Conductor Temperature Research Articles

Conductivity spectra of lithium ion conducting glassy ceramics

Study of ac conductivity spectra of Li2O doped different glassy ceramics in wide frequency and temperature regime using Jonscher's power law model and Almond-West formalism reveals that Li+ migration depends upon nature of doping reagent. It also points that the ratio of power law pre-factor to the exponent (–log10 A/S) indicates temperature and composition dependency of present conductors. Motion of Li+ may predict that the process of conduction is percolation or pseudo three dimensional types. These glassy ceramics should be suitable candidates for lithium ion battery application. Improvements in the capacity of modern lithium (Li) batteries can be made by enhancing conductivities and ionic diffusivities in various anode and cathode materials. Fundamentally, such improvements can be achieved in the present electrolyte compositions. It is also interestingly noted that constantly changing nature of electrical conduction in present systems are strongly microstructure dependent.

Study on the Impacts of Uncertain Meteorological Parameters on Line Transmission Capacity

Abstract Traditionally, transmission lines have been operated based on static thermal rating, which is determined by fixed and conservative meteorological data. It causes underutilization of potential transmission capacity. To overcome this limitation, this paper presents seasonal time scale, which can provide flexible ratings. Seasonal meteorological parameters are uncertain. The uncertainty can directly impact the conductor temperature, and eventually impact transmission capacity of the lines. In order to account for the uncertainty, this paper presents an uncertainty analysis model. This model consists of three parts: establishment of probability distribution models, Monte Carlo simulation, and operation risk assessment. In the case study, the actual meteorological data for 7 years in the Weihai is utilized, and is divided into four subsets by spring, summer, autumn and winter. The uncertainty analysis model is tested on an actual 47 km Wei-Kun line and a 4-bus power system. Results show that potential transmission capacity can be extracted if seasonal meteorological parameters are taken into account.

Performance and Accuracy Investigation of the Two-Step Algorithm for Power System State and Line Temperature Estimation

Data concerning actual temperatures of line conductors constitutes essential information for the power system operator. The temperature of the power lines can be used to improve the accuracy of the power system model, thereby increasing the accuracy of the state estimation. This article presents a two-step algorithm for the power system state and line temperature estimation. In its second stage, the proposed method searches for a line temperatures vector, which corrects the uncertain power system base model and allows for further minimization of an objective function. As a result, a more accurate estimation is obtained along with a more precise model of the estimated system. The derived model can then be used for more accurate optimization. The presented method enhances standard procedures of power system state estimation, and its advantage is that it does not require direct measurements performed by phasor measurement units or measurements of line conductor temperatures and weather conditions realized by dynamic line rating systems. The results of simulations made on various test models have been examined, confirming the convergence of the procedure to the point at which the average temperature of the line wires together with the voltage values and phase angles are achieved. The algorithm’s performance and improvement method have also been presented. An advantage of the investigated approach is the possibility to calculate the temperature of line wires with the use of primary measurements in the power system. The presented and examined method, however, is sensitive to the measuring device errors. Additionally, an analysis of the method’s errors and ways of reducing them has been performed.

Power System Advanced Scheduling Based on Advanced Thermal Rating

ABSTRACTThe dynamic thermal rating (DTR) can improve the thermal load capacity of transmission lines. The integration of DTR into power system scheduling achieves full utilization of the line load capacity. Thus, this paper proposes the concept of advanced DTR and applies it to the advanced scheduling of power system. Based on advanced thermal rating, combining with conductor temperature, safe running time, and system power flow, the advanced scheduling is realized to achieve the predictive use of line thermal load capacity. In addition, based on the wind power forecast, the advanced scheduling in the wind turbine system is studied. The influence of the randomness of wind power on the advanced scheduling is presented. The results prove that the advanced scheduling based on advanced thermal rating can improve the economy and safety of power grid operation.

Optimal power flow considering line-conductor temperature limits under high penetration of intermittent renewable energy sources

Forecasts of the power generated by intermittent renewable energy (IRE) sources are typically characterized by high uncertainty levels. Hence, recent formulations of the optimal power flow (OPF) problem incorporate the costs associated with the increased risk of generation shortage due to IRE uncertainty. Additionally, IRE generation increases the power flow uncertainty, thereby increasing the possibility of violating the thermal limits of overhead conductors. Real-time monitoring of the thermal statuses of overhead lines has been considered effective in increasing the transmission-system usage; in addition, it can influence IRE scheduling and the associated uncertainty costs. This paper proposes the formulation of an OPF problem incorporating the thermal characteristics of the conductor, calculated from the monitored weather parameters, for a system with significant IRE-source generation. The resulting convex nonlinear optimization problem is solved using a primal-dual interior point solver. A simplified form of the overhead-conductor heat balance equation that expresses the conductor temperature as an explicit function of the current is proposed, simplifying the incorporation of the conductor thermal characteristics in the problem formulation. The application of the proposed formulation is demonstrated using a modified version of the IEEE 30-bus test system with IRE generation.

