|
|
| Home |
| PPD |
| Sites |
| ABdA |
| Help |
|
|
WEEK 06: TRANSMISSION: OVERHEAD AC Sections: Voltage | Conductor | Environment | Line | Mechanical | Support | Accessories | Foundation Corona and Field Effects There are two categories of electrical environmental effect of power transmission lines. Corona effects are those caused by electrical stresses at the conductor surface which result in air ionization and include radio, television, and audible noise. Field effects are those caused by induction to objects in proximity to the line. This latter effect is further divided into two types: electric field effects and magnetic field effect. Electric fields, related to the voltage of the line, are the primary cause of induction to vehicles, buildings and objects of comparative size. Magnetic fields, related to the currents in the line, are the primary cause of induction to long objects, such as fences and pipelines. Audible Noise Corona-produced audible noise during foul weather, particularly during or following rain, can be an important design parameter for high-voltage ac transmission lines. Audible noise has two components, a random noise component and a low-frequency hum, each produced by different physical mechanism. While the hum component is closely correlated with corona loss on the line, the random noise is not, but the latter is the most frequent cause of annoyance. Audible noise are considered on A-weighted sound level [dB(A)] during rain. Gaseous Oxidants can be produced by corona activity in air, and in sufficient concentrations may produce adverse effects on flora and fauna. The most important oxidants are ozone (O3) and oxides of nitrogen (mainly NO and NO2). Standards limit photochemical oxidants to 0.12 part per million for a maximum of 1-hour concentration not to be exceeded more than once a year. Ozone can be detected by smell at minimum concentrations of 0.01 to 0.15 ppm. |
