High voltage extruded powercables are critical components of power distribution systems. Therefore, a lot of investment is put into their continuous development to ensure their safe operation. There is a growing interest in the study of the high frequency properties of high voltage distribution cables. One reason is the potential to use these widely distributed cable networks for high capacity data communications . Another is the possibility to make diagnosis of the insulation condition of a cable along its length. The insulation system of cables is designed to sustain the electrical stress caused by the applied voltage and its quality determines the reliability of the cables. However, the insulation may deteriorate with time for many reasons and it is of great value to diagnose the deteriorated condition before the cable fails and causes disruption of power in the distribution network. Methods which could be used to determine the degradation of the electrical insulation along the cable length would greatly assist in decision making on replacements of cable sections or joints. The degradation along the cable could be due to water tree intensity in XLPE cables, partial discharges in small volumes of the total insulation system and humidity in oil/paper cables.
It is not possible to study the loss mechanisms of powercables with measurements on thin film samples because of the following reasons: 1) the morphological characteristics (crystalline lamella) of thin films are different from the bulk insulation layer of XLPE cables; 2) unlike film samples, the carbon black filled polymer semiconducting layers have unique dielectric properties and may contribute to the dielectric loss of powercables; 3) the concentration and distribution of insulation defects (by-products and impurities) inside powercables produced by the triple extrusion manufacturing process is different from film samples.
In order to study the dielectric properties of powercables more accurately, model cables with triple extrusion comprising a conductor, semiconducting layers and XLPE insulation were prepared. Their dielectric characteristics were studied by means of both frequency and time domain dielectric spectroscopy, in order to determine the loss mechanisms of the XLPE powercables. Thermal ageing effects were investigated in this paper for different types of model powercables with dielectric spectroscopy systems from 10 -4 Hz to 10 2 Hz.
The condition of powercables can be measured in two ways: using on-site testing , ,  or laboratory testing . On-site testing is performed directly on the in-service cables. In the laboratory testing, ﬁrst, a new cable undergoes accelerated aging processes to simulate the condition of aged cables, which are then analyzed. In both of these methods the amount of PD, oil analysis, and bulk properties of insulation, e.g. tang δ measurement, are used to determine the cables condition. The tang δ measurement is a diagnostic test conducted on cables’ insulation to measure their deteri- oration. In fact, the tang δ measurement is used as the loss factor of the insulation material which will increase during the aging process. The assessment of the in-service cables should be performed every 3-5 years and the results classify the investigated cables into different categories based on which future maintenance can be performed. Both of these measurements are very costly and complex processes.
the apparatus needs to be repaired or replaced. This means that the detected signal needs to be accurately calibrated. In most cases, calibration is done by injecting a known amount of charge and measuring the voltage amplitude from the detector. It is generally accepted that the conventional PD detection technique is very difficult to implement on-site for cable insulation because of the limited sensitivity due to the strong high-frequency attenuation of high-voltage cables. For powercables, different sensor types and methods to distinguish noise and PD have been proposed and partially put into service. A review on non-conventional methods can be found in . If it is the aim to detect PD occurring in the cable itself, detection techniques operating in a frequency range of not more than a few MHz have to be utilized due to the high attenuation at higher frequencies in shielded polymer insulated cables [4, 5]. The high interference level in this frequency range requires sophisticated methods for noise suppression [6, 7]. However, due to recent advances in cable manufacturing technology it has been generally recognized that the PD in cable insulation itself is no longer a major threat. Consequently, attention has been paid to the cable accessories such as cable joints/terminations where the complex structure and the construction can cause potential hazard to the whole system. For polymer-insulated cables, pre-moulded slip-on joints are increasingly being used owing to their advantages over conventional taped joints, including production of the active part under optimal conditions in the factory, each joint is routinely tested in the factory prior to the installation and the reduction of risk of introducing imperfections during jointing work. However, compared with cable the accessories are prone to partial discharges due to several interfaces between insulating materials and possible contamination during on-site assembly . In our earlier paper , it has been demonstrated that placing two capacitive couplers close to the cable accessories is an attractive option. Theoretical simulation and laboratory tests have shown that the technique has several advantages, such as on-site PD tests, online monitoring, high signal-to-noise ratio, high sensitivity and accurate location. However, the conventional calibration method based on the charge injection from the end of a cable was used to quantify the apparent discharge. This is not a problem when a piece of short cable is concerned in a laboratory. From a practical point of view this is not suitable since the high-frequency components will be lost over a long cable. In this paper, a new method has been proposed and the results compared with the conventional method as well as existing non-conventional methods.
