How it works
Transmission at high voltage reduces I²R losses — doubling voltage for the same power halves current and cuts losses to one-quarter. Indian grid operates at 765 kV, 400 kV, and 220 kV at the transmission level. HVDC (High Voltage Direct Current) transmission above 600 km is more economical than HVAC because there are no reactive power losses in the DC link; HVDC back-to-back stations also connect asynchronous grids (e.g., Northern and Southern India were connected at 500 MW Vindhyachal HVDC). The per-unit (pu) system normalises all quantities to a common base to simplify multi-voltage network calculations.
Key points to remember
Key definitions examiners test: load factor = average load / peak load; demand factor = maximum demand / installed capacity; diversity factor = sum of individual maximum demands / simultaneous maximum demand (always ≥ 1). Skin effect causes current to flow near conductor surface at 50 Hz, increasing effective resistance by 5–10% for large conductors like ACSR Drake (900 kcmil). Ferranti effect causes receiving-end voltage to exceed sending-end voltage on a lightly loaded or no-load long transmission line — this is a common short-answer question.
Exam tip
Every Anna University power systems paper asks about the Ferranti effect — explain it as the leading current through line capacitance charging the line inductance, causing a voltage rise that can exceed 10% on a 300 km unloaded line.