Losses In Xlpe Insulated Cables Engineering Essay

losings In Xlpe Insulated Cables Engineering Essay world-beater stocks, master(prenominal)ly immunity antecedent airs mannikin a hatful part of galvanic index finger g overnances network. Accordingly, when median(a) authorization drop XLPE teleph champion circuits were first inst in alled in the late 1960s, short letter manufacturers and electrical utilities expect them to run reliably for 20 to 30 years. However, history has shown that these overseas telegrams had high percentage of life age losings whereby the service life of more or less(prenominal) of these cables was far shorter than expected. M both cables failed afterward moreover 10 to 15 years in service. The failure of XLPE cables was happened referable to the maturement transition. Aging of XLPE cables is related to the temperature of the disengagement. For XLPE cables, the typical uttermost direct temperature is 90 C. At this maximum value, the consumption rate of anti-oxidant has been ca lculated to afford a cable life of 30 years. Increasing the XLPE cables opemilitary military rank temperature bequeath outgrowth the rate which the anti-oxidant is utilize up. Subsequently, it will reduce the service life of XLPE cables. The reaction fol deplorables the Arrhenius relationship which is an exponential function. From this, even a small increase in temperature, it will hence give signifi lavt impact on the senescent mental change of XLPE cables. Once the anti-oxidant in the cables is used up, the cables will start to oxidate and get down easily broken. Then, the cables will be subject to stress chap and electrical failure at positions of mechanical stress. In rise to world-beater, the straw man of agreeables in great military group body curtilages a managing director to overheat. This hot up swear out makes the cable to increase in term of temperature to its separation. Therefore, cable will soften and the mechanical performances will reduce whic h is called as premature aging. Thus, it is classical to investigate the presence of kindly in any electrical equipment. From this we could know the temperature payable to the overheating process and evaluate the life losses of any associated cables.TABLE OF contentCHAPTERTITLEPAGEDECLARATION1ACKNOWLEDGEMENT2 accost3TABLE OF CONTENTS41INTRODUCTION81.1 Background81.2 Premature Aging due to concordant91.3 maturement of federal agency Cables91.3.1 Oil-Impregnated Paper federal agency Cables101.3.2 Solid-Dielectric-Extruded Power Cables111.3.2.1 Technology of XLPE Cables131.4 losses in Power Cables151.5 Objectives of Study161.6 Scopes of study172LITERATURE followup182.1. Introduction182.2. Power System harmoniseds182.2.1. rendering of Harmonics192.2.2. citation of Harmonics192.2.3. The Harm of Harmonic202.2.4. personal put ins of Harmonics on Power System212.2.4.1 Motors and Generators212.2.4.2 Transformers222.2.4.3 Power Cables222.2.4.4 Capacitors232.2.5. Economical Damag e due to Harmonic losses232.3 Underground Power Cables242.3.1 Gas-filled Cable242.3.2 XLPE Cables273EVALUATION OF THE AGING COST DUE TOHARMONIC losses IN XLPE CABLES293.1 Introduction293.1.1 Flowchart303.2 unhurriedness of Losses313.2.1 Resistance of the conductor313.2.2 Skin substance323.2.3 Proximity Effect333.2.4 Total Power Losses333.2.4.1 Joule Losses343.2.4.2 Dielectric losses343.3 Probabilistic Evaluation of the Economical Damage due to Harmonic Losses353.3.1 Expected Value of the Aging Cost dueto Harmonic Losses353.4 Conclusion394DATA, MODELLING AND ASSUMPTIONS404.1 Data404.2 Assumptions415RESULTS, ANALYSIS, AND DISCUSSIONS425.1 Results425.2 Discussions456CONCLUSIONS AND RECOMMENDATIONS466.1 Expected termination466.2 Conclusions476.3 Recommendations47REFERENCES49APPENDICES attachment A52APPENDIX B58APPENDIX C67APPENDIX D68APPENDIX E69APPENDIX F72APPENDIX G73BackgroundBy means of the disco truly(prenominal) of electricity in the early 19th Century, all countries in the world nowadays suck virtually utilized electricity as a source of heat and energy. This has led to the existence of distribution- transmittal line remains carrying current, even if at distinguishable potential drops and transporting it over long distances till the end users or customers. For the distribution-transmission line placement, engineers had suasion critically in finding the suitable occasion cables for magnate system.Mainly, intumesce-nigh of the bulk electrical energy generated from the generation centers is being transported to major debase centers at heart a large geographical argona by the transmission systems using disk overhead lines 1. In the otherwise words, the distribution system delivers the electrical energy from these load centers to customers who argon within a smaller geographical argona. For safety, reliability and aesthetics, the electric circuits used to transport energy to such(prenominal)(prenominal)(prenominal) customers be usually beneathground situation cables, though this kind of arrangement is valuable but has more advantages than the overhead lines 2.Over the years, high demand of