Rating of Overhead Transmission Line vs Surge Impedance Loading:

• The rating of an overhead transmission line is slightly more than the surge impedance loading due to several factors.
• Overhead transmission lines are designed to carry large amounts of power over long distances, which requires them to have a higher rating than the surge impedance loading to accommodate the power flow.
• The rating of an overhead transmission line takes into account factors such as conductor size, insulation, and temperature ratings, which all contribute to its ability to handle higher power levels.

Rating of Cables vs SIL:

• The rating of cables is typically less than the surge impedance loading (SIL) due to their design and construction.
• Cables are generally used for shorter distances and lower power levels compared to overhead transmission lines, so they do not need to have as high of a rating as the SIL.
• The rating of cables is determined by factors such as conductor size, insulation material, and temperature ratings, which all play a role in determining the maximum power that the cable can safely carry.
• While the SIL is a theoretical measure of the maximum power that a transmission line can carry without causing a voltage drop, the rating of cables is based on practical considerations such as heat dissipation and insulation breakdown.

In conclusion, the rating of overhead transmission lines is slightly more than the surge impedance loading due to their higher power carrying capacity and design considerations, while the rating of cables is less than the SIL due to their shorter distances and lower power levels.