The first example is taken from one of my PhD students, Alex See, who was working on an EU project called ARTEMIS: Ageing and Reliability TEsting and Monitoring of powercables: diagnosis for Insulation Systems 4 . The cables investigated had a 1600 mm 2 copper conductor and a 26.6 mm thick XLPE insulation The cables were aged under a variety of fields and temperatures up to a maximum of 27.5 kV/mm and 95C. Samples were prepared by peeling the cables and volatiles were removed using a thermal treatment. A typical result from a PEA measurement is shown in Fig. 12. The positions of the cathode and anode are marked by regions of negative and positive charge that were induced on these electrodes. Next to the electrodes, heterocharge is clearly seen, which has increased in the case of the aged cable. The work was complemented by other techniques including conduction and electroluminescence. The broad conclusion from this work was that ageing resulted in an increase in the concentration of shallow and deep trapping levels. Note that these are quite high levels of space charge density, but even these are caused by a small amount of charge. By this I mean that a charge density of 1 C/m 3 is roughly equivalent to the charges from only 6 electrons in a cubic micron of material. This would be comparable with the density of free charges found in a well- made undoped silicon wafer at room temperature.
Insulation strength is limited by the presence of particles and other contamination and voids in synthetic materials. Electrical discharges are initiated in the void or in the vicinity of insulation due to the presence of a localized high electric field. Therefore, the computation of the electric field in a three-core cable is important for the proper design and safe operation of powercables [1-3]. Salama et al.  introduced the application of charge simulation method (CSM) for the computation of the electrical field in high voltage cables. In  M.Salama and R.Hackam consider a non–shielded insulated conductor placed at a varying distance from a conducting plane using a small number of fictitious charges. In the other paper  they used CSM to calculate the electric field in three core belted cables surrounded by a grounded sheath. Salama et al. did not consider the effects of the position of the charges on the accuracy of computation, and this is a weak point of their paper.
XLPE cable is the major developing technology and has wide industry acceptance at voltages up to 132-154kV. This type of cable uses vulcanised polyethylene insulation, which is solid insulation extruded onto the conductor during cable manufacture. For high quality insulating properties, the raw materials must be free of even minute contaminants and the extrusion and vulcanising process must ensure homogeneity and absence of voids and moisture in the insulation. Compared with oil-filled cable it is considered to be a simplified technology. According to Karlstrand et al. , During the last decade, no other powercables have had such a high rate of improvement as XPLE cable technology. Improvements were made possible due to the overall cost savings, along with environmental focus and de-regulation of electricity markets which makes XLPE cable systems more attractive solutions where they were not even an option in the past . Figure 5.3 shows typical XLPE underground cable as manufactured by Olex in Melbourne.
Powercables for energy supply, preferably used for underground laying, especially in subscriber networks, power stations as well as control cables for the transmission of control impulses and test datas. Overall, where increased electrical and also mech- anical protection are required. Those cables are installed in open air, in under- ground, in water, indoors and in cable ducts. The corrugated concentric conduc- tor (CW) is allowed to use as neutral-, pro- tective or earth conductor. Simultaneously, this also is permitted to apply as a screen for example earthed-connected protection against contact. Due to the typical con- struction of corrugated concentric conduc- tors (Ceander), are possible to obtain many more cable joints, without cutting any con- ductor. In that way the operating reliability is guaranteed.
When laying heavy subsea powercables for high voltage rate at great sea depths it is of the utmost importance to have a cable laying vessel with all necessary cable laying facilities and adequate knowledge and experience to handle the cable in a safe way. The installation process has developed substantially over the past 20 years . The laying vessels are bigger with higher turntable, are more suitable for harsh weather conditions and are built with satellite-based navigation system. The cables are getting longer with developed manufacturing methods which make the installation easier and quicker as there are fewer joints. The oil and gas industry has gained a lot of experience which has been transported into subsea power cable installations along with all the experience from fibre cable installation. The marine survey can be done much more easily than before which allows a close up look at the sea bottom. And the development of remote operated vehicles has helped in a way no one could have imagined . Remote operated vehicles (ROV) are e.g. used to monitor the best possible cable route between obstacles or pipe and cable crossings.
