Medium Voltage Underground Cables Research Articles

Thermal State Effects on Potential Augmentation of the Ampacity of a Medium Voltage Underground Cable in Power Distribution: A Case Study

Thermal State Effects on Potential Augmentation of the Ampacity of a Medium Voltage Underground Cable in Power Distribution: A Case Study

Study on the Capacitive Effects of Underground Power Cables on the Operational Electricity Distribution Network

In this study, known compensation methods are mentioned and the reactive components of medium voltage underground cables used in the lines are emphasized. Iğdır University electricity distribution network is considered as the application area. Based on the information that XLPE type medium voltage cables used in electricity distribution networks show capacitor properties when they are unloaded, capacitive analyses of medium voltage cables forming Iğdır University electricity distribution network were made by considering the distance and cross-sections of the medium voltage cables, the layout plan and single line diagram of the distribution network were drawn and the powers of the transformers were classified. Iğdır University electricity consumption components were analyzed and what should be done was investigated. Because as a result of the researches, it was learnt whether the capacitive consumption is caused by the cables or the wrong connection of the meters or the presence of loads with permanent capacitive properties in the system. A shunt reactor panel was designed for capacitive consumption caused by the presence of XLPE (Cross-related Polyethylene) cables and the results were analyzed. A comparative evaluation of the results of the economic analysis of this shunt reactor panel was carried out. A pricing system has been established in which these limits will not be exceeded.

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.

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.

Published Papers Volume 30 - Issue 4 (Award Issue) Awarded Paper Use of insulation resistance imbalance degree for the condition assessment of power distribution cables

Medium-voltage (MV) underground power distribution cables are critical assets of The Hong Kong Electric Co., Ltd. (HK Electric) for ensuring reliable customer power delivery. The inspection and condition assessment of these power distribution cables are conducted regularly to determine their health. During diagnostic tests, all MV cables have to pass a threshold of insulation resistance (IR) before they can be energised. Low IR readings may indicate a deterioration in insulation related to a high leakage current. However, defining a threshold value to assess the intrinsic condition of the power distribution cables for every test is challenging. This is because the reference value is determined by several factors such as cable length, the composition of the cable circuit, e.g., cable type, number and types of cable joints, service years and surface leakage from cable splices and terminations. In order to tackle this problem, a concept of imbalance degree in IR testing is developed to supplement the existing tests on dielectric losses for the purpose of enhancing the condition assessment of three-phase power MV distribution cables when performing IR measurement. The effectiveness of this method has been validated with historical testing records of 11kV distribution power cables at HK Electric. Based on our experience and study results, this improved method could further enhance the diagnosis and maintenance efficacy of HK Electric’s power distribution cables.

Numerical Analysis and Comparison of Magnetic Fields Caused by Constant and Time Varying Currents in Medium Voltage Underground Cables

The magnetic fields formed around the conductors carrying current alternating current in the power system adversely affect human health. Especially in medium voltage systems, where energy is mostly carried by underground cables for electrical safety, due to the high current levels and the installation of cables in areas where people live, studies in this field have gained importance. In literature, many studies have been carried out on the calculation of magnetic fields caused by underground cables using numerical methods and their comparison with limit values. In some of these studies, the boundary conditions for phase currents are defined as constant. However, alternating current, which is the source of the magnetic field, is a time-varying vector quantity. For this reason, it is important for the accuracy of the analysis to take into account the direction of the current, the time-dependent change of the current and the phase difference while calculating the magnetic flux density. In this study, the magnetic flux density values caused by a sample medium voltage underground cable system at the reference plane one meter above the ground surface are determined using Comsol Multiphysics. Analyzes are performed both in the stationary domain where the current is constant and in the time domain when it changes depending on time, and the results are discussed and compared. According to the results, it is determined that the maximum magnetic flux density exceeded the limit value of 0.2 mT, while the phase current values are constant. However, it is seen that the magnetic flux density obtained in time-dependent analyzes remains within the safe limit. In addition, it has been determined that the results obtained in the stationary domain are considerably higher than the results obtained in the time domain. As a result, it has been revealed that the time-dependent variation of the current must be taken into account in order to accurately determine the magnetic flux density in the magnetic field analyzes to be performed for underground cables or overhead lines carrying alternating current.

