Dynamic characteristics of corona discharge generated under rainfall condition on AC charged conductors

Abstract

By synchronous measurement of corona current and the water droplet deformation process on a conductor surface, different types of corona discharge are visualized when AC voltage is applied on a line-ground electrode system. The corona characteristics are closely related to the applied voltage and water supply rate. With the increase of AC voltage, the positive Taylor cone discharge firstly appears and then disappears, replaced by the dripping and crashing discharge. Furthermore, the number of pulses in each pulse train increases with the increase of applied voltage. The mechanism of the transfer from the positive Taylor cone discharge to the dripping and crashing discharge is found to be related to the oscillation process of the water droplet. The water supply rate also has a great influence on the characteristics of corona currents. The number of positive pulse trains increases linearly when the water supply rate gets larger, leading to a higher audible noise and radio interference level from the AC corona, which is quite different from that of the DC corona. The difference between the AC and DC coronas under rainfall conditions is analyzed finally.

HVAC Corona Current Characteristics and Audible Noise During Rain

“…For AC corona, recent studies of the authors have found different possible mechanisms based on a scaled single-drop line to ground setup using high-speed footage. This difference is found to be closely related to the altered response of the water drop under the influence of AC and DC electric field [20], [21]. Under rainfall condition, DC corona discharge is mainly caused by Taylor cone deformation [13].…”

“…Thus, a higher rain rate contributes to lower DC audible noise due to an increase in the ionic space charge, shielding the conductor as well as the instability of the Taylor cone [20]. As demonstrated in a recent publication of some of the authors [21], the oscillation of water droplets under AC electric field weakens the stability of Taylor cone formation, and there are two kinds of corona discharge occurring instead. Firstly, for the so-called "dripping" discharge, a gap discharge will occur on the upper side when raindrops dripping on the conductor.…”

“…Furthermore, also the corona current pulses, which are known to have a strong correlation with the audible noise [22], are captured to explain the observed audible noise behavior. The results are then compared to previous results and discussed based on the introduced corona types in [21].…”

“…Under rainfall condition, DC corona discharge is mainly caused by Taylor cone deformation [13]. Generally, the stability of water drops on the conductor surface decreases with the increase of rain rate [20], [21]. Thus, a higher rain rate contributes to lower DC audible noise due to an increase in the ionic space charge, shielding the conductor as well as the instability of the Taylor cone [20].…”

“…Furthermore, both these types have shown to increase with the rain rate under certain electric fields. As a result, the AC corona performance gets worse with the increase of rain rate [21]. Due to these explained uncertainties regarding the effect of rain rate on the AC corona performance, this study will investigate the transient AC corona characteristics during periods of constant rain for different rain intensities in a larger laboratory setup as described in [13].…”