Power Cable Model Research Articles

Research on the rapid calculation method of temperature rise of cable core of duct cable under emergency load

In order to facilitate engineers to manage dynamic loads in real time and improve the utilization of power cables, it is necessary to accurately calculate the temperature rise of cable cores under duct laying conditions. The transient thermal circuit model involved in this paper helps to improve the speed of dynamic response and the accuracy of transient temperature rise calculation for power cable cores under duct laying conditions. Since the impact of the environmental conditions, exploring the computational relationships of the thermal circuit model parameters helps to improve the engineering applicability of the model. The duct cable can be broken down into three parts: the cable body, the air inside the pipe and the external environment. In engineering, the thermal circuit model parameters of the cable body can be made into a table and applied by looking up the table. The thermal circuit model parameters of air in duct are related to the cable outside diameter and duct inside diameter, and can also be engineered using tables for application. The fit gives the third part of the equation with respect to the thermal resistance coefficient of the duct and soil and the burial depth. The error in applying the decentralized thermal circuit model and parametric expressions is less than 1 °C compared to the results of finite element calculations. This proves that the decomposition of the duct power cable model improves the accuracy of the transient temperature rise calculation. The relationship equation between the parameters of the thermal circuit model and the laying conditions helps to improve the engineering adaptability of the method.

An efficient strategy triggered crosslinking of polyethylene and its application in degassing‐free ultrahigh voltage power cables

AbstractPolyethylene has excellent electrical insulation, but its low thermal stability and breakdown strength limit its application in the field of high‐voltage (HV) and ultrahigh voltage (UHV) power cables. In this work, we have developed a new organic peroxide, 2,5‐dimethyl‐2,5‐di(tert‐butylperoxy) hexane (Bi25), which can efficiently trigger the crosslinking of polyethylene (Bi25‐XLPE). Bi25‐XLPE does not produce gas byproducts and has a longer scorching time. All performance of Bi25‐XLPE sheets fulfill the standard of the 500 kV power cable insulation due to the void‐free nature, higher crosslinking density and crystallinity. In addition, one 500 kV power cable model was constructed by COMSOL, which confirmed the breakdown strength (up to 61.66 kV/mm) and stability of Bi25‐XLPE.

Fault Identification and Localization of a Time−Frequency Domain Joint Impedance Spectrum of Cables Based on Deep Belief Networks

To improve the accuracy of shallow neural networks in processing complex signals and cable fault diagnosis, and to overcome the shortage of manual dependency and cable fault feature extraction, a deep learning method is introduced, and a time-frequency domain joint impedance spectrum is proposed for cable fault identification and localization based on a deep belief network (DBN). Firstly, based on the distribution parameter model of power cables, we model and analyze the cables under normal operation and different fault types, and we obtain the headend input impedance spectrum and the headend input time-frequency domain impedance spectrum of cables under various operating conditions. The headend input impedance amplitude and phase of normal operation and different fault cables are extracted as the original input samples of the cable fault type identification model; the real part of the headend input time-frequency domain impedance of the fault cables is extracted as the original input samples of the cable fault location model. Then, the unsupervised pre-training and supervised inverse fine-tuning methods are used for automatically learning, training, and extracting the cable fault state features from the original input samples, and the DBN-based cable fault type recognition model and location model are constructed and used to realize the type recognition and location of cable faults. Finally, the proposed method is validated by simulation, and the results show that the method has good fault feature extraction capability and high fault type recognition and localization accuracy.

