Power Generation, Transmission and Distribution
What this domain tests
You must know how a thermal, hydro or nuclear station drives a three-phase alternator, why transmission uses high voltage, the standard Indian voltage levels, and the layout from grid to consumer.
Core rules
- Generation is three phase at 11–25 kV, stepped up for transmission and stepped down for distribution.
- Standard Indian levels include 11 kV, 33 kV, 132 kV, 220 kV and 400 kV; distribution to homes is 415 V three phase, four wire, giving 240 V single phase.
- Grid frequency in India is 50 Hz. Frequency falls when generation is less than demand.
- Line loss = I²R. For the same power, raising voltage lowers current, so loss falls by the square of the voltage ratio.
- Transmission lines use ACSR conductors and towers; distribution uses poles, LT lines and transformers of 11 kV/415 V.
Worked example
100 kW is sent through a line of 1 Ω resistance at 11 kV and then at 33 kV. Compare the losses. At 11 kV: I = 100,000/11,000 = 9.09 A; loss = 9.09² × 1 = 82.6 W. At 33 kV: I = 100,000/33,000 = 3.03 A; loss = 3.03² × 1 = 9.2 W. Tripling the voltage cuts the current to one third and the loss to about one ninth - exactly what the I²R rule predicts.
Traps that cost marks
Saying higher transmission voltage increases line loss; confusing 11 kV distribution voltage with 400 kV transmission; forgetting the four-wire system gives 240 V between phase and neutral; quoting 60 Hz for India.