Power Systems (Generation, Transmission, Distribution, Protection and Switchgear)
What the exam tests
Power Systems covers generation economics, transmission line modelling, distribution voltage drop, fault analysis, protection coordination, and switchgear. MPPSC SES questions often combine per-unit calculations with relay reach and circuit-breaker duty.
Core rules
- Per-unit quantities remove transformer ratios: Zpu = Zactual/Zbase, with Zbase = Vbase²/Sbase.
- Short lines use series impedance; medium lines use nominal π or T; long lines need distributed parameters.
- Surge impedance Zc = √(L/C); surge impedance loading SIL = VLL²/Zc. A line loaded near SIL has low reactive demand.
- Distance relay zones: zone 1 about 80% of line, zone 2 reaches into the next line, zone 3 provides backup. Directional blocking prevents maloperation.
- CTs must never be open-circuited; VTs must never be short-circuited.
Worked example
A 220 kV line has surge impedance 400 Ω. SIL = (220 kV)²/400 Ω = 48,400/400 = 121 MW. If the receiving end is open, the voltage rises above sending-end value because the line capacitance supplies charging current-this is the Ferranti effect, more pronounced on long extra-high-voltage lines.
Traps
Do not use line-to-neutral voltage in the three-phase SIL formula; use line-to-line kV and three-phase MW. Do not assume a distance relay is unaffected by arc resistance and infeed. Do not forget DC offset when selecting breaker making capacity. Neutral grounding affects earth-fault current and insulation coordination.