Underground Cables Research Articles

Adaptive Wavelet De-noising Algorithm using Absolute Difference Optimization Technique for Partial Discharge Signal

Discrete Wavelet Transform (DWT) de-noising method is widely used for one-dimension partial discharge (PD) signals measured from medium voltage underground cable. However, DWT de-noising has several drawbacks that prevent the DWT de-noising from improving its de-noising effectiveness In DWT de-noising, the two most important parameters are decomposition level and mother wavelet. The aforementioned parameters must be varied according to the noise level in the measured PD signal in order to effectively suppress the noise of the measured PD signal. In this paper, an adaptive DWT de-noising algorithm based on the Absolute Difference Optimizing (ADO) technique is presented to effectively suppress the varying noise levels in measured PD signal. First, the measured PD signal will be de-noised using a Daubechies 3 (db3) mother wavelet and a DWT decomposition level ranging from 1 to 10. Second, the de-noised PD signal will be subjected to the ADO technique. The sum of the absolute difference of local maxima in the de-noised PD signal will be used as an indicator to select the best decomposition level for the de-noised PD signal. Finally, the best-selected de-noised PD signal by using the ADO technique will be used to estimate the PD location on the underground cable. The results of PD location error using the ADO technique and normal DWT de-noising will be compared. The findings show that the ADO-based adaptive DWT de-noising algorithm significantly improved the de-noising process of the measured PD signal.

Derating Factors for Underground Power Cables Ampacity in Extreme Environmental Conditions: A Comparative Study

Derating Factors for Underground Power Cables Ampacity in Extreme Environmental Conditions: A Comparative Study

An investigation of electromagnetic transient characteristics on a practical 500 kV submarine cable system

This paper performs an investigation on electromagnetic transients for a practical 500 kV cable system. The system consists of 500 kV overhead lines, submarine and underground cables. In order to study the insulation coordination of the cable system, the transient simulations are performed using EMTP. The modal propagation constants of submarine cable are also investigated. Moreover, the cable series and shunt parameters are calculated using the newly developed Line/Cable Data Module in EMTP. The voltage and current characteristics of the cable system in steady-state, and for switching, fault and lightning transients, are studied. The transient overvoltage levels are also compared with requirements of insulation coordination in local standards. The work shown in this paper could provide a reference for the insulation design of 500 kV cable system.

Lightning induced disturbances in the power network considering losses, frequency effect and non-linearities

The malfunctions and even the material damage caused by lightning stroke are generally significant in electrical networks.. To help design equipment that can withstand lightning disturbances (e.g. electrical insulation, surge arresters, etc.), while compromising with the economic problem, researchers and engineers use numerical simulation. In this paper, we propose a new modeling to study the direct or indirect impact of lightning stroke on an electrical network of power transmission overhead lines or overhead or underground power cables. This modeling is carried out directly in the time domain and takes into account the losses, the frequency dependence and the presence of components with non-linear behavior (example: surge arresters). The new formalism that we propose uses the transmission line equations, the numerical method of Finite Differences Time Domain (FDTD) and the approximation technique called vector fitting. To stimulate the direct or indirect effects of lightning, our modeling is carried out with only the 1D spatial discretization (1D meshing) of the conductive parts, and provides access simoulenatlously to transient voltages and currents at any point of the network. Also consideration to surge arresters is rendered easy in our modeling.

Method for determining the locations of power cable damage

Problem. Existing methods for remotely detecting cable damage locations, except in the case of cable breakage, have a common drawback. They are unable to accurately separate the cable core resistance from the transient resistance at the short-circuit location, leading to low accuracy in fault detection. The posterior transient resistance at the short-circuit location can vary widely, depending on when the repair crew arrives. Goal. The goal of this study is to propose a method for identifying the location of "floating breakdown" cable damage. Methodology. The method involves using short-circuit indicators to determine the type and area(s) of the short circuit. The UNI-TUT255A device, a current clamp type, is then installed on the damaged cable core. The Imax option with memory is set, and the cable is switched on at the rated voltage. By comparing the recorded shock current value with the values obtained from a short-circuit model of the cable in MATLAB, the location of the damage along the length of the cable is determined. The point where the shock current value of the model matches the recorded value corresponds to the location of the short circuit. Originality. The proposed method addresses the challenge of locating faults in power cables, specifically those of the "floating breakdown" type. This type of cable damage, which occurs when the cable is accidentally disconnected during a short circuit, poses difficulties in detection, as traditional methods may show normal readings. The method presented in this study overcomes these limitations and provides a practical solution for identifying "floating breakdown" faults. Practical value. The results obtained from this method allow for the accurate detection of faults at the nominal voltage, without the need for burning the cable. This reduces the probability of additional damage caused by overvoltage. Furthermore, the method requires only one operator to carry the necessary equipment, eliminating the need for transport with powerful burning installations typically used in traditional methods.

