Development of a multi-range lightning current measurement system with a wide dynamic range from milli-amps to hundreds of kilo-amps

Abstract

Measuring the lightning current in a lightning rod with a wide dynamic range is a challenge. Currently, there is a lack of suitable equipment to study the current variation in the streamer process of lightning. The existing lightning current observation equipment is mainly designed to measure the peak current generated by the stroke, with a measurement range typically from tens of amperes to hundreds of kiloamperes. While a few devices can observe leader currents of a few amperes, they are incapable of measuring corona discharges and the streamer process ranging from a few milliamps to hundreds of milliamps. This lack of observational data severely hinders the understanding of lightning initiation processes. Herein, in this thesis, we have proposed and implemented a wide dynamic range lightning current measurement and acquisition system with multi-channel active preamplifiers, which has the ability to measure lightning channel current as low as 10mA with a shock tolerance capability of 400kA. The contents in this thesis include a thorough literature review of relevant works, the framework and design principle of each subsystem of the proposed wide range current measurement system, laboratory and field test results of the system, and preliminary analyses of the field observation results using this system. The complete wide-range current measuring system we developed consists of two large parts: hardware and software. The hardware design mainly includes input signal attenuation and protection units, a four-channel preamplifier with different optimization directions, Analog-Digital-Converters (ADC), digital signal processing, optical communication, timing and isolated power supply. The software mainly includes the multi-channel data merging, signal triggering and buffering, Graphical-User-Interface (GUI) display, and data storage. The feasibility and successful implementation of this proposal are attributed to the commercialization of ultra-low noise op-amps and the increasing processing capability of computers. And the Shenzhen Meteorological Gradient Tower (SZMGT) also provided an excellent experimental platform for lightning currents observation. After installing this system on SZMGT, the background noise of current measurement is reduced to below 10 mA. We have successfully observed the corona discharge phenomenon with a current of several hundred milliamperes just before the occurrence of a lightning stroke, with the return stroke current exceeding 220 kA. This is the first time that lightning currents over seven orders of magnitude have been continuously observed and recorded, ranging from a few milliamperes to hundreds of kiloamperes. This observation will be beneficial in studying the physical processes in the initiation stage of lightning. Additionally, the system design has optimized its ability to resist electromagnetic interference, reduced installation space requirements, and simplified data path communication. These improvements make it more suitable for installation on SZMGT with complex electromagnetic environment.