Corona Discharge Characteristics under Variable Frequency and Pressure Environments

Abstract

More electric aircrafts (MEAs) are paving the path to all electric aircrafts (AEAs), which make a much more intensive use of electrical power than conventional aircrafts. Due to the strict weight requirements, both MEA and AEA systems require to increase the distribution voltage in order to limit the required electrical current. Under this paradigm new issues arise, in part due to the voltage rise and in part because of the harsh environments found in aircrafts systems, especially those related to low pressure and high-electric frequency operation. Increased voltage levels, high-operating frequencies, low-pressure environments and reduced distances between wires pose insulation systems at risk, so partial discharges (PDs) and electrical breakdown are more likely to occur. This paper performs an experimental analysis of the effect of low-pressure environments and high-operating frequencies on the visual corona voltage, since corona discharges occurrence is directly related to arc tracking and insulation degradation in wiring systems. To this end, a rod-to-plane electrode configuration is tested in the 20–100 kPa and 50–1000 Hz ranges, these ranges cover most aircraft applications, so that the corona extinction voltage is experimentally determined by using a low-cost high-resolution CMOS imaging sensor which is sensitive to the visible and near ultraviolet (UV) spectra. The imaging sensor locates the discharge points and the intensity of the discharge, offering simplicity and low-cost measurements with high sensitivity. Moreover, to assess the performance of such sensor, the discharges are also acquired by analyzing the leakage current using an inexpensive resistor and a fast oscilloscope. The experimental data presented in this paper can be useful in designing insulation systems for MEA and AEA applications.

Measurement of Corona Discharges under Variable Geometry, Frequency and Pressure Environment

“…Higher values of the frequency increase the global electric stress of the air surrounding the electrode, thus favouring corona inception conditions. This same effect was observed in our previous work [2], although in the present work, the effect of the radius of the spherical electrode is also analysed.…”

“…Therefore, to meet strict weight requirements, distribution voltage levels must rise in order to maintain the crosssection of the conductors below certain limits. However, operation at high-voltage pose aircraft insulation systems in a big challenge, since the combined effect of higher voltages, high compactness ratios, high power-to-weight ratios, higher operating frequencies and low-pressure operation greatly increase the risk of partial discharge (PD) occurrence [1,2]. It is well known that low-pressure operation significantly reduces the dielectric strength of air [3][4][5], and thus, surface discharges tend to initiate at lower voltages compared to the voltages at which they initiate at sea-level.…”

“…It is known that surface discharges can be detected by measuring their effects, including electromagnetic radiation, visible and ultraviolet light [2,3,14], acoustic emissions [14] or chemical components such as ozone [15], among others. There are different commercially available sensors for detecting surface discharges such as PD detectors, audible noise detectors [16], radio interference voltage detectors [17] or radio frequency antennas, among others.…”

Surface Discharges Performance of ETFE- and PTFE-Insulated Wires for Aircraft Applications

“…In such tests, the performance and sensitivity of the solar blind R9533 UVTRON sensor was compared with that of a single-loop antenna sensor and a back-illuminated CMOS imaging sensor. The results verified the sensitivity and accuracy of the UV-sensitive solar blind sensor in detecting UV radiation emitted by the discharges at a very early stage [23].…”

“…Before complete breakdown, electrical discharges produce partial discharges, which in air gaps are perceived as corona discharges [ 23 ] in the most stressed areas [ 24 , 25 ]. Partial discharges can be detected using expensive devices, including UHF detectors [ 26 ], partial discharge detectors and radio interference voltage devices [ 27 ], acoustic noise meters [ 28 , 29 ], or spectrophotometers [ 30 ], among others.…”