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  1. 1. STANDARDDOCUMENT CLASSIFICATION CONTROLLED DISCLOSURE REFERENCE REV ESKASABK1 1TITLE: DETERMINATION OF CONDUCTOR DATE: May 2005 CURRENT RATINGS IN ESKOM PAGE 1 OF 12 REVISION DATE: May 2008 TESCOD APPROVEDCOMPILED BY FUNCTIONAL RESP APPROVED BY AUTHORISED BYSigned Signed Signed Signed.............................. ................................. ................................. .................................M Rapapa R Stephen A Bekker MN Bailey Corporate Consultant for TESCOD DTM for MD (R&S)This document has been seen and accepted by:R Stephen Study CommitteeA Bekker for TESCODMN Bailey DTMContents PageIntroduction......................................................................................................................................... 21 Scope ............................................................................................................................................. 22 Normative References.................................................................................................................... 23 Definition......................................................................................................................................... 34 Requirements ................................................................................................................................. 34.1 General........................................................................................................................................ 34.2 Probabilistic methods .................................................................................................................. 44.3 Application of the absolute method in Eskom ............................................................................. 54.4 Ampacity tables ........................................................................................................................... 84.5 Application of ampacity tables................................................................................................... 105 Revisions ...................................................................................................................................... 11AnnexA Impact assessment ...................................................................................................................... 12
  2. 2. DOCUMENT CLASSIFIACTION: CONTROLLED DISCLOSUREDETERMINATION OF CONDUCTOR REFERENCE REVCURRENT RATINGS IN ESKOM ESKASABK1 1 PAGE 2 OF 12IntroductionThe power transfer on transmission lines affects the sag of the conductor and hence the height of theconductor above the ground. This in turn affects the safety of the line. The determination of theallowable power transfer is thus not only a function of the properties of the conductor but also of thesafety to the public. It is thus essential that the designers are aware of the factors that affect the safetyof a transmission line as well as the types of accidents or factors that are pertinent to the utility.The present situation in Eskom is that the conductor thermal rating or ampacity is determined by adeterministic method using conservative ambient conditions. These conservative ambient conditionsof 40 ºC ambient temperature, 1120W/m2 solar radiation and 0,44m/s wind speed were used, togetherwith equations derived in the 1940s by Hutchins and Tuck and described in a book by Butterworth, todetermine the conductor current rating.Ratings were calculated for normal and emergency conditions at 75 °C and 90 °C. The lines werethen templated at 50 °C according to an internal Eskom directive, EED 15/6/1-1 1970. This means thatif the conductor temperature reached 50 °C, the height of the conductor above the ground would be atthe height prescribed by law. It follows that if the line was operated at the rated normal current and thesevere ambient conditions were present, the conductor temperature would be near 75 ºC, whichwould result in the line being under clearance, in terms of legislation. The directive stated that theprobability of this occurring was so low that it was acceptable to template at 50 °C and determine thecurrent rating for 75 °C and 90 °C. This probability was not quantified.This practice served Eskom well for almost thirty years and there were no known incidents of acontact occurring due to the thermal limit being exceeded. However in today’s economic environmentit is necessary to use assets more effectively and, on power lines, costs can be deferred or saved byfinding ways to operate the lines closer to the safe design limits.One way to do this is to provide the means to calculate the line ratings at different templatingtemperatures which was not possible using the previous directive.This document provides this means. It also quantifies the probability of an unsafe condition arisingassociated with the rating and keeps this constant for conductors of a similar type.It is important to note that the probabilities applied are based on the present practices so that if