tried electricity business office supply has led the electricity markets to be super competitive. Electric utility companies now take for to develop means of accommodateing, upgrade the safety and reliability of their expensive power system components to steer considerably and meet the demands of their customers.One of power system component that constitutes a bulk part of the distribution and transmission line systems in urban beas is the subway power cable. For instance, in the United Kingdom there be closely 93000 km of 11 kV cable and more than 13000 km of 33 kV 6. In Malaysia with rush of development has led to increasing demands of electrical energy. Doing this, belowground cable distribution is increasing significantly. It is estimated that there argon most 180000 km of to a lower placeground cables in M alaysia, forming about 80 % of the underground power distribution system. This shows that, the technology of underground power cables has grown up very fast by the time as the world is moving extremely in science and technology.However, lately the presence of appealing in electrical energy systems is well known 3. The benevolents argon due to non elongate dozens such as static converter and can victimize the system components 6. In the font of the cables, kindlys can font relevant improveral losses in the conducting and in the insulating sensibles which can non be neglected. From the economical render of view, the presence of large-hearteds can cause economical damage which increasing the operating be and lessen the useful life of the system components.The economical damage due to sympathetical losses can be defined as the summation of the operating be and the aging costs. As stated in 13, the operating costs are referred to the costs of the incremental energy losses caused by the concordant flow in the component, where the term incremental means that these losses are superimposed to the ones at the complete while the aging costs are referred to the incremental investment costs caused by the premature aging of the components caused by the harmonic pollution.Premature Aging due to HarmonicAging failures defend become a major and urgent concern in many another(prenominal) utilities since many power system components are approaching the turning conduct to the end of life. For the case of power cables, the premature aging occurs due to harmonic pollution. The harmonic flow can lead to additional heating in power cables. Subsequently, temperature will rise and premature aging may result.Development of Power Cables 1Power cable technology had its beginnings in the 1880s when the fatality for power distribution cables became pressing. With urban growth, it became increasingly necessary to replace both(prenominal) of the overhead lines for power transmission and distribution system with underground cables. The lighter of the big cities proceeded at such a quick pace that under more or less circumstances it was im assertable to accommodate the number and size of feeders take for distribution, using the overhead line system approach.In fact this mooring deteriorated so notably in New York City that, in addition to the technical and aesthetic considerations, the overhead line system began to pose a safety hazard to the line workers themselves, the firemen, and the public. As a result, the city passed an legislation law in 1884 requires removing the overhead line structures and replacing them with underground power cables. Similar laws and public force were apply in other cities, with the matter that by the early 1900s, underground electrification via insulated cables was on its way to becoming a well-established practice 14.A practical lead press was invented in 1879 and later on employed to manufacture 2kV cables f or Vienna in 1885. During the same period, vulcanized safety was used to produce cables on a commercial scale, although use of guttapercha had already been do as early as 1846. Impregnated- newspaper publisher power cables were first vomit on the market in 1894 by Callender Cables of England, using impregnant mixtures of rosin petroleum, rosin and castor oil and all in 1918 were these replaced by mineral oils. In North America, impregnated-paper cables were first supplied by the Norwich Wire Company. Varnished cambric cables were introduced by the public Electric Company in 1902. The behavior of these cables with hightemperature was subsequently change the addition of black asphalt.Some of the more common early solid and bland insulating employed in various underground cable innovations were natural rubber, gutta-percha, oil and wax, rosin and asphalt, jute, hemp, and cotton. In 1890, Ferranti developed the first oil-impregnated-paper power cable. By pastime their manufact ure, his cables were installed in London in 1891 for 10 kV operations. In addition, the cables were made in 20 ft lengths as the total circuit was 30 miles in length about splicing joints were four needful. Nevertheless, these cables per make so well that the last cable length was removed from service scarce in 1933. Cable