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What is the value of current density permitted for transmission line?
150 A/cm┬▓
100 A/cm┬▓
50 A/cm┬▓
Cu-150 A/cm┬▓ & Al-100 A/cm┬▓
Cu-150 A/cm┬▓ & Al-100 A/cm┬▓
Current density in transmission lines is defined as the current carrying capacity per unit cross-sectional area of the conductor. The permitted values are specifically determined by the material properties, thermal stability, and the voltage drop constraints, with copper typically being allowed a higher density than aluminum due to its superior conductivity.
Current density in transmission lines is defined as the current carrying capacity per unit cross-sectional area of the conductor. The permitted values are specifically determined by the material properties, thermal stability, and the voltage drop constraints, with copper typically being allowed a higher density than aluminum due to its superior conductivity.
J=AIтАЛ тАФ Formula for current density where I is current in amperes and A is cross-sectional area in cm2
PlossтАЛ=I2R тАФ Ohmic power loss constrained by conductor size
The current density J is calculated as J=AIтАЛ, where I is the current and A is the cross-sectional area. In power engineering, this limit is constrained by the I2R heat dissipation, which determines the maximum permissible temperature rise of the conductor. Exceeding these values leads to excessive heating, potential loss of mechanical tensile strength (annealing), and increased transmission losses.
Current density limits prevent overheating of conductors.
Copper allows a higher density (150A/cm2) compared to Aluminum (100A/cm2).
Thermal limit is the primary factor for overhead transmission design.
Higher current densities result in higher voltage drops per unit length.
Maintains mechanical integrity of conductors.
Ensures operation within design thermal ratings.
Prevents premature insulation failure in cables.
Limits the maximum power transfer capacity of the line.
Requires larger cross-sections for high current loads, increasing infrastructure cost.
Overhead line design for rural and urban electrification.
Sizing of underground power cables.
Switchgear and busbar dimensioning.
| Feature | Copper (Cu) | Aluminum (Al) |
|---|---|---|
Material | 150 A/cm┬▓ | 100 A/cm┬▓ |
These values are engineering thumb rules used for initial estimation in power systems.
Actual design values may vary based on specific cooling conditions (e.g., buried cables vs. overhead air cooling) and material purity.
D is correct тАФ The permitted current density is generally accepted as 150A/cm2 for copper and 100A/cm2 for aluminum in transmission systems.
In competitive exams, always remember that Copper is denser and more conductive than Aluminum, allowing it to support a higher current density under similar thermal constraints.