Corona Discharge Characteristics under Variable Frequency and Pressure Environments.
Bas-Calopa, P.; Riba, J.-R.; Moreno-Eguilaz, M. Sensors 2021, 21, 6676. https://doi.org/10.3390/s21196676
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.
Performance Evaluation of Solar-Blind Gas-Filled Sensors to Detect Electrical Discharges for Low-Pressure Aircraft Applications
Riba, J.-R.; Moreno-Eguilaz, M.; Boizieau, M.; Ibrayemov, T. Sensors 2022, 22, 492. https://doi.org/10.3390/s22020492
Unpressurized aircraft circuits facilitate the initiation of electrical discharges in wiring systems, with consequent damage to related insulation materials and safety hazards, that can and have already caused severe incidents and accidents. Specific sensors and solutions must be developed to detect these types of faults at a very incipient stage, before further damage occurs. Electrical discharges in air generate the corona effect, which is characterized by emissions of bluish light, which are found in the ultraviolet (UV) and visible spectra. However, due to sunlight interference, the corona effect is very difficult to detect at the very initial stage, so the use of solar-blind sensors can be a possible solution. This work analyzes the feasibility of using inexpensive non-invasive solar-blind sensors in a range of pressures compatible with aircraft environments to detect the electrical discharges at a very incipient stage. Their behavior and sensitivity compared with other alternatives, i.e., an antenna sensor and a CMOS imaging sensor, is also assessed. Experimental results presented in this paper show that the analyzed solar-blind sensors can be applied for the on-line detection of electrical discharges in unpressurized aircraft environments at the very initial stage, thus facilitating and enabling the application of predictive maintenance strategies. They also offer the possibility to be combined with existing electrical protections to expand their capabilities and improve their sensitivity to detect very early discharges, thus allowing the timely identification of their occurrence.
Arc Fault Protections for Aeronautic Applications: A Review Identifying the Effects, Detection Methods, Current Progress, Limitations, Future Challenges, and Research Needs
Riba, J.-R.; Moreno-Eguilaz, M.; Ortega, J.A. IEEE Transactions on Instrumentation and Measurement, 2022, 71. https://doi.org/10.1109/TIM.2022.3141832
Arc faults are serious discharges, damaging insulation systems, and triggering electrical fires. This is a transversal topic, affecting from residential to aeronautic applications. Current commercial aircrafts are being progressively equipped with arc fault protections. With the development of MEAs, future airliners will require more electrical power to enhance fuel economy, save weight, and reduce emissions. The ultimate goal of MEAs is electrical propulsion, where fault management devices will have a leading role, because aircraft safety is of utmost importance. Therefore, current fault management devices must evolve to fulfill the safety requirements of electrical propelled aircrafts. To deal with increased electrical power generation, the distribution voltage must be raised, thus leading to new electrical fault types, in particular arc tracking and series arcing, which are further promoted by the harsh environments typical of aircraft systems, i.e., low pressure, extreme humidity, and a wide range of temperatures. Therefore, the development of specific electrical protections which are able to protect against these fault types is a must. This article reviews the state-of-the-art of electrical protections for aeronautic applications, identifying the current status and progress, their drawbacks and limitations, the future challenges, and research needs to fulfill the future requirements of MEAs, with a special emphasis on series arc faults due to arc tracking, because of the difficulty in detecting such low-energy faults in the early stage and the importance and harmful effects of tracking activity in cabling insulation systems. This technological and scientific review is based on a deep analysis of research and conference papers, official reports, white papers, and international regulations.
Surface Discharges Performance of ETFE- and PTFE-Insulated Wires for Aircraft Applications
Riba, J.-R.; Moreno-Eguilaz, M.; Ibrayemov, T.; Boizieau, M. Materials 2022, 15, 1677. https://doi.org/10.3390/ma15051677
Compared to their predecessors, the next generations of aircrafts will be more electrified, require more electrical power and operate at higher voltage levels to meet strict weight and volume constraints. The combined effect of low-pressure environments, increased voltage levels and compact designs intensifies the risks of premature insulation degradation due to electrical discharge activity. This paper studies the resistance to surface discharges of PTFE (polytetrafluoroethylene) and ETFE (ethylene tetrafluoroethylene), two insulation materials widely used in today’s aircraft wiring systems due to their outstanding properties, such as a wide temperature operation range and a high dielectric strength. The study is carried out in a low-pressure chamber, which was pressurized within the pressure range of 10–100 kPa that includes most aircraft applications. There is a compelling need for experimental data to assess the resistance of insulation materials to surface discharges at a very early stage as a function of the environmental pressure. Data on resistance to surface discharges in low-pressure environments for aeronautical applications are lacking, while most standards for insulation systems are based on tests under standard pressure conditions. The results provided in this work can be useful to design wiring systems for future more electric aircrafts, as well as to design fault detection systems for an early detection and identification of faults related to surface discharges. Therefore, the data and analysis included in this paper could be of great interest to design and develop insulation systems for wiring systems and standard assessment methods, as well as to design fault detection strategies for the early detection and identification of surface discharges for future generations of more electric aircrafts.
