Types of Conductors MCQ Quiz in मल्याळम - Objective Question with Answer for Types of Conductors - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

• Electrical Conductivity is the evaluation of a material's ability to allow the transport of an electric charge.
• Silver is by far the most electrically conductive metal on earth. Since silver has only one valence electron which is free to move around with little resistance, it has great electrical and thermal conductivity.
• After silver, copper is the second most electrically conductive metal. Gold and Aluminium are other metals which are good conductors of electricity.

Aluminium conductor steel-reinforced cable (ACSR) is a type of high-capacity, high-strength stranded conductor typically used in overhead power lines.

The outer strands are high-purity aluminium, chosen for its good conductivity, low weight and low cost.

The center strand is galvanised steel for additional strength to help support the weight of the conductor.

Steel is higher strength than aluminium which allows for increased mechanical tension to be applied on the conductor.

Steel also has lower elastic and inelastic deformation (permanent elongation) due to mechanical loading (e.g. wind and ice) as well as a lower coefficient of thermal expansion under current loading.

• The cross-sectional area of conductor for house wiring is usually expressed in mm².
• Frequency is expressed in Hertz or Hz.
• Length is expressed in mm or cm or meter.

The correct answer is "option 3"

Concept:

• The conductor material is nearly always an aluminium or aluminium alloy (AAC, AAAC or TAL).
• Made into several strands and possibly reinforced with steel strands or composite core.
• Some examples of cables that are often used include ACSR, ACSR/AS and HTLS Cable (ACCC).

Additional Information

• Based on Resistivity or Conductivity :
  • Low resistivity or high conductivity conducting material
  • High resistivity or Low conductivity conducting material
•  Material having low resistivity or high conductivity are very useful in electrical engineering products.
  • These material used as conductors for all kind of windings required in electrical machines, apparatus and devices.
  • These material are also used as conductor in transmission and distribution of electrical energy.
    • Silver
    • Copper
    • Gold
    • Aluminum
• Materials having High resistivity or Low conductivity conducting are very useful for electrical engineering products.
  • These material are used to manufacture the filaments for
    • incandescent lamp, heating elements for electric heaters, space heaters and electric irons
  • Some of materials having High resistivity or Low conductivity are :
    • Tungsten
    • Carbon
    • Nichrome 
    • Manganin

Representation of ACSR Conductor:

A standard conductor is represented as A/S/D for ACSR conductor.

Where,

A is the number of aluminum strands.

S is the number of steel strands.

D is the diameter of each strand.

Example: If the ACSR conductor having 7 steel strands surrounded by 25 aluminum conductors will be specified as 25/7.

Additional Information

Calculation of the number of strands in a stranded conductor:

If there are ‘n’ layers of strands in a stranded conductor.

Number of strands of the conductor = 3n² - 3n + 1

Calculation of overall diameter of a stranded conductor:

If d mm is the diameter of a single strand in the conductor.

The overall diameter of the conductor = (2n - 1) d unit

The correct answer is option 1.

Cost should be always less, in order to help in the purchase of many quantities of the material for more applications. It should also be highly flexible, in order to mold according to people’s choices.

Properties of high-conductive materials

• Highest possible conductivity (ideally zero)
• Least possible temperature coefficient of resistance (ideally zero)
• High melting point
• High mechanical strength
• High ductility, so that can be drawn in the form of wire easily
• High corrosion resistance (free from oxidation)
• Low cost
• Long life or durable
• High flexibility

Advantages of high transmission voltage:

1. Reduces the volume of conductor material

The volume of conductor material required is inversely proportional to the square of transmission voltage and power factor. The greater the transmission voltage, the lesser is the conductor material required.

2. Increases transmission efficiency

Transmission efficiency increases when the line voltage is increased.

3. Decreases percentage line drop

Percentage line drop decreases when the transmission voltage increases.

Important Points

Limitations of high transmission voltage:

1. The increased cost of insulating the conductors

Advantages of Aluminum Conductor:

• Aluminum is considerably less expensive than copper:  
  • This makes it more desirable to use, especially in large projects requiring extensive wiring and when runs span long distances. 
  • The cost of copper in these types of installs can easily outweigh the cost of using aluminum.
• Aluminum is lighter and more flexible than Copper:
  • Its density is 2.68 g/cm³ which means that aluminum is much lighter than copper. 
  • This characteristic may lend to faster installs with wire pulls being much quicker in long runs. 
• Like copper, it can be easily drawn into thin wires.
• Aluminum is soft metal but when alloyed with some other materials like magnesium, silicon, or iron, it acquires higher mechanical strength and can be used for overhead transmission lines.
• Like copper, aluminum also forms an oxide layer over its surface when exposed to the atmosphere and that layer prevents the material from further oxidation and acts as a resistance layer to corrosion.

Disadvantages of Aluminium Conductor:

• The electrical conductivity of aluminum is lower than copper.
• Its resistivity is 2.8 × 10^-8 ohm-m, i.e. about 1.6 times higher than copper.
• As aluminum is a soft material, there is always a possibility of loose contact. Due, to the insulating property of aluminum oxide formed on the surface, it is difficult to solder aluminum wires.
• For the applications like the winding of electrical machines and transformers, it is difficult to substitute aluminum for copper.
• This is because aluminum wires have lower tensile strength than copper.
• Aluminum wires require higher maintenance than copper wiring.
• This includes inspection of the conductors for tight connections and the presence of oxidation. 

Aluminium conductor steel-reinforced cable (ACSR) is a type of high-capacity, high-strength stranded conductor typically used in overhead power lines.

The outer strands are high-purity aluminium, chosen for its good conductivity, low weight and low cost.

The center strand is galvanised steel for additional strength to help support the weight of the conductor and provide additional mechanical strength.

Steel has higher strength than aluminium which allows for increased mechanical tension to be applied on the conductor.

Steel also has lower elastic and inelastic deformation (permanent elongation) due to mechanical loading (e.g. wind and ice) as well as a lower coefficient of thermal expansion under current loading.

Skin effect:

• Skin effect is the tendency of an alternating electric current (AC) to become distributed within a conductor such that the current density is largest near the surface of the conductor and decreases exponentially with greater depths in the conductor. 
• The electric current flows mainly at the "skin" of the conductor, between the outer surface and a level called the skin depth.
• Skin depth depends on the frequency of the alternating current; as frequency increases, current flow moves to the surface, resulting in less skin depth.
• Skin effect reduces the effective cross-section of the conductor and thus increases its effective resistance.
• Skin effect is caused by opposing eddy currents induced by the changing magnetic field resulting from the alternating current. 

Corona effect:

• A corona discharge is an electrical discharge caused by the ionization of a fluid such as air surrounding a conductor carrying a high voltage.
• It represents a local region where the air (or other fluid) has undergone an electrical breakdown and become conductive, allowing charge to continuously leak off the conductor into the air.
• A corona discharge occurs at locations where the strength of the electric field (potential gradient) around a conductor exceeds the dielectric strength of the air.
• It is often seen as a bluish glow in the air adjacent to pointed metal conductors carrying high voltages and emits light by the same mechanism as a gas discharge lamp.

ACSR conductor is utilized for reducing the Skin effect as well as the Corona effect. This is due to:

In ACSR (Aluminium core steel reinforced) conductors, the core is made up of aluminum while the outer layer is of steel. The mixture of aluminum increases the cross-sectional area of the conductors, thus decreasing skin and corona effect.