An Enhanced Method to Achieve Exact DC Values for Frequency-dependent Transmission lines

This paper proposes an improved method to enhance the dc response of a frequency-dependent transmission line model used in EMT studies. A modification to the rational function approximation of propagation and characteristic admittance matrices of a transmission line is introduced to enforce exact dc values at 0 Hz. Furthermore, weighting factors are applied to improve accuracy at low frequencies. Finally, the order of the propagation function is reduced to decrease the computational effort.The validity of the proposed approach is demonstrated using examples involving underground cables and overhead lines. First, the effect of dc correction is demonstrated by comparing transmission line frequency domain characteristics. In addition, time domain simulations via open and short circuit conditions show a more accurate simulation of HVDC transmission lines with the proposed method.

Multi-section frequency dependent line model enabled underground cable fault location in MMC-HVDC grids using dynamic state estimation

Line parameters of underground cables (UGCs) in MMC-HVDC grids experience severe frequency dependent characteristics. For fault location of UGCs in MMC-HVDC grids, existing methods usually neglect the frequency dependent line parameters, which limits the fault location accuracy. To overcome this issue, a dynamic state estimation based fault location (DSEFL) method for UGCs in the MMC-HVDC grid is proposed in this paper. Firstly, the dynamic line model of the UGC based on the multi-section multi-layer model is formulated to consider both frequency dependent and distributed characteristics of the line parameters. Next, the DSE algorithm is used to solve the dynamic line model and the consistency indicator with respect to the determined fault location and resistance. Due to the complexity of the multi-layer model, a multi-step algorithm is designed to efficiently obtain the fault location result. Numerical experiments on MMC-HVDC grids verify that the proposed DSEFL method presents higher fault location accuracy for different fault types, locations, and resistances. compared to the existing methods. In addition, the computation burden, effects of measurement noises, parameter errors, and sampling rates are also discussed.

Risk evaluation of photovoltaic power systems: An improved failure mode and effect analysis under uncertainty

Photovoltaic (PV) power systems are confronted with many failure risks threatening operational security and leading to adverse impacts on the sustainable development. This paper identified the potential PV system failures and extended the traditional failure mode and effects analysis (FMEA) that has been questioned due to its inadequacy in industrial applications. First, the risk factor evaluation system was expanded from the original 3 indicators to 7 indicators associated with PV system failures, including personal safety, power loss, property damage, frequency of failure, visualization, maintenance expense, and technical difficulty. Second, a modified FMEA approach combining rough set theory, cloud model theory and multiplicative Multi-objective Optimization by Ratio Analysis (MULTIMOORA) method was developed. The proposed approach could not only settle various uncertainties (i.e., intrapersonal uncertainty, interpersonal uncertainty, and randomness) by integrating cloud model and rough sets, but also introduce the triple subordinate method MULTIMOORA to obtain a final risk ranking of PV system failures. Finally, the improved FMEA model was adopted to a PV system failure risk assessment case, verifying its effectiveness and superiority. It revealed that hot spots and disconnection of underground cables were the riskiest potential failures in PV systems. Essential risk mitigation measures should be implemented in advance to maintain the safety and promote the sustainable development of PV systems.

A new algorithm for fault location in multi-end underground cables using traveling waves

<p>A quick, reliable, and accurate fault location approach is essential in underground power systems protection. Being the most optimistic research topic of electrical power systems, this article presents an optimized algorithm for fault location in multi-end underground cables using travelling waves. Existing algorithms based on wavelet theory have fewer reliability and accuracy issues that raise an error to the power systems in fault location. The proposed layout presents a multiterminal underground cables system where the entire system is segregated into several fault identification sections where this model identifies the faulty section and the faulty half. Voltage and current wave transient at the mid-point of each fault locator are taken into account to eliminate the time-synchronous error. Traveling waves models are modelled using Bewley diagrams. Detecting the first and second traveling wave transient at both ends of each cable keeps the system reliable. Extensive simulations are simulated using the alternative transient program (ATP) to discriminate, identify, and locate several faults, while the system can also validate the faults near the busbar. The model is developed in MATLAB, and the obtained results depict the proposed algorithm's higher accuracy in fault location.</p>

