New range of special alloy conductors Advantages over ACSR & AAAC conductors

Transcription

1 New range of special alloy conductors Advantages over ACSR & AAAC conductors Author G L Prasad Document: WP0007 Abstract A new Aluminum alloy conductor having higher conductivity has been developed. By using these special alloy conductors, electric utility can achieve significant saving in both transmission and distribution lines Keywords Alloy, Swedish conductors, AL-59, ACSR, AAAC

2 INTRODUCTION The categories of conventional type of Aluminium and Aluminium alloy overhead conductors available globally are: Homogeneous Conductors AAC All Aluminium Conductors AAAC All Aluminium Alloy Conductors Non Homogeneous Conductors ACSR Aluminium Conductor Steel Reinforced AACSR-Aluminium Alloy Conductor Steel Reinforced ACAR Aluminium Conductor Alloy Reinforced For several years, distribution and transmission lines have been designed using aluminum conductors steel reinforced (ACSR) or in some countries all aluminum alloy conductors (AAAC). Both types normally have a conductivity calculated on the total area of 53-54% copper (IACS). Since the mid-1970s the cost of producing electric energy has grown rapidly, leading to an increase in the cost of losses. An attempt to find new conductor material producing fewer losses in the network was started in Sweden at the beginning of the 1970s and led in 1979 to the release of a new conductor standard called Al-59, where 59 stands for its conductivity (IACS). HISTORY In 1920 s, within about 20 years of introducing ACSR, France introduced for the first time a new type of electrical conductor made of an alloy of aluminium with magnesium and silicon alloy. Other European countries also developed similar material as their conductor material US also followed the same in 1960 s The electrical conductor made of such alloy had higher strength than EC grade aluminium of equal size with slight loss in conductivity. Due to the increased strength the conductors did not require steel reinforced. AAAC thus made its advent as the most suitable current carrier in transmission and distribution. IEC recommendation number 208 provides an internationally acceptable standard for AAAC (Aluminium Alloy Conductors) Figure 1 Power Conductor Manufacturing Process: Rod Manufacture

3 At the beginning of 70 s AB Electrokopper in Helinsburg developed an alloy with the trade name DUCTALEX. It has a better conductivity than the alloys developed by the France but a slightly lower mechanical strength. Figure 2 Power Conductor Manufacturing Process: Rolling Mill This new conductor alloy was laboratory tested at the Swedish State Power Board with respect to creep, corrosion resistance, self damping and fatigue strength, all tests showed the same or better properties than the ordinary alloy. Figure 3 Power Conductor Manufacturing Process: Wire Drawing Figure 4 Conductor Manufacturing Process: Wire Stranding

4 Tests were made on actual distribution lines starting in As only satisfactory results were obtained the new alloy was installed in 400 KV line. The measurement of sag after five years showed a high degree of agreement with what was predicted. Concurrent with all trials the Swedish Standardization Committee worked out and issued the standards SS for AL-59 wires and SS for AL-59 conductors. APPLICATION Figure 5 AL-59 Alloy OF Conductor AL-59 ALLOY CONDUCTORS Al-59 Alloy Conductors are used in power transmission and distribution lines for a wide voltage range - low voltage to Ultra high Voltage. COMPLIANCE WITH STANDARDS AL-59 alloy conductor complies with the standard SS and AL-59 alloy wires complies with standard SS that specifies the limits for conductivity, strength and creep irrespective of the chemical composition which is not discussed in this standard. Other properties are similar to conventional AAAC conductors. REFERENCE OF USE OF AL-59 ALLOY CONDUCTORS Al-59 Alloy Conductors have been used extensively by Swedish Electricity, Swedish Railways and Norway Electricity. MATERIAL PROPERTIES Size of the Conductor AL-59 conductors range from AL sq-mm (7/2.38 mm) to AL sq-mm (61/4.36 mm). Strength of the wire - For diameter less than 3.5 mm: 250 MPA - For diameter less than 4 mm: 240 MPA - For diameter less than 4.5 mm: 230 MPA Resistivity of the wire - Individual resistivity: nωm - Average resistivity: nωm Creep of the conductor Maximum conductor Creep at 23 o C at 40 % of rated tensile strength and 1500 hours are as follows - 7 strands: 350 mm/km

