Electrical Materials
What the domain tests
Electrical Materials tests why copper, aluminium, PVC, XLPE, porcelain, silicon steel and soldering alloys are chosen for particular jobs. The examiner looks for the property behind the choice: conductivity, insulation strength, heat resistance or magnetic behaviour.
Core rules
- Conductors: copper has high conductivity and good mechanical strength; aluminium is lighter and cheaper but has lower conductivity, so it needs a larger cross-section for the same current. ACSR combines aluminium strands for conduction with a steel core for strength in overhead lines.
- Insulators: PVC is flexible and used for LT wiring; XLPE withstands higher temperature and is common in power cables; porcelain and glass are used for line insulators; mica resists high heat.
- Magnetic materials: CRGO silicon steel is used in transformer cores because it has high permeability and low hysteresis loss; ferrites are used at high frequency.
- Contact materials need low resistance and resistance to arcing; silver alloys are common in contacts.
- Thermal class and voltage grade must match the application; a material’s dielectric strength falls with heat, moisture and contamination.
Worked example
A long LT run needs a conductor. Copper would carry the current in a smaller size, but aluminium is selected because it is lighter and cheaper, which reduces pole loading and cost. The trade-off is a larger cross-section and careful jointing, because aluminium oxide forms an insulating film and needs proper bimetallic connectors or abrasion and compound.
Traps
Do not say silver is used for overhead lines because it is the best conductor-cost rules it out. Do not treat porcelain as a conductor. Do not use PVC insulation where high temperature demands XLPE or silicone. Do not join aluminium to copper without suitable connectors.