ELECTENG 101 Chap.10 Electricity Generation and Distribution
Electricity Generation and Distribution
Electricity supply links generation, high-voltage transmission, distribution and loads. Balanced three-phase systems use phase displacement to deliver power efficiently. Transformers change voltage and current approximately inversely, allowing transmission current and I²R line loss to be reduced before voltage is lowered near consumers.
Generation converts mechanical or other primary energy into electrical power, after which step-up transformers raise voltage for long-distance transport. For fixed delivered power and power factor, greater voltage means smaller current and therefore sharply reduced conductor loss. Distribution equipment later lowers voltage to practical utilisation levels.
Ideal transformer ratios relate turns, voltage, current and reflected impedance, while real equipment adds winding, core and leakage losses. Three-phase calculations must distinguish line and phase quantities because star and delta connections impose different geometric relationships.
What this chapter covers
- 01
Generation stages
- 02
Balanced three-phase supply
- 03
Line and phase quantities
- 04
Transmission loss
- 05
Transformer turns ratio
- 06
Current ratio
- 07
Reflected load resistance
Worked example · free
Refer a load through a transformer
- +1Secondary voltage is 200 V rms.
- +4Secondary current is 20 A rms and primary current is 1 A rms.
- +2The primary sees 4 kΩ and both sides carry 4 kVA.
Key terms
- Three-phase supply
- Three sinusoidal phase quantities separated by 120 electrical degrees.
- Transmission loss
- Conductor heating loss proportional to current squared times line resistance.
- Reflected resistance
- A secondary load as seen from the primary after multiplication by squared turns ratio.
Electricity Generation and Distribution FAQ
Why transmit at high voltage?
For a given real power and power factor, higher voltage allows lower current. Since conductor loss is I²R, the reduction in loss is squared. For example, halving line current reduces resistive loss to one quarter when resistance is unchanged. The tradeoff is greater insulation, clearance and equipment demand at higher voltage.
How does an ideal transformer change current?
Current ratio is inverse to turns and voltage ratio, preserving apparent power in the ideal model. A step-up in voltage therefore gives a step-down in current for power transferred through the transformer. State primary and secondary sides before taking a ratio, because reversing the turns ratio reverses both conclusions.
Why label line and phase values?
Star and delta connections relate line and phase voltage or current differently. The square-root-of-three factor depends on which quantities are being compared. Label every given symbol with line or phase before choosing a formula; inserting the factor from memory without the connection and quantity labels is the usual source of a plausible but wrong result.
How is a load reflected through an ideal transformer?
An impedance on one side appears on the other multiplied by the square of the relevant turns ratio. A load referred to the primary is multiplied by primary turns over secondary turns squared. The square follows because voltage changes by the ratio while current changes inversely, so their quotient changes twice.
What does an ideal transformer model omit?
It omits winding resistance, leakage flux, magnetising current, core loss and imperfect voltage regulation. The simple model is valuable for ratio and first-pass power calculations, but its input and output power equality is an assumption rather than a measured efficiency claim. Name real losses when interpreting practical equipment.
Why use balanced three-phase generation?
Three equal sinusoidal phase quantities displaced by 120 electrical degrees produce a smoother total power transfer and use conductors effectively. Balanced formulas rely on equal magnitudes and symmetric displacement, so an unbalanced load cannot automatically be reduced to one phase multiplied by three without examining the connection and return paths.
Exam move
Trace energy through generator, step-up transformer, line, step-down transformer and load. Attach voltage and current labels at every stage. Practise ideal transformer calculations from either side and check apparent-power equality. For three-phase work, write line or phase beside every given value before selecting a formula, then explain why current reduction lowers loss.
Build a supply-chain diagram and annotate where voltage rises, current falls, line loss occurs and voltage is reduced for consumers. Solve transformer questions in both directions, then reflect one load and verify that the primary voltage-current ratio matches the reflected resistance. Compare line loss before and after a specified voltage increase while holding real power and power factor fixed.
For balanced systems, make separate star and delta relation cards rather than using one square-root-of-three mnemonic. End by listing which ideal assumptions would make a real substation measurement differ from the calculated result.
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