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NEW RANGE OF SPECIAL ALLOY CONDUCTORS: ADVANTAGES OVER CONVENTIONAL ACSR AND AAAC CONDUCTORS

Mr G. L. Prasad

Sterlite Technologies Limited, Pune

INTRODUCTION

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

At the beginning of 70’s AB Electrokopper in Helinsburg developed an alloy with the trade name DUCTALEX. It has a better conductivity than ordinary alloys used for conductors but a slightly lower mechanical strength.

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, in some aspects better than the ordinary alloys need. Tests were made on actual distribution lines starting in 1975.

As only satisfactory results were obtained, the new alloy conductors were installed in 400 KV lines. 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 SS4240813 for Al 59 wires and SS4240814 for Al 59 Alloy Conductors.

APPLICATION OF 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 SS4240814 and Al-59 alloy wires comply with standard SS4240813. These standards specify the limits for conductivity, strength and creep irrespective of the chemical composition. Other properties are similar to conventional AAAC conductors.

Figure 1 (Original photo attached)

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MATERIAL PROPERTIES

Size of the Conductor

Al-59 conductors ranging from Al-59 31Sq.mm (7/2.38 mm) to Al-59 910 Sq.mm (61/4.36mm)

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 – 29.30 nΩm

Average resistivity -29.08 nΩm

Creep of the conductor

Maximum conductor Creep at 23o Celcius, 40 % of rated tensile strength and 1500 Hours are as follows:

7 strands: 350 mm/Km

19 and 37 strands: 400 mm/Km

61 strands: 450 mm/Km

COMPARISION WITH CONVENTIONAL ACSR AND AAAC

For comparison based on the current carrying capacity, Power transfer capacity, Strength of the conductor and Sag calculated after 10 years from the creep value, please refer Table 1.

Table 1

PROPERTIES ACSR MOOSE

AAAC MOOSE 6201 Alloy

Al59 593 Sq.mm

Cross sectional Area Sq.mm

597 604 593

Current carrying capacity - Amperes

Operating Temp 65Deg.Cel

838

Operating Temp 85 Deg.Cel

1233 1307

Power Transfer Capacity - Mwh

Twin Bundle 901 1326 1405

Quad Bundle 1802 2652 2811

Sag after 10 Years - Mtrs

Sag 10.33 9.3 9.83

Strength of the conductor - MPA

UTS 270.02 264.57 240.86

Mass of the conductor – Kg/Km

Mass 2004 1666 1640

Note: CCC calculation based on wind velocity of 1 m/sec and solar absorption coefficient is 0.6

Even though strength of the Al59 conductor is less compared to conventional AAAC. But 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

Lower Sag

Commercial benefits due to lower power loss and higher power transfer capacity

REFERENCE OF USE OF AL-59 ALLOY CONDUCTORS

Al-59 Alloy Conductors have been used extensively by Swedish Electricity, Swedish Railways and Norway Electricity.

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 2012.

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

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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 2006. 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 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:

SS4240814: Aluminium alloy stranded conductors for overhead lines – Al 59 Conductors.

SS4240813: Aluminium alloy wire for stranded conductors for overhead lines – Al 59 Wires.