Correct Answer

⚙️ TE • Technical Concept & PrincipleElectricalPower System

Option A

Full load

Quick Summary:

Power transformers are designed to have maximum efficiency at or near full load because they operate continuously under stable load conditions in transmission and distribution networks. This design philosophy minimizes copper losses and heat dissipation during peak load operation.

⚙️TETechnical SolutionConcept & Principle

💡 Explanation

🔢 Key Formulas

$\eta = \frac{V_2 I_2 \cos \phi_2}{V_2 I_2 \cos \phi_2 + P_{iron} + I_2^2 R_{eq}}$ — General efficiency formula for a transformer

$P_{iron} = I_{FL}^2 R_{eq}$ — Condition for maximum efficiency at full load (where $I_{FL}$ is full-load current)

⚙️ Working Principle

Transformer efficiency ( $\eta$ ) is defined by the ratio of output power to input power. Efficiency reaches a maximum when variable copper losses ( $I^2R$ ) equal constant iron (core) losses. By designing the transformer such that these losses are equal at full load, the efficiency curve peaks at the operating point where the grid expects the highest throughput.

📌 Key Points

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Power transformers are base-load devices, unlike distribution transformers.
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Distribution transformers are designed for maximum efficiency at 50-70% load due to varying load cycles.
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Maximum efficiency occurs when variable losses equal constant losses.
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Core losses are constant for a given voltage and frequency.

✅ Advantages

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Optimized energy transfer at nominal capacity
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Reduced thermal stress during high-load periods

❌ Disadvantages / Limitations

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Lower efficiency at light loads
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Not suitable for fluctuating load profiles where average load is low

🛠️ Applications / Uses

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High-voltage transmission substations
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Grid interconnect transformers

📄 Additional Information

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The constant loss (Iron loss) includes hysteresis and eddy current losses.
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Option B (50% load) is typically the design target for 'Distribution Transformers' to maximize 'All-Day Efficiency'.

📊 Diagram / Illustration

✅

A is correct — Power transformers are intentionally optimized to reach maximum efficiency at full load to suit steady-state industrial and grid operations.

Core Concepts Used

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Transformer Efficiency Loss Analysis Design Optimization

💡 EXAM TIP

Always differentiate between 'Power Transformers' (max efficiency at full load) and 'Distribution Transformers' (max efficiency at partial load) in competitive exams.

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