Cable Temperature Research Articles

Fast Analytical Approaches for the Transient Axial Temperature Distribution in Single Wire Cables

In various technical areas, the requirements and the complexity of electrically conductive structures (cables and printed circuit board traces) and their insulating materials are increasing, which leads to higher demands on reliability. Therefore, better diagnosis and control functions are needed. Intelligent fusing strategies with electronic fuses, where the current flow can be switched by semiconductors, can play an important role. One approach is to monitor the insulation temperature in order to detect thermal overloads and switch off a current branch before the insulation is damaged. As especially in cables, a direct temperature measurement is troublesome, most approaches are based on current measurements. From a measured current, the cable insulation temperature can be derived using an electrothermal model. Those models can be very complex, especially when the transient and axial heat flow in a cable should be considered. The computational efforts for the commonly used numerical solution methods are high. Analytical approaches potentially reduce these efforts significantly. In this article, a new analytical approach for the calculation of the transient axial temperature distribution along an insulated single wire cable, considering the nonlinear temperature dependence of the cable parameters, is presented. It enables a precise and fast calculation of cable temperatures, e.g., for automotive cable harnesses. There it can be beneficial for the control of electronic fuses where computing resources are low. The cable insulation can be operated closer to the limits and the overload protection can still be guaranteed.

Combustion Characterization according to Accelerated Deterioration Temperature of a Non-class 1E Cable

In this study, the temperature effect of accelerated deterioration on combustion characteristics was investigated when accelerating aging a non-class 1E cable for nuclear power plants. The accelerated aging of 40 years was conducted under five temperature conditions of 90 °C, 100 °C, 110 °C, 130 °C and 150 °C. In the early period of combustion when the first peak of the heat release rate emerged, the heat release of the non-aged cable exhibited the largest peak value of 225 kW/m2 while the heat release of the aged cables exhibited a comparatively low first peak value. The first peaks of aged cables decreased as the temperature condition increased. This tendency is considered to emerge from the thermal decomposition and destabilization of long-chained polymer structure when the sheath and insulation of cables are exposed to a thermal degradation environment. Hence, this loosening of the chemical bond and its decomposition severely affected the degradation of the flame retardant performance. In particular, in the combustion characteristics for the aged cables under temperature conditions of 100 °C or higher, the first peak value of the heat release rate did not exceed 200 kW/m2. In the middle period of combustion, the heat release rates of both the non-aged and the aged cables were kept constant at approximately 25-30 kW/m2 without significant change. In the later period of combustion, the second heat release peaks emerged for only non-aged, 90 °C and 100 °C cables because the cables aged under low temperature conditions (90 °C and 100 °C) maintained a certain level of flame retardant performance while those aged above 100 °C did not. Therefore, it can be considered that the higher accelerated deterioration temperature triggers the higher degradation of the flame retardant performance, and 100 °C is a critical temperature that involves the significant degradation effect.

Experimental investigation of energy consumption for the process of initial heating of a substrate for the use of electric heat-mechanical system

Purpose. Experimental determination of energy consumption for the process of initial heating of the substrate to the temperature of anaerobic digestion in a biogas reactor using an electrothermal-mechanical system with automatic control to assess the energy efficiency of the process of heating the substrate and the profitability of further processing of the resulting biogas into thermal and electrical energy.
 Methodology. Experimental studies of the dynamics of temperature changes in an heating cable placed in an electrothermal-mechanical system, determining the duration of the process and the energy consumed by the initial heating of the substrate, processing and analysis of the obtained data arrays, summarizing the results obtained.
 Findings. Biogas technologies play an important role in the formation of a modern energy system, the profitability of which directly depends on the energy efficiency of anaerobic digestion intensification. The process of digestion of waste is long, so one of the main methods of intensification of biogas production is the mixing of waste in the process of anaerobic fermentation. There is a need to improve the energy efficiency of anaerobic digestion intensification and the profitability processing of biogas into heat and electricity. Ways to improve energy efficiency mainly consist in reducing the time of heating the substrate in a biogas reactor, reducing the consumption of electrical energy for the process of thermal stabilization of anaerobic digestion, structural combination of energy-efficient systems for mixing and heating raw materials in reactors, and introducing automatic production systems. The implementation of these actions will make it possible to establish the optimal geometric dimensions of an electrothermal-mechanical system with automatic control for mixing and heating the substrate in a biogas reactor and significantly increase the energy efficiency of biogas plants and the subsequent processing of the resulting biogas into thermal and electrical energy.
 Originality. As a result of the experimental study and analysis of the data obtained, it was found that with the same power of the heating sections, the change in the temperature of the electric cable in each blade does not occur in the same way. The authors found that the average value of the temperature of the sections of the electric heating cable of the lower blades is 12.9% higher compared to the upper blades of the electrothermal-mechanical system. In the course of experimental studies, the authors found that when using a heating system made of an electric heating cable mounted in the blades of a two-tier paddle mixer, it consumes J, on the process of initial heating of the substrate from before °С in a biogas reactor with a volume of 40 liters. The duration of the heating itself is 300 minutes. In the course of experimental studies, the authors established the energy efficiency from dividing the electrothermal-mechanical system into heating sections, when each blade is a separate section with its own automatic temperature control of the electric heating cable mounted in the corresponding section, while the consumption of electrical energy is reduced by 27.9%.
 Practical value. The results obtained can be used in the design, construction and modernization of biogas production intensification systems, namely, mixing and heating of the substrate in biogas plants. This will improve the energy efficiency of the biogas formation process and the profitability of its processing into heat and electricity.