Extreme Weather Conditions Effects On Underground Cable Joints Failures: Strategies For Reliability And Resilience Improvement

In recent years, an abnormal increase of faults in underground Medium Voltage (MV) cable joints has been recorded, especially during summer, by distribution system operators in Italy and worldwide. To preserve an adequate level of reliability and resilience, the causes of such failures have to be investigated to find the most appropriate countermeasures in terms of technological improvement and new planning and operation approaches. Based on the field experience gained by Unareti on Milano and Brescia distribution networks, this paper reports the main results of the analysis of extreme weather conditions' effects on MV underground cable joint failures. Moreover, actions making in place by Unareti, the distribution system operator of Milano and Brescia, for reliability and resilience improvement are listed. The gained information could help re-design innovative, more robust, and resilient joints for MV underground cables and guide distribution system operators in re-thinking their distribution network planning and operation paradigms.

DIGITAL TOOL TO COMPUTE HEALTH INDEX FOR UNDERGROUND MEDIUM VOLTAGE CABLES

For E-REDES, the Portuguese main DSO, asset management is a key pillar to maximize returns on the long-term investment plans and to provide an optimal service. The underground grid poses as a challenge because due to its nature, it is difficult to asses its condition through visual inspection and any unnecessary digging has high costs involved. A better vision on this assets condition is essential to improve the asset management methodologies. Aligned with the digitalization process held across the company, it was developed a minimum viable product of a digital tool to estimate the health index and the probability of failure of the medium voltage underground grid cables. In this first phase the model, that was designed for a specific geographical area of interest, was based on the CNAIM methodology and adjusted to fit E-REDE's and the scope area's reality. In this paper it will be described the modelling approach, the data model designed to support the analytic tool and the data transformations required to face the data gaps in the internal systems. This tool enables a data-driven approach to analyze the condition of the underground medium voltage grid, optimizing the maintenance and investment planning activities.

Failure Prevention and Malfunction Localization in Underground Medium Voltage Cables

A smart monitoring system capable of detecting and classifying the health conditions of MV (Medium Voltage) underground cables is presented in this work. Using the analysis technique proposed here, it is possible to prevent the occurrence of catastrophic failures in medium voltage underground lines, for which it is generally difficult to realize maintenance operations and carry out punctual inspections. This prognostic method is based on Frequency Response Analysis (FRA) and can be used online during normal network operation, resulting in a minimally invasive tool. In order to obtain the good results shown in the simulation section, it is necessary to develop a lamped equivalent circuit of the network branch under consideration. The standard π-model is used in this paper to analyse sections of a medium voltage cable and the parameter variations with temperature are used to classify the state of health of the line. In fact, the variation of the electrical parameters produces a corresponding variation in the frequency response. The proposed system is based on the use of a complex neural network with feedforward architecture. It processes the frequency response, allowing the classification of the cable conditions with an accuracy higher than 90%.

Development of smart online partial discharge monitoring system for medium voltage power cable

This paper presents, the development of smart online partial discharge (PD) monitoring system for medium voltage (MV) underground power cable. PD monitoring is the highly efficient tool to monitor insulation degradation for high voltage (HV) equipment in order to avoid failures or breakdown. Selection of improved technology and performance of PD detection sensor, effective measurement technique and smart user friendly of graphical user interface (GUI) system are contributed towards the development of efficient monitoring system. This paper addresses three main aspects which are needed in completing the monitoring system. They are, the use of Rogowski coil (RC) as detection sensor, processing unit using Alterra board and integrated with GUI PD monitoring system for underground cable using LabVIEW. The monitoring system is compared to the conventional method with the PD signal used is measured from the real on-site measurement in order to analyse its performance. The analysis is performed in MATLAB and LabVIEW software’s environment and the maximum peak of PD signal is enabled to view using GUI which complete with the location information of PD source. Furthermore, this paper has contributed to solve the problem in selection the simplified and practical approach for PD sensor and monitoring system. In the perspective of automated condition monitoring, this smart online PD monitoring system provides a complete solution towards latest industrial revolutions

An Effective Method to Calculate Frequency Response of Distribution Networks for PLC Applications