elicitation continued to proceed at a rapid pace, so that by the turn of the 20th century many major cities throughout the world had many miles of underground power cables. For example, already by the end of 1909, the Commonwealth Edison Company in Chicago had 400 miles of underground cable operated in the potential difference range amid 9 to 20 kV. Montreal had some 4500 ft circuits of three-conductor cables installed in ducts under the Lachine canal for 25kV operations the same voltage was used for cable traversing the St. Lawrence River in 1906. With some experiences behind them, cable manufacturers were increasingly gaining confidence and during the St. L ouis Exposition in 1904 power cables developed for voltages as high as 50 kV were post on display 14.Oil-Impregnated Paper Power Cables 14During the period prior to military man War I, extensive use was made of oilimpregnated paper cables of the three-conductor belt out cause for voltages up to 25 kV. Due to non-uniform stress distribution in the cable construction, the belted cable proved to be highly partial derivative recede susceptible when attempts were made to extend the operating voltage range with larger wall thickness to approximately 35 kV, to meet the increased power demand following World War I 18. This line of work was contumacious by shielding the individual conductors, using 3-mil-thick hair tapes. The outside of the protect conductors was thus maintained at the same ground potential.Figure 1.3.1 crosswise of an Oil-impregnated Paper Insulated CableIn addition, the belt disengagement was replaced with a tying consisting of fabric tapes and strands of inter woven copper wire. The purpose of the latter was again to maintain the shields of the three cables at the same potential. Over the years, the conductor shapes of the three-conductor shielded paper insulated cables fork up evolved into three forms, namely circular, oval, and sectoral.In many utilities a veridical portion of the present-day distribution load is still carried at 35 kV via three-phase oil-impregnated paper belted cables, with the three conductors individually grounded. There is fiddling inducement to replace these cables with solid extruded nonconductor cables, whose outer diameter for an resembling power rating would drop dead that of the ducts accommodating the more compact threephase oil-paper belted cables. Moreover, the oil-paper belted cables have been characterized by remarkably long in-service lifetimes that often exceed 65 years. Belted cables with unshielded conductors are still deployed but only for working voltages equal to or less than 15 kV.With the individual conductors shielded, it was possible to extend the use of the three-phase belted cables for voltages as high as 69 kV, though on the bonnie their application has been confined to voltages below 35 kV. The main reason for this upper limit has again been associated with the occurrence of partial discharges, which had in numerous instances led to the deterioration and failure of the insulator at the elevated voltages. The partial discharges were found to take place in voids, which were formed either during the manufacturing process or during the load cycling while in service.Solid-Dielectric-Extruded Power Cables 1, 14With the discovery of the hydro snow thermoplastic resin polythene (PE) in England in 1933, polyethylene became rapidly, the insulant of choice for RF coaxial cables. PE was first used as an insulant for power cables in the 1950s. In the mid 1960s, conventional PE became the material of choice for the rapidly expanding URD systems in the United States. It was known to be superscript to butyl rubber for moisture resistivity, and could be readily extruded. It was used with tape shields, which achieved their semi-conducting properties because of carbon black. By 1968, virtually all of the URD installations consisted of polyethylene-insulated medium voltage cables.The polyethylene was referred to as HMWPE this simply meant that the insulation used had a very high average molecular burthen. The high the molecular weight, the better the electrical properties. The highest molecular weight PE that could be readily extruded was adopted. Jacketed construction was seldom employed at that time. Extruded thermoplastic shields were introduced between 1965 and 1975 leading both to easier processing and better reliability of the cable 19.XLPE was first patented in 1959 for a filled compound and in 1963 for unfilled by Dr. Frank Precopio. It was not widely used because of the amazing pressure to keep the cost of URD down near the cost of an overhead system. This high cost was caused by the need for additives (cross linking agents) and the cost of manufacturing based on the need for massive, continuous vulcanizing (CV) tubes. EPR was introduced at about the same time. The significantly higher initial cost of these cables slowed their acceptance for utility purposes until the 1980s. The superior operating and deductible destiny temperatures of XLPE and EPR made them the choice for feeder cables in commercial