Detection of power transmission lines faults based on voltages and currents values using K-nearest neighbors

The critical factors to consider when implementing a maintenance plan for energy transmission lines are, accuracy, speed, and time, because of the increased global demand for electricity power caused by rapid development, and overuse of electric power transmission lines (both underground cables and overhead transmission lines), which in turn reduces the efficiency of the lines. Consequently, the efficiency of the lines may be reduced as a result of overuse or other activities like excavation that may have tampered with the cables. Thus, it becomes important to investigate the faults to which the lines are exposed. To this end, this article focuses on the detection of fault in transmission lines through the use of k-nearest neighbor algorithm. Using this algorithm, the characteristics were obtained (voltage, current), and these characteristics enable the identification of faults in the transmission lines, and in the specific location (the entire system, phase B, and phase A). The benefits that can be derived from the use of this algorithm include time, accuracy, speed, which are the requirements for the maintenance of transmission lines. Euclidean distance used in the application of the k-nearest neighbor technique for weights, and K = 3 for number of neighbors. The dataset was split into two parts, 70% training set and 30% testing set.

Ampacity Calculations of Underground Power Cables With End Effects

Ampacity Calculations of Underground Power Cables With End Effects

Numerical and Analytical Analysis of the Low-Frequency Magnetic Fields Generated by Three-Phase Underground Power Cables with Solid Bonding

There is a special concern for measuring and simulating low-frequency magnetic fields generated by underground power cables, particularly in human exposure studies. In the present study, an accurate 2D finite element model for computing magnetic fields generated by three-phase underground power cables with solid bonding is proposed. The model is developed in ANSYS Maxwell 2D low-frequency electromagnetic field simulation software for a typical 12/20 kV (medium-voltage) three-phase underground power cable in both trefoil and flat formations, but it can be adapted to any cable system. Model validation is achieved by analytical computations conducted with a software tool based on the Biot–Savart law and the superposition principle. RMS magnetic flux density profiles calculated at various heights above the ground with these two methods correlate very well. This is also true for induced shield currents. The application of the finite element model to multiple three-phase power cables laid together is also considered.

Cost Effective Reliability Improvements in 33kV/11kV Electricity Distribution Networks – A Case Study in Western Province South 1, CEB, Sri Lanka

Electricity Distribution system in Sri Lanka consists of 33 kV, 11 kV and LV (400V/230 V) networks. Providing reliable supply to the end user is a challenging task to any utility. Therefore, utility is committed to develop its network to provide reliable supply to electricity users by investing in system developments. In this research, a methodology is introduced for selecting cost-effective solutions to improve the reliability of the 33 kV and 11 kV distribution systems among different proposals. Improvement of conductor, its insulation and protection of short duration faults are focused to develop the system in this research. Part of the method developed includes a software tool (named as DisFeeRIA) to analyse the reliability indices and economic parameters for the relevant proposal. Database of the DisFeeRIA software tool includes failure rate improvement, mean time to repair and costing of each option under consideration. Medium Voltage Underground Cable (MVUGC), Medium Voltage Aerial Bundle Conductor (MVABC), Medium Voltage Covered Conductor (MVCC), Room Temperature Vulcanizing (RTV) Si-R coating on existing bare overhead line ceramic insulators are considered as options for improving conductor and its insulation. One of the latest and innovative technologies used in distribution network, Pulse Closing Technology, is used to reduce short duration faults (momentary interruptions) and enhance the lifetime of the equipment used in distribution networks. Developed tool and method were tested by a case study done for distribution network in Western Province South – 01 of Ceylon Electricity Board (CEB). Three (03) feeders were selected in different areas from Urban, Coastal and Rural for this purpose. MVCC and RTV Si-R coating for existing Medium Voltage Bare Overhead lines can be used for improving the reliability of Coastal, Urban and Rural distribution feeders in a cost-effective manner after proper analysis, based on technical and economic aspects. However, depending on the safety concerns, MVUGC or MVABC can be used irrespective of the economical aspect. Intelirrupter pulse closers can be used to replace traditional auto recloses, especially with MVUGC, MVABC and MVCC in rural feeders. It helps to reduce momentary interruption failures and enhance the equipment lifetime by reducing thermal and mechanical stress on all distribution equipment and cables. Furthermore, it improves the power quality of the system.