Perspectives of temperature assessment based on wave propagation for dynamic rating of medium-voltage power cables

This paper explores the feasibility of wave propagation characteristics as means of probing the temperature of an underground power cable. It utilises the relation between wave velocity and relative permittivity. The permittivity and its temperature dependency are specific for the applied insulation materials. The investigated cable is a three-phase XLPE-insulated mediumvoltage cable with a common earth screen. Combined thermal and electromagnetic analysis is applied to account for the temperature distribution over the cable cross section. The corresponding permittivity distribution is based on the temperature dependency measured for an XLPE sample. Temperature monitoring is achieved by observing the signal transit time along the power cable. The measured variation in signal propagation velocity and attenuation, compared to model predictions, provides an estimate of the cable temperature. It is shown that a sensitivity within 2°C can be achieved for a temperature near the maximum operating value for XLPE insulation.

Fiber optic high temperature sensor based on ZnO composite graphene temperature sensitive material

The working temperature of the cable is particularly important for the safe operation of the power system, which requires high temperature detection for its working environment, but the sensitivity of the ordinary optical fiber temperature sensor in the high temperature state cannot meet this demand. For this purpose, an optical fiber high temperature sensor based on ZnO composite graphene temperature sensitive material is developed in this paper. MMF-TSCF-MMF temperature sensing unit is composed of two sections of multimode fiber (MMF) and a tapered seven core fiber (TSCF). Three different shapes of ZnO@Gr (ZnO composite graphene) temperature-sensitive materials were prepared by hydrothermal method. The experimental results show that the sensor has high stability and good interference effect. Meanwhile, the wavelength sensitivity reached 0.33268 nm/°C in a temperature measurement range of 89–98 °C. The fiber sensor is used for precision temperature measurement of cable temperature in fields such as electrical engineering due to its high temperature sensitivity, small size and low cost.

Power Inspection Design by Internet of Things and RFID Technology in Smart City

As the basic element and module unit in the construction architecture of smart city, the Internet of things (IoT) is also the key foundation and important support for realizing "automatic perception, rapid response, and scientific decision-making" of smart city. The study aims to improve the efficiency of power inspection in power enterprises and provide intelligent technology for power inspection. After the theoretical analysis of IoT and RFID technology under the background of smart city, the study discusses the information acquisition principle of RFID technology. Second, based on IoT and smart grid, the study takes the power equipment of power company A as an example, and puts forward the power inspection scheme, including the information required for inspection and the inspection of primary and secondary equipment. The specific contents are as follows: health assessment is carried out according to the real-time alarm of power equipment, and the control command is sent to the downstream control equipment to confirm the alarm information. Meantime, based on the alarm information of power equipment and related equipment, the expert analysis system is used for reasoning and analysis, and the RFID tag is used to supervise the inspectors to arrive at the site and inspect the situation according to the predetermined route. The temperature of the cable of power company A is measured under normal and hidden dangers, and the body insulation test is conducted on No. 1 main transformer. The results show that under normal operation, the cable temperature at each point is slightly different, which is basically about 40 °C. The temperature before the fourth point of the cable rises obviously, indicating that the fourth point has faulty. Over time, the more chemical molecules are detected in phase A. When phase B and phase C are tested on the same day, the difference of chemical molecular content is relatively small. It indicates that the chemical molecular content detected by chromatographic test of bulk insulating oil is normal. To sum up, smart power, as the objective need of urban intelligent development, is an important foundation of smart city. The power inspection scheme based on IoT and RFID technology proposed has high detection efficiency.