theline is utilized at a higher temperature, the probability of an unsafe condition arising is no more thanthe probability designed for at present. The lines are therefore just as safe as in the past albeit theyare operating at a higher temperature with a higher rating.1 ScopeThe document covers the different means of determining ampacity and gives the reasons for themethods chosen. It then presents the ratings for different templating temperatures and conductortypes in the form of simple tables. The application of the table by planners, designers and operators isalso discussed.The use of local conditions to determine the likely increase in ampacity by using real time monitoringon certain lines is not covered in this document.2 Normative ReferencesThe following documents contain provisions that, through reference in the text, constituterequirements of this standard. At the time of publication, the edition indicated was valid. All controlleddocuments are subject to revision, and parties to agreements based on this standard are encouragedto investigate the possibility of applying the most recent edition of the documents listed below.Information on currently valid national and international standards and specifications can be obtainedfrom the Information Centre and Eskom Documentation Centre at Megawatt Park.The following documents contain provisions that, through reference in the text, constituterequirements of this standard. At the time of publication, the editions indicated were valid. All
  3. 3. DOCUMENT CLASSIFIACTION: CONTROLLED DISCLOSUREDETERMINATION OF CONDUCTOR REFERENCE REVCURRENT RATINGS IN ESKOM ESKASABK1 1 PAGE 3 OF 12standards and specifications are subject to revision, and parties to agreements based on this standardare encouraged to investigate the possibility of applying the most recent editions of the documentslisted below. Information on currently valid national and international standards and specifications canbe obtained from the Information Centre and Technology Standardization Department at MegawattPark.EED 15/6/1-1:1970, Thermal limits of transmission line and busbar conductorsERA Publications OT/4:1953, Electrical characteristics of overhead lines (S. Butterworth)Swan, J. November 1995. Determination of conductor ampacity - A probabilistic approach. Adissertation submitted to the School of Electrical Engineering at Vaal Triangle Technikon South Africa,in fulfilment of the requirements for the Magister Technologiae Degree.Working Group 12 Cigre:1992, The thermal behaviour of overhead conductors − Sections 1 and 2Mathematical model for evaluation of conductor temperature in the steady state and the applicationthereof (Electra number 144 October 1992 pages 107 to 125).Working Group 12 Cigre:1996, Probabilistic determination of conductor current rating (ElectraNumber 164 February 1996 pages 103 to 119).3 Definitions and Abbreviations3.1 Definitions3.1.1 ampacity: The ampacity of a conductor is that current that will meet the design, security andsafety criteria of a particular line on which the conductor is used.4 Requirements4.1 GeneralThe formulas used in the determination of the ampacity tables were obtained from the Cigre WorkingGroup 12 document, “The thermal behaviour of overhead conductors Sections 1 and 2 Mathematicalmodel for evaluation of conductor temperature in the steady state and the application thereof”. Theseformulas take into account the wind direction, conductor absorbtivity, more accurate forced convectionformulas as well as a mixed convection rather than the simplistic forced and natural convectionformulas found in EED 1970.There are two methods of calculating conductor ampacity tables: the deterministic approach and theprobabilistic approach.The deterministic approach assumes certain bad cooling conditions (low wind speed, high ambienttemperature, etc.) and calculates the current that would result in the design temperature of the linebeing reached. The line templating or design temperature, is that temperature, at which the height ofthe conductor above the ground is the minimum permissible. The deterministic approach has beenused by utilities for a number of years. It is a quick and simple method. Bad cooling conditions areassumed and the current that will result in the line design temperature being achieved is calculated.The drawback is that the method does not address the safety or the relationship between safety andthe power transfer capability.Eskom is at present designing and operating its lines and power systems based on, inter alia, theallowable current (or ampacity) that can flow down the line. This current is usually calculated using adeterministic approach with assumed bad cooling conditions. It is assumed that by limiting the currentthe safety criteria will be met and the line will not contravene any regulations.It is known however, that conditions may result at some stage in the conductor exceeding the linedesign temperature causing the line to be under clearance. What is needed therefore is thequantification of the safety aspect of the design.