Novel Harmonic Distortion Prediction Methods for Meshed Transmission Grids with Large Amount of Underground Cables

The tremendous and fast green transition in Denmark has initiated the large-scale grid-integration of renewable energy sources, electrification of energy consumption, and establishment of PtX and Energy Islands, setting goals for transmission grid development—such as the establishment of new connections—and for grid reconstruction—such as the extensive substitution of overhead lines (OHLs) with underground cables (UGCs). The share of UGCs in the Danish transmission grid is increasing. Presence of UGC has resulted in that resonances of the harmonic impedance characteristics of the transmission grid are brought within the harmonic order range coinciding with the harmonic emission sources and causing systemwide increase of the harmonic voltage distortion in the 400 kV transmission grid. The transformation of the 400 kV transmission grid has given rise to the need to predict harmonic voltage distortion using simulation models to secure an adequate power quality and support investment decisions and harmonic mitigation for the grid stage, which has not yet been established and which differs from the present grid. This paper presents the experiences of Energinet, the Transmission System Operator (TSO) in Denmark, with harmonic distortion in the Danish transmission grid due to the establishment of 400 kV UGCs, and the development of measurement-validated methods for harmonic distortion simulation and prediction. The paper also presents ongoing developments within, and research addressing, the prediction of harmonic distortion in meshed grids; for example, it explores where and how an analytical approach can replace observational studies with many numerical simulations. The methods shall make it possible to predict whether, where in the transmission grid, and for which harmonic orders connections that have not yet been commissioned may cause the violation of the planning levels, and which mitigations are necessary for bringing the harmonic distortion below the planning levels with respect to a given margin.

Multi‐type defect detection and location based on non‐destructive impedance spectrum measurement for underground power cables

AbstractPower cable defect detection and location is a crucial aspect in power asset maintenance. Impedance spectrum measurement can be used as a non‐destructive tool for cable monitoring. Defects from overheating and moisture ingress are investigated by the authors, and it is shown that multi‐type cable defects can be detected and located by this methodology. With both electromagnetic analysis and experimental investigation, the relation between impedance variation and the dielectric permittivity is studied to reveal the method's mechanism. An approach to implement such impedance measurement online is proposed and its perspectives in terms of sensitivity is investigated by field scale tests. It is shown that 2% impedance variation due to defect should be detectable. Field scale tests show perspectives for online application with signal coupling through a high‐frequency current transformer with focus on the differences in waveforms obtained from the impedance measurements.

Model test on deformation and failure mechanism of tunnel support with layered rock mass under high ground stress

To control the large deformation of the Changning Tunnel, based on the constant resistance and energy absorption characteristics of the NPR anchor cable, first, through the physical model test, the mechanics of the NPR anchor cable controlling the deformation of the floor heave was studied, including the temperature field, strain field, and displacement field during the tunnel excavation and loading process. Then, through field tests, the control effect of NPR anchors was studied. The results of the model test show that under the support of NPR anchor cables, with the increase of geostress, the asymmetric deformation of the vault and floor is obvious. During the loading process, the shallow rock mass pressure strain area at both ends of the floor is larger, squeezing the floor and causing strong temperature changes and floor heave failures of the rock mass, while the deep rock mass strain value changes smoothly and is relatively stable. After the axial force of the NPR anchor cable transitions from the growth stage to the stable state, the rock mass deformation converges and stops growing. In the field test, the NPR anchor cable can reduce the primary support deformation from more than 2000 mm to 108 mm, and reduce the stress on the support structure, which is helpful in avoiding the risk of initial support deformation and secondary lining damage in the deep-buried, layered rock mass tunnels.

Heterogeneous public attitudes toward high-voltage power transmission lines and willingness to pay for undergrounding projects

On the path to carbon neutrality by 2050, the expansion and improvement of high-voltage power transmission lines (HV-PTL) is a critical and unavoidable energy issue that may become a potential source of public conflict. However, the discussion on this issue in South Korea has been insufficient. In this study, we analyzed public attitudes toward HV-PTLs and classified people into subgroups based on their common characteristics using latent class models. In addition, we used the contingent valuation method to estimate the public's willingness to pay (WTP) for the conversion of overhead lines to underground cables, focusing on the differences among the identified subgroups. According to the empirical analysis, people in South Korea can be divided into four classes based on their perceived need for resident participation in the decision-making process, perceived health risk, and perceived property loss risk. According to the WTP analysis using the spike model, the estimated mean and median WTP values were KRW 4184 (USD 3.8) and KRW 2632 (USD 2.4) per household per month, respectively. In addition, we found a significant difference in WTP by class. Those who perceived HV-PTL as risky were less willing to pay for undergrounding projects compared with those whose perceived risk was relatively low. This study contributes to the understanding of academics and policymakers on the relationship between public attitudes toward HV-PTL and overhead to underground conversion.

