good conductor should have the following properties:

high electrical conductivity
high tensile strength in order to withstand mechanical stresses
relatively lower cost without compromising much of other properties
lower weight per unit volume

Conductor Materials-

Copper was the preferred material for overhead conductors in earlier days, but, aluminium has replaced copper because of the much lower cost and lighter weight of the aluminium conductor compared with a copper conductor of the same resistance. Following are some materials that are considered to be good conductors.

Copper: Copper has a high conductivity and greater tensile strength. So, copper in hard drawn stranded form is a great option for overhead lines. However, due to its higher cost and non-availability, copper is rarely used for overhead power lines.

Aluminium: Aluminium has about 60% of the conductivity of copper; that means, for the same resistance, the diameter of an aluminium conductor is about 1.26 times than that of a copper conductor. However, an aluminium conductor has almost half the weight of an equivalent copper conductor. Also, tensile strength of aluminium is less than that of copper.

Cadmium-copper: Cadmium-copper alloys contain approximately 98 to 99% of copper and up to 1.5% of cadmium. Addition of about 1% of cadmium to copper increases the tensile strength by up to 50% and the conductivity is reduced only by about 15%. Therefore, cadmium-copper conductors can be useful for exceptionally long spans. However, due to high cost of cadmium, such conductors may be uneconomical in many cases.

Other materials: There are many other metals and alloys that conduct electricity. Silver is more conductive than copper, but due to its high cost, it is not practical in most of the cases.
Galvanised steel may also be used as a conductor. Although steel has very high tensile strength, steel conductors are not suitable for transmitting power efficiently due to the poor conductivity and high resistance of steel. High strength alloys such as phosphor-bronze may also be used sometimes at extreme conditions.

Types of Conductors-

AAC : All Aluminium Conductor
AAAC : All Aluminium Alloy Conductor
ACSR : Aluminium Conductor, Steel Reinforced
ACAR : Aluminium Conductor, Alloy Reinforced

1-AAC – All Aluminium Conductor-

AAC stands for All Aluminium Conductor. It is made up of stranded aluminium wires without any steel core.

Construction:

Composed entirely of aluminium strands (usually hard-drawn, 1350-H19 grade).
Strands are twisted (stranded) to form a single conductor.
No steel reinforcement is used.

Properties:

High conductivity – Aluminium offers about 61% of copper’s conductivity but is much lighter.
Low tensile strength – Since there is no steel core, it cannot withstand very high mechanical stress.
Lightweight and corrosion resistant.

Applications:

Used in urban and short-span distribution lines where mechanical strength requirement is low.
Suitable for low and medium voltage lines in cities and towns.

Advantages:

High current-carrying capacity.
Low cost compared to copper.
Light in weight – easy to install and handle.
Good corrosion resistance.

Disadvantages:

Low tensile strength – unsuitable for long spans.
Higher sag compared to ACSR or AAAC.
Not suitable for very long-distance transmission lines.

In short:

AAC = All Aluminium Conductor → High conductivity, light weight, but low strength → used for short-span urban distribution lines.

2-AAAC – All Aluminium Alloy Conductor-

Key Points:

Composition: Made from aluminium-magnesium-silicon (Al-Mg-Si) alloy strands.
No steel core – all strands are of aluminium alloy.
Stranded construction for flexibility and strength.

Properties:

Higher tensile strength than AAC.
Better corrosion resistance than ACSR (because no steel).
Slightly lower conductivity than AAC.
Lighter weight and less sag compared to AAC.

Applications:

Used for medium and long-span overhead lines.
Suitable for coastal regions (excellent corrosion resistance).
Common in rural transmission and distribution systems.

Advantages:

High strength-to-weight ratio.
Better corrosion resistance.
Lower sag and longer span possible.
Maintenance-free and durable.

Disadvantages:

More expensive than AAC.
Conductivity slightly less than AAC.

In short:

AAAC = All Aluminium Alloy Conductor → Stronger and more corrosion resistant than AAC → used for medium/long spans and coastal lines.