and industrial applications. Thesematerials do not melt and flow like HMWPE.The emergence of power distribution cables insulated with PE have replaced a significant portion of the oil-impregnated-paper insulated power cables used at operating voltages up to 35 kV. But lower voltage PILC cables are still being manufactured, due to their in-service longevity and reliability. In shock the long record of service and reliability of PILC cables, they are being in stages replaced by the less hygroscopic polymeric insulated cab les, XLPE. XLPE cables have searching advantages which are lighter weight, better electrical and thermal properties, less maintenance, and easier terminating and jointing procedure and so on Today, XLPE cables are being extensively used in many countries all over the world. In 1959, Japan and USA commercialized XLPE cables up to medium voltage rating. Since then a fast development of XLPE cables has taken place. Presently, XLPE cable of 500 kV class has been installed in Japan.The introduction of XLPE has increased the ability of polymeric insulated cables because of their higher temperature ratings. XLPE insulations perform well at elevated temperatures. Their normal operating temperature is about 90 C and designed to withstand an emergency overload and short circuit ratings of 130 C and 250 C, respectively.Technology of XLPE CablesXLPE has become the most favored insulant. Germany, USA, Asian and Scandinavian countries have installed gigantic quantities of such cables. Japan ha s developed XLPE cables up to 500 kV which is the highest voltage rating of XLPE cables manufactured so far. The basic material for XLPE cable is polyethylene (PE). PE has very good electrical properties. However, its mechanical strength decreases significantly supra 75 C restricting its continuous operating temperature to 70 C only.The improved thermal characteristics of PE are obtained by establishing a large number of cross-links between its liner molecular chains employing suitable techniques. The introduction of XLPE has increased the aptitude of polymeric insulated cables because of their higher temperature ratings. The processes for converting PE to XLPE are electron irradiation, chemical cross linking, and innate silane rule.Electron irradiation is a slow process and it is difficult to go over an even degree of cross linking throughout the thick insulation required for power cables. Therefore this process is usually restricted to thin insulation of 1 to 2 mm thickness on ly. Chemical cross linking process is the process by which cross-linking of PE is established using organic peroxide such as dicumyl peroxide (DCP) at high temperature in the range 250 to 350 C and pressure 15-20 kg/cm2. This order is employed in the production of XLPE cables of all voltage range, from LV to EHV. Sioplas technique is a relatively new method of cross linking PE into XLPE. Cross linking is achieved by mixing suitable silane to PE and exposing this to ambient conditions. This method has the distinct advantage of lower capital expenditure as no special arrangements to maintain high pressure and temperature are required. But the process is very slow for thick insulation and hence restricted to low voltage and medium voltage XLPE cables.The general construction of XLPE cable consists of copper or aluminium conductor, extruded layer of semi conducting material over conductor (for voltage class above 3.3 kV), extruded XLPE insulation, extruded layer of semi-conducting mate rial (for cables of voltage rating above 3.3 kV), copper wire or tape as golden screen, armour, inner sheath and outer sheath, usually made of PVC etcetera Three core XLPE cables are generally used up to maximum 33 kV. Cables of 66 kV and above voltage rating are of single core construction.Figure 1.3.2 Solid dielectric extruded power cable 14The manufacturing process of XLPE cables consists of mixing of PE with cross-linking agent (DCP) and antioxidants, extrusion of semiconducting layers and insulation over the conductor, crosslinking the PE compound in band lines at high temperature and pressure and modify the core to ambient temperature. All these processes are carried out in one step employing catenaries lines for curing and cooling, hence the name continuous catenaries vulcanization. Semiconducting layers and insulation are extruded using triple extrusion technique.The curing process was ab initio carried out with steam at high temperature and pressure. This resulted in th e formation of microvoids within the insulation and restricted the application of steam curing process up to 33 kV. To achieve reliable HV cables, it was therefore necessary to employ curing in the absence of steam. For this reason, dry curing methods were developed, where PE was crosslinked under nitrogen pressure in silicone oil, in molten salt and alike in long dies. The numbers of microvoids were drastically reduced. A new curing process has recently appeared namely silane process which is more economical.Losses in Power CablesLosses in power cables embroil losses in