The Effect of Humidity and Temperature Variations on the Behavior of Wire-to-Plane Coronas

The effect of temperature and humidity on the current-voltage relationship and uniformity of positive and negative air coronas has been studied. Variations in temperature and absolute humidity seem to have a comparatively small effect on the behavior of coronas. By contrast, variations in the relative humidity have readily noticeable effects on the current-voltage relationship. At high voltages (positive or negative) the corona current decreases as the relative humidity increases due to ion and electron hydration effects. By contrast, both positive and negative coronas are initiated at lower voltages at high relative humidities, presumably due to the formation of miniscule water droplets with low ionization potential. The relative humidity also affects the uniformity of negative corona but not positive corona. Presumably the electron emitting properties of a negative wire are altered by moisture adsorbed on the wire surface at high relative humidities. By contrast, positive corona is not grossly affected because it is primarily a gas phase phenomena while negative corona is also sensitive to the electron emitting properties of the wire.