Impact of Conductor Temperature Time–Space Variation on the Power System Operational State

The conductor temperature of an overhead transmission line varies with time and space, which has an important impact on the system operation. In this paper, the conductor temperature is solved iteratively by the CIGRE heat balance equation. The time–space variation of conductor temperature of a 220-kV transmission line is analyzed using real meteorological data from Weihai. Considering the temporal distribution characteristics, the seasonal model of the conductor temperature is given. Considering the spatial distribution, the mean value model, the weight average model, and the segmentation model are established. The system power flow involving the conductor temperature is established based on the relationship between conductor temperature and transmission line parameters. Through the calculation of power flow and the analysis of the maximum power transmission capability, the accuracy of the segmentation model is verified. The results show that the conductor temperature of overhead lines has obvious time–space variation characteristics. It is necessary to consider the time–space variation when analyzing the operation state of power systems.

Optimal Distribution System Operation for Enhancing Resilience Against Wildfires

Natural disasters can cause significant damage to power grids. During summer, in countries with high temperatures, distribution systems passing through forested areas are prone to wildfires. This paper proposes a stochastic programming approach for increasing resiliency of a distribution system exposed to an approaching wildfire. Dynamic line rating of the overhead lines is considered in order to model the impact of the wildfire on conductor temperature and flowing current. The uncertainties associated with solar radiation, wind speed, and wind direction that affect the progression of the wildfire and the production of stochastic distributed generators are taken into account. A scenario reduction algorithm is applied to reduce the number of scenarios in a tractable size and subsequently the computational burden. The proposed model is transformed to a mixed-integer problem with quadratic constraints, which provides effective solution to the operation of a distribution system against an approaching wildfire. A modified IEEE 33-bus distribution system is used to illustrate the applicability of the proposed approach.

A Novel Weather Information-Based Optimization Algorithm for Thermal Sensor Placement in Smart Grid

Although dynamic thermal rating is an effective and proper tool in assisting the planning and operation decisions of a smart grid, it closely depends on the weather information to determine the deployment of large numbers of sensors. This paper proposes a method, named gappy proper orthogonal decomposition-based genetic algorithm (GPOD-GA) for effectively determining the minimum number of thermal sensors and the optimal placements. The middle section of 345 kV transmission lines in the Taipower system was selected as a test grid and hourly weather data obtained from the Central Weather Bureau of Taiwan was used to examine the validity of the proposed method. The results show that the proposed method can significantly reduce the number of sensors that should be originally deployed on each span of power grid lines. A decrease of 64.61% and 79.61% of sensor deployment is obtained for the case of the entire grid and the individual transmission lines, respectively. Using the partial measurements from the minimum sensor deployments determined by the GPOD-GA algorithm, the accuracy test results also indicate that conductor temperatures of all lines in the power grid can be fully tracked and accurately reconstructed.

Work specification for the construction of 33kv overhead lines across a lagoon using equal level dead-end lattice tower supports

Bare overhead distribution conductors are typically flexible and uniform in weight along their lengths. This weight causes the span to form a catenary (sag) which changes with conductor temperature, ice, wind loading and time. This catenary is capable of tripping circuits because it often results to short circuit and damage power system equipment with attendant loss of revenue to utility company. This paper presents a case study of 33kV overhead line construction crossing a 200m wide ‘Lagoon’ which requires minimum sag-tension design and estimation of Dead-End Lattice Tower weight specification that would determine weight of Tower foundation. These two parameters were obtained using the standard mathematical equations and the specifications for Aluminium Conductor Steel Reinforce (ACSR). The results of various Parameters evaluated in this research work are presented and discussed. The Sag and Tower weight results were applied to the proposed project which was successfully completed and commissioned. http://dx.doi.org/10.4314/njt.v37i1.28

Comparison of Conductor-Temperature Calculations Based on Different Radial-Position-Temperature Detections for High-Voltage Power Cable

