Cable Insulation System Research Articles

Accurate Identification of Partial Discharge Signals in Cable Terminations of High-Speed Electric Multiple Unit Using Wavelet Transform and Deep Belief Network

Cable termination serves as a crucial carrier for high-speed train power transmission and a weak part of the cable insulation system. Partial discharge detection plays a significant role in evaluating insulation status. However, field testing signals are often contaminated by external corona interference, which affects detection accuracy. This paper proposes a classification model based on wavelet transform (WT) and deep belief network (DBN) to accurately and rapidly identify corona discharge in the partial discharge signals of vehicle-mounted cable terminals. The method utilizes wavelet transform for noise reduction, employing the sigmoid activation function and analyzing the impact of WT on DBN classification performance. Research indicates that this method can achieve an accuracy of over 89% even with limited training samples. Finally, the reliability of the proposed classification model is verified using measured mixed signals.

Development of Multicellular Converter with Magnetic Coupler for Space Charge Measurement on DC Cable

One of the main issues on high voltage direct current (HVDC) cable is the electric field distribution on the insulation induced by space charges accumulation. Indeed, the space charges can cause a local increase of the electric field, which will accelerate ageing and may lead to dielectric breakdown. The TSM is one of the techniques that allow space charge measurements. The principle of the TSM consists in disturbing the electrostatic balance of the cable insulation system using a short thermal stimulus. For this study, the thermal pulse is created by Joule effect. This paper describes the structural optimization of a multi-cell DC-DC converter and its use in a high-current application to produce thermal stimulus. The design of the converter is first presented, then a multi-objective optimization is proposed for minimizing volume and losses. Finally, experimental results using a converter prototype which confirmed the space charge measurement principle are presented.

Mechanical Characterization of Nb3Sn Cable Insulation Systems Used for HL-LHC Accelerator Magnets at Ambient Temperature

The performance of accelerator magnets is strongly relying on the dielectric strength and mechanical robustness of the insulation system. This is in particular relevant for the current development of high field superconducting Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn magnets with the insulation system made from resin-impregnated glass fibres. During the assembly and operation at cold temperature, this insulation system is exposed to high mechanical compressive and shear stresses. The focus of the study was the investigation of the mechanical shear strength of the insulation composite. The experimental tests have been performed at room temperature, determining the mechanical strength and the failure mechanisms of the cable insulation system. Within this test the inter-laminar shear strength (ILSS) and non-standardized combined shear compressive strength were determined. The test sample preparation was based on the manufacturing procedures and materials used in the series fabrication for the CERN HL-LHC Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn coils. The individual insulation systems are varying in the S2-glass yarn density, the sizing, and the fibre volume fraction. Furthermore, the presence of mica insulation on the mechanical strength has also been studied. This paper describes the applied measurement procedures used during the test campaign, and presents the relevant measurement results, identifying the mechanical limitations of the insulation system.

Electric Field Distribution and Dielectric Losses in XLPE Insulation and Semiconductor Screens of High-Voltage Cables

This article presents the electric field distribution E and dielectric losses ΔPdiel. in the insulation system of high-voltage cables. Such a system consists of inner and outer semiconductor screens and XLPE insulation. The aim of this study was to compare the values of E and ΔPdiel. between semiconductor screens and XLPE insulation. The objects of the research were high-voltage cables of 110 kV, 220 kV, 400 kV, and 500 kV. The geometrical dimensions of the cables, especially the radii of individual layers of insulation, as well as the electrical properties of the screens and XLPE, were taken from the literature. Semiconductor screens and XLPE insulation were treated as a system of three concentric cylinders. When determining the electric field distribution, both the electrical permittivity and electrical conductivity, which, in the case of semiconductor screens, play important roles, were taken into account. The obtained results prove that both the electric field distribution E and dielectric losses Pdiel. are significantly larger in XLPE insulation than in semiconductor screens. The intensity E in XLPE insulation is about four orders of magnitude greater than the intensity in semiconductor screens. Dielectric losses ΔPdiel. in XLPE insulation are about eight orders of magnitude greater than the losses occurring in semiconductor screens.

A Novel Dampness Diagnosis Method for Distribution Power Cables Based on Time-Frequency Domain Conversion

Dampness invasion of power cable joints may lead to cable insulation degradation gradually. Once the cable joint is severely damp, it rapidly leads to breakdown failure for the power cable insulation system and finally results in catastrophic cable accidents. To avoid power outages, it is of great significance to diagnose cable joints with severe dampness defects. Existing methods have certain limitations. In this article, a novel time-frequency domain conversion method for determining cable joints with severe dampness defects is proposed. For this method, the cable joint is first located by applying the conventional frequency domain reflectometry (FDR) technology. Then, the time domain waveform at the cable joint is obtained based on the proposed time-frequency domain conversion algorithm. Finally, the cable joint with severe dampness defect can be distinguished by judging the polarities of the time domain spectrum at the cable joint. To verify the effectiveness of the proposed method, simulations and experiments are performed with comparisons with the conventional FDR method. Simulation and field detected results prove that the proposed method can effectively distinguish cable joints with severe dampness defects.

