The Electric Strength of Air-IV

An experimental study of the corona voltmeter

“…Later, J. B. Whitehead (2,3), after a careful study of the electric strength of air, suggested the initial formation of corona on clean, round wires as a means for the accurate determination of crest voltage. He and his coworkers (3) subsequently devised and studied instruments making use of this phenomenon and called them corona voltmeters.…”

“…In the case of concentric cylinders g= r 10~c(R/r) (2) in which Vc is the crest voltage between the outer cylinder and the rod at which corona begins to form and rand R are the radii in centimeters of tho rod and outer cylinder, respectively. 0 is called the density factor by P eele It is defined by T 273.1 + t (3) in which P is the absolute pressure in centimeters of mercury reduced to 0° C., and T is the absolute temperature in degr ees centigrade.…”

“…Using the electroscope for detecting ionization resulting from corona formation, Whitehead and Brown (3) observed that initial formation of a. c. corona coincided with negative d. c. corona, which occurs at a higher value of voltage than positive d. c. corona. Willis (7) working with a. c. corona on a cylindrical electrode about 1 mm in diameter, separated at adjustable distances from a plano wire-gauze electrode with a sensitive galvanometer and polarizing battery for detection of ions passing through the gauze electrode, found that the initial positive discharge or ionization current could not be detected at atmospheric pressure for separations greater than 8 cm.…”

“…It may be shown that, as an approximate rule, the relative error in crest voltage may be taken as numerically equal to 0.8 times the relative error in either temperature or pressure. In order to compare the results obtained by using formula (22) with values of t he per cent change in gradient p er ° C. as determined by previous experimenters, the data given by Whitehead and Fitch (3) in their Table III …”