In this paper, the calculation of the conductor temperature is related to the temperature sensor position in high-voltage power cables and four thermal circuits—based on the temperatures of insulation shield, the center of waterproof compound, the aluminum sheath, and the jacket surface are established to calculate the conductor temperature. To examine the effectiveness of conductor temperature calculations, simulation models based on flow characteristics of the air gap between the waterproof compound and the aluminum are built up, and thermocouples are placed at the four radial positions in a 110 kV cross-linked polyethylene (XLPE) insulated power cable to measure the temperatures of four positions. In measurements, six cases of current heating test under three laying environments, such as duct, water, and backfilled soil were carried out. Both errors of the conductor temperature calculation and the simulation based on the temperature of insulation shield were significantly smaller than others under all laying environments. It is the uncertainty of the thermal resistivity, together with the difference of the initial temperature of each radial position by the solar radiation, which led to the above results. The thermal capacitance of the air has little impact on errors. The thermal resistance of the air gap is the largest error source. Compromising the temperature-estimation accuracy and the insulation-damage risk, the waterproof compound is the recommended sensor position to improve the accuracy of conductor-temperature calculation. When the thermal resistances were calculated correctly, the aluminum sheath is also the recommended sensor position besides the waterproof compound.

An algorithm to calculate feasible operating conditions of electrical network, given overhead conductor temperature and sag constraints

The paper presents an algorithm to calculate feasible steady-state conditions of an electrical network. A distinctive feature of the calculation is the consideration of constraints on the temperature of bare conductor and the clearance of a controlled span of overhead line. This consideration is based on forming and solving an equation of conductor heat balance to calculate the conductor temperature depending on the current flowing through the conductor and environmental factors, including the actual values of air pressure and air temperature. The paper presents the results of numerical calculations performed for individual overhead lines and for a test 16-node scheme of electrical network. The results illustrate the algorithm performance and the importance of considering the above constraints.

Improvement of the Conductor Temperature Calculation Algorithm for Calculating the Allowable Current in the Underground Channel

Improvement of the Conductor Temperature Calculation Algorithm for Calculating the Allowable Current in the Underground Channel

On Dispatching Line Ampacities of Power Grids Using Weather-Based Conductor Temperature Forecasts

Finding ways to improve the line ampacity supplied by existing power grids is an inevitable problem that electricity dispatch operators are now facing. Generally, the overhead power grid can operate at a proper rating when the weather dependant dynamic thermal rating (DTR) of lines is provided. A comprehensive understanding of future variation of line temperature is necessary and useful for line operators to decide a proper dispatch measure. However, line operators usually lack real-time DTR information. Thus, this paper proposes a principal component regression (PCR)-based method, which can predict the DTR of lines by only using the weather data forecasted by meteorological stations. The possible thermal bottlenecks at different locations along the line and the margin of line ampacity can be real-time determined by the proposed PCR-based prediction method. A case study of the 161 kV transmission grid of TaiPower in Taiwan is utilized to examine the performance of the proposed forecasting model. The experimental results show that the proposed method is useful to enhance line ampacity of the power grids without installing any costly sensing instruments.

Validation of a Simplified Model for Estimating Overhead Conductor Temperatures under Dynamic Line Ratings

Validation of a Simplified Model for Estimating Overhead Conductor Temperatures under Dynamic Line Ratings

An approach to dynamic line rating state estimation at thermal steady state using direct and indirect measurements

Dynamic line rating has emerged as a solution for reducing congestion in overhead lines, allowing the optimization of power systems assets. This technique is based on direct and/or indirect monitoring of conductor temperature. Different devices and methods have been developed to sense conductor temperature in critical spans. In this work, an algorithm based on WLS is proposed to estimate temperature in all ruling spans of an overhead line. This algorithm uses indirect measurements – i.e. weather reports and/or downscaling nowcasting models as inputs as well as direct measurements of mechanical tension, sag and/or conductor temperature. The algorithm has been tested using typical atmospheric conditions in Iceland along with an overhead line's real design, showing robustness, efficiency and the ability to minimize error in measurements.