  4. 4. DOCUMENT CLASSIFIACTION: CONTROLLED DISCLOSUREDETERMINATION OF CONDUCTOR REFERENCE REVCURRENT RATINGS IN ESKOM ESKASABK1 1 PAGE 4 OF 12The probabilistic approach uses the actual weather data and conditions prevailing on the line or in thearea to determine the likelihood or probability of a certain condition occurring. Such a condition couldbe, for example, the conductor temperature rising above the design temperature. These methodshave been developed to include a measure of safety of the line. This can be used as a means ofcomparison of practices between utilities in all countries.There may be a problem in obtaining accurate low wind speed data. Very low wind speeds (< 1,0 m/s)are not recorded accurately by cup anemometers generally used by national weather services. Datareceived from these services may, therefore, be of limited use.4.2 Probabilistic methodsThere are three main methods available at present.The first is the method whereby the probability of an accident occurring can be quantified. Thebenefits of this method are that an absolute measure of safety is achieved. The drawback is that thenature of the parameters (later described in 4.2.1) is extremely difficult to determine. In addition thecorrelation between the parameters, for example, the weather parameters need to be determined.The second method uses the existing weather data to determine the temperature of the lineconductors for a given current flow. The amount of time that the temperature exceeds the line designtemperature can be determined for each current level. The utility can then decide on the current levelto use based on the percentage of excursion or "exceedence". The advantage of this method is that itis relatively easy to determine the percentages and decide on a level by which to operate. Thedisadvantage is that there is no way of determining the difference in safety (to the public) between, forexample, the 5 % and 6 % excursion levels.An adaptation of this method is to simulate the weather data and the current flow to determine thecumulative distribution of the conductor temperature as a function of current. This curve could be usedto determine the current and excursion level.The third approach is to simulate the safety of a transmission line by incorporating all the factors thataffect the safety of a line. From this method a measure of safety can be developed whereby thepractices in different countries can be compared on an objective basis. The advantage of this methodis that all factors are considered. The variation of the occurrence of objects under the line e.g. a trafficpattern can be related to the safety of a line. Designers can use a wider range of methods to increasethe thermal rating of the line not generally used before. An example of this is the reduction of surgemagnitudes or the number of surges per year can be used to increase the current carrying capacity ofa line.By using the measure of safety, system planners and line designers are in a position to determine theconsequences of decisions in an objective way, rather than a subjective way.Similarly System Operators, by using the measure of safety together with data from a real timemonitoring system, could operate transmission lines at higher than rated currents during emergencies.Utilities worldwide would be in a position to determine the safety of their lines in relation to otherutilities.This standard deals exclusively with the absolute probability method, as this method is the onepreferred for the generation of ampacity tables.4.2.1 Determination of the absolute probability of an unsafe condition arisingResearch to date has primarily been confined to attempts at determining the probability of an unsafecondition arising. This is determined by ascertaining the probability of each factor occurring andmultiplying the probabilities.
  5. 5. DOCUMENT CLASSIFIACTION: CONTROLLED DISCLOSUREDETERMINATION OF CONDUCTOR REFERENCE REVCURRENT RATINGS IN ESKOM ESKASABK1 1 PAGE 5 OF 12This is represented as: P(acc) = P(CT) × P(I) × P(obj) × P(surge) (Stephen 1991)where P(acc) is the probability of the accident arising. P(CT) is the probability of a certain temperature being reached by the conductor and is calculated from existing weather conditions, conductor types and an assumed current. P(I) is the probability of the assumed current being reached and is determined from the actual current being measured on a system. P(obj) is the probability of the electrical clearance being decreased by an object or person. P(surge) is the probability of a voltage surge occurring in the line and may be determined from fault records kept by the power utility as well as simulations on switching surge overvoltages on the system. If the surge occurs simultaneously with the object being under the line the likelihood of a flashover is increased.Each of the above is considered to be determined independently.P(CT) is determined by the Monte Carlo simulation technique sampling from distributions of ambienttemperature, wind speed, wind direction and solar radiation to calculate the probability of a certaintemperature being reached given a current transfer. The ambient temperature, solar radiation, windspeed and wind direction are sampled independently to form a set of parameters from which thetemperature of the conductor is determined.The problem with this method is that it assumes there is no correlation between weather parametersor the current, object and surge occurrences. This may not be correct in all cases. The correlationbetween the individual weather parameters, as well as the weather parameters and the surgeoccurrences and objects being under the line, must be ascertained.This problem can be partly overcome by using sets of weather parameters, measured at the sametime. These sets will be used to determine the P(CT). Since each set used is determined from actualrecordings of ambient temperature, solar radiation, wind speed and wind direction taken at the sametime, the correlation between the parameters is taken care of.4.3 Application of the absolute method in EskomIn system planning and design, overhead line transmission capacity is a parameter of majorimportance. It is therefore necessary to have exhaustive information regarding the factors affectingthis capacity in order to be able to design a transmission system under the best possible technical andeconomic conditions.The power transfer capability of transmission lines is limited by economic, physical and statutoryconstraints. Conductor current and temperatures generally determine the amount of power that can betransmitted over a given circuit. The maximum temperature at which a conductor can safely operate isdetermined by:a) permissible sag, that is governed by statutory requirements;b) annealing and long term creep, and;c) the reliability of joints and fittings.In addition, limits imposed by temperature, line transfer limit or losses may limit the load capability ofspecific transmission lines.Because of the economic pressures to increase the current carrying capacity of both existing andplanned overhead lines, there is a growing interest in using probabilistic methods which take intoaccount the variability of the stochastic nature of the meteorological parameters.