An approach to thermal modeling of power cables installed in ducts

The power cables laying in the urban areas require utilization of the protective ducts, mainly to facilitate the faulty section replacement. However, the use of cable ducts results in reduced capacity to dissipate generated heat to the surroundings. Thus, the thermal analysis of cables placed in ducts is very important for proper power cable operation. The thermal response of cables laid in mutual and in separate ducts, respectively, is considered at two values of current load. The full-scale field measurement setup is utilized to carry out the analysis of both steady-state and dynamic power cable heating under actual field conditions for the two backfill configurations. The measurement results provide the insight into the power cable heating dynamics related to the situations of a short-term over-loads and fault drive-through responses and also the opportunity to verify the proposed numerical approach based on the use of finite element method and the boundary conditions on the interior duct surface. The approach could be considered as a compromise between the standardized procedure and the tedious procedure involving the computational fluid dynamics simulations due to straightforward implementation and very good accuracy. The results obtained suggest that cables laid in mutual duct lead to a less favorable thermal situation when compared to cables laid in separate ducts. Also, the numerical results suggest that the use of non-uniform heat flux around the inner duct surface results in a significantly better agreement with measurements, compared to the purely numerical approach utilizing the concept of the effective thermal conductivity to model heat transfer in the air gap between cable and duct. Finally, the sensitivity analysis has been carried out to assess the effects of various backfill thermal conductivities and the ground surface temperature on the resulting thermal field. • Full scale field measurements. • Simplified approach for thermal field estimation when cabled are placed in ducts. • Nonuniform heat flux distribution along the cable duct is implemented. • Better agreement with measurements when non-uniform heat flux distribution is used. • Use of effective thermal conductivity results in notable temperature underestimation.

A novel transient thermal circuit model of buried power cables for emergency and dynamic load

In order to improve the utilization rate of cable while ensuring safety and reliability, accurate and rapid evaluation of transient temperature rise of directly buried power cables is useful to improve the management level of dynamic capacity increase and emergency load conditions. Since the existing thermal circuit model is relatively complex or not very accurate, an equivalent three-branch transient thermal circuit model is presented for the complex cable structure and heat dissipation environment based on the uniqueness of the temperature field. Considering the electric circuit similarity, the transient analysis method of the centralized parameter network in the circuit is used to establish the transient adjoint model of the thermal capacity branch, provide the node conduction matrix of the transient thermal circuit model, and write the node temperature rise equation as a function of the node heat flow. By comparing the solution of the thermal circuit model with the finite element results, and the genetic algorithm is used to optimize and obtain the equivalent thermal resistance and thermal capacity parameters of the transient thermal circuit model. The comparison of finite element calculation results proves that the proposed three-branch transient thermal circuit model is more accurate than the two-branch thermal circuit model. Compared to the traditional all-part thermal circuit model, the three-branch model can be rapidly solved and easily applied in engineering.

A novel fault diagnosis method of power cable based on convolutional probabilistic neural network with discrete wavelet transform and symmetrized dot pattern

To accurately diagnose the XLPE power cable insulation fault, this research proposed a novel hybrid algorithm combined with Convolutional Probabilistic Neural Network (CPNN) based on Discrete Wavelet Transform (DWT) and Symmetrized Dot Pattern (SDP) analysis. First, it built seven different power cable insulation defect models to measure partial discharge signals of power cable insulation faults. Then, a discrete wavelet transform was used for noise filtering. The time-domain partial discharge signal was directly converted into the point coordinate feature image of visual polar coordinates by SDP analyses. Finally, the feature image was trained and recognized by CPNN. After the important feature information of the feature-image was extracted by convolution layer and pooling layer operations, it is applied to the power cable insulation fault state diagnosis system based on the rapid learning and highly parallel computing of Probabilistic Neural Network (PNN). The experimental results proved that the method proposed in this research could accurately diagnose the power cable insulation fault type and the recognition accuracy is higher than 96%. The proposed method has a short detection time and high diagnostic accuracy. This proves that it can be applied to detect the power cable insulation fault type.

Hybrid Methodology Based on Symmetrized Dot Pattern and Convolutional Neural Networks for Fault Diagnosis of Power Cables

This study proposes a recognition method based on symmetrized dot pattern (SDP) analysis and convolutional neural network (CNN) for rapid and accurate diagnosis of insulation defect problems by detecting the partial discharge (PD) signals of XLPE power cables. First, a normal and three power cable models with different insulation defects are built. The PD signals resulting from power cable insulation defects are measured. The frequency and amplitude variations of PD signals from different defects are reflected by comprehensible images using the proposed SDP analysis method. The features of different power cable defects are presented. Finally, the feature image is trained and identified by CNN to achieve a power cable insulation fault diagnosis system. The experimental results show that the proposed method could accurately diagnose the fault types of power cable insulation defects with a recognition accuracy of 98%. The proposed method is characterized by a short detection time and high diagnostic accuracy. It can effectively detect the power cable PD to identify the fault type of the insulation defect.

