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Classification and need of high voltages

Short answer

Voltages are classified as LV (<1 kV), MV (1–33 kV), HV (66–230 kV), EHV (300–765 kV) and UHV (>800 kV). High voltage is needed to reduce current and losses proportional to 1/V², increase power capacity, and save conductor material.

Discuss the classification of high voltages and the need of high voltage for transmission line.

Classification of high voltages

Voltage levels are commonly classified as below (limits differ a little between standards and textbooks):

ClassRange (line voltage)Typical use
Low voltage (LV)up to 1 kVConsumers (230/400 V)
Medium voltage (MV)1 kV – 33 kV (up to about 66 kV)Distribution (11, 33 kV)
High voltage (HV)66 kV – 230 kVSub-transmission, transmission (66, 132, 220 kV)
Extra high voltage (EHV)300 kV – 765 kVBulk transmission (400, 500, 765 kV)
Ultra high voltage (UHV)above 800 kV AC (1000, 1100 kV); ±800 kV DC and aboveVery long bulk transmission

In Nepal, NEA uses 400 kV and 220 kV (EHV/HV backbone), 132 kV and 66 kV (HV), and 33 kV and 11 kV (MV) levels.

Need of high voltage for transmission

  1. Less current, less loss: I=P3Vcos⁡ϕI = \frac{P}{\sqrt{3}V\cos\phi}, so loss 3I2R∝1V23I^2R \propto \frac{1}{V^2}.
  2. Higher power capacity: P=V2Xsin⁡δP = \frac{V^2}{X}\sin\delta and SIL=V2ZcSIL = \frac{V^2}{Z_c} both rise with V2V^2.
  3. Less conductor material: for the same loss, conductor volume ∝1V2\propto \frac{1}{V^2}.
  4. Better voltage regulation and efficiency.
  5. Fewer lines and less right-of-way for large power, so lower cost per MW-km over long distances.

✓ Answer checked by Claude Opus 5.5 (high effort)

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