Comparative Study of AC and Positive and Negative DC Visual Corona for Sphere-Plane Gaps in Atmospheric Air

Abstract

Due to the expansion of high-voltage direct current (HVDC) power systems, manufacturers of high-voltage (HV) hardware for alternating current (ac) applications are focusing their efforts towards the HVDC market. Because of the historical preponderance of ac power systems, such manufacturers have a strong background in ac corona but they need to acquire more knowledge about direct current (dc) corona. Due to the complex nature of corona, experimental data is required to describe its behavior. This work performs an experimental comparative analysis between the inception of ac corona and positive and negative dc corona. First, the sphere-plane air gap is analyzed from experimental data, and the corona inception voltages for different geometries are measured in a high-voltage laboratory. Next, the surface electric field strength is determined from finite element method simulations, since it provides valuable information about corona inception conditions. The experimental data obtained are fitted to an equation based on Peek’s law, which allows determining the equivalence between the visual corona surface electric field strength for ac and dc supply. Finally, additional experimental results performed on substation connectors are presented to further validate the previous results by means of commercial high-voltage hardware. The results presented in this paper could be especially valuable for high-voltage hardware manufacturers, since they allow determining the dc voltage and electric field values at which their ac products can withstand free of corona when operating in dc grids.

Experimental Study of Visual Corona under Aeronautic Pressure Conditions Using Low-Cost Imaging Sensors

“…Table 2 summarizes the linear dependencies of the CEV versus the pressure of air, showing a very linear and thus predictable behavior. These results show a slightly higher slope of the CEV versus the pressure under positive DC supply, although at 100 kPa, the CEV values are lower under negative DC supply, as stated in the technical literature [22]. The results provided in Figure 9 show an almost linear behavior of the CEV values versus the pressure, for both positive and negative DC polarities of the applied voltage.…”

“…A corona is a type of partial discharge occurring in a gaseous dielectric, i.e., a discharge producing incomplete electrical breakdown of the interelectrode gap, which occurs under non-uniform field conditions whose strength is not sufficient to produce electrical breakdown [19]. Corona discharges take place when the field at the outer surface of a high-voltage electrode is beyond a critical value [20][21][22] since the molecules of the gaseous medium are likely to be ionized [23] because of collisions with electrons, thus initiating a cascade or avalanche of electrons under the influence of an intense electric field which is capable of accelerating the generated free electrons to ionization speeds. It is believed that the initial electrons can be generated by cosmic rays and energetic photoelectrons, which are more abundant and energetic at high altitudes.…”

Optical Radiation from an Electric Arc at Different Frequencies

“…They also compared the corona discharge measurements for positive and negative DC and AC for 50 Hz. Experimental results presented in [18] clearly show that the sphere-plane gap follows a correlation similar to Peek's law for cylindrical conductors. This conclusion is true for 50 Hz AC, positive DC and negative DC supply.…”

Arc Tracking Control in Insulation Systems for Aeronautic Applications: Challenges, Opportunities, and Research Needs

“…Under low pressure environments sound propagates with difficulty, so electromagnetic and UV-visible radiation can be used to detect corona [1,5]. Arcing in short gaps usually is preceded by corona discharges occurring at the region with highest electric field strength [11,78,79]. Corona discharges are key sources of premature failure of insulation systems operating at high altitude [5], occurring earlier at low pressure than at atmospheric conditions [13,80], so surface discharges are among the main causes for early failure of electronic equipment operating in low pressure environments [13].…”