High-Voltage Lines Flashcards

Flashcards based on lecture notes about high-voltage lines and related components.

Conductors (HV lines)

Stranded wires (not solid), with Z-profile, aluminum with steel core. Mechanically strong, lighter than copper, cheaper, and better for corona effect.

Corona Effect

Ionization of air around the conductor at high field strength. Causes energy loss – prevented by larger radius or bundle conductors.

Bundle Conductors

Multiple wires per phase, kept at a distance. Reduce corona effect, distribute current, limit skin effect.

Grounding and Lightning

Vertical electrodes, counterpoise, lightning conductors at the top of the mast. Prevent flashover to the line during lightning strikes – must have low impedance.

Working Under Voltage

Helicopter (equalize potential), Faraday cage (suit). Safety during maintenance of HV lines.

Mast Types

Line mast, angle mast, anchoring mast, end mast, crossing mast. Different functions and forces – especially anchoring mast and end mast are structurally important.

Insulators – Support Insulators

Used for MS and LS (up to 36 kV), extended leakage path with mushroom shape. Pollution affects operation – regular cleaning is essential.

Insulators – Cap Insulators

In chains (±20 kV per cap), used for HS. Emphasis on breakdown vs flashover – flashover is preferred over breakdown.

Maintenance of Insulators

Spraying with 100% pure water. Dirt reduces insulating effect – the need for cleaning is emphasized.

Surge Arresters

Conduct overvoltage away during lightning strikes. Prevent destructive breakdown – must be placed at a sufficient distance from insulator chains.

Rod Insulators

One piece, used above 100 kV. Lighter, more compact, but completely replaced in case of damage – stem emphasizes disadvantages in case of defect.

Cables (XLPE vs PVC)

PVC has high losses – no longer used above 10 kV. XLPE is standard. XLPE allows higher temperature and current.

Cable Cross-section (MS vs HS)

MS = sector-shaped, HS = cylindrical. Sector-shaped at HS leads to too high a voltage gradient – risk of breakdown.

Rails

Solid conductors (copper, aluminum, brass). Protected against contact by insulation, distance, or shields, depending on voltage level.