Electrical Power Systems Review

Flashcards based on lecture notes covering electrical power systems.

What is load impedance?

The total opposition a load offers to current in an AC circuit, including both resistance (R) and reactance (X): Z = R + jX

What are the 4 key areas of power transmission?

Generation, Transmission, Distribution, Utilisation (GTDU)

What is the difference between PVC and XLPE insulation?

PVC: Lower temp rating, cheaper, less durable. XLPE: Higher thermal stability, better chemical resistance

What are the uses of conduit, trunking, and trays in electrical systems?

Conduit: Encloses/protects cables. Trunking: Carries multiple cables in buildings. Trays: Supports heavy-duty cables, allows airflow

What are the advantages of overhead power lines?

Cheaper, easier access, simple maintenance

What are the disadvantages of overhead power lines?

Exposed to weather, less safe, visual impact

What are the advantages of underground power lines?

Protected from weather and damage, safer, better aesthetics

What are the disadvantages of underground power lines?

Expensive to install/repair, harder fault detection

What is the purpose of an RCD (Residual Current Device)?

Detects current imbalance between live and neutral, trips during leakage to protect from shock/fire

What is the difference between Apparent, Real, and Reactive power?

Apparent (S): Total power (VA). Real (P): Useful power (W). Reactive (Q): Stored/released power (VAR)

Why are electrical installations typically inductive?

Motors and transformers are inductive, causing lagging power factor

What are the effects of poor power factor?

Increases bills and losses, leads to penalties and overheating

What is an APFC unit?

Automatically switches capacitors to correct power factor, improving efficiency and reducing cost

What are four issues that can arise from harmonic distortion?

Overheating, tripping protection, communication interference, reduced efficiency

What is hybrid filtering?

Combines passive and active filtering to target a broad range of harmonics

What is a harmonic spectrum?

A graph showing harmonic components, with amplitude vs frequency

What is the difference between an Oscilloscope and a Spectrum Analyser?

Oscilloscope: Time-domain view. Spectrum Analyser: Shows harmonic content

What is the difference between a Power Transformer and a Distribution Transformer?

Power: High voltage, transmission, always full load. Distribution: Lower voltage, local use, variable load

What are two transformer loss tests and what do they measure?

Open-circuit: Core loss. Short-circuit: Copper loss

What is transformer efficiency and what determines it?

Efficiency = output/input power ratio, determined by copper & iron losses. Good efficiency = 95-99%

Why is voltage increased in power transmission?

Reduces current -> lowers losses, more efficient long-distance delivery

Who manages Ireland's electricity grid?

EirGrid: Balances load, plans infrastructure, manages renewables

What are 5 key elements of an electrical system?

Generation, Transmission, Distribution, Protection, Utilisation

Name two common current faults in electrical systems.

Short circuit, Earth fault

What are the key differences between underground and overhead cabling?

Underground: safer, costlier, harder to repair. Overhead: cheaper, exposed to weather

What are some sources of harmonics in electrical systems and their impacts?

Sources: Non-linear loads like VFDs, rectifiers. Impacts: overheating, protection errors, cost penalties

What are the two main types of transformer power losses and how are they quantified?

Iron (core) loss and copper (winding) loss, quantified by open/short circuit tests