Power Systems (Generation, Transmission, Distribution and Protection)
Power Systems spans generation, transmission, distribution, and protection. The exam tests per-unit quantities, line parameters, sag, insulators, load flow, faults, relays, and circuit breakers.
Core rules
- Thermal plants use the Rankine cycle; hydro uses potential energy; nuclear uses fission heat.
- Transmission line series impedance includes resistance and inductive reactance; shunt capacitance causes charging current and Ferranti voltage rise at light load.
- Skin effect raises effective AC resistance; corona depends on voltage gradient, conductor size, and weather.
- Sag depends on weight, tension, and span; ice and wind increase effective load.
- Per unit: actual/base; choose S_base and V_base, then Z_base=V_base²/S_base.
- Protection: CT steps current down, PT steps voltage down; distance relay uses Z=V/I; Buchholz protects oil-filled transformers.
Worked example
A balanced 3-phase load of 10 MW at 0.8 power factor lags on an 11 kV bus. Line current I=P/(√3 V_L pf)=10×10^6/(1.732×11×10^3×0.8)≈656 A. Apparent power is 10/0.8=12.5 MVA.
Traps
Do not open-circuit a CT secondary while energized; high voltage can appear. Do not confuse demand factor with diversity factor. Ferranti effect raises, not lowers, receiving-end voltage on a lightly loaded line.