Power Generation, Transmission and Distribution
Power Generation, Transmission and Distribution
This domain tests how electricity is generated, why it is transmitted at high voltage, and how it reaches low-tension consumers through substations and feeders.
Core rules
- Generation: thermal (coal, steam turbine), hydro (potential energy), nuclear (fission heat), solar PV and wind, each with different capital cost, running cost and load-following behaviour.
- Transmission voltages in India include 132, 220, 400 and 765 kV AC, with HVDC for very long bulk corridors. ACSR conductors are standard; bundled conductors reduce corona and reactance.
- For the same power, raising voltage lowers current (P = √3 V I cos φ), reducing I²R loss and conductor size.
- Distribution: 33/11 kV substations step down to 11 kV feeders; distribution transformers give 400 V three-phase and 230 V single-phase.
- Radial, ring-main and interconnected systems differ in reliability and cost.
- Load factor = average load / maximum demand; diversity factor = sum of individual maxima / maximum demand on the system.
Worked example
A balanced three-phase load of 100 kW operates at 400 V and 0.8 power factor lagging. Find the line current. I = P/(√3 × V × cos φ) = 100 000/(1.732 × 400 × 0.8) = 100 000/554.2 = 180.4 A. If power factor were corrected to 0.95, current would fall to about 152 A, cutting cable and transformer loading without changing the useful kW.
Traps that cost marks
- Using 400 V as a phase voltage; in a 400 V star system the phase voltage is 231 V.
- Omitting cos φ from the three-phase current formula.
- Confusing kW (real), kVA (apparent) and kvar (reactive).
- Claiming high-voltage transmission reduces loss by reducing resistance; it reduces current, and loss falls as I²R.
- Mixing up transmission and distribution voltage levels in India.