  6. 6. DOCUMENT CLASSIFIACTION: CONTROLLED DISCLOSUREDETERMINATION OF CONDUCTOR REFERENCE REVCURRENT RATINGS IN ESKOM ESKASABK1 1 PAGE 6 OF 12The probability of a certain load current, that will result in the template temperature being met, is equalto the product of the individual probabilities of the weather conditions and conductor surfacetemperature (Swan1995). P(Tc) = P(I) × P(Ta) × P(GSR) × P(WS) × P(WD) ==> P(I) = P(Tc) /(P(Ta) × P(GSR) × P(WS) × P(WD))where P(Tc) is the probability of a conductor temperature; P(I) is the probability of a current; P(Ta) is the probability of an ambient temperature; P(GSR) is the probability of global solar radiation; P(WS) is the probability of wind speed; and P(WD) is the probability of wind direction.The weather model was constructed from historical hourly weather data between the hours of 11h00and 15h00 (inclusive) for a period of 30 years. The reason for this choice is that the highest conductortemperature will occur during that time of the day under full load conditions, considered to be the worstcase condition. The data has been tested statistically for correlation in order to ensure that no specialsimulation techniques are required. The highest correlation was found to be in the order of 3 %. Nospecial simulation techniques are required for such low correlation.A range of conductor current values are generated from the above that will result in the templatetemperature being met. In order to identify the optimal current from the range, it is necessary toidentify conditions that may lead to a possible dangerous condition. Typical high-risk factors are:a) with high traffic density road crossings andb) the possibility of a flashover from the conductor to an object underneath the conductor.The main factors that may cause a flashover are:a) a vehicle, at least 4,65 m high, underneath the conductor;b) full load current;c) weather conditions that together with full load current will result in the conductor surface temperature being equal to the template temperature;d) maximum system voltage; ande) an impulse, switching or as result of lightning, that will transiently raise the system voltage to at least 2 per unit (p.u).The above are assumed to be occurring independently. Therefore the probability of an unsafecondition or accident is equal to the product of the individual probabilities (Swan 1995). P(acc) = ((P(Ta) × P(GSR) × P(WS) × P(WD))/P(Tc)) × P(OBJ) × P(S.I) × P(U.max) × P(2,5p.u)where P(acc) is the probability of an unsafe condition occurring, calculated for the Eskom design practice prior to 1987 i.e. 75 °C conductor thermal rating and 50 °C template temperature; P(OBJ) is the probability of an object under the line, based on the Ben Schoeman Highway traffic patterns i.e. 800 vehicles per hour of which 40 % are trucks with a maximum height of 4,2 m; P(S.I) is the probability of switching impulse occurring, calculated based on transmission performance database; P(U.max) is the probability of maximum system voltage, assumed to be 1; and P(2.5p.u) is the probability of the surge magnitude being 2 p.u based on a simulation representative line in the system.
  7. 7. DOCUMENT CLASSIFIACTION: CONTROLLED DISCLOSUREDETERMINATION OF CONDUCTOR REFERENCE REVCURRENT RATINGS IN ESKOM ESKASABK1 1 PAGE 7 OF 12For the purpose of generating the table the probability of an unsafe condition occurring was calculatedfor the Eskom design philosophy prior to 1987. With this philosophy the conductor was thermally ratedfor a 75 °C electrical rating, but the line template temperature was at 50 °C. The probability of anunsafe condition was then kept constant and the ratings at different temperatures were thencalculated. The table of ampacity values will therefore not increase the Eskom operational risk. Forexample, the probability for Wolf conductor at 370 A at a templating temperature of 50 °C for normaloperation was then calculated. This probability was kept constant in order to calculate the rating ofWolf conductor at different templating temperatures. This method was in turn used for otherconductors. The probability used for Wolf conductor was used for all double layer ACSR conductors. Asimilar method was used for other conductor configurations. The same approach was used for theemergency ratings in that the probability was calculated for the present emergency conditions andkept constant for the different templating temperatures.The use of hourly weather data between 11h00 and 15h00 will not affect the calculated values in thetable. A more comprehensive database will however affect the calculated value of the probability of anunsafe condition {P(acc)}. If this method is to be used for international benchmarking exercises, the useof a comprehensive weather database will be required.In addition, transmission lines in service may be further optimized using hourly weather data and theactual load profile of the line. The uprating of lines with this method would not result in the sameincrease in power transfer capacity that would be possible with real time monitoring. It is however lesscostly, it requires a once-off resource, and may potentially increase the transfer capacity up to 25 %.The potential increase of 25 % is in most cases sufficient to delay capital expenditure. In some casescapital expenditure may even be deferred indefinitely. The potential increase in power is dependent ona number of factors i.e. the terrain, the original design criteria, survey tolerances, equivalent spansetc. The successful uprating of a line can only be achieved once the impact of all these factors hasbeen accessed in terms of the safety and reliability of the line in question.When the new ampacity values are used for the planning and design of new lines, it is of vitalimportance that the template temperature and conductor thermal rating are the same. If the templatetemperature and conductor thermal rating are different the probability of an unsafe condition {P(acc)}will not be the same as the calculated values in this table. The operational risk to Eskom and thesafety to the public will therefore be adversely affected. Please note that no lines should be templatedabove 80oC for reasons listed in 4.5.3.
  8. 8. DETERMINATION OF CONDUCTOR REFERENCE REVCURRENT RATINGS IN ESKOM ESKASABK1 1 PAGE 8 OF 124.4 Ampacity tables Double TT Normal Emergency Triple layer TT Normal Emergency Single TT Normal Emergency AAAC TT Normal Emergency layer Deg C Amps Amps Amps Amps layer Amps Amps Amps Amps TIGER 50 330 425 TERN 50 611 814 SQUIRREL 50 106 135 ACACIA 50 114 142 TIGER 60 405 507 TERN 60 784 991 SQUIRREL 60 130 160 ACACIA 60 140 169 TIGER 70 464 574 TERN 70 911 1138 SQUIRREL 70 149 181 ACACIA 70 160 191 TIGER 80 514 633 TERN 80 1023 1257 SQUIRREL 80 165 198 ACACIA 80 177 210 WOLF 50 378 501 BUNTING 50 807 1077 FOX 50 148 192 35 50 163 204 WOLF 60 473 602 BUNTING 60 1029 1321 FOX 60 184 228 35 60 200 243 WOLF 70 548 683 BUNTING 70 1198 1506 FOX 70 210 258 35 70 229 275 WOLF 80 610 751 BUNTING 80 1347 1663 FOX 80 233 283 35 80 254 303 LYNX 50 417 557 ZEBRA 50 642 859 MINK 50 209 272 PINE 50 227 288 LYNX 60 519 665 ZEBRA 60 818 1049 MINK 60 258 324 PINE 60 279 343 LYNX 70 606 759 ZEBRA 70 963 1203 MINK 70 297 367 PINE 70 320 389 LYNX 80 671 831 ZEBRA 80 1080 1325 MINK 80 330 402 PINE 80 355 427 CHICADEE 50 433 576 DINOSAUR 50 852 1151 HARE 50 292 380 OAK 50 312 402 CHICADEE 60 541 690 DINOSAUR 60 1091 1405 HARE 60 357 454 OAK 60 385 482 CHICADEE 70 625 786 DINOSAUR 70 1284 1615 HARE 70 408 515 OAK 70 443 544 CHICADEE 80 698 864 DINOSAUR 80 1436 1781 HARE 80 455 565 OAK 80 490 597