Dielectric Characteristics of Liquid Nitrogen/Synthetic Paper Composite Insulation System for Extra High Voltage HTS Cable

For extra-high-voltage high-temperature superconducting (HTS) cables, not only high electrical insulation performance but also low dielectric loss is required. Therefore, we focus on a porous synthetic paper with lower dielectric loss, e.g., Tyvek polyethylene nonwoven fabric, than that of polypropylene laminated paper (PPLP), which has been used for a conventional HTS cable insulation system. In this paper, we compare partial discharge inception characteristics for different liquid nitrogen/synthetic paper composite insulation systems. The partial discharge inception electric field strength in the composite insulation system depends on the electric field strength in the porous area of synthetic paper.

Evaluation of Abnormal Conditions of Oil-impregnated Insulation Papers in Aged Oil-filled Cable Joints and Terminations Removed After Service and Proposal of Classification Method for Ranking of their Abnormal Conditions

Degradation rate of electrical insulation performance of oil-filled (OF) cables has been considered small since void-less conditions are realized due to their oil-impregnated insulation systems under insulation oil pressure that exceeds atmospheric pressure. However, recently, insulation breakdowns have occurred in OF cable joints at extra-high voltage, and they were not predicted by dissolved gas analysis (DGA) of insulation oil. Therefore, it is necessary to improve the prediction accuracy of DGA for detection of partial discharges (PDs), which are known as a pre-breakdown phenomenon. Recently, it has been reported that traces of black color in oil-impregnated insulation papers are sometimes compounds of oxide sludge or copper sulfide, which were all regarded as carbonization due to PDs. Moreover, it has been reported that PD inception fields decrease with an increase in the rate of the total thickness of insulation papers with discoloration to the insulation thickness. To improve the prediction accuracy of DGA, such new findings should be taken into account when ranking abnormal conditions of insulation systems of cable joints and terminations, which gives the basic data for the prediction by DGA. In this study, abnormal conditions of oil-impregnated insulation papers were redefined and classified into trace of occurrences of PDs and two types of discoloration, and those of 264 aged OF cable joints and terminations removed after service were investigated. In addition, the above-mentioned rate was quantitatively evaluated for cable insulation systems, and locations of the abnormal conditions were investigated in detail for reinforced insulation systems. Taking these results into account, a new classification method for the ranking of abnormal conditions of oil-impregnated insulation systems was proposed.

Impact of High-Frequency Voltage Distortion Emitted by Large Photovoltaic Power Plant on Medium Voltage Cable Systems

Switching processes of voltage source converters can emit significant high-frequency distortions of frequencies between 5 to 20 kHz. Furthermore, the distortions can partly propagate from the place of their origin into a medium voltage system via capacitive coupling of power transformers. The origin, parameters, and propagation process of distortions were clarified by a numerical simulation of a 1-MW photovoltaic power plant connected to the medium voltage distribution grid. The determined results provided input data for the following accelerated aging test setup. The main idea behind the accelerated aging tests was to confirm the effect of the high-frequency distortions on the degradation rate of cable insulation systems. The tests were performed on cable samples, with terminations mounted on each end, which were split into three groups. The first sample group was stressed by increased power frequency voltage and by maximum operating temperature. The second group was stressed similarly, but with superposed high-frequency distortions present. The last group was not stressed to provide reference values for the other groups. Partial discharge, dissipation factor, and breakdown voltage measurements were carried out on both aged groups. The results indicate that cable insulation degradation progresses faster under power frequency voltage with superposed high-frequency distortions.

Ageing behaviour of a polyethylene blend: influence of chemical defects and morphology on charge transport

The properties of novel cable insulation systems will rely critically upon the morphology of the material. Here, a blend of high and low density polyethylene was processed in order to generate three sets of samples with different morphologies. The influence of thermo-oxidative ageing at 120 °C was then considered. The resulting chemical changes included the introduction of unsaturation and oxygen-containing groups and was determined by antioxidant consumption and oxygen permeability. Such chemical defects were found to be concentrated in the fraction of each system that was molten at 120 °C and, consequently, served to inhibit recrystallisation following ageing. The resulting spatial distribution of charge trapping sites was therefore strongly dependent on morphology. The electrical conductivity of each system varied non-monotonically with ageing: short times reduced the conductivity; a rapid increase in conductivity over five orders of magnitude occurred beyond a critical ageing threshold. Despite the pronounced structural differences between the morphologically distinct sets of samples, all exhibited comparable conductivity values beyond this threshold, implying that while charge transport is strongly influence by chemical factors, crystallinity is relatively unimportant. This experimental finding appears at odds with theoretical studies of the electronic states in crystalline and amorphous polyethylene.