A Power Cable Reference Frame dqn Model for Fundamental Frequency Analysis

This paper proposes an underground power cable dqn model that can be used for both electric machines analysis and control at or around the fundamental rated power frequencies (50Hz or 60Hz). The model can be used as an observer to estimate the cable output states. This makes the far end measurements available through estimations for long cable applications such as electrical submersible pumps and wind generations. The model can be used also in simulation analysis with accelerated simulation time. Advantages include fast computation, decoupled network, and ability to work under unbalanced supply or network conditions without requiring an interface stage, such as the Eigen vectors calculation, between the cable and electric machine models. Detailed model derivations and analyses, including balanced, unbalanced, and transient conditions, are provided. Verifying using MATLAB SIMULINK, the model has a higher accuracy in balanced and unbalanced conditions when compared to the per-phase shifted frequency analysis (SFA) model in simulations, along with one of the shortest computation times among all simulated models. For the experiment, the researchers design a test consisting of a 20 ft cable operating at 6 kHz used to emulate an equivalent 2,000 ft cable with the proposed cable model as an observer., the results prove to be accurate, with the maximum error between the measured cable output and the model output estimation at 0.12%. Therefore, the model is verified by the experiments in the same given conditions as the simulations, and it can be considered as a reference in the future.

An Approach to Thermal Modeling of Power Cables Installed in Ducts

An Approach to Thermal Modeling of Power Cables Installed in Ducts

On-line monitoring aided evaluation of power line cable shapes

The paper presents a novel method that by coupling of the measurement data with an advanced 3D, extensible cable model allows for the prediction of power line configuration. The method, which may be considered as an example of the predictive digital twin, is presented in two variants that were validated throughout a comparison of the predictions with an in situ geodetic surveying. It has resulted in an excellent agreement of the computed and the real power cable shapes and confirmed reliability of the proposed approaches. We use on-line measured temperature and inclinations at a certain point on a cable to enhance the non-linear mechanical model (not the simple catenary curve) of the cable sag. The proposed coupling of the real data and a computational model is done twofold, by modification of either selected parameters or equations used to model power cable configuration. In both approaches, our power cable model is combined with a rigid body model of insulator chains. The proposed predictions with quantified uncertainties may support the power line dynamic rating that in turn may significantly increase the capacity of electric transmission systems. The key component of such systems is the processing of the collected data in order to determine the maximum current that can be transmitted safely, without violating the required clearance space. Making use of the advanced 3D, extensible cable model, instead of the catenary curve, insignificantly increases computation time, however it enables taking into account out of plane loading (wind), data overload as well as effective using of measurement uncertainties.

High-Frequency Modeling and Filter Design for PWM Drives with Long Cables

Aiming at the problems emerging in a pulse width modulation (PWM) drive system with long cables, the accurate modeling of power cables is the premise for predicting and analyzing these relevant phenomena, and a proper filter design is the key solution to these problems. This paper proposes high-frequency cable models to represent these frequency-dependent characteristics, especially for the high-frequency resistance of cables, which is an easily overlooked factor that determines the damping of overvoltage. The proposed models can be used for accurately representing the cable characteristics in a wide frequency range, and correctly simulating the differential mode (DM) overvoltage and common mode (CM) current, including the peak value, oscillation frequency, and damping of the transient waveform. In addition, improved filter networks are proposed to suppress the DM voltage and CM current, with the merit of low losses, small volume, and excellent abilities for suppressing overvoltage. The proposed cable models and the filter design were validated in a 750 W PWM drive system with 200 m power cables.

Two VHDL-AMS-based models of multi-conductor power cables for EMI simulations

Due to the fast switching of the commutation cell in a motor drive system, high-frequency electromagnetic disturbances propagate through cables to reach the loads. Mismatched impedances lead to an overvoltage at the loads terminals. In order to study this EMI issue, accurate circuit models of power cables are required. In this context, this paper proposes two multi-conductor cable models. Our approach takes into consideration the frequency dependence of the cable per-unit-length parameters, the coupling between conductors and propagated induced phenomena. The power cables used in motor drive systems are characterized by their rotational symmetry. Thus, the complexity of the model is reduced by means of both a set of mathematical functions approximating the frequency behavior of the cable and using a modal domain-based transfer matrix. So, the VHDL-AMS frequency model can be easily deduced. Once the model is established, the simulation of any cable length becomes an easy task. The model is implemented in ANSYS Simplorer software. After that, the time domain model is built up based on the vector-fitting algorithm. In order to validate our proposal, a comparison of the common mode and the differential mode frequency responses of the reduced cable model with those of the well-known cascaded cell model and measurements found in the literature is performed. The results demonstrate the accuracy and the speed of our approach in the predefined frequency range. Also, a time-domain comparison between the frequency model and the time model is performed. The results obtained validate the two models.

