Why do electric utility companies distribute alternating current (AC) rather than direct current (DC) for most public power grids?

Introduction:
The choice of AC for public grids dates to the 'war of currents' and persists for practical engineering reasons. Understanding why AC dominates clarifies design decisions in generation, transmission, and distribution.

Given Data / Assumptions:

• Focus on large-scale transmission and distribution.
• Historical and technical context: transformers and line losses.
• Safety and application considerations are secondary to efficiency.

Concept / Approach:
Long-distance transmission favors high voltage and low current to reduce I^2 * R losses. AC voltages are easily stepped up or down with transformers, enabling efficient high-voltage transmission and safe local distribution. Although modern HVDC exists for specific corridors, AC remains the default due to transformer simplicity and network interconnectivity.

Step-by-Step Solution:
1) Goal: minimize power loss P_loss = I^2 * R over long lines.2) Strategy: increase transmission voltage to reduce current for given power.3) Enabler: transformers efficiently change AC voltage levels.4) Outcome: AC systems provide flexible, economical transmission and distribution.

Verification / Alternative check:
Compare AC transformer simplicity to DC conversion historically; until modern power electronics matured, DC voltage conversion was inefficient, cementing AC as the standard. AC grids also synchronize many generators, aiding reliability.

Why Other Options Are Wrong:
No longer a need for DC: false; DC is widely used in electronics and specific transmission links.DC is more dangerous: safety depends on many factors; not the key reason.Not enough batteries: irrelevant to bulk generation and grid design.

Common Pitfalls:
Overgeneralizing HVDC's niche advantages (long undersea links, asynchronous ties) as reasons to prefer DC everywhere; grid reality is more nuanced.

Final Answer:
it is easier to transmit ac