5 - 19 and 37 strands: 400 mm/km - 61 strands: 450 mm/km Figure 6 Specialized Laboratory for Quality Testing COMPARISION WITH CONVENTIONAL ACSR AND AAAC The comparison is based on the current carrying capacity, strength of the conductor and sag. The comparison for transmission as well as for the distribution is as detailed below: Table 1 - Comparison of various Transmission conductors ACSR MOOSE AAAC MOOSE AL-59 Alloy Typical Factors 54/7/ / /3.52 Reference Specification IS 398 PART II IS 398 PART IV SS Conductor Diameter (mm) Cross Sectional Area (sqmm) Ambient Temperature ( o C) Current Carrying Capacity (Amperes) at 80 o C Current Carrying Capacity (Amperes) at 100 o C *** Sag (meter) At 350 meter span, 80 o C At 350 meter span, 100 o C *** Mass per unit length

6 kg/km Tensile Strength Kgf DC Resistance Ohm/km Note: Current Carrying Capacity calculation based on wind velocity of 1 m/sec and solar absorption coefficient is 0.6 Table 2 - Comparison of 7 strand Distribution conductors ACSR WEASEL AAAC WEASEL AL-59 Alloy Typical Factors 6/1/2.59 7/2.50 7/2.50 Reference Specification IS 398 PART II IS 398 PART IV SS Conductor Diameter (mm) Cross Sectional Area (sqmm) Ambient Temperature ( o C) Current Carrying Capacity (Amperes) at 80 o C Current Carrying Capacity (Amperes) at 100 o C *** Sag (meter) At 350 meter span, 80 o C At 350 meter span, 100 o C *** Mass per unit length kg/km Tensile Strength Kgf DC Resistance Ohm/km

7 CURRENT(Amps) AAAC Weasel 7/2.50 ACSR Weasel 7/2.59 AL 59 7/ TEMPERATURE (Degrees C) Figure 7 - Comparison of AAAC Weasel, ACSR Weasel and AL-59 conductors. CURRENT(Amps) AL-59 61/4.36 AAAC 61/4.26 ACSR BERSIMIS /42/ / TEMPERATURE (Degrees C) Figure 8 - Comparison of AAAC 61/4.26, ACSR Bersimis and AL sq.mm conductors. CURRENT(Amps) AL-59 61/3.52 ACSR 54/3.53+7/3.53 AAAC 61/ TEMPERATURE (Degrees C) Figure 9 - Comparison of AAAC Moose, ACSR Moose and AL-59 conductors.

8 Even though strength of the AL-59 conductor is less compared to conventional AAAC, AL-59 is strung at the same tension as like conventional AAAC. The Important factor for choosing tension from the vibrating point of view is tension divided by the conductor mass. This value is independent of Ultimate tensile strength. ADVANTAGES OVER ACSR AND AAAC - Higher current carrying capacity with lesser cross sectional area. - Higher power transfer capacity with lesser cross sectional area. - Commercial benefits due to lower power loss and higher power transfer capacity. APPROVALS AND AWARDS Sterlite s 774 sq-mm AL-59 sample was type tested (for creep and ultimate tensile strength) and approved by J-Power Systems Corporation, Japan. The result of creep achieved was 436 mm/km which superior to the specified requirement of 450 mm/km. Sterlite has supplied these conductors globally. Sterlite received the Best Product Award from by IEEMA for AL- 59 Alloy Conductors. Figure 10 IEEMA Best Product Award CONCLUSION Power for all by the year 2012 is the vision of the Ministry of Power, Government of India. The Government of India s Transmission Perspective Plan focuses on the creation of a National Grid in a phased manner by adding over 60,000 km of Transmission Network by Such an integrated grid is envisaged to evacuate additional 1, 00,000 MW by the year 2012 and carry 60% of the power generated in the country. The existing inter-regional power transfer capacity is 9,000 MW, which is to be further enhanced to 30,000 MW by 2012 through creation of Transmission Super Highways. On a global level, ABS Research, UK reports that the global market for power transmission conductors was valued at about US$12.3 Billion in 2006 and has a CAGR of 7% from 2004 through ABS Research also anticipates a stable demand growth in the global market from 2007 through 2010 at a CAGR of about 7%. In view of development of new power transmission and distribution grids by global power incumbents, Al-59 Alloy Conductors would have a special significance while designing

9 transmission line networks, as the properties of these conductors enable superior power evacuation while optimizing the cost of the entire grid. REFERENCE STANDARDS Swedish Standards: SS : Aluminium alloy stranded conductors for overhead lines Al 59 Conductors. SS : Aluminium alloy wire for stranded conductors for overhead lines Al 59 Wires.

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