The maximum power can be achieved in a transmission line by

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Option D: Both 1 and 2

Explanation & Concepts:
The maximum power transfer capability ($P_{max}$) of a transmission line is governed by the steady-state stability limit formula. It is directly proportional to the square of the voltage and inversely proportional to the transfer reactance, meaning that increasing voltage or decreasing reactance will increase the power transfer limit.

Working Principle: The power flow through a lossless transmission line is given by $P = \frac{V_s V_r}{X} \sin\delta$. By increasing the terminal voltage ($V$), the numerator increases quadratically, while reducing the line reactance ($X$) decreases the denominator, thereby maximizing the power transfer capability. Reactance can be reduced using series compensation (capacitors).

Key Formulas: $P_{max} = \frac{|V_s||V_r|}{X}$ — Maximum steady-state power transfer; $X = \omega L = 2\pi f L$ — Definition of transfer reactance

Key Points: Increasing voltage ($V$) is the most effective way to increase power capacity as $P \propto V^2$.; Series capacitive compensation is commonly used to reduce the effective line reactance ($X$).; Transmission lines are usually operated below the stability limit to maintain a safety margin.; Higher voltage levels also reduce transmission losses ($I^2R$ losses) for a fixed power delivery.

Advantages: Increased transient stability limits; Enhanced steady-state power transfer capability; Improved voltage regulation

Disadvantages: High cost of series compensation equipment; Complexity in protection due to sub-synchronous resonance (SSR); Insulation costs increase significantly with higher voltage levels

Applications: EHV (Extra High Voltage) transmission networks; Long distance power transmission corridors; Inter-regional power grid interconnection

Additional Info: Reducing reactance is typically achieved by adding series capacitors in the line.. The option 'Both 1 and 2' is technically correct as both methods increase the power transmission capacity of a line.. Increasing voltage levels is a standard practice for long-distance bulk power transmission (e.g., 400kV, 765kV).

Answer: D is correct — The maximum power transfer capability of a transmission line is enhanced by increasing the operating voltage level and reducing the total transfer reactance of the system.

Exam Tip: Always remember that stability limits are distinct from thermal limits; power transfer is limited by angle stability for long lines and thermal capacity for short lines.

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Option A: Reducing system

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Option B: transfer Reactance

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Option C: Increasing the Voltage level

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