My high school science teacher used to work as a power tech. He showed us photos of a substation transformer that had been blown apart, not by the heat, but put the magnetic forces on the shorted secondary. 3" x 1" copper strapping (windings) that looked like some giant hand had picked at the turns. Gave us all a great respect for the forces a little electromagnetism can generate (the teaching topic of the day). R Mike Hawkshaw wrote: > > ----- Original Message ----- > From: "Nate Duehr" > To: > Sent: Friday, March 05, 2004 10:27 PM > Subject: Re: [OT:] More stupid electrical tricks... > > > A direct strike ......... > I've been on one of our sites during a storm, and experienced a few direct > strikes. (This is hardly a domestic evironment, being 550 metres above sea > level with a 220 metre mast - I suppose it's asking for trouble, really) > I've seen solidly earthed electrical trunking flash over to solidly earthed > equipment bays; flashovers inside equipment bays; equipment that has been > blown off walls.....Scary. > > On our large medium wave sites, we have a thing called a prematch coil > between the mast (which is the antenna and so is live) and ground. These > things are also called static leaks (direct short to DC and open circuit to > RF) You would think that a coil made of 30 or so turns of 1/2 inch copper > pipe would be quite a mechanically strong thing. We recently had one damaged > by a direct strike, where some of the turns ended up shorted together, > pesumably by the huge magnetic fields set up by the currents involved. We > had to do an emergency repair, and had to use a crow bar to get enough force > to put it right!! > > Static leaks are definately the way to go, because they'll always provide > protection even when the antenna is in use. > > All the best...Mike. -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu