Tower of power

Tower of power: what happened to engineer Greg Leyh when he climbed to the top of a giant electrical transformer that throws lightning bolts into the sky? - Physical - Electrum, world's largest tesla coil - Cover Story
Current Science, Jan 2, 2004 by William Speed Weed

Save a personal copy of this article and quickly find it again with Furl.net. Get started now. (It's free.)

Greg Leyh stands calmly at the ground-based controls of a four-story tower that looks like the scepter of a giant king. He takes a deep breath, throws the switch, and--zap!--the metal sphere atop the tower throws out dazzling 12-meter (40-foot) lightning bolts that sizzle in the cloudless night. An audience standing at a safe distance around the base of the tower gasps, then cheers.

Leyh, an electrical engineer, built the tower, called Electrum, with artist Eric Orr in 1998. Inside it is the world's largest tesla coil. A tesla coil is a powerful transformer, a device that increases or decreases the voltage of an electricity supply. Electrum's huge tesla coil charges the sphere on top of the tower to 3 million volts--enough to power 1,200 electric chairs. When the sphere is at that voltage, Leyh told Current Science, "it rips electrons off the atoms in the air and makes the bulk of the air conduct electricity. As those electrons recombine and fall back into a lower energy state, they produce lightning"--and gasps from onlookers.

MASTER OF LIGHTNING

Nicola Tesla (1856-1943), a physicist who worked in Thomas Edison's lab, invented the tesla coil. In Tesla's day, all electricity was delivered by direct current (DC), in which electricity flows along a wire in one direction. "Tesla was a really creative and intelligent guy who had a lot of amazing patents" said Leyh. One patent was for the invention of alternating current (AC), wherein the electricity switches direction along a wire, usually hundreds or thousands of times a second.

The advantage of AC over DC is that AC creates a magnetic field around the wire. "When an AC wire generates a magnetic field," Leyh said, "that's something another wire can 'hear.'" Energy can be transferred magnetically from one wire to another without the two being physically connected. That is how transformers work in today's modern electrical grids--the networks of wires that carry electricity to our homes.

MAGNETIC TUNING

Tesla discovered that the magnetic transfer of energy happened most efficiently if the magnetic field created by a wire is "tuned" to the fight frequency. That tuning takes advantage of a physical property of wire coils called resonance. Think of a musical tuning fork that's pitched to the note middle C. If you hold the turning fork near a piano and play middle C, the tuning fork vibrates on its own, even though you didn't hit it. That's because the tuning fork resonates to the note middle C. Similarly, any coil of wire has a resonant frequency--not of musical sound but of magnetic energy.

A tesla coil actually has two coils, a primary one and a secondary one. The primary coil is charged to generate just the right magnetic field so that the secondary coil resonates. The primary coil has a low voltage but a high current (measured in amperes), and the resonating secondary coil has a low current but a high voltage. In an electrical grid, a high voltage is necessary for the long-distance transmission of electricity.

Electrum's primary coil is made of thick copper piping, and its secondary coil is made of very thin copper wire that winds and winds up the tower. Stretched out, the secondary coil would extend a mile and a half. The secondary coil generates the 3 million volts that produce Electrum's big lightning bolts.

ELECTRIC HIGHCHAIR

So if an electric chair with 2,500 volts can kill a person, what would happen if someone entered the metal sphere at the top of Electrum? "I hate to get electrocuted!" Leyh said, but he decided to find out anyway. With Leyh standing inside the sphere, Electrum was turned on, and "the lightning started just a foot from my face," he said. He lived to tell the tale.

That stunt wasn't as daring or as dumb as you might think. Why? Volts don't kill people; current does. And current flows only when there is an electric potential (voltage difference) between two objects. When Leyh stood inside the sphere, both he and the sphere were at 3 million volts. That's certainly a high voltage, but because no electric potential existed between them, no current was created, and Leyh was just fine. If Leyh had stuck his hand through the metal cage into the sky, where there was a lower voltage, it would have been curtains for him.

YET BIGGER

Leyh calculates that the biggest possible tesla coil could be 36 meters (118 feet) tall, or about three times the height of Electrum. He hopes to build not one but two such coils next to each other on a field, a project he calls the Advanced Lightning Facility (ALF). Between the two towers, ALF would generate lightning across an expanse the size of a football field, with 10 million volts.

ALF could be an important tool for understanding how natural lightning works. "We still don't know exactly how lightning does what it does, how it starts, how it propagates," said Leyh.

For now, ALF is just a paper dream. Building the towers would cost a few million dollars. "We're ready to start tomorrow," he said, "if we can just find someone who's rich enough--and crazy enough--to finance the project."

INSIDE ELECTRUM

Engineer Greg Leyh's Electrum, the world': largest tesla coil, is 11.8 meters (39 feet) tall. Leyh stood inside the stainless-steel sphere at the top of Electrum when it was switched on and shot bolts of lightning into the sky. "The lightning started just a foot from my face," said Leyh.

Like all tesla coil Electrum has two coils. The secondary coil, made of thin copper wire, made its way up the entire length of the inside of the fiberglass shaft that supports the sphere. The primary coil, made of copper pipe, measures just 0.6 meters (2 feet) in height and sits inside the bottom of the shaft. A rope ladder inside the shaft enabled Leyh to climb to the sphere.