  9. 9. DETERMINATION OF CONDUCTOR REFERENCE REVCURRENT RATINGS IN ESKOM ESKASABK1 1 PAGE 9 OF 12Double layer TT Normal Emergency Triplelayer TT Normal Emergency Single layer TT Normal Emergency AAAC TT Normal Emergency Amps Amps Amps Amps Amps Amps Amps Amps PANTHER 50 459 612 BERSFORT 50 875 1183 MAGPIE 50 33 40 ASH 50 410 539 PANTHER 60 573 736 BERSFORT 60 1119 1438 MAGPIE 60 47 52 ASH 60 507 642 PANTHER 70 664 837 BERSFORT 70 1311 1645 MAGPIE 70 58 62 ASH 70 584 727 PANTHER 80 742 920 BERSFORT 80 1463 1827 MAGPIE 80 67 70 ASH 80 648 800 PELICAN 50 487 654 YEW 50 792 1057 PELICAN 60 611 785 YEW 60 978 1268 PELICAN 70 709 892 YEW 70 1131 1440 PELICAN 80 789 980 Quadlayer TT Normal Emergency COPPER YEW 80 1264 1584 BEAR 50 529 715 Amps Amps SYCAMORE 50 583 772 BEAR 60 663 860 800-IEC-72/7 50 930 1339 C7/0.104 50 197 246 SYCAMORE 60 717 921 BEAR 70 770 976 800-IEC-72/7 60 1180 1625 C7/0.104 60 241 293 SYCAMORE 70 829 1045 BEAR 80 859 1076 800-IEC-72/7 70 1411 1860 C7/0.104 70 277 333 SYCAMORE 80 920 1149 KINGBIRD 50 590 793 800-IEC-72/7 80 1592 2066 C7/0.104 80 306 364 ELM 50 455 599 KINGBIRD 60 738 955 C7/0.152 50 316 402 ELM 60 563 716 KINGBIRD 70 855 1088 C7/0.152 60 388 480 ELM 70 648 810 KINGBIRD 80 956 1196 C7/0.152 70 446 544 ELM 80 719 889 GOAT 50 607 822 C7/0.152 80 496 597 GOAT 60 763 990 GOAT 70 884 1130 GOAT 80 988 1240The template temperature (TT) and the conductor thermal rating shall be the same if the above table values are being used.
  10. 10. DOCUMENT CLASSIFIACTION: CONTROLLED DISCLOSUREDETERMINATION OF CONDUCTOR REFERENCE REVCURRENT RATINGS IN ESKOM ESKASABK1 1 PAGE 10 OF 124.5 Application of ampacity tablesThe tables have been generated for all the conductor types, with different templating temperatures.The planners now have a far wider choice of options than previously. If, for example, a plannerrequires a power transfer of 600A the planner can choose a Wolf conductor at 80 °C, a Lynxconductor at 70 °C, a Panther conductor at 60 °C, or a Goat conductor at 50 °C. This will depend onwhat the line is to be used for. This is covered in 4.5.1 and 4.5.2. The same applies with lines forupgrading: if a 50 °C Wolf line exhibits a load of 600A under emergency conditions, it is possible thatinvestigations can be done to see if the templating temperatures cannot be increased by 10 °C.4.5.1 Short line with high emergency load requirement. Peaky load profile, no voltageor stability problems (no line length dependent transfer limit)For this condition it is preferable to use a quad or hex bundle with small conductors. This increasesthe cooling efficiency, improves corona performance and surge impedance loading (SIL). It also allowsthe optimum aluminium area to be used. However, the templating temperature is fixed to a maximumof 80 °C with regard to line service considerations listed in 4.5.3 below.4.5.2 Long line, level load profile voltage and stability problemsIn most cases with these problems use the smallest number of conductors in a bundle that is possible.The more conductors that are used in a bundle the higher the resultant mechanical loading on thetowers and foundations. The hardware and damping are also more expensive. Corona limits (at highvoltages such as 400 kV) are likely to be the limiting criteria. The large aluminium area will ensure thelowest life cycle cost. Compactness should be an option to improve the SIL. If possible, seriescompensation or FACTS (Flexible AC Transmission Systems) devices such as thyristor switchedcapacitors shall be used. The templating temperature can be reduced due to the low current density. Aprobabilistic approach using the ampacity tables could result in the optimum templating temperaturebeing