a universal modeling algorithm and allow us to describe the transients in the object under study, which is a part of the digital twin of the underground cable. The model is easy to use and requires little machine time. It can be easily used in generative design practice.

Cell model of transient heat processes in underground electric cable and surrounding ground

One of the most essential consequences of short circuits in underground cable networks of 6–10 kV is heating up the insulation with its possible inflammation and damage of adjacent objects of an electrical supply system that enlarge the concomitant damage many times as much. Various methods (including the methods, which are based on reference documents) to calculate the thermal state of underground cables are known. Despite the part of them are of extra complexity and require a lot of poorly identified parameters, the issue of the accuracy of forecasting calculations remains open. Hence, the issue of development of new approaches to model transient thermal processes in a cable, combining the simplicity, small computational time, and the reasonable accuracy of forecasting the process thermal parameters is an important one. The method of mathematical modeling is used to solve the problem. The model uses the mathematical tools of the Markov chains theory. It is adapted to the representation of ground as multilayer medium, and the non-stationary heat source may be placed in one of the layers. The heat transfer deep down into the ground is described by heat conduction, and the heat exchange with neighboring ground and environment is described by heat emission. The study of influence of the process parameters on the heat process behavior is carried out by numerical methods. The experimental validation of the model is not planned at the current stage of this investigation. The developed mathematical model allows predicting temperature in a cable and in surrounding ground depending on the heat capacity and depth of layout of the heat source, determined by the value of current in the cable. The results of numerical experiments come to agreement with the physical essence of the process. The obtained results have the scientific novelty as they are based on the universal algorithm of modeling and allow describing the transient processes in the object under consideration. The authors have proposed a mathematical tool to estimate the heat state of an underground electric cable depending on the heat capacity of the current, its depth of location in the ground and the thermo-physical properties of the ground. The model is simple to operate and takes exceedingly small computational time. It can be easily used in engineering practice.

Appraisal of electrical wiring and installations status in Isoko area of Delta State, Nigeria

Electricity is the prime mover of every economy; hence there is a need to maintain its generation, distribution and consumption. This study was carried out to appraise the status of electrical wiring in the Isoko area of Delta State, Nigeria. A total of 300 residential buildings, 200 makeshift shops and 100 artisan workshops were sampled and their structures, state of connection, overvoltage protection (cut-out fuse) and earthing were accessed. 100 questionnaires were distributed to electricians involved in electrical wiring and installations in the study area. Results obtained from the questionnaires revealed that only 71% of the residential buildings, 23% of the makeshift shops, and 8% of the artisan workshops made use of electric cables that met the NIS recommendations. For electric cable connections, it was observed that there was a lapse in the connections; mostly in the artisan workshops, as some service cables were not properly tightened to the distribution lines. Only 75% of the residential buildings, 53% of the makeshift shops, and 5% of the artisan workshops had approved rating cut-out fuse. It was observed that in artisan workshops, welding machines were connected directly to the service lines. Furthermore, the results revealed that 42% of the residential buildings, 87% of the makeshift shops and 99% of the artisan’s workshops lacked proper earthing. These results revealed electrical risks in many makeshift shops and artisan workshops and the need for the relevant authorities to act fast to minimize power outrage and prevent electrical tragedies in the study area. Keywords: Artisan, electrical wiring, energy theft, makeshift shops, residential buildings

Development of Strong Mooring Rope With Embedded Electric Cable

Synthetic fibre ropes are in widespread use in maritime applications ranging from lifting to temporary and permanent mooring systems for vessels, fish farm, offshore equipment and platforms. The selection of synthetic ropes over conventional steel components is motivated by several key advantages including selectable axial stiffness, energy absorption and hence load mitigation, fatigue resistance and low unit cost. The long-term use of ropes as safety critical components in potentially high dynamic loading environments necessitates that new designs are verified using stringent qualification procedures. The International Organization for Standardization (ISO) is one certification body that has produced several guidelines for the testing of synthetic ropes encompassing quasi-static and dynamic loading as well as fatigue cycling. The paper presents the results of tension-tension tests carried out to ISO 2307:2010, ISO 18692:2007(E) and ISO/TS 19336:2015(E) on 12-strand rope with embedded electric cable constructions manufactured by Ashimori Industry Co. Ltd from Vectran fibres. The purpose of the tests was to characterise the performance of a novel strand construction (SSR) and compare this to a conventional 12-strand construction. Utilising the Dynamic Marine Component test facility (DMaC) at the University of Exeter several key performance metrics were determined including; elongation, minimum break load (MBL), quasi-static, dynamic stiffness and embedded cable resistance. During the ISO 2307:2010(E) test programme the samples were tested dry and during the ISO 18692:2007(E) and ISO/TS 19336:2015(E) test programmes the samples were fully submerged in tap water after being soaked in water for at least 24 hours. Two methods were used to quantify sample extension: i) an optical tracking system and ii) a potentiometer. Axial compression fatigue and cyclic loading endurance tests were also carried out on Vectran sample. Failure of the Vectran sample or embedded cable did not occur during tests carried out using DMaC. Further tests and sample analysis were also carried out by Ashimori Industry Co. Ltd. Quasi-static bedding-in at 50% MBS and cyclic load endurance test with 6000 cycles between 3.57% MBS and 53.6% MBS was completed. The Effective Working Length (EWL) was 3.821 m before testing and 3.974m after testing. The resistance of the cable increased from 9.6962 Ω to 9.7693Ω during the test and importantly the embedded cable did not fail. Each tensile loading cycle of the rope caused a measurable variation in wire resistance; approximately 0.01Ω. The data obtained during these tests will provide insight into the behaviour of these materials, which will be of use to rope manufacturers and mooring system designers, in addition to offshore equipment and vessel operators.