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Different types of conductors
An electric conductor is a material that allows the flow of electric current to pass through. The electric conductivity will depend on the actual material of the conductor. If the material allows high mobility of free electrons this will make them great conductors of electricity.
Metals are some of the best conductors because there are spaces between their atoms which allows electrons to move. Of all the materials, the top three are silver, copper and aluminum.
Silver is known to be the best conductor of electricity but it is not widely used for economic reasons. It is only used for special equipment like satellites.
Copper, though not as high as silver, also has high conductivity. In fact, the official point of reference for conductors is the International Annealed Copper Standard (IACS). The most common grade of copper is ETP (electrolytic-tough pitch) copper. This is the metal used in wires, cables, busbars and motor windings. The conductivity of this copper is 101% IACS.
Aluminum only has 61% of the conductivity of copper but it is the preferred material for building wires because of the low cost. Aluminum has higher conductivity when compared to copper by weight but it requires a compatible connector to avoid the formation of resistive oxide within connections. When used in building wiring, it slowly deforms under load and that leads to the loosening of device connections. When it has the right connector and is installed properly, it works well for low voltage distribution (e.g. service drops, buried cables).
There are certain nonmetals that can also be conductors of energy like water, graphite, concrete or glass. These are less conductive compared to metals but under the right circumstances, they can become effective conductors.
Pure water (H2O) is not a conductor but when it becomes dirty (or mixed with other elements like salt), electricity can flow through it. Most of the water on Earth is actually “dirty water” because it has other compounds added to the pure water. Other liquids, oil or organic compounds, cannot conduct energy because of their composition.
Glass is usually an insulator but when it is heated, it can become a conductor. This is in contrast with metals that become better conductors when cooled but less when heated.
AAC, AAAC, ACSR Aluminium Conductors
AAC, AAAC, ACSR form part of the family of Overhead Conductors, Transmission Conductors and Power Distribution Conductors. These cables are formally known as All Aluminium Conductor (AAC), All Aluminium Alloy Conductor (AAAC) and Aluminium Conductor Steel Reinforced (ACSR). These overhead aluminium conductors are used as power transmission and distribution lines. All aluminium conductors are made up of one or more strands of aluminium wire depending on the specific application.
Our range of aluminium overhead conductor cables includes:
AAC–ASTM-B All Aluminium Conductor
AAC are a refined Aluminium stranded conductor with a minimum metal purity of 99.7%. It is principally used in urban areas where spacing is short and the supports are close. It can be used in coastal regions owing to its high degree of corrosion resistance and is also used extensively within the Railway and Metro industries.
AAAC-ASTM-B All Aluminium Alloy Conductor
AAAC are used as a bare conductor cable on aerial circuits that require a larger mechanical resistance than the AAC and a better corrosion resistance than the ACSR. The sag characteristics and the strength-to-weight ratio of the AAAC conductor cable is better than both AAC and ACSR.
ACSR-ASTM-B Aluminium Conductor Steel Reinforced
ACSR are available in a range of steel contents ranging from 6% to 40% for additional strength. The higher strength ACSR conductors are commonly used for river crossings, overhead earth wires, and installations involving extra-long spans. The ACSR conductor can, against any given resistance, be manufactured to different tensile strengths, so a high tensile strength combined with its lightweight properties means it can cover longer distances with fewer supports. Due to the greater diameter of the ACSR conductor, a much higher corona limit can be obtained which is advantageous on high and extra high voltage overhead lines.
Why use aluminum alloy conductors?
In order to understand where aluminum is a good choice as a conductor, we need to look at the properties of aluminum, copper, and other conductive metals and alloys. While aluminum has only 60% of the conductivity of copper, aluminum is the smarter choice for many electrical conductor applications when density and cost consideration are taken into account.
The optimal conductor material depends on the specific applications such as microelectronics, PCBs, electronic connectors, electrical power cables, electrical power connectors or lugs, electric vehicles and circuit breaker electrical contacts. Copper has replaced aluminum in microelectronics conductors because of the continued trend toward miniaturization. As the conductive interconnects shrunk in size, copper on IC chips became a better choice because copper’s higher conductivity reduced resistance and joule heating. Future IC chips use photonics interconnects because even copper conductors would generate too much heat. Copper tends to be the material of choice on PCBs to reduce heat as circuits become denser. In certain conductor applications, reducing connector or interconnect size and heat generation are a factor. A large fraction (80% in some cases) of the resistance in electrical and electronic devices arises from the contact resistance and not the bulk resistance in the conductors. Contact resistance is a function of the contact material conductivity, contact hardness, contact pressure, contact sliding and environmental factors such as oxidation and corrosion. Silver and gold have excellent oxidation and corrosion resistance, which is a requirement on certain conductors for electronic and microelectronic connectors and contacts. While we do not typically use solid gold conductors, many microelectronic connector contacts are plated with gold, which maintains uniform contact resistance over time. Electrical power contacts in circuit breakers and contactors utilize silver or a silver composite, which has resistance to wear, oxidation, arcing and welding. While silver has the highest conductivity (108% IACS [International Anode Copper Standard]), silver is a poor choice for interconnects or conductive paths on circuit boards due the migration of the metal. Silver and gold are very expensive, so these materials are used sparingly and engineers are constantly looking for ways to minimize their use by increasing performance or by finding lower cost alternatives.
We can adjust for the lower conductivity of aluminum by increasing the radius, diameter or wire gauge size. The increase in volume will not increase the weight because aluminum is so much lower in density compared to copper. Cost is another advantage of aluminum alloys conductors over copper. The cost of aluminum is about one third the cost of copper. At the time of publication, copper is U.S. $2.57/lb and U.S. $0.88/lb. If a copper conductor has a volume of 1 cubic inch, then an aluminum conductor with equivalent resistance will have a volume of 1.67 cubic inches. The aluminum conductor will have half the weight of the copper conductor. The copper conductor would have $0.83 of material cost, while the equivalent aluminum conductor would cost $0.14.
High tensile steel cores for overhead power lines
Protect your investment. Rely on steel.
Using a steel reinforcement core is the most cost-effective, long-term choice for your conductors. Though initial costs might be lower if you choose not to reinforce your conductor with a steel core, you increase the risk of premature failure and related costs, annihilating any initial cost-savings.
The next generation steel cores for improved grid performance
Bekaert offers three types of high tensile steel cores: Ultra, Mega and Giga. The wires in each strand feature outstanding tensile strength, allowing the strand to move with the environment without creating excessive sag. The combination of these features results in conductors with a much higher capacity and which allow a more efficient distribution of energy.
Recently the International Electrotechnical Commission released the new IEC 63248 Norm which covers also high tensile strength Mega and Giga steel cores ( S7A, S8A) for overhead power lines. The advantages of the high tensile steel cores are described in CIGRE paper which you can find below in downloads.
Steel core solutions for conductors in special conditions
Adding a steel core increases the breaking strength of an aluminum conductor by a factor of 2 to 3. Conductors with a steel core are more resistant to thermal sag and sag caused by various load conditions such as heavy winds and ice loading. Moreover, the cores reduce horizontal blowout distances and, as a consequence, the probability of horizontal clearance violations.
For Transmission of power to the end user there is huge and complex network of conductors between the generating stations and the consumers.
These networks together form a complete Transmission and Distribution system but the function of both the systems is marginally different from each other. The main function of Transmission system is to deliver bulk power from generating stations to the load centers and large industrial consumers who are residing beyond the economical service range of regular primary distribution lines. The power is further stepped down in substations where it is distributed to domestic and commercial users. The power can be transmitted either employing overhead system or underground system.
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