Space charge behavior evolution of thermal-aged double-layered polyimide films

Polyimide film (PI) is widely used as dry-type smoothing reactor insulation for ultra-high voltage direct current (UHVDC) projects. In practice, the temperature of a central conductor can reach 80 °C to 100 °C at the rated power flow. Thus, the inner insulation composed of PI sustains these high temperatures. In this study, the space charge characteristics of PI at different temperatures (40 °C, 60 °C, and 80 °C) and thermal aging degrees (336, 500, 1000, and 1500 h) were examined with an improved pulsed electro-acoustic (PEA) measurement system to investigate the effects of temperature and thermal aging on dielectric performance. The apparent trap depths corresponding to various aging degrees were obtained according to the space charge decay dynamics at the interface. Results indicate that positive charges likely accumulate within the bulk of the material because of the thermal aging of homogeneous materials. The polarity of space charge at the interface also changes from positive to negative as aging degree increases. The space charge decay dynamics at the interface further shows that the trap energy increases as the thermal aging degree increases. The amount of residual space charge also increases remarkably as the electric strength and aging degree increase. The electric field distortion is closely related to temperature, thermal aging degree, and electric strength.

A Model for Calculating Core Temperature of Bare Overhead Conductor Based on Neural Network

Operation Security of transmission line is affected by operating temperature of bare overhead conductors. IEEE Standard Model has reflected that the current of a conductor should be decreased when the temperature difference between the core and surface exceed the special value. In order to accurately estimate the operating risk of bare overhead conductors, a model is proposed to calculate core temperature of a conductor based on BP neural network in this paper. An experimental plate was designed to validate the proposed model under the free convection and forced convection condition. The experimental and calculated results are analyzed and discussed.

DLR-supported overcurrent line protection for blackout prevention

Analysis of recent blackouts over the past decade has indicated overloads as being responsible for initiation and development of most large area failures. The overload occurrences have also been found to correspond especially with the overcurrent and distance protection, often causing their overfunction under allowable power system operating conditions. It is highly desired to improve the operation of protection relays for the sake of avoiding future blackout occurrences or at least lowering their scale. One of the possibilities to do so is an application of the Dynamic Line Rating algorithms into the standard overcurrent relay with the hope of ensuring safe relay behavior during overloads.The Dynamic Line Rating is usually proposed to be used for increasing the line transfer capacity by monitoring of the overhead conductors temperature and weather conditions. It is clear that one must also take into account the impact of DLR-operated line on the existing protection devices. It is required to adapt their decision-making algorithms to the new conditions, while satisfying arbitrarily established protection principles.This paper presents firstly chosen recent decade blackouts, highlighting the main causes of their formation and development process. Applicable solutions for overcurrent relay improvement are then proposed, which is followed by analyses of the new relay algorithms’ operation during allowable overloads and faults. The enhanced overcurrent relay solution introduced in this paper proved to be an efficient technique also for blackout prevention.

Thermal performance optimization of the underground power cable system by using a modified Jaya algorithm

This paper presents a modified Jaya algorithm for optimizing the material costs and electric-thermal performance of an Underground Power Cable System (UPCS). A High Voltage (HV) underground cable line with three 400 kV AC cables arranged in flat formation in an exemplary case study is considered. When buried underground, three XLPE high voltage cables are situated in thermal backfill layer for ensuring the optimal thermal performance of the cable system. The study discusses the effect of thermal conductivities of soil and cable backfill material on the UPCS total investment costs. The soil thermal conductivity is assumed constant and equal to 0.8 W/(m K). The cable backfills considered in the study are as follows: sand and cement mix, Fluidized Thermal Backfill™ (FTB) and Powercrete™ a product of Heidelberg Cement Group. Constant thermal conductivities of the backfills in the dry state are assumed, respectively, 1.0 W/(m K), 1.54 W/(m K) and 3.0 W/(m K). The cable backfill dimensions and cable conductor area are selected as design variables in the optimization problem. The modified JAYA algorithm is applied to minimize material costs of UPCS under the constraint that the cable conductor temperature shall not exceed its optimum value of 65 °C. The cable temperature is determined from the two-dimensional steady state heat conduction equation discretized using the Finite Element Method (FEM). The performance of the modified Jaya algorithm was compared with classical Jaya and PSO algorithms. The modified Jaya algorithm, for the presented case study, allows one to obtain lower values of the cost function.

Thermal analysis of underground power cable system

The paper presents the application of Finite Element Method in thermal analysis of underground power cable system. The computations were performed for power cables buried in-line in the ground at a depth of 2 meters. The developed mathematical model allows determining the two-dimensional temperature distribution in the soil, thermal backfill and power cables. The simulations studied the effect of soil and cable backfill thermal conductivity on the maximum temperature of the cable conductor. Also, the effect of cable diameter on the temperature of cable core was studied. Numerical analyses were performed based on a program written in MATLAB.