established.It is stressed that the use of the tables is a first pass at the final conductor selection. The best tower,conductor combination will depend on the terrain, cost of hardware, towers and construction. The bestthermal solution of bundled conductor with small conductors may not prove the best mechanicalsolution due to high wind load and hardware costs. The main benefit of using the tables is that it opensfar more options to the planner.4.5.3 Thermal constraints when applying ampacity tablesIn the light of thermal constraints considered for a line in service, the templating temperature has beenreduced to 80 °C on all conductor sizes and types as listed on the ampacity tables.The main reasons are:a) The accelerated rate of annealing of the aluminium at temperatures exceeding 80C with a consequential loss of mechanical strength. The implication is more sag than anticipated and under clearance of lines.b) High temperature operation increases the risk of joint failures that will impact negatively on the reliability of the circuit/system.c) The I^2R losses become significant hence the system losses become extensively high to offset the initial potential cost savings.d) With greased conductors the protective grease melts and oozes out of the conductor leaving the conductor steel without corrosion protection.e) Bird caging may occur transferring the entire mechanical load onto the steel portion of the conductor. In addition, during bird caging, the aluminium goes into compression and therefore adding an additional mechanical load onto the steel portion of the conductor. Sag will be more
  11. 11. DOCUMENT CLASSIFIACTION: CONTROLLED DISCLOSUREDETERMINATION OF CONDUCTOR REFERENCE REVCURRENT RATINGS IN ESKOM ESKASABK1 1 PAGE 11 OF 12 than anticipated and Eskom will be in contravention of statutory requirements due to sag and exceeding design safety factors.f) Voltage regulation requirements may not be achieved due to high voltage drop on the circuit/system (95-105%).g) Smaller conductors at high current may not satisfy system stability criteria and requirements.5 Equipment/Software DATE REV. NO. NOTES Jun ‘00 0 Document issued. Oct ’04 0(A) Templating Temperature reduced from 100oC to 80oC April ‘05 1 Document approved.
  12. 12. DOCUMENT CLASSIFIACTION: CONTROLLED DISCLOSURE DETERMINATION OF CONDUCTOR REFERENCE REV CURRENT RATINGS IN ESKOM ESKASABK1 1 PAGE 12 OF 12 Annex A (informative) Impact Assessment Impact assessment Document title: Determination of conductor current ratings in Eskom Document no: ESKASABK1 Revision no: 1 Activity Detail1. What training is required to implement this document? N/A (e.g. Awareness training, practical / on job, module.)2. Who will require training? (State designations.) N/A3. What prerequisites are needed for students? N/A4. What equipment will be required for training? (Computers etc.) N/A5. What special tools will be required for training? N/A6. What special requirements are needed for the trainer? N/A7. Time period for training to be completed? N/A8. What special tools / equipment will be needed to be purchased by N/A the Region to effectively implement?9. Are there stock numbers available for the new equipment? N/A9. Does the document affect the budget? N/A10. Time period for implementation of requirements after training is N/A completed?11. Does the Buyers Guide or Buyers List need updating? N/A12. What Buyer’s Guides have been created? N/A13. Was Training & Development consulted w.r.t training requirements? N/A14. Were the critical points in the document determined? Yes15. Is any training material available on the subject in this document? N/A16. Was the document SCSPVABE0 adhered to? Yes Total implementation period Total training cost Total cost of tools / equipment Total cost involvedComments: Assessment Compiled by: Recommended by (Functional Responsibility):Name: M Rapapa Name: J SwanDesignation: Engineer Designation: Transmission ConsultantDept: Distribution Technology Dept: TransmissionDate: March 2005 Date: March 2005

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