A range of experimental and field measurements of partial discharge (PD) activity under high voltage direct current (HVDC) conditions have been conducted with the goal of developing effective monitoring techniques for PD in HVDC cables and ancillary equipment, particularly in offshore renewable energy HVDC grid installations. Laboratory measurements on insulation test objects and cross linked polyethylene (XLPE) cable samples have been conducted to better understand the characteristics of PD activity under direct current (DC) stress in comparison with AC. In addition, long-term PD measurements carried out at both an HVDC cable aging laboratory and an in- service HVDC interconnector circuit are presented together with a description of the monitoring system architecture.
which is totally passive without any power requirements. All other instruments are placed at the substation, where a mains supply is available. Potentially, new cables could be laid together with optical fibres and new joints could be designed to include optical network ready PD sensors. This approach would have a clear advantage because over the lifetime of the transmission cable asset the substation instrumentation/software can be easily accessed allowing the on-line system to match any technological improvements. With current established analytical approaches as shown in Figure 5, the optical receiver-measured signals could be input into a spectrum analyzer, a digital oscilloscope or a bespoke signal processing unit for phase-related plots, statistical distribution and trend analysis . A peak detection circuit could be used to obtain the peak value of every signal waveform. When the measured signal amplitude, histogram or trend turns abnormal, attention should be raised and if necessary an alarm should be given in order to warn of the likely occurrence of breakdown. This approach would create a system that still requires the expertise of a cable engineer in order to make an informed decision based on the information provided by the system (e.g. is it a false alarm?, should the circuit be derated? Should the circuit be switched out?). Consequently, the development of data processing methodologies capable of analyzing data from the remote sensing system in order to assist with this process is under consideration.
The duty cycle can also be used for receivers without capacitive decoupling, to compensate for the stray currents and for possible electrolytic effects, which may build up at the probe tips. For the pinpointing of sheath faults the rule “less is more” applies as well. Large currents will logically produce larger, better detectable voltage gradients, but the current for the location of sheath faults performs better between 10 and 100 milliamps. The sheath tester should also provide the possibility of an automatic current limitation. Both of these limitations have the purpose to avoid a drying up of the sheath fault due to thermal effects, and will protect other cable system in the vicinity of the fault. Lower currents will also limit the damage of the sheath fault which will then allow an easier repair since the inner conductors remain undamaged. A current limited location procedure has the advantage, that the full power of the sheath tester is only applied during a short moment, during the change of the fault from high to a low
The parameters obtained are shown in table 1, along with the parameter values found from fitting the model to PET film samples and XLPE insulated mini- cables . These other fittings were carried out using the Levenberg-Marquardt algorithm to minimise the difference between experimental data and the DMM lifetime predictions, which is a more sophisticated method than a grid search. A grid search was used here due to the higher level of complexity of the equation to be minimised.
wires, optical fibres, cables and cable systems for communication and infrastructure projects it is our responsibility to constantly optimise the sustainability and durability of our products, system solutions and services and thus lower the environmental load. We have to increase the amount of environmentally compatible raw materials in our cable products as well as the recyclability of processed materi- als or components and in doing so create end products that are developed for the environmental standard of tomorrow today.
Harmonics in power systems is increasingly at high level. Also, there has been an incredible growth in the use of cross linked polyethylene (XLPE) cables in distribution systems. Harmonics cause additional power loss/temperature rise; causing premature failure of cables. Catastrophic failure of powercables leads to great inconvenience to consumers and loss of system reliability and money. To avoid the overheating of powercables; the additional power loss due to har- monics should be accurately calculated and properly accommodated by derating the cable. The present method of cal- culating the power loss in cables in harmonics rich environment is very arduous. The aim of this paper is to present the reasonably accurate method for evaluating effects of harmonics on the power loss in XLPE cables. Computational mod- el is developed in MATLAB for power loss calculation using conventional method. Using this model, calculations are performed for aluminium and copper conductor XLPE cables of different size and type; for three different types of harmonics spectrums having total harmonics distortion (THD) of 30.68%, including all odd harmonics components up to 49 th order. Using these results; a mathematical model in the form of simple empirical formula is developed by curve fitting technique. The results obtained by various models are presented and compared with error justification.
Flammability test of control and powercables which were applied to the nuclear plants were conducted by the combustion test machine shown in figure.1. The small cable tray specimen with electrical cables, was able to apply to the flammability test. The capacity of load-cell device was increased from general cone-calorie meter machine to apply heavy cable tray specimens to the flammability tests. The heat chamber and cable tray specimen and state of flammability test were shown in figure 2. The diameter and maximum temperature of cone-calorie heater were 180mm and 750 Υ , respectively.