Research on Operation Management Technology of Cable Joints of Ring Network Cabinet Based on Temperature Sensors

In this paper, aiming at the operation and maintenance of the internal cable joints of the ring main unit, the research on the operation and management technology of the ring main unit cable joints based on temperature sensors is carried out. Starting from the principle of temperature sensing technology for cable joints, an online temperature monitoring system for the cable joints of the ring network cabinet is developed during the operating cycle. Comprehensive consideration of factors such as seasons, ambient temperature and humidity, line load current, etc., to evaluate the operating status of the cable joint temperature data as the main basis. A simple and adjustable bracket suitable for the fixed installation of the non-contact temperature sensor of the ring main unit has been developed. A method of managing the cable joints of the ring main unit during the operating cycle is proposed to realize the effective evaluation of the cable joint status. It can greatly improve the accuracy of condition monitoring, and improve the efficiency and level of operation and maintenance.

Conductor Temperature Monitoring of High-Voltage Cables Based on Electromagnetic-Thermal Coupling Temperature Analysis

As a key state parameter of high-voltage cables, conductor temperature is an essential determinant of the current carrying capacity of cables, but in practice, this is difficult to measure directly during the operation of high-voltage cables. In this paper, the electromagnetic-thermal coupling analysis model of a 110 kV high-voltage cable is established using the finite element analysis software COMSOL. By analyzing the temperature distribution law of high-voltage cables under different load currents and ambient temperatures, the relationship between the change in the high-voltage cable surface temperature and the conductor temperature is deduced, which allows the monitoring of the high-voltage cable conductor temperature. Taking the 110 kV cable of the Yanzhong line in Shanxi Province as an example and using the electromagnetic-thermal coupling temperature field analysis method, the conductor temperature of the high-voltage cable can be measured using the data obtained from the cable surface temperature, which is measured by the self-developed Raman Distributed Temperature Sensor (RDTS) system with a maximum measurement error of about 2 °C. The method is easy to use and can achieve the accurate measurement of the conductor temperature without damaging the cable body.

Cable Temperature Alarm Threshold Setting Method Based on Convolutional Neural Network

Power cable is used more and more in the power network, and its significance to the safety and stability of the power network is increasingly prominent. Especially in the urban power grid, the high voltage cable is related to the normal production and life of the city. Because of the particularity of the laying environment, it is very difficult to find and eliminate the fault points once the cable faults occur, which seriously affects the reliability of the power grid. Currently, 25% of cable faults are caused by elevated cable temperature, so it is important to set the cable temperature alarm threshold accurately. In this paper, a method of setting temperature alarm threshold using convolutional neural network is proposed. Experiments show that this method is 60% more accurate than other methods.

EXPERIMENTAL INVESTIGATION OF ENERGY LOSSES OF A BIOGAS REACTOR IN THE ENVIRONMENT FOR MESOPHILIC MODE OF FERMENTATION

The aim of the work is an experimental study of energy losses to the environment for the mesophilic mode of fermentation in order to increase the duration of substrate cooling and reduce energy costs for the process of biogas formation. To achieve the goals set, the following tasks have been solved: a methodological approach has been developed for conducting experimental studies; an experimental plant for a biogas reactor with an electrothermal-mechanical system with automatic control for mixing and heating the substrate was made; experimentally investigated energy losses to the environment for the mesophilic mode of fermentation; processing, analysis and comparison of the obtained experimental data were carried out. The working hypothesis of the research was that the use of an heating cable built into the stirrer paddles would provide a longer process of cooling the substrate to the heating switch-on temperature, which would reduce energy costs for the biogas formation intensification process. The most significant result of the study is to obtain the dependences of the change in the temperature of the heating cable, the substrate in the lower, middle and upper tiers of the reactor and the duration of the substrate cooling to the heating switch-on temperature in the operating biogas plant. The significance of the results of experimental studies lies in the fact that when placing a heating cable built into the stirrer paddles, the process of cooling the substrate to the heating switch-on temperature occurs later, on average, by 35 minutes, when the substrate is fermented in a biogas reactor with a volume of 40 liters. The implementation of the data obtained will increase the energy efficiency of the processes of intensification of biogas production and the profitability of further processing of biogas into heat and electricity.

Photoelectric composite cable temperature calculations and correction of the parameters

A method for correcting the thermal resistance of the insulation layer by using the current difference and the conductor temperature difference is proposed in this paper. The optical fibre temperature of the three-core photoelectric composite submarine cable is measured by BOTDA; and the corresponding relationship between the temperature variation of the optical fibre and the conductor is performed by finite element analysis, thereby obtaining the difference in temperature of the conductor. After finite element analysis, the corrected thermal resistance is therefore replaced in the calculation. It has been shown by comparison that, the correction of the thermal resistance of the insulation layer can effectively improve the transmission capacity requirements of the cable and the accuracy of the calculation of the transient temperature rise of the conductor.

