| Title |
Characteristics of the Electric Fields Produced by Multiple Lightning Return Strokes |
| Keywords |
Multiple lightning return strokes ; Electric field ; Rise time ; Zero-crossing time ; Lightning electromagnetic pulse ; Lightning protection ; Electric field measuring device ; Magnetic field measuring device |
| Abstract |
In this work, in order to obtain the detailed information about lightning electromagnetic pulses, the electric fields radiated from multiple lightning return strokes were measured and analyzed statistically. The electric field measuring system consists of a hemisphere antenna of 30cm in diameter, integrator and data acquisition device, and its frequency bandwidth ranges from 200Hz to 1.56MHz, and the sensitivity is 0.96㎷/V/m. The electric field signals are digitized every 200ns with the transient signal analyzer having the resolution of 12-bit and the recording length of 5 kilowords and are registered at personal computer. As a result, the electric fields produced by the first return stroke begin with a slow initial part or front, which starts just after or during the last stepped leader. On the average the rise times of the electric fields for the positive first, second and third strokes are 4.21μ textrm{s}, 3.94μ textrm{s} and 2.75μ textrm{s}, respectively, and those for the negative first, second and third strokes are 3.46μ textrm{s}, 3.15μ textrm{s} and 2.79μ textrm{s}, respectively. The zero-crossing times of the electric fields for first return strokes range from about 10 to 80μ textrm{s}. The mean zero-crossing times for subsequent return strokes are shorter than those for first lightning return strokes. |