Experimental Validation of a Heat Transfer Model in Underground Power Cable Systems

This paper presents the laboratory test stand that is used for experimental validation of underground power cable system models. Determination of temperature distribution in the vicinity of the cable is the main goal of the study. The paper considers a system of three power cables, situated in the in-line arrangement, and buried in sand. Three electrical heaters of special construction are used in order to simulate the heat flux that is generated in the power cables during their operation. The test stand is designed to be placed in a thermoclimatic chamber, which allows testing the system in various thermal conditions when the ambient temperature changes by 20 °C to 30 °C. Numerical computations of the steady-state temperature fields are performed using the finite element method.

Study on AC Over-Current Transport Characteristics of the ReBCO Thin-Film-Type Superconducting Wire With the Different Specific Resistance Values

The main goal of the superconducting cable is lossless power transmission, and it does not function the fault current limiting performance. In this study, the use of the fault current limiting type superconducting power cable model is proposed to maximize its current limiting performance within the stable range using only the relationship between the current transporting and current limiting parts, without additional devices. For this, the current transporting and current limiting parts were configured using ReBCO thin film wires with different specific resistance characteristics, and a jig was fabricated to integrate the whole parts. After a fault current was applied, the current transporting, current limiting, and thermal stability characteristics were examined. The current transport characteristic was normal under the suggested condition, and the current limiting rate also complied with the operation condition at the 1/2th, 3rd, and 5.5th cycles. The thermal stability was analyzed, and the temperature of the current limiting part increased to 270 K at the 5.5th cycle, which might present a possibility of damaging the superconducting wires. The aforementioned results are highly valuable as the basic data for the design of fault current limiting superconducting cables.

Dynamic ice accretion process and its effects on the aerodynamic drag characteristics of a power transmission cable model

An experimental study was conducted to examine the dynamic ice accretion process over the surface of a high-voltage power transmission cable model and characterize the effects of the ice accretion on the aerodynamic forces acting on the test model. The experimental study was carried out by leveraging the unique Icing Research Tunnel of Iowa State University (i.e., ISU-IRT) to generate typical wet glaze and dry rime icing conditions experienced by power transmission cables. A cylindrical power cable model, which has the same diameter as that of typical power transmission cables, was mounted in ISU-IRT for the ice accretion experiments. In addition to using a high-speed digital imaging system to record the dynamic ice accretion process, a novel digital image projection (DIP) based technique was utilized to quantify the 3D shapes of the ice structures accreted on the surface of the power cable model as a function of the ice accretion time. The time variations of the aerodynamic drag force acting on the test model during the dynamic ice accretion process were also measured quantitatively by using high-sensitive force/moment traducers mounted at two ends of the test model. The ice structures accreted over the surface of the power cable model were found to change significantly under different icing conditions (i.e., rime icing vs. glaze icing). The characteristics of the aerodynamic drag acting on the test model was found to vary significantly during the dynamic ice accretion process depending on what types of ice structures were accreted on the test model. The acquired snapshots of the ice accretion images and the measured 3D shapes of the accreted ice structures on the test model are correlated with the aerodynamic force measurement results to elucidate the underlying physics.

A 3-D nonlinear thermal circuit model of underground MV power cables and their joints

A 3D thermal model of underground power cable is presented in this paper. A detailed representation of the cable and its joints, the laying condition, the soil and the heat exchanges between soil upper surface and air, considering different weather conditions, is given. The model solves the thermal problem by means of an equivalent electric circuit and has been validated against field measurements, showing its applicability both for steady state and transient studies.In order to verify if any correlation between the occurrence of overheatings and the anomalous increase of failures, observed by Italian Distribution System Operators (DSOs) during summer 2015, exists, the model has been applied to simulate one-year operation of an existing underground cable. The cable is located in the MV distribution network owned by A.S.M. Terni S.p.A., the DSO in Terni, a city placed in the Central Italy. Ambient temperature and relative humidity trends have been taken from registrations made by a weather station, whereas the current profile along the cable has been assumed equal to that measured in 2015 by A.S.M., sampled every ten minutes. A second current profile has been also used, derived from the measured one in order to have the cable loaded at ampacity for a considerable time span during the year. In all cases, results show that no overheating occurred and, moreover, that the joint is the coldest part of the underground power cable.

