Study Committee B2 Technical Advisory Group B2-AG-06

Transcription

1 Study Committee B2 Technical Advisory Group B2-AG-06

2 Cigré AG06 Seminar Bangkok Types and Uses of High Brian Wareing Brian Wareing.Tech Ltd Chester, UK Convenor Cigré AG06 WG48 Experience with the Mechanical Performance of New Conductor types Secretary Cigré AG07 WG28 Weather effects on Overhead Lines

3 Scope Look at the range of new bare conductor types available Appreciate new conductor characteristics and suitability in comparison with standard conductor types Make you aware of the requirements when choosing conductors Covers construction, design and operation See how network up-grading problems can be solved cost-effectively by conductor choice 3

4 Basic Types Cigré has categorised new conductors in four basic types Type 1. composed of a steel core and an envelope for which the high temperature effects are controlled by means of thermal- resistant aluminium alloys (e.g. GAP, TAL HACIN) Type 2. composed of a steel core and an envelope for which the high temperature effects are controlled by means of annealed aluminium or aluminium alloy (e.g. ACSS) 4

5 Basic Types New conductor types Type 3. composed of a non-metallic core, and an envelope for which h the high h temperature t effects are controlled by means of thermal resistant aluminium alloys (e.g. ACCR) Type 4. composed of a non-metallic core, and an envelope for which the high temperature effects are controlled by means of annealed aluminium or aluminium alloys (e.g. ACCC) 5

6 Basic Structure of traditional bare wire conductors AAAC, AAC, ACAR, Copper ACSR Compacted ACSR 6

7 Aluminium Standard Aluminium and Aluminium Alloys can only operate continuously at temperatures up to 93ºC without causing metallurgical decay resulting in lifetime reduction TAL and ZTAL aluminium have essentially the same conductivity and tensile strength as ordinary electrical conductor grade aluminium but can operate continuously at temperatures up to 150ºC and 210ºC, respectively, without any loss of tensile strength over time. Fully annealed aluminium is chemically identical to ordinary hard drawn aluminium and can operate indefinitely at temperatures at 250ºC (and higher) without any change in mechanical or electrical properties but has a much reduced tensile strength. 7

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9 Core Material Galvanised steel is the normal core material for standard ACSR conductors. This is subject to corrosion and potential failure when the galvanising has disappeared High Tensile steel is used when stronger conductors with less sag are required Invar steel is used for low sag because of its very low thermal expansion coefficient High strength, th low conductivity it aluminium i alloy can be used as a core material to give improved strength to AAAC conductors. 9

10 Steel, aluminium or composite cores A conductive core will take part of the AC current and heat up Steel can sag more due to heating Ceramic fibre reinforced aluminium can be stressed under thermal cycling due to mis-match match in expansion coefficients Pure composite core will not take significant current 10

11 4.5 11

12 High temperature conductor types 12

13 High High Conductor is defined as a conductor that is designed for applications where continuous operation is above 100 C or the conductor is designed to operate in emergency conditions above 150 C C. In fact some can be run at over 200 C continuously and over 220 C for short times. This gives us spare capacity or redundancy in the network for future expansion To take advantage of the high temperatures (and so Ampacities) low sag is also required and this uses the technique of the Knee point 13

14 Knee Point Occurs for all ACSR type conductors when the tensile load is transferred from the (high expansion coefficient) aluminium to the (low expansion coefficient) core This produces a change of angle in a sag/temperature graph The point at which this occurs is known as the Knee point 14

15 15 14 Original 400 mm 2 Zebra ACSR C 560 mm 2 ZTACIR C 366 m Standar rd L2 Span, m Original design maximum sag, 1950s 620 mm 2 Matthew GZTACSR C Sag of 10 Knee points mm 2 Sorbus AAAC C C Conductor, 0 C

16 New Conductor Types 3M ACCR ACSS Lumpi HACIN CTC ACCC J-Power Gap 16 16

17 Type 1- J-Power Gap 1. High aluminium alloy 2. Inner layer forms a tube containing free moving high tensile steel core in grease 1. Very low vibration levels 2. Used world wide 17 17

18 Pros and Cons - Gap Low vibration levels Knee point at erection temperature* Long history of use Cannot be joined Special fittings Grease can dissociate Sag relies on steel core Can be noisy * Erection temperature can be 5ºC in UK, 50ºC in Middle East, 30ºC in SE Asia All this affects the final sag! 18

19 Type 1 - Lumpi-Berndorf HACIN High Zirconium Aluminium alloy Aluminium coated Invar steel core no corrosion Uses standard d ACSR fittings Galvanised steel High ampacity Salt spray test ACS Used by NIE in UK 19 19

20 Pros and Cons ZTAL/HACIN Uses standard fittings Canbejoined ACS has long history of use in OPGW Can be treated as conventional ACSR Aluminium coating avoids corrosion Invar use gives low sag Higher knee point than Gap p( (~50 C) High strength low sag Invar Steel core can be expensive 20

21 Annealed Aluminium Type 2 - ACSS ACSS can be stranded using either round or trapezoidal shaped annealed aluminium wires. In either design, the conductor depends primarily on the steel core wires for mechanical St l strength. This core may be aluminised, galvanised, zinc-5%aluminium Mischmetal coated or aluminium clad steel 21 Steel core

22 Pros and Cons - ACSS TW means smaller cross-section and so lower wind loads Can be joined Sag determined by steel High conductivity Used in USA Soft aluminium m requires care in handling Higher knee point than Gap Pure Aluminium has lower strength than alloy Can suffer corrosion 22