Modelling and estimating power-line communication (PLC) channels are complicated issues due to the complex network topologies, various junctions, and changeable loads. This paper focuses on the frequency response characteristics (FRCs) of medium-voltage (MV) PLC networks with special consideration of two scenarios that are often neglected but generally exist. In the first scenario, the MV distribution network is of the ring topology. In the second scenario, the MV overhead lines and underground cables join at junctions, and the shields of underground cables are grounded with nonzero grounding impedances at the junctions. These conditions lead to the failure of currently popular methods to different degrees. For this reason, we developed an effective method to calculate the FRCs of distribution networks for PLC applications. With this method, the frequency responses of nodes are simply expressed as the binary function of the overall tube propagation matrix and overall node scattering matrix, which is convenient for calculations and analyses. The proposed method was validated by the agreement between the calculated and measured FRCs. The results of two test examples showed that the proposed method performed better in comparison with the traditional approximate method when nonideal grounding conditions were taken into account. The proposed method is also independent of the network topology, so it can adapt to the dynamic changes of the network structure.

Characteristic Impedance Analysis of Medium-Voltage Underground Cables with Grounded Shields and Armors for Power Line Communication

The characteristic impedance of a power line is an important parameter in power line communication (PLC) technologies. This parameter is helpful for understanding power line impedance characteristics and achieving impedance matching. In this study, we focused on the characteristic impedance matrices (CIMs) of the medium-voltage (MV) cables. The calculation and characteristics of the CIMs were investigated with special consideration of the grounded shields and armors, which are often neglected in current research. The calculation results were validated through the experimental measurements. The results show that the MV underground cables with multiple grounding points have forward and backward CIMs, which are generally not equal unless the whole cable structure is longitudinally symmetrical. Then, the resonance phenomenon in the CIMs was analyzed. We found that the grounding of the shields and armors not only affected their own characteristic impedances but also those of the cores, and the resonance present in the CIMs should be of concern in the impedance matching of the PLC systems. Finally, the effects of the grounding resistances, cable lengths, grounding point numbers, and cable branch numbers on the CIMs of the MV underground cables were discussed through control experiments.

Thermal behaviour of medium-voltage underground cables under high-load operating conditions

The dynamic management of electric power distribution lines has become a topic of great interest at present. Knowledge of the ampacity of cables is fundamental to carrying out dynamic management. In this study, the ampacity of buried cables in different soil resistivities and depths was calculated. A small-scale model was built in the laboratory to simulate the operating conditions of a buried cable. With the experimental results, a numerical model based on the finite element method was validated to evaluate the ampacities calculated by two standards. A comparison was made between the ampacities calculated from the IEC 60287-1 and UNE 211435 standards and those obtained from the simulated model. In addition, a comparison was made regarding the steady-state temperatures obtained at each calculated ampacity. The results obtained from the simulated model design show that the ampacity calculation method of the IEC 60287-1 standard where drying-out of the soil occurs is the most accurate, and has the least risk of exceeding the maximum permissible cable temperature.

Identification and Location of PD Defects in Medium voltage Underground Power Cables Using High Frequency Current Transformer

Fault location is an important diagnostic task in condition monitoring of underground medium voltage cables. Available solutions are well capable of determining the location of a single partial discharge (PD) defect on a cable section. In case several PD defects are active simultaneously along a cable section, the interpretation of the measured data becomes complex to identify the presence of more than one PD sources. In this paper, experimental investigation of two PD defects/sources at different locations on a medium voltage (MV) cable section is presented. A high frequency current transformer is used for single end PD measurements. Time domain reflectometry-based in-depth study of the reflected pulses provides the most valuable information to identify the presence of PD sources which further leads to the location of the individual PD sources. In this paper, the proposed solution is presented for two PD sources, however, the same methodology can be extended to locate multiple PD sources on the cable.

