Aluminum was first introduced as an electrical conductor in the late 19th century. Initially, cable were more expensive than copper cable due to the higher cost of producing pure aluminum. However, as technology advanced, the production of aluminum became more efficient and cost-effective. By the early 20th century, aluminum emerged as a viable and economical alternative to copper for electrical power transmission and distribution applications.
Physical Properties of Aluminum
Aluminum has a silvery-gray metallic appearance and is the third most abundant element found in the earth’s crust. It is lightweight with a density of about one-third that of copper. Aluminum Cable is highly ductile and malleable which allows it to be drawn easily into wires. While copper is a better electrical conductor, aluminum conducts electricity reasonably well. The electrical conductivity of aluminum is about 60% of copper.
Benefits of Using Aluminum Cable
Some key benefits of using aluminum cable include:
Cost Savings: Aluminum is more plentiful than copper. It is cheaper to produce which makes aluminum cable more affordable than copper cable of the same capacity. This lower material cost translates to significant savings for utilities and installers.
Weight Reduction: Compared to copper, aluminum weighs about one-third less. This makes aluminum cable lighter and easier to handle during installation and maintenance activities. Lighter weight cable are also advantageous for overhead installations where weight is an important design consideration.
High Ampacity: Though aluminum has lower conductivity than copper, its lighter weight allows for larger cable cross-sections using the same diameter. This higher ampacity allows aluminum to carry more current compared to a copper conductor of identical size. This is beneficial since cable ampacity ultimately determines circuit capacity.
Corrosion Resistance: Pure aluminum resists corrosion reasonably well in most environments. When properly selected and installed, aluminum cable offer long-term corrosion resistance comparable to that of copper in normal outdoor conditions. Their corrosion resistance has been proven through decades of extensive use worldwide.
Design and Installation Considerations for Aluminum Cable
While aluminum offers technical and economic advantages, some special considerations need to be taken into account in the design and installation of aluminum cable:
Termination Issues: Connecting aluminum to other metals requires special fittings, connectors and termination techniques to prevent galvanic corrosion at the interface. Compression tools, contact grease and high-quality aluminum-to-copper transition terminals help establish reliable joints. Proper torque is critical for long-term performance.
Skin Effect: At higher frequencies, current tends to flow near the surface of conductors. This skin effect causes increased resistance in aluminum compared to copper. So, aluminum is generally limited to 60Hz power transmission applications unless special larger conductor designs are used.
Cable Ampacity Derating: Due to its greater sensitivity to elevated temperatures, the ampacity of aluminum must be derated compared to tables for copper. NEC requires specific derating factors be applied based on ambient temperature and installation methods.
Compatible Materials: Aluminum may not be compatible chemically with some plastic insulating jackets, lug/connector materials over long periods. It requires insulation, lugs and connectors formulated for use specifically with aluminum.
Proper Size: Due to its lower conductivity, aluminum cable size must be increased to carry the same current as a copper conductor. Over-sizing avoids overheating concerns.
With appropriate cable selection, splicing techniques and installation practices that address these unique characteristics, aluminum performs reliably for outdoor distribution, service entrance and other overhead/underground power applications.
Applications of Aluminum Cable
Here are some common applications where aluminum cable is widely used:
Utility Distribution Lines: Aluminum dominates in overhead/underground distribution lines ranging 4kV to 35kV. Its physical attributes are well-suited and it offers clear economic benefits for utilities.
Service Entrance Cable: Most service entrance cable use aluminum rather than copper due to cost advantages. These include cable between the utility pole and residence main panel.
Substation Busbars: Distribution substations commonly employ aluminum for internal busbar systems linking transformers and feeder breakers.
Street Lighting Circuits: Municipal street lights are usually connected through overhead circuits made of aluminum secondary cable.
Renewable Energy: Aluminum cabling plays an important role in connecting large solar/wind farms to the grid. It provides a lower-cost solution for these applications.
MV and HV Cable: Higher voltage cable (up to 138kV) is produced using aluminum conductor composite core (ACCC) or stranded compressed aluminum designs.
Mining and Oil/Gas Applications: Tough conditions demand durable cable like aluminum which stands up well in these industrial/harsh environments.
By accounting for its technical nuances, aluminum has emerged as a preferred cable choice in many power transmission and distribution systems globally due to attractive electrical performance and significantly lower deployment costs compared to copper.
With continuous material innovations and design improvements addressing aluminum’s unique properties, this durable and economical metal has established an enduring role as an electrical conductor. After more than a century of research and field experience, aluminum cable dominates many overhead and underground distribution systems worldwide. It will likely remain the workhorse of electrical grids and industrial applications for decades to come. Careful consideration of aluminum’s attributes is essential for optimized, long-lasting system designs and installations. When properly applied with suitable termination techniques and insulation coordination, aluminum delivers reliable electrical service in a cost-effective manner.
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