With the increase in voltage level of the distribution network... | Technical Ability MCQ | Examoogle

Technical AbilityElectrical Power Systems

With the increase in voltage level of the distribution network, the weight and corresponding cost of the conductor material will be _________ and _________, respectively, for the same voltage drop.

increased; decreased

decreased; decreased

increased; increased

decreased; increased

Correct Answer

⚙️ TE • Technical Concept & PrincipleTechnical AbilityElectrical Power Systems

Option B

decreased; decreased

Quick Summary:

Increasing the distribution voltage for a fixed power transmission and fixed percentage voltage drop significantly reduces the required current. Consequently, the conductor cross-sectional area decreases, leading to a reduction in both weight and the overall cost of the conductor material.

⚙️TETechnical SolutionConcept & Principle

📜 Standard Reference & Code Clause

IS 1255:1983

💡 Explanation

🔢 Key Formulas

$I = \frac{P}{\sqrt{3} V_L \cos \phi}$ — Current relationship

$\text{Voltage Drop} \propto I \times R \propto \frac{P}{V} \times \frac{\rho l}{A}$ — Voltage drop relation

$A \propto \frac{1}{V^2}$ — Conductor area requirement for constant percentage voltage drop

⚙️ Working Principle

For a given load, the current $I$ is inversely proportional to the voltage $V$ ( $I = \frac{P}{V \cos \phi}$ ). Since the power loss $I^2R$ and voltage drop $IR$ are constrained, increasing the operating voltage $V$ allows for a smaller conductor cross-section $A$ . As conductor weight is directly proportional to volume ( $\text{Area} \times \text{Length}$ ), a smaller $A$ results in lower weight and reduced material cost.

📌 Key Points

▸
Increasing voltage reduces the current required to transmit the same amount of power.
▸
For a constant percentage voltage drop, the required conductor area is inversely proportional to the square of the voltage.
▸
Lower conductor area leads to lower volume, mass, and investment cost for copper/aluminum.
▸
High voltage transmission is limited by insulation costs and corona loss considerations.

✅ Advantages

▸
Reduced conductor material cost
▸
Lower transmission line losses
▸
Increased transmission capacity

❌ Disadvantages / Limitations

▸
Increased cost of insulation
▸
Higher cost of substation equipment (transformers/switchgear)
▸
Increased tower height and clearances

🛠️ Applications / Uses

▸
Primary distribution networks
▸
Long-distance bulk power transmission

📄 Additional Information

▸
This principle is the fundamental basis for the shift from low voltage (e.g., 415V) to high voltage (e.g., 11kV or 33kV) distribution.
▸
Option A is incorrect because the conductor weight does not increase.
▸
Option C is incorrect because both weight and cost decrease with higher voltage.
▸
Option D is incorrect as it describes inverse trends for weight and cost.

📊 Diagram / Illustration

✅

B is correct — With the increase in voltage level, the current decreases, resulting in a reduced conductor cross-section, which in turn decreases both the weight and the cost.

Core Concepts Used

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Transmission Line Economics Voltage Drop Analysis Ohmic Losses

💡 EXAM TIP

Always remember that for a fixed power, increasing voltage by factor $k$ reduces conductor volume by factor $k^2$ for the same percentage power loss.

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