Counting the discs
Stories from Physics
for 11-14
14-16
High voltage power lines typically use disc insulators to prevent current entering the metal pylon. Counting the number of discs can give an indication of the line voltage:
| Line Voltage (kV) | Number of discs |
|---|---|
| 34.5 | 3 |
| 45 | 4 |
| 69 | 5 |
| 92 | 7 |
| 115 | 8 |
| 138 | 9 |
| 161 | 11 |
| 196 | 13 |
| 230 | 15 |
| 287 | 19 |
| 345 | 22 |
| 360 | 23 |
When winds blow, high voltage power lines respond in three modes of oscillation: Gallop (0.1-0.5 Hz), Aeolian (8-60 Hz) and Wake-induced vibrations (0.5-2.5 Hz). Stockbridge dampers are dumbbell-shaped dampers consisting of two concrete or metal masses attached to a piece of cable or other flexible material. They reduce Aeolian vibration that can cause dangerous stresses in power lines.
References
S. Mukherjee, The Science of Clays: Applications in Industry, Engineering, and Environment, Dordrecht, Springer, 2013, p. 227.
A. Simpson, Wind-induced vibration of overhead power transmission lines. Science Progress, vol. 68, no. 270, 1983, pp. 285-308.