Enhancement of the thermal analysis of harmonics impacts on low voltage underground power cables capacity

This article investigates the harmonic impacts on the underground low voltage cables by using new algorithm. The heating of cables by harmonics may lead to form dry zones around the cables causing insulation failure. De-rating factors due to the influence of the load harmonics for different soil types as back-fill materials are presented. The de-rating factors are calculated for different typical non-sinusoidal current loads with different harmonic order ingredients. The influences of the harmonics in the cable current and also the effect of the dry zone formation in the soil surrounding the cable on the cable capacity and its temperature rise are investigated. New thermal model of three-cores with a neutral low voltage cable that is usually used in low voltage distribution circuits is considered. The proposed technique is based on the heat balance at any node of the cable thermal equivalent circuit. The influences of the neutral conductor area of low voltage cable, on the cable conductor's temperature and cable current are investigated. One of the advantages of the proposed method is that different percentages of harmonics can be considered for each phase separately and the mutual heating between the three phases and neutral cable conductors is considered. De-rating factors due to the harmonic influence on the cable buried in different soil types with and without dry zone formation in the soil surrounding the cable are presented.

Characterization and Modeling of LV Cables Considering External Parameters for Distribution Networks

In response to the climate emergency, new uses are plugged to low voltage (LV) electrical networks. The development of self-consumption complicates the LV grid operation, and force distribution system operators (DSOs) to better model and characterize their networks. DSOs mainly use a three-conductor model (3 CM) to compute power flows, and consider error margins of 2% for voltage profiles to reflect their model inaccuracy. The characteristics of the future LV grids call into question these margins, and the models used. In this paper, a four-conductor model (4 CM), and an additional model named 4 CMext, that considers external parameters (i.e., cable temperature, ground electrical resistivity, and value/number of the earthing resistances) are proposed. The best model for cable characterization and voltage profile calculation is chosen; the 4 CMext is more adapted for the characterization, and corresponds with the finite element model, with an error margin of 4%, experimental measurements of 15%, and French cable manufacturer data of 0.5%. For the voltage profile, the 4 CMext provides a more detailed view of the critical cases that could lead to a violation of the limits of the EN 50160 standard than 3 CM and 4 CM. Violations of high or low voltages are underestimated by two to six times by the 3 CM and 4 CM. Not considering external parameters can lead to a voltage profile error of above 3%. In this paper, we recommend that DSOs use the 4 CMext to represent LV networks, which would allow LV networks to be used closer to their physical limits, and avoid or postpone network reinforcements.

Influence of multi-layered sediment characteristics on the thermal performance of buried submarine high-voltage cables

The safe and efficient operation of submarine high-voltage cables depends on their thermal performance. Based on the electromagnetic heat coupling and heat transfer theory, the cables’ heat dissipation in multi-layered sediments is simulated using FEM. The proposed models are validated by comparing with the results of IEC 60287 and illustrated the limitation of IEC 60287 which ignores convective heat transfer. Further, the width of the cable embedding layers greater than 9 m can promote heat dissipation when the permeability of the cable embedding layer is relatively high, but the effect of depth is less pronounced. Also, the cable temperatures increase with the decrease of sediments thermal conductivity and increase of the buried depth when permeability is below 10−12 m2. The temperature decreases as the permeability increases, the range of decay is between 10% and 55% when the permeability reaches 10−9 m2. The heat dissipation is great when the permeability is greater than 10−11 m2. When the characteristic of the cable embedding layers is different from its upper and lower layers, the high permeability of the upper layers reduces the cable conductor temperature more efficiently than the lower layers. The findings give some reference in improving the transmission efficiency of cables.

IMPACT OF ENERGY INTERMITTENCE ON CABLES AND THEIR ACCESSORIES RELIABILITY

The production of electricity from wind turbine farms or solar power plants can't be controlled with very important intermittence (brutal change in the wind speed, dust accumulation and cloud cover). This could affect the reliability of cables and their accessories in the distribution grid. In this work, we carried out to calculate the cable temperature variation when such an intermittence occurs. The results showed that the temperature variation is not very important in the case of cables used for solar energy distribution but could reach 80°C for those used to carry electricity from wind turbine farms. Despite of temperature swing, we concluded that the risk of cable early fatigue (mechanical or electrical) is negligible. However, we demonstrated, by means of experiments, that the impact of the cable thermomechanical stress on the accessories is severe and irreversible. Indeed, due to the mechanical stress on the cable core and its limited degrees of freedom, the connector resistance decreases. Consequently, a thermal runaway occurs, causing joints damages.

