Pa. Calva et Fp. Espino, CORRECTION FACTORS FOR POSITIVE DC VOLTAGES, IEEE transactions on dielectrics and electrical insulation, 5(4), 1998, pp. 541-544
Direct-current voltages are used mainly to test equipment utilized in
HV dc transmission systems, as an alternative to ac for testing cables
, capacitors, insulations in which internal discharges may lead to deg
radation of the insulation under ac testing conditions, in investigati
ons in discharge physics and dielectric behavior. For atmospheric air
the voltage measurements under any conditions are related to the stand
ard conditions employed the IEC-60 standard. It is demonstrated that t
he IEC correction procedure is not adequate for dc voltage measurement
s at high altitude; for example for rod-plane gaps there is a differen
ce > 10% between experimental data obtained at 2240 m above sea level
and those corrected with the IEC-60 procedure. This is mostly a conseq
uence of the fact that the physical model employed, which is based on
the field of propagation of streamers, fails to account for the combin
ed effect of humidity and altitude. It is surmised that the propagatio
n held of the prebreakdown streamers varies linearly with the air-dens
ity. The experimental rod-plane results obtained by the authors are be
tter modeled by an alternative semi-empirical model.