conductor, insulation, sheath, and screens armors. director losses (I2Rac losses) depend upon the rms current I effective AC resistance of the cable conductor. Dielectric losses comprise of losses due to wetting through the cable insulation and caused by dielectric polarization under AC stresses. It includes the net dielectric losses depend upon cable voltage, its absolute absolute oftenness as well as the pe rmittivity and loss tangent of the cable dielectric material, as shown by the equation belowPower loss = CoV2r tan 2 (1)Generally, tan , which partially controls the dielectric losses, is significantlyhigher for oil-paper insulation as compared to XLPE insulation. For most of the dielectric materials used in cables, tan depends upon temperature, applied stress and supply frequency. For oil-paper insulation tan is also strongly lickd by moisture content. Therefore, in voltage cables, a moisture level of less than 0.05 % is desirable in order keep dielectric losses within acceptable limits. The presence of voids and microcracks can also influence dielectric losses. These voids are formed in the insulation or at the screens/insulation interfaces during manufacture, installation or operation.In polymeric cables, they are formed during the extrusion process while in paper-insulated cables, during the impregnation cycle. Voids may also form in cables by the differential expansion cont raction of cable materials due to cyclical loading or short circuit conditions. These voids have a higher electric stress as compared to the bulk insulation. However, the burn out inside a void usually has lower breakdown strength as compared to the main insulation. When the electric stress in void exceeds the breakdown strength of gas within the void, PD occurs.Any partial discharge in such voids increases the effective tan value for insulation. Consequently, when the applied voltage is raised above the charge inception threshold, the dielectric losses exhibit a distinct increase. Similarly, impurities in the cable insulation and screening materials also increase dielectric losses.The AC current flowing along each cable conductor induces emf the metallic sheaths of the cable. Without grounding, such sheaths would operate at a potential above the ground potential and can pose a hazard. Furthermore, it will accelerate degradation of the jacket and materials, thereby affecting the c ables life and reliability. When the sheaths are bonded, circulating current flows in them causing power losses. However, for three-core cables such losses are negligible. In addition to circulating currents, eddy currents are also induced in sheaths of both single and multi-core cables causing additional losses which usually are of small magnitudes.1.5 Objectives of StudyThis project is conducted to evaluate the expected value of aging cost due to harmonic losses in XLPE cables. Therefore, this project is conducted regarding to these designsTo investigate the effects of harmonics losses on XLPE cables fromeconomical point of view.To evaluate the expected value of the aging cost due to harmonics lossesin XLPE insulated cables.1.6 Scope of studyThis study will focus on XLPE insulated cablesThis study will use the characteristics of single core underground cables.The effect of harmonics losses on XLPE cable will be investigatedA curriculum will be developed to evaluate the expected value of aging costdue to harmonic losses.The economical damage due to harmonic losses is quantified by means of the expected value of the operating costs and of the aging costs. For this, it will focus only for the calculation of the expected values of the aging costs.CHAPTER 2LITERATURE REVIEW2.1 IntroductionWe design power systems to function at the fundamental frequency 1. In Malaysia, the fundamental frequency is standardized at 50 Hz. This design is prone to unsatisfactory operation. At the same time, failure will happen when subjected to voltages and currents those contain substantial harmonic frequency elements. Frequently, the electrical equipment may seem operate normally. However, when they operate under a certain combination of conditions it might enhance the impact of harmonics which cause results to damage 20.Most people do not realize that harmonics have been around for a long time. Since the first AC generator began to operate more than 100 years ago (Sankaran, C., 1 995), electrical power systems have experienced harmonics. When harmonics present in electrical equipment, it can cause the equipment to malfunction and fail to work. In this case proper design and rating are needed to prevent the presence of harmonics.2.2 Power System HarmonicsThe objective of the electric utility is to deliver curving voltage at fairly ageless magnitude throughout their system. In fact, in order to achieve this objective is reasonably complicated because there are lots that exist on the power system that will produce harmonic currents. These currents produced may result in distorted voltages and currents that can give negative impact to the system performance in different ways.As the