Partial discharges activated by impulses and superimposed voltages in a high voltage cable model

In practice, High-voltage (HV) cables are occasionally exposed to impulse and superimposed transient conditions, which may initiate partial discharges (PD) temporarily. Whether such PDs persist under AC voltage after the transient conditions have vanished, is at focus in the research described in this paper. Since for cross-linked polyethylene (XLPE) cables the accessories are weak links in the HV cable insulation system, we investigated the PD behavior of an artificial joint defect in a HV cable model under impulse and superimposed voltages. By applying a dedicated PD measuring system it was found that, the impulse and superimposed voltages can initiate PD in the artificial defect, which under local electrical field conditions can persist for some time. The different parameters of the applied voltages have different effects on the PD behavior.

Modification of Polypropylene-based Cable Insulation Material

Polypropylene (PP) is one of the recyclable and ease processed thermoplastics，and it expected used as the cable insulation material to reply the unrecoverable material crosslinked polyethylene(XLPE). However, isotactic polypropylene which is too stiff with a lower electrical character cannot be directly used into the high voltage cable insulation system. In this paper, several polymers have been blended with polypropylene to improve the properties of the PP blend samples. Electrical and mechanical experiments of the modifying PP blends will also be done. In accordance with the experimental results, blends of PP and propylene-ethylene copolymers (PEC) are potentially more suitable for modifying PP in HV insulation.

Modeling for Underground Cable Water Tree Growth Dynamics

Underground cable faults, whether transient or permanent, are traceable to in-sulation failure problems, most of which are water tree initiated. Insulation breakdown, which usually leads to costly power outages, may be prevented by taking pre-emptive actions. The most decisive pre-emptive action is one in which real-time tracking of water tree advancement within the cable insulation system is possible. Such pre-emptive actions, however, depend on accurate modeling of the phenomenon. Earlier water tree models are static in that they focused on the cable insulation property change at a time segment. Thus, they lack the properties needed for tracking water tree progress and for determining the onset of transient and permanent faults. This paper presents a new ap-proach to water tree modeling, focused on insulation degradation geometry in the form of parabolic expansion of water tree. We developed a dynamic model centered on the computation of the capacitance of a vented water tree as a function of time. The dynamic model accounts for the time-dependence of the radial growth of the water tree to track insulation degradation. The model was tested in predicting cross-linked polyethylene (XLPE) cable’s insulation lifespan. The result was found to be within the range of the recorded lifespan of field aged cables in the literature. Also, performance comparison with an earlier analytical model validated with COMSOL Hyperphysics software shows a signif-icant correlation between them.

High performance thermoplastic cable insulation systems

High performance thermoplastic cable insulation systems

Electric Field and Thermal Properties of Wet Cable: Using FEM

A Single phase medium voltage power cable (XLPE) buried in soil and it can be used to investigate electric field, potential distribution and increased temperature of the cable insulation with rising load currents, are known to accelerate the formation of water and electric trees in cables which ultimately lead to cables failure. To determine the thermal and electrical behavior of a given wet cable installation. The work presented in this paper involves the use of COMSOL multiphysics Finite Element software to develop an integrated electrical, thermal model with 3 micro meter water bubble radius. The presence of water tree results in the reduction of their dielectric strength. Here the Finite Element simulation technique is used to 11 kV and 20 kV power cables. A model that illustrates the water-dielectric interface within the cable insulation system is proposed.

ELECTROSTATIC STRESS ANALYSIS OF HIGH VOLTAGE CABLES

Power cable as one of the main components of power networks, play an important role in electric power transmission between different zones. In cable, stress will maximum nearer to the surface of the conductor and it will get decreases as we move away from core to outer sheath. So, dielectric will be unnecessarily strong and expensive. Moreover, in cable insulation system, due to presence of pollutant such as air voids, water voids and also occurrence of water treeing phenomena, local field increases. As a result, enhancing electric field may cause to local breakdown in cable insulation. The presence of water within the insulation material can only lead to forming water trees if a sufficient electric field exists which may shorten life of cable. In this thesis, Finite element method is used to computing and evaluating of the electric field in the power cable by considering to existence of water particle and air void inside the polyethylene insulation. For equal stress distribution, grading methods are also considered. For all this purpose FEMM software is used for modeling. The results indicate that the stress is influenced by the void permittivity, shape of void, sharpness of void and also void position. By providing grading of the cable we can equally distribute the stress along the cable insulation.