Underground Cable Fault Detection System

Abstract: Underground cables have been widely used with the development of power system grid .Underground cables are prone to a wide variety of faults due to underground conditions, wear and tear, rodents. Detecting fault source is difficult because entire line is to be dug in order to check fault at cable line. The repairmen know exactly which part has fault and only that area is to be dug to detect the fault source. Thus it saves a lot of time, money and allows to service underground cable lines faster. The aim of this project is to determine the distance of underground cable fault from base station in Km

Особенности моделирования воздушных и кабельных участков линий электропередачи 110–750 кВ при использовании фазного координатного базиса

Power system steady state and transient analysis require correct modeling of overhead transmission lines and cables operating at 110–750 kV. The key difficulties to model sections of overhead and cable lines are caused by complex conductor geometry, their transposition, as well as grounding schemes of ground wires of overhead lines and screens of underground cables. The paper covers various aspects of 110–750 overhead line and cable modeling that must be taken into consideration to obtain a reliable mathematical model in a phase domain. Modern software does not provide a universal solution to determine line parameters. The 110–500 kV cable line modeling issues have not been worked out properly and require careful analysis of specialized foreign literature. Thus, the task to develop the algorithms of calculating the parameters of overhead and cable power lines is relevant, taking into account the various configuration options of these lines which are possible in operational practice. To derive overhead transmission line and cable line models, electric circuit theory and matrix algebra methods have been used. The ATP/ATPDraw and MATLAB/Simulink software environment has been used to investigate what tools are available to determine line parameters, as well as to verify some of the calculation results. Analysis has been carried out to reveal the options available in the ATP/ATPDraw and MATLAB/Simulink software to compute line parameters in a phase domain. An algorithm has been developed and verified to calculate overhead line parameters regardless of the number of parallel circuits. The key features of the calculation of the matrix of linear resistances of overhead power transmission lines are outlined. The main features of modern cable lines operating at 110–500 kV are also described. The paper presents various cable layouts possible in real-field conditions, as well as provides expressions that allow obtaining correct impedances and admittances for a system of cable line conductors. Study of the options of various software tools dedicated to overhead line parameter calculation in a phase domain has revealed that these tools cannot be deemed universal to represent an overhead line of whatever configuration. However, the developed algorithm is universal as it allows computing line parameters regardless the ground wire grounding approach. The expressions presented in this paper consider various layouts of 110–500 kV cable lines that could be encountered in the Russian power system.

Practical Approach to Underground Distribution Power Cable Fleet Management

With the growing requirements imposed by regulatory authorities, grid operators and power utilities firms are confronted with the challenging task of ensuring the reliability, safety, and resilience of distribution networks amid aging asset infrastructure and a lack of resources. Over the past 15 years, the health index (HI)-based analysis has become an increasingly popular asset management tool for several power utilities. This strongly focuses on HI-based analysis to consider not only factors such as the cable vintage, type, and operating conditions, but also maintenance testing data. In this regard, the best industry practices for cable maintenance testing, including VLF Tan-Delta, partial discharge (PD), and time domain reflectometry (TDR), are outlined. Moreover, online tests, such as infrared thermography, ultrasonic PD scan, and temperature monitoring, are discussed. This paper also summarizes the classic asset management strategies for underground (UG) distribution power cables. The paper offers a practical approach for cable fleet management based on authors’ experience dealing with distribution power utility cable management for North American power utilities firms in the past 10 years. The proposed approach ensures reliable cable management at the lowest total life cycle cost. The topic of fleet management for UG power cables considering various condition parameters and an overall risk assessment is outlined. The fleet management guideline of UG power cables covers both cables and their accessories, such as terminations and joints. The main contributions of the paper are to: (1) determine the key parameters and testing factors for condition assessment of cables; (2) offer a practical approach to cable management that is not only based on technical issues, but also considers risk and impact costs, such as financial impact, reliability impact, etc.; and (3) propose a methodology for translating the HI/calculated risks into GIS, making it possible to identify major degradation patterns for fleet assessment. Considering budget and resource limitations around testing UG cable installations, this paper aims to assist asset managers, engineers, and asset owners in developing an effective cable fleet management strategy.