23 Type 3-3M ACCR Aluminium i matrix core Very strong No steel High temperature aluminium alloy Expensive 23 23

24 Pros and Cons - ACCR No steel so no corrosion Core as strong as steel High temperature operation (>200ºC) Core lower expansion coefficient than steel Low kg/m High knee point (~70 C) Can creep Expensive 24

25 Type 4 - CTC ACCC Carbon fibre core (stronger and lighter than steel) High temperature, high conductivity aluminium Can operate up to 250 C Low tension so less stress on structures Very low sags Installed in several countries 25 25

26 Pros and Cons - ACCC Extremely strong composite core (50% stronger than steel) Virtually no increase in sag above knee point High conductivity alloy Can be used up to very high temperatures Used world-wide Very low kg/m Special fittings Soft aluminium requires care in handling Minimum bending radius for core 26

27 Fittings Most new conductor types require special fittings An exception is the ZTAL/HACIN ACSR which can use existing conventional fittings These fittings may run hotter than normal and so may incur some overheating unless specifically designed for high temperature operation But commonly many HT conductors are run at <100ºC in normal operation so fittings only have to withstand t high h temperatures for short periods 27

28 Conductor range The new conductor types are mainly aimed at tower lines The reason for this is that t there is a minimum i size that trapezoidal stranded conductors can be made However, these conductors can be used on wood pole lines and some (e.g. ACCC) are in use on 33kV networks in USA and UK (HACIN is due to be erected in Oman at 33kV). 28

29 Economics New conductors are expensive between 3 and 6 times more than conventional conductors but it is generally towers that are expensive and conductor costs <10% of overall line costs. So is doubling of power capacity worth a 20% increase in line cost? Generally yes! However, many HT conductors are run at <100ºC in normal operation (N-1 basis) and this reduces I²R losses 29

30 Economic re-conductoring In the UK, re-conductoring 132kV wood pole lines with Poplar (200mm² AAAC) and tower lines with Sycamore (250mm² AAAC) size equivalent HT conductors should need no tower strengthening so reduce overall costs. Typically, y CTC ACCC Casablanca can give an 80% ampacity gain (when restricted to 150ºC) and Lumpi- Berndorf s 194TAL/HACIN a 50% increase in ampacity compared with Poplar at 75ºC 30

31 New Build For new lines the sag limitation imposed by Poplar will not be present. So in terms of ampacity only, without taking into account sags, the best performing conductors on a UK P27 summer rating at 150ºC were CTC ACCC Amsterdam with 110% increase 3M ACCR 575-T23, CTC ACCC Oslo and Lumpi-Berndorf 294TAL with around a 90% increase Cigré AG06 Bangkok

32 Uses of new conductors The optimum use of new conductors depends on the problems with current networks and the local l environment Polluted areas High ambient temperatures Ice prone areas Non-icing areas Sag problems Span lengths 32

33 Network Requirements 33 Affordable re-conductoring or new-build Efficient (low loss) conductor High capacity Low Sag Running cold a conductor that delivers high ampacity at a lower temperature has Lower line losses Longer fitting life Less chance of breaking regulatory clearances

34 Polluted areas Need to choose a conductor which does not have an unprotected steel core that is likely to corrode e.g. Composite C i cored conductors Aluminium coated steel cores Gap has a steel core in a grease layer so will not corrode if grease stays 34

35 High ambient temperatures Need to have a conductor that can operate at well above ambient temperature to get high power capacity e.g. HT conductors with annealed aluminium i can operate continuously at up to 250ºC ZTAL can operate up to 200ºC 35

36 Ice prone areas Heavy ice loads can cause excessive sags Some conductors can have customised cores for heavy ice load areas ACCC has the option of high pre-tension so that nearly all the load falls on the extra strong core 36

37 Small sag at high ampacity Main emphasis here is on electrical low sag performance which requires high ampacity and low expansion coefficient of the core e.g. The carbon fibre composite core which has lowest electrical sag of all HT conductors Invar steel which has a much lower coefficient of thermal expansion than other steels 37

38 Span lengths Long spans require very strong and low sag conductors The strongest conductor by far is that with a carbon fibre composite core which is more than twice as strong as any steel or aluminium m matrix core 38

39 Specific Tensile Strength Conductor strength and weight directly impact the amount of sag (D) and tension (H) in an overhead conductor. Specifically, D= w*s²/(8*h) where; S=span length w= weight per unit length Thus (H/w) is directly related to specific tensile strength. th Generally the higher the H/w, the less the conductor sags. 39

40 Typical values of H/w for Sycamore equivalent conductors Sycamore equivalent HT conductors Conductor UTS (kn) kg/m H/w (kn.m/kg) Sycamore ACCC Oslo Gap HACIN ACCR 575 T

41 Summary Described the more commonly available High temperature conductors Briefly given advantages and disadvantages of the four basic types Explained why they can be of benefit even if not required to be run at high temperatures Explained the importance of the knee point Provided some basic examples of use GAP, ACCC and ZTAL/HACIN currently being field tested in UK Have a read of Cigré TBs 425 and 426 Cigré AG06 Bangkok

42 Finally SCB2 AG06 WG48 will look at Experience with the Mechanical Performance of New Conductor types SCB2 AG07 WG51 under Dale Douglass looks at the electrical aspects 42