3-ACSR : Aluminium Conductor, Steel Reinforced

Key Points:

Construction:
Outer layers – Stranded aluminium wires (for conductivity)
Core – Galvanized steel wires (for strength)

Properties:

High tensile strength due to steel core.
Good conductivity from aluminium strands.
Higher mechanical strength → suitable for long spans.
More sag-resistant than AAC and AAAC.

Applications:

Used in long-span overhead transmission lines.
Ideal for river crossings, tall towers, and high-voltage lines.

Advantages:

Very high mechanical strength.
Can cover long spans with less sag.
Economical and durable.
Good current-carrying capacity.

Disadvantages:

Corrosion may occur between aluminium and steel.
Heavier than AAC or AAAC.
Slightly less conductivity due to steel core.

In short:

ACSR = Aluminium + Steel core → High strength, good conductivity → used for long-span transmission lines.

4-ACAR – Aluminium Conductor, Alloy Reinforced

Key Points:

Construction:
- Outer strands – Aluminium (for conductivity)
- Core – Aluminium alloy (for strength)
No steel core is used.

Properties:

High conductivity (almost equal to AAC).
Better tensile strength due to alloy core.
Lighter weight than ACSR.
Good corrosion resistance.

Applications:

Used in overhead transmission and distribution lines.
Suitable for medium and long spans.
Preferred in coastal or corrosive environments.

Advantages:

High strength-to-weight ratio.
Excellent corrosion resistance.
Less sag than AAC.
Better conductivity than ACSR.

Disadvantages:

More expensive than AAC and AAAC.
Requires careful handling during installation.

In short:

ACAR = Aluminium + Alloy core → High strength, high conductivity, corrosion resistant → used for medium/long-span overhead lines.

MCQ-

Q. Which conductor has the best conductivity among all?

A. AAC
B. ACSR
C. AAAC
D. ACAR

✅ Answer: A. AAC

Explanation:

AAC (All Aluminium Conductor) is made of pure aluminium strands, which provide maximum electrical conductivity, but it has low strength.

Q. Which conductor has the best corrosion resistance?

A. ACSR
B. AAC
C. AAAC
D. ACAR

✅ Answer: C. AAAC

Explanation:

AAAC (All Aluminium Alloy Conductor) is made from aluminium-magnesium-silicon alloy, which gives it excellent corrosion resistance, especially in coastal regions.

Q. Which conductor is most economical for short-span distribution lines in urban areas?

A. AAC
B. AAAC
C. ACSR
D. ACAR

✅ Answer: A. AAC

Explanation:

AAC is low-cost, lightweight, and provides high conductivity, making it suitable for short-span distribution lines where mechanical strength is not critical.

**Q. Which conductor type does not contain any steel core?**

A. AAC
B. AAAC
C. ACAR
D. All of the above

✅ Answer: D. All of the above

Explanation:
Only ACSR contains a steel core.

AAC, AAAC, and ACAR are made entirely of aluminium or aluminium alloys.

Q. Which conductor offers the best balance between strength and conductivity?

A. AAC
B. AAAC
C. ACAR
D. ACSR

✅ Answer: C. ACAR

Explanation:

ACAR (Aluminium Conductor, Alloy Reinforced) provides high strength (from alloy core) and high conductivity (from aluminium strands) — offering the best balance between both.

Q. For which type of lines is AAC generally preferred?

A. Long-span transmission lines
B. Short-span distribution lines
C. River crossing lines
D. EHV lines

✅ Answer: B. Short-span distribution lines

Explanation:

AAC is used in urban distribution systems with short spans, where mechanical strength is not critical.

Q. Which conductor is least suitable for river crossings or hilly terrains?

A. AAC
B. ACSR
C. AAAC
D. ACAR

✅ Answer: A. AAC

Explanation:

AAC cannot handle high mechanical stress, so it’s unsuitable for long spans, river crossings, or hilly regions. ACSR is preferred in such cases.