A Simplified Model of Coaxial, Multilayer High-Temperature Superconducting Power Cables with Cu Formers for Transient Studies

Bypassing transient current through copper (Cu) stabilizer layers reduces heat generation and temperature rise of high-temperature superconducting (HTS) conductors, which could protect HTS cables from burning out during transient conditions. The Cu layer connected in parallel with HTS tape layers impacts current distribution among layers and variations of phase resistance in either steady-state or transient conditions. Modeling the multilayer HTS power cable is important for transient studies. However, existing models of HTS power cables have only proposed HTS cables without the use of a Cu-former layer. To overcome this problem, the authors proposed a multilayer HTS power cable model that used a Cu-former layer in each phase for transient study. It was observed that resistance of the HTS conductor increased significantly in the transient state due to a quenching phenomenon, which made the transient current mainly flow into the Cu-former layers. Since resistance of the Cu-former layer has a significant impact on the transient current, detailed modeling of the Cu-former layer is described in this study. The feasibility of the developed HTS cable model is evaluated in the PSCAD/EMTDC program.

Diagnosis of abnormal temperature rise observed on a 275 kV oil-filled cable surface — A case study

This paper presents a case study on a 275 kV oil-filled cable. The condition assessment and diagnosis are based on analysis of cable surface temperature in relation to its current load and insulation dielectric loss. The work was initiated by a local abnormal temperature rise of 5.2 °C in cable surface temperature, which was observed during a routine inspection. The temperature rise occurred at bend area with a length of approximately one metre in the Blue phase. No PD activity was identified using on-line PD measurement. The relation between cable surface temperature, cable core temperature and cable insulation condition was then simulated based on the thermal model of power cables. According to simulation analysis, poor condition of cable insulation or oil from an oil duct penetrating a region under the cable surface were identified as possible reasons for the problem observed. An in service X-ray scanning technique was employed for further investigation and to aid diagnosis. The X-ray images revealed a slight distortion of the PVC sheath and the presence of multiple voids between cable insulation paper and the lead sheath. It was concluded that an oil leakage from the oil duct to the voids under the cable lead sheath was responsible for the local cable surface temperature rise. The result removed the concern of incipient cable breakdown, and a potential unplanned outage.

Comparing frequency‐dependent and distributed parameter with lumped losses power cable line models for cable insulation coordination against overvoltages

Simulations of transients are an obliged step for the insulation coordination of cable lines. Although a frequency-dependent power cable line model better takes into account real conditions since resistive and inductive parameters vary with frequency, a distributed parameter with lumped losses power cable models can be useful to simplify and give higher flexibility to the insulation coordination study. In such a case, a dilemma rises up when a frequency shall be selected for the determination of the cable parameters. In this study, a comparative analysis between the two models has been performed considering a typical configuration layout, i.e. an overvoltage coming from an overhead line and stressing the cable line terminated on a transformer. The overvoltages stressing both cable insulation wall and cable thermoplastic jacket are evaluated using the same system configuration with both frequency-dependent and distributed parameter with lumped losses power cable line models, in the latter case sweeping different frequency values for the determination of the cable parameters. A frequency range that minimise the differences between the overvoltage estimation using the two models is suggested.

Research and Construction of Cable 3D Intelligent Management and Control Platform Based on Parametric Modeling Technology

Traditional three-dimensional modeling is not only tedious, but also can’t edit existing three-dimensional model, parametric modeling technology can flexibility modify graphics under design or drawing state through dimension driving. Model changes automatically following relevant design parameters and environmental modification, this progress improves modeling efficiency greatly [1]. Basing on analyzing the power cable traditional management model, this paper integrate cable 3D graphics information, geographic information and cable asset information, upgrade traditional power cable management to digital, visual, information modern management, improve operation and management level of power cable, improve reliability of power supply [2].