Lightning phenomena: II — Instruments for the measurement of lightning surges

Abstract

A number of special instruments have been developed to secure the information about lightning which utility system engineers must have if they are to devise adequate protection for the system. Such instruments are described in this second part of a series of three articles on lightning, of which part I appeared in the August issue, and part III is scheduled for next month. OF primary importance in the lightning protection of transmission lines is a knowledge of the magnitude, duration, and wave shape of the voltage and current surges appearing on utility systems. The characteristics of the stroke itself determine the resulting surges which occur on the electrical systems. Thus it becomes desirable to have instruments capable of measuring not only the system voltages and currents, but also the properties of the stroke. One difficulty encountered in the development of such instruments is the wide recording range both in magnitude and time that must be covered. Currents vary from a few amperes to 200,000 amperes. Portions of the wave change so rapidly that time intervals of the order of a microsecond need be measured, while at the same time the duration of the complete stroke may be longer than one second or 1,000,000 microseconds.