The transformer which is more feasible to use in the distribution ends should be

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Examoogle · Accepted Answer

delta-star

Explanation: The Delta-Star ($Delta-Y$) configuration is the industry standard for distribution transformers. It enables a 3-phase, 4-wire system that provides both 3-phase power for industrial loads and single-phase power for domestic lighting and appliances.

Working Principle: In a $\Delta-Y$ transformer, the primary is delta-connected to handle high voltage without requiring a neutral, while the secondary is star-connected. The star connection provides a neutral terminal, allowing the use of $V_{phase} = \frac{V_{line}}{\sqrt{3}}$ for domestic loads while maintaining $V_{line}$ for power loads. The neutral point is grounded, which helps in balancing unbalanced loads and provides path for fault currents.

Key Formulas: $V_{line} = \sqrt{3} V_{phase}$ (Star secondary); $I_{line} = I_{phase}$ (Star secondary)

Key Points: Provides a stable neutral point for single-phase distribution.; Eliminates third harmonic currents by circulating them within the delta winding.; Efficiently handles unbalanced loads typical in residential distribution.; Grounding the neutral provides safety and protects against overvoltages.

Advantages: Availability of two voltages: phase and line voltage.; Superior handling of unbalanced phase currents.; Harmonic suppression due to delta primary.

Disadvantages: Neutral point can shift if the secondary load is severely unbalanced and not properly managed.; Requires careful insulation of the neutral terminal.

Applications: Residential electricity distribution grids.; Commercial building power supply units.

Additional Info: The neutral wire allows for $230V$ (phase-to-neutral) and $400V$ (line-to-line) in standard 3-phase Indian domestic systems.. Option D (Delta-Delta) is generally used for high-voltage transmission where no neutral is needed, making it unsuitable for distribution.

Answer: B is correct — The Delta-Star transformer is preferred for distribution because it provides a neutral terminal necessary for domestic loads while effectively managing harmonic distortion.

Exam Tip: Remember: Star connection on the secondary side is essential whenever you need a neutral wire, which is mandatory for most domestic low-voltage distribution.

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