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T/F: HVDC better for longer lines

Short answer

True. HVDC avoids line reactance and stability limits, has no charging current, fewer conductors, and lower line losses. Despite costly terminals, beyond 500–800 km overhead, HVDC becomes the more economical choice for long-distance transmission.

State whether the following statement is TRUE or FALSE. Justify your answer with a brief explanation: HVDC transmission system is better choice in case of longer length than HVAC transmission system.

TRUE.

  • No stability limit: AC power transfer P=VsVrXsin⁡δP = \frac{V_s V_r}{X}\sin\delta falls as line reactance XX grows with length; HVDC has no reactance in steady state, so it has no length-based stability limit.
  • No charging current and no need for intermediate compensation on long lines.
  • Lower line cost and loss: two conductors instead of three, smaller towers, narrower corridor, no skin effect and lower corona loss.
  • Economics: HVDC terminal stations are costly, but the line saving per km is large. Beyond the break-even distance (about 500–800 km overhead, 30–50 km cable) HVDC has lower total cost.

So for long lengths (above break-even distance) HVDC is the better choice; for short lines HVAC remains cheaper.

✓ Answer checked by Claude Opus 5.5 (high effort)

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