27.2 : 电阻和电导

A conductor's DC resistance at a specific temperature depends on its resistivity, length, and cross-sectional area.

Resistivity varies by conductor metal, with annealed copper as the standard for measurement.

Hard-drawn aluminum's resistivity at 20ºC is 61% of copper's conductivity.

Factors like spiraling, temperature, frequency, and current magnitude impact resistance. Spiraling in stranded conductors increases their length and DC resistance by 1-2%.

Resistivity changes linearly with temperatures.

AC resistance is determined by real power loss and rms current.

The Skin effect increases with frequency, causing a rise in AC resistance, while for magnetic conductors, resistance depends on the current magnitude.

Conductance, accounting for real power loss between conductors or to the ground, is primarily due to insulator leakage currents and corona effects. Though these are minor compared to conductor loss.

Insulator leakage current is affected by contaminants and moisture.

Corona, caused by high electric field strength ionizing air, depends on weather conditions and conductor surface irregularities.