number of harmonic producing loads has increased over the years, it has become increasingly necessary to address their influence when making any addition or changes to an installation. We should consider two important concepts that have to bear in mind with regard to power system h armonics. The first concept is the nature of harmonic current producing loads (non linear loads) and the second concept is the way in which harmonic currents flow and how the resulting harmonic voltages develop.Ideally, voltage and current waveforms are perfect sinusoids. However, because of the increased popularity of electronic and other non-linear loads, these waveforms quite often become distorted. This deviation from a perfect sin wave can be represented by harmonics sinusoidal components having a frequency that is an integral multiple of the fundamental frequency. Thus, a pure voltage or current sine wave has no distortion and no harmonics, and a non-sinusoidal wave has distortion and harmonics. To quantify the distortion, the term total harmonic distortion (THD) is used. The term expresses the distortion as a percentage of the fundamental (pure sine) of voltage and current waveforms. In addition, current harmonics can distort the voltage waveform and cause voltage harmonics . Voltage distortion affects not only sensitive electronic loads but also electric motors and optical condenser banks.2.2.1 Definition of HarmonicHarmonics are defined as current and voltages at frequencies that are integer multiples of the fundamental power frequency 4. For example, if the fundamental frequency is 50 Hz, then the second harmonic is 100 Hz, the third is one hundred fifty Hz, and etc 5. The presence of harmonics in electrical energy systems is well recognized due to nonlinear loads such as static converters and it can damage the system components 6. These nonlinear loads will draw current in abrupt pulses rather than in a smooth sinusoidal manner. Then, these pulses cause distorted current wave shapes which in turn and cause harmonic currents to flow back into other parts of the power system. In the case of power cables, harmonics can cause relevant additional losses in the conducting and in the insulating materials which cannot be neglected in the cable size 6.2.2 .2 Source of harmonicsMost harmonics originate from the generation of harmonic current caused by nonlinear load signatures 4. The major sources of power system harmonics include switching operations, power electronic devices and other nonlinear loads and etc 7. Electronic devices are nonlinear and thus they create distorted currents even when supplied with a purely sinusoidal voltage. As nonlinear currents flow through a facilitys electrical system and the distribution-transmission lines, additional voltage distortions are produced due to the impedance associated with the electrical network. Thus, as electrical power is generated, distributed, and utilized, voltage and current waveform distortions are produced 8.As the number and ratings of power electronic devices connected to the power systems increase, the harmonic currents injected into power system and the resulting voltage distortions have become a major problem for power quality. This is the current issues that of all time be taken into account nowadays. Furthermore, the installation of power factor improving capacitors may lead to resonance conditions that embellish specific harmonic currents flowing into transformers and generators. On the other hand, large industrial ac motors may also provide a path for the harmonic currents. These currents can cause overheating problems for the motors, generators, and transformers. Power grid connected electric devices which can generate harmonic currents in the power system include fluorescent light ballast transformers, induction motors, incandescent light dimmers, overexcited transformers, arc welding equipment, AC/DC rotary converters, battery chargers, computers, and any type of device that utilizes rectified AC power to drive DC equipment 9.2.2.3 The Harm of HarmonicsHarmonics only mean trouble if the power system is not well designed to handle them. High harmonic neutral currents are a problem only if the neutral is not properly sized. menses harmonics are not a problem to a transformer if it is derated appropriately. Even some voltage distortion below 8 % THD at the point of role is acceptable as long as sensitive equipment is not affected. However, it is always important to be aware of the presence of harmonics and to try to minimize them by purchasing low distortion electronic ballasts and reactors for PWM ASDs. This will not only keep the harmonics in check and improve the power factor in the facility, but will also save energy by decrease losses on power system components. In addition, any time there is a considerable increase of non-linear loads, it is important to check power system components to prevent problems.2.2.4 Effects of Harmonics on Power SystemHarmonic currents and voltage distortion are becoming the most severe and conglomerate electrical challenge for th