generation, transmission, and distribution of electrical power

generation, transmission, and distribution of electrical power

1. What the Power System Is (3 stages)

Electrical power system = (1) Generation (produce) → (2) Transmission (bulk carry over long distance) → (3) Distribution (deliver to consumers) — the grid.

2. Stage 1 — Generation

Source	How	Typical Voltage
Thermal (coal/gas)	Heat → steam → turbine → synchronous generator	$11$ kV generated
Hydro	Water → turbine	$11$ kV
Nuclear, Solar, Wind	Various → generator/inverter	$0.4$–$11$ kV

Power station generates 11 kV (or $6.6$ kV) 3-phase AC (standard).

3. Stage 2 — Transmission (Long Distance, Bulk)

• Step-up via power transformer (generator transformer) to high voltage for transmission: 132 kV, 220 kV, 400 kV, 765 kV (EHV/UHV) to reduce $I$ and $I²R$ loss for same $P=√3 V_L I_L cosφ$.
• Transmission lines: overhead ACSR conductors on towers, 3-phase 3-wire (no neutral, balanced).
• Substations with step-down transformers.

Why high voltage? For $P$ constant, $I∝1/V$ ⇒ loss $∝I²∝1/V²$ ⇒ high $V$ drastically cuts loss and allows smaller conductors.

4. Stage 3 — Distribution (Local)

• Primary distribution: 33 kV / 11 kV from distribution substation to distribution transformers (pole-mounted).
• Secondary distribution: Distribution transformer steps down to 400V 3-phase (line-line) / 230V phase-neutral for 4-wire distribution to homes/industry (230V single-phase from one phase + neutral, 400V three-phase for motors).
• Loads: Domestic (single-phase 230V), industrial (3-phase 400V).

5. Single-Line Diagram (exam expects sketch)

Generation (11kV G) → Step-up Tx (11→220kV) → Transmission lines (220kV towers) → Step-down Substation (220→33kV) → Primary distribution (33kV feeders) → Distribution Tx (33kV/400V) → Secondary distribution (400V/230V) → Consumer

6. Exam Points

• Describe 3 stages (generation 11kV → transmission 132–765kV → distribution 33kV/400V/230V) — 7 marks, very frequent (the most common power system question).
• Explain why step-up for transmission ($I²R$ loss $∝1/V²$) — 5 marks, very frequent.
• Give transformer roles (step-up/down) — 3-5 marks, frequent.
• Mention 4-wire distribution (400V/230V) — 3 marks.
• Draw single-line diagram — 5-7 marks, very frequent.