Analysis of Transient Operating Characteristics of the 10 Kv Tri-Axial HTS Cable Under Fault Current

The Tri-axial high temperature superconducting (HTS) cable usually subjects to the impact of the fault currents in the power system. During the fault, a large amount of the Joule heat is generated, which may be damage cable. In this paper, an analysis model of electromagnetic thermal transient characteristics of the 10 kV/1 kA cable is built. The transient characteristics of the HTS cable are analyzed under a fault current of 15 kA rms lasting 0.14 s, and the current, resistance and temperature of the HTS cable are obtained. The maximum temperature of the HTS cable is 153.1 K under fault current. Meanwhile, the safe operating range of the HTS cable under the fault current of 15 kA to 25 kA is obtained. the analysis results will provide the theoretical basis for the quench protection and relay protection strategy of the tri-axial HTS cable in the Grid.

The algorithm of current prediction based on multi-dimensional Long Short Term Memory networks

Precisely predict the current on the node circuit in advance, which can facilitate the manager to manage and control the risk in advance. The current, voltage, residual current, cable temperature, ambient temperature, and ambient humidity on the circuit constitute a multi-dimensional sequence characteristic sequence data. This paper proposes an improved Long Short-Term Memory (LSTM) cyclic neural network method, which combines multi-dimensional Train the neural network in a specific way to obtain the LSTM current prediction model. The experiment is validated with the perception data in an intelligent building, and compared with the classic neural network and Recurrent Neural Network (RNN) prediction method. The experimental results show that, compared with the prediction methods such as BP neural network and RNN network, the multi-dimensional LSTM has a higher accuracy in predicting the current in the circuit, and the MSE index is as low as 0.5. And this method can detect potential electrical fire hazards and give early warning 1–2 time intervals in advance to avoid electrical fires.

Temperature Analysis of HTS Cables in Superconducting DC Energy Pipeline During Short-circuit Fault

Superconducting energy pipelines (SEPs) which can simultaneously transmit liquefied natural gas (LNG) and electricity over long distances are proposed these years. SEPs combining LNG pipelines and high-temperature superconducting (HTS) cables together have higher transmission efficiency. The stable and reliable operation of SEPs during short-circuit faults is important. The HTS cable generating heat may cause the liquid protective medium (LPM) inside the copper former of the cable to boil, endangering the safety of SEP during short-circuit faults. The objective of this paper is to obtain the influence of short-circuit faults on the temperature of HTS cables in SEPs. Three different structures of copper former in HTS cables of a ±100 kV/1 kA SEP are investigated including copper rod and two different copper tubes. One inside of the copper tube is vacuum calling internal vacuum copper tube (IVCT) and the other one is LPM calling internal LPM copper tube (ILCT). Simulation results show that the ILCT has the best properties due to its lowest temperature during short-circuit faults. When a fault current of 20 kA transports in the HTS cable for 100 ms, the cross-sectional area of the copper former should be larger than 187.46 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> to ensure safety.

The Structure and Heat Leakage of MgB2 Superconducting Current Lead

In superconducting system, current lead connecting cryogenic device and normal temperature copper cable is the main leakage heat source of entire system. Its performance directly affects cooling cost of cryogenic system. Multi-current leads have advantages of eliminating Joule heat and reducing heat conduction leakage. As a commonly superconducting material, MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (magnesium diboride) has broad application prospects. In this paper, the current lead of 200 A MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> cable and normal temperature copper cable are designed and calculated. The heat transfer power of superconducting section and the conventional current lead section are 17.90 W and 18 W, respectively. The numerical simulation method is used to verify and analyze calculation results. The temperature at interface between normal temperature copper wire and current lead is lower than 70 K.

Simulation Analysis of Current in Metal Sheath of Power Cable Considering Temperature Characteristics

This paper proposes a cable broadband circuit model considering the temperature characteristics. This paper establishes the equivalent circuit model of the cross-bonded power cable and proposes the broadband parameter calculation method considering the temperature. The cable parameters are calculated by the vector fitting method. Based on the operating current and cable temperature data of the cable on a certain day, the simulation analysis of the cable sheath current considering the temperature is carried out using Simulink. Finally, the simulation results show that the cable sheath current is significantly affected by temperature.