Optimal Sizing and Location of Shunt Capacitors in Medium Voltage Underground Power Cables: A Case of Minimum Cost

This paper introduces a method to determine optimal sizing and location of shunt capacitors in medium voltage Underground Power Cables or in distribution system. To execute this method, two models of standard branch and the Newton-Raphson method are also mentioned to analyze and determine values of bus voltage and currents going through lines in whole system. The EN 50160 standard is introduced to evaluate all operational parameters and propose solutions to reduce risks. In additionally, the cost function method is introduced basing on cost of purchasing compensative device, power loss in own compensators and whole system after compensating. By considering partial derivative of cost function with respect to variables, optimal sizing and location of shunt capacitors can be determined for all buses in the system. Analyzing the system by using the Newton-Raphson method in stable mode, all operational parameters are evaluated to see the benefit of placing capacitors in some criterions: reduce the current going through all lines and increase value of bus voltage in whole system. Theory research are verified by simulation results carried out in Matlab 2016 software.

A New Contribution in Reducing Electric Field Distribution Within/Around Medium Voltage Underground Cable Terminations

Ιn medium voltage cables, the stress control layers play an important part in controlling the electric field distribution around the medium voltage underground cable terminations. Underground cable accessories, used in medium voltage cable systems, need a stress control tube in order to maintain and control the insulation level which is designed for long life times. The term “electrical stress control” refers to the cable termination analysis of optimizing the electrical stress in the area of insulation shield cutback to reduce the electrical field concentration at this point in order to reduce breakdown in the cable insulation. This paper presents the effect of some materials of different relative permittivities and geometrical regulation with the curved shape stress relief cones on the electric field distribution of cable termination. The optimization was done by comparing the results of eight materials used. Also, the effect of the change in the thickness of the stress control tube is presented. The modeling design is very important for engineers to find the optimal solution of terminator design of medium voltage cables. This paper also describes the evolution of stress control systems and their benefits. A developed program using Finite Element Method (FEM) has calculated a numerical study to the stress control layering electric field distribution.

A New Contribution in Reducing Electric Field Distribution Within/Around Medium Voltage Underground Cable Terminations

A New Contribution in Reducing Electric Field Distribution Within/Around Medium Voltage Underground Cable Terminations

External conductive layer on EDP medium voltage underground cables leads to new oversheath requirements

External conductive layer on EDP medium voltage underground cables leads to new oversheath requirements

Multicycle Incipient Fault Detection and Location for Medium Voltage Underground Cable

Early and accurate detection of incipient cable faults is of a great interest to the utility industry. Such faults can be classified into subcycle and multicycle types. Although a lot of research has been conducted on subcycle types of faults, little work has been done for multicycle types of faults. This paper proposes a novel method for detecting and locating a multicycle incipient fault in a cable. The incipient fault is modeled as a self-clearing arcing fault. The distortion degree of calculated voltage is used to detect the occurrence of an incipient fault. The degree of match between the measured and calculated waveforms is used to guide the search for the fault distance. The accuracy is further improved by taking into account the incipient fault angle as seen in the voltage waveform and the power loss characteristics. The proposed method has been verified by PSCAD/EMTDC simulations. Lab experiments are also conducted to further validate the proposed detection method.

Multi-end PD location algorithm using segmented correlation and trimmed mean data filtering techniques for MV Underground Cable

Medium voltage underground cables are widely used in urban area as distribution power lines due to their advantages over overhead cables. Underground cables may suffer from partial discharge because of insulation degradation after certain period of time. In this paper, an improved multi-end partial discharge location algorithm called segmented correlation trimmed mean algorithm is proposed. The algorithm uses segmented correlation technique and trimmed mean data filtering technique to enhance the accuracy of partial discharge location algorithm. The algorithm had been tested in MATLAB environment which consists white Gaussian noise. First, discrete wavelet transform is carried out to suppress noisy signals. Next, segmented correlation technique is applied to the de-noised segmented partial discharge signals. Segmented correlation technique has manipulates partial discharge signals by performing cross correlation process on segmented partial discharge signals in order to reduce memory usage and algorithm execution time. Lastly, trimmed mean data filtering technique is applied to the estimated partial discharge location values to estimate new partial discharge location value. Trimmed mean data filtering technique does statistical process control on estimated partial discharge location values in order to minimize the error of estimated partial discharge location. The segmented correlation trimmed mean algorithm had been compared with the existing multi-end correlation-based algorithm. The result shown that the segmented correlation trimmed mean algorithm has better accuracy than multi-end correlation-based algorithm.