The main consideration for higher and higher operating voltage of transmission is to

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Option C: Increase power transfer capability

Explanation & Concepts:
The primary objective of increasing transmission voltage is to enhance the power transfer capability of the line, which follows the relationship $P \approx \frac{V^2}{Z} \sin \delta$. Higher operating voltages allow the system to transmit more power over longer distances while minimizing the volume of conductor material required.

Working Principle: According to the power transfer formula $P = \frac{V_S V_R}{X} \sin \delta$, power flow is directly proportional to the square of the voltage. By raising the voltage ($V$), the surge impedance loading (SIL) capacity increases, allowing more power to be delivered through the same line impedance ($X$) without violating stability constraints.

Key Formulas: $P = \frac{V_S V_R}{X} \sin \delta$ — Power transfer equation for a lossless line; $SIL = \frac{V^2}{Z_0}$ — Surge Impedance Loading representing power capability

Key Points: Power transfer capacity increases with the square of the voltage.; Higher voltage reduces current for a given power level, reducing $I^2R$ losses.; Increased voltage allows for smaller conductor cross-sections, saving capital cost.; Corona loss and insulation requirements increase significantly at higher voltages.

Advantages: Increased power transmission capacity; Reduced percentage voltage drop; Improved transmission efficiency; Reduced conductor volume

Disadvantages: Increased tower height and span requirements; Higher cost of insulation and switchgear; Increased corona loss and radio interference

Applications: EHV (Extra High Voltage) AC transmission (400kV, 765kV); UHV (Ultra High Voltage) DC transmission

Additional Info: The limitation for higher voltage is usually determined by the economical balance between transmission cost (insulation, towers) and the cost of power losses.. Option B (Reduce power losses) is a significant byproduct but not the *main* design driver for higher voltages, as current decreases for the same power, but insulation costs climb sharply.

Answer: C is correct — Increasing the operating voltage directly scales the power transfer capability of a transmission line by the square of the voltage factor.

Exam Tip: Always remember: If a question asks for the 'main consideration', it refers to the primary physical capability (Power Transfer), whereas secondary effects like 'efficiency' or 'loss reduction' are consequential benefits.

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Option A: Increase efficiency of transmission

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Option B: Reduce power losses

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Option D: and (b)

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