Abstract
The surge impedance of transmission-line towers is very important
in the design of electric transmission lines. The surge impedance
has similar effect as a resistance in direct current circuits.
A large surge impedance implies large voltage between the terminals
as determined by Ohm's law. When designing transmission lines,
engineers need to estimate the surge impedance of the tower
in order to estimate voltage of the tower top when the top is struck
by lightning carrying huge currents. The large voltage at
the tower top causes flush-over phenomena from the tower arm to the
transmission lines. Eventually, traveling wave carrying huge electric power
penetrates into substations and damages various equipment such
as transformers. Finally, there is electric blackout on a large scale.

In 1934, C. A. Jordan proposed a formula to calculate the surge impedance
of transmission-line towers. The formula is well known,
has been cited even in textbooks, and has been used
by many researchers and engineers for over 50 years.

However, the formula is erroneous. Where did C. A. Jordan make a mistake?
In this talk, we derive the formula and identify the mistake made.
Furthermore, we provide the correction and a slightly better approximation
by taking into account the structure of the transmission tower.

Biography

Kohshi Okumura graduated from the Department of Electrical Engineering,
Kyoto University, Japan in 1966. He received the doctoral degree in Electrical
Engineering from Kyoto University in 1974.
He held Assistant Professor, Lecturer, and Associate Professor
positions in the Department of Electrical Engineering at Kyoto University.
He has been Full Professor since April 1992. In April 2004, he became
Full Professor at Hiroshima Institute of Technology and Professor Emeritus
at Kyoto University. From 1989 to 1990, he was a guest researcher
at University of London (Queen Mary College), United Kingdom and
at Ulm University, West Germany.
He is a Fellow of the Institute of Electronics, Information and
Communication Engineers (IEICE) and a Senior Member of the IEEE Circuits and
Systems Society. He served a Vice President of the Institute of Electrical
Engineers of Japan (IEEJ).

His areas of research are the analysis of nonlinear circuits as well as
the surge phenomena of transmission systems. He is interested in
the application of mathematics to nonlinear circuit analysis,
such as interval analysis and homotopy and multi-scale methods.