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A STANDARD FOR THE MEASUREMENT OF HIGH VOLTAGES. 
C. Francis Harpinac. 
Modern developments in the generation, transmission, distribution and 
utilization of electricity at high voltages have greatly outstripped the accurate 
measurement of such voltages. Those familiar with the very accurate stand- 
ards and measurements of voltage, current and power at low potentials may 
be surprised to learn that the recognized standard for the determination 
of high voltages is the needle or sphere spark gap. In other words the voltage 
if measured simply by the distance that it will cause a spark to Jump in air 
between needle points or spheres under specified conditions. 
It is hardly necessary to point out that such a standard is readily affected 
by temperature, humidity and barometric changes, not to mention the 
presence of other conductors which may be in the immediate vicinity. It 
is therefore not readily reproducible and it is most difficult to make the two 
standards agree at 50 kilovolts at which voltage both should be accurate. 
With these facts in mind, an attempt is being made in the electrical 
laboratories of Purdue University to develop a more satisfactory standard 
for the measurement of high voltages which is based upon the fundamental 
principles of the electrostatic field. Although many forms of electrostatic 
voltmeters have been developed in the past, in the endeavor to commercialize 
them and make them compact, the very uniform field upon which their 
accuracy depends has been sacrificed. No attempt has been made to make 
the standard voltmeter described herein portable or a thing of beauty, for it 
is believed that such qualities are quite subordinate im the consideration 
of a primary standard. 
If a perfectly uniform electrostatic field is produced between two parallel 
metal plates it can be readily shown that the force action between such 
plates expressed in dynes is 
AK?K 
a 
Srt? 
where A = area of plate in square centimeters 
E = potential expressed in electrostatic units 
Kk = dielectric constant (unity for air) 
t = distance between plates in centimeters. 
