We went to the Museum of Science and Industry in Manchester. For me, the highlight was coming face to face with a high voltage pylon insulator. It came a day after my friend in Australia sent me a proper explanation of the parallel bars on pylons that I blogged about last week. They now have a name: arcing horns.
In certain conditions, there can be a voltage surge (overvoltage). This can lead to the electric field strength exceeding the breakdown in the air: you get a spark through the air. This is called FLASHOVER. It can spark round the insulator cups. This isn't good because it can burn tracks into the insulator that make future flashover more likely.
The arcing horns are designed to provide a safe route for flashover that misses the surface of the insulators. Flashover can be made more likely by things like volcanic dust in the air which would reduce the breakdown field strength on the air. There is an excellent picture of flashover on this website from New Zealand
http://www.nhrc.canterbury.ac.nz/Research/Transmission.shtml and scroll down.
More on these insulators to follow...