Design of Cable Main Insulation and Outer Sheath Insulation Online Monitoring System

An online monitoring system of main insulation and outer sheath of power cable is designed in this paper. The system can monitor the insulation of the power cable without change the normal power cable wiring and grid structure. Changes of the main insulation and outer sheath of power cable can be monitor and recorded. Alarm of given when the insulation of the power cable is abnormal. System managers arrange outage maintenance depends on the status of the power cable.

Electric and Thermal Properties of Wet Cable 10kV and 15kV

The increased temperature of the cable insulation with rising load currents, are known to accelerate the formation of water and electric trees in cables which ultimately lead to cables failure. There are several factors which will determine the thermal and electrical behaviour of a given wet cable installation. These include the assumed ampacity, the cable construction and circumstances of installation, the thermal properties of the surrounding soil and the electrical properties. The work presented in this paper involves the use of COMSOL multiphysics finite element software to develop an integrated electrical, thermal model with 5micro meter and 2.5 micro meter water bubble radius. The presence of water tree results in the reduction of their dielectric strength. Here the finite element simulation technique is used to evaluate the electric field, potential and temperature distribution inside the 10 kV and 15 kV power cables. A model that illustrates the water-dielectric interface within the cable insulation system is proposed. DOI: http://dx.doi.org/10.11591/telkomnika.v10i7.1298 Full Text: PDF

Artificial aging and diagnostic measurements on medium-voltage, paper-insulated, lead-covered cables

Present and future condition-based maintenance methods and preventive maintenance strategies will require knowledge of the present condition of the equipment. For cable networks in gen eral, and for PILC cables in particular, our understanding of the physical phenomena that occur inside cable insulation systems during operation, and their influence on the remaining service lifetime, is still fragmentary. The ICAAS system was developed primarily to facilitate an artificial aging program on MV PILC cables, based on tan δ, return voltage, and PD measurements. An extensive database was built up over a period of two years. Further results will be presented in due course. It should be noted that the ICAAS is fairly freely configu rable so that, with a little effort, it could be applied to other cable types, cable garnitures, sleeves, and terminations. It could also be used to study specific cable defects introduced during manu facture or for the general verification of production quality.

An investigation of the potential of polypropylene and its blends for use in recyclable high voltage cable insulation systems

Most modern extruded high voltage cables employ cross-linked polyethylene (XLPE) as the insulation material. XLPE has excellent thermo-mechanical properties, is relatively cheap and has a low dielectric loss, which make it an ideal material for this application. Unfortunately, XLPE is not easily recycled at the end of its lifetime leading to questions concerning its long-term sustainability. A previous investigation in this series considered the potential of a range of ethylene-based systems to provide suitable recyclable alternatives to XLPE. Whilst blending could allow systems having similar thermo-mechanical and electrical properties to XLPE to be designed, it was not possible to obtain better performance than XLPE using these systems. Polypropylene offers, potentially, a route to improved insulation systems by virtue of its higher melting point and excellent dielectric properties. However, traditional isotactic polypropylenes have always had the problem of being too brittle for inclusion into practical cable designs. Recently a broad range of propylene co-polymers having improved ductility have become available, which may prove more suitable. The current study compares traditional isotactic and syndiotactic polypropylenes to a range of commercially available propylene co-polymers and focuses on their morphology, thermal, thermo-mechanical and electrical properties. These parameters were then taken together to identify the most suitable candidate materials for future cable applications. The use of blending as a means to further optimise the various material properties was also explored.

Characterization of partial discharge in composite insulation system with PPLPR for HTS cable

High-temperature Superconducting (HTS) cable systems with high power density and low loss are expected to be a solution for improving the power grid. Many researchers have worked on the development of the HTS cable. For insulation testing it is necessary to consider a partial discharge (PD) which is generated in butt gaps of the insulation layers. The electrical insulation system of HTS cables consists of liquid nitrogen (N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (l)) and polypropylene laminated paper (PPLP). N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 2 (l) cooling system is installed in the power system and N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 2 (l) will flow through the cables after their installation in the system. Filling the HTS cable with N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 2 (l) in order to perform pre-shipment inspection is costly for cable manufacturers. Therefore, they are trying to find a cost effective method for pre-shipment inspections. One alternative is to use atmospheric pressure air or N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 2 (g) instead of N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 2 (l) for pre-shipment inspections. This paper discusses PD characteristics in a butt gap of HTS cables in different environment such as atmospheric pressure air or N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 2 (g) composite insulation. The results are compared with PD characteristics in N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 2 (l)/PPLP to find the difference between insulation material in PD characteristics. High temperature superconducting cable, partial discharge, polypropylene laminated paper, insulation system.