Measurement of Corona Discharges under Variable Geometry, Frequency and Pressure Environment
Bas-Calopa, P.; Riba, J.-R.; Moreno-Eguilaz, M. Sensors 2022, 22, 1856. https://doi.org/10.3390/s22051856
Aeronautical industry is evolving towards more electric aircrafts (MEA), which will require much more electrical power compared to conventional models. To satisfy this increasing power demand and stringent weight requirements, distribution voltages must be raised, which jointly with the low-pressure environment and high operating frequencies increase the risk of electrical discharges occurrence. Therefore, it is important to generate data to design insulation systems for these demanding applications. To this end, in this work a sphere-to-plane electrode configuration is tested for several sphere geometries (diameters ranging from 2 mm to 10 mm), frequencies of 50 Hz, 400 Hz and 800 Hz and pressures in the 20–100 kPa range, to cover most aircraft applications. The corona extinction voltage is experimentally determined by using a gas-filled tube solar blind ultraviolet (UV) sensor. In addition, a CMOS imaging sensor is used to locate the discharge points. Next, to gain further insight to the discharge conditions, the electric field strength is calculated using finite element method (FEM) simulations and fitted to equations based on Peek’s law. The results presented in this paper could be especially valuable to design aircraft electrical insulations as well as for high-voltage hardware manufacturers, since the results allow determining the electric field values at which the components can operate free of surface discharges for a wide altitude range.
Analysing the Influence of Geometry and Pressure on Corona Discharges
Riba, J.-R.; Bas-Calopa, P.; Moreno-Eguilaz, M. European Journal of Physics 2022, Vol. 43 (5), pp. 055201. https://doi.org/10.1088/1361-6404/ac78a4
In this work, the authors propose an experiment aimed for undergraduate laboratories with the aim of introducing different novelties as a topic for practical sessions or student projects. The topics here investigated are appropriate for students with intermediate physics knowledge. Corona discharges are little studied in regular physics courses despite their practical importance in different areas, such as the distribution and transmission of electrical power, generation of ozone, particulate removal in air conditioning systems, improvement of wettability in polymeric materials, or the removal of electrostatic charges from the surface of airplanes among others. This work analyses the minimum voltage level leading to corona discharges and the influence of geometry and atmospheric pressure because these two factors are the most influential to determine the minimum voltage at which corona discharges appear.
Application of Image Sensors to Detect and Locate Electrical Discharges: A Review
Riba, J.-R. Sensors 2022, 22, 5886. https://doi.org/10.3390/s22155886
Today, there are many attempts to introduce the Internet of Things (IoT) in high-voltage systems, where partial discharges are a focus of concern since they degrade the insulation. The idea is to detect such discharges at a very early stage so that corrective actions can be taken before major damage is produced. Electronic image sensors are traditionally based on charge-coupled devices (CCDs) and, next, on complementary metal oxide semiconductor (CMOS) devices. This paper performs a review and analysis of state-of-the-art image sensors for detecting, locating, and quantifying partial discharges in insulation systems and, in particular, corona discharges since it is an area with an important potential for expansion due to the important consequences of discharges and the complexity of their detection. The paper also discusses the recent progress, as well as the research needs and the challenges to be faced, in applying image sensors in this area. Although many of the cited research works focused on high-voltage applications, partial discharges can also occur in medium- and low-voltage applications. Thus, the potential applications that could potentially benefit from the introduction of image sensors to detect electrical discharges include power substations, buried power cables, overhead power lines, and automotive applications, among others.
Using CMOS Image Sensors to Determine the Intensity of Electrical Discharges for Aircraft Applications
Riba, J.-R.; Bas-Calopa, P.; Aziz-Qolla, Y.; Pourraz, M.; Ozsahin, B. Applied Sciences 2022, 12(17), 8595. https://doi.org/10.3390/app12178595
The development of more electric aircrafts (MEA) and all electric aircrafts (AEA) inevitably implies an increase in electric power and a consequent increase in distribution voltage levels. Increased operating voltages coupled with low pressure in some areas of the aircraft greatly increase the chances of premature insulation failure. Insulation failure manifests itself as surface discharges, arc tracking, arcing, and disruptive or breakdown discharges, in order of increasing severity. Unfortunately, on-board electrical protections cannot detect discharges at an early stage, so other strategies must be explored. In their early stage, insulation faults manifest as surface and corona discharges. They generate optical radiation, mainly in the near-ultraviolet (UV) and visible spectral regions. This paper focuses on a method to detect the discharges, locate the discharge sites, and determine their intensity to facilitate predictive maintenance tasks. It is shown that by using small size and low-cost image sensors, it is possible to detect, locate, and quantify the intensity of the discharges. This paper also proposes and evaluates the behavior of a discharge severity indicator, which is based on determining the intensity of digital images of the discharges, so it can be useful to apply predictive maintenance tasks. The behavior and accuracy of this indicator has been tested in the laboratory using a low-pressure chamber operating in the pressure range of 10–100 kPa, which is characteristic of aircraft applications, analyzing a needle-plane air gap geometry and using an image sensor. The proposed method can be extended to other applications where electrical discharges are an issue.
Spectrum of Corona Discharges and Electric Arcs in Air under Aeronautical Pressure Conditions
Riba, J.-R. Aerospace, 2022, 9, 524. https://doi.org/10.3390/aerospace9090524
Due to the increase in electrical power demand, future more electric and all-electric aircraft designs will operate at higher voltage levels compared to current aircraft. Due to higher voltage levels and reduced operating pressure, insulation systems will be at risk. Air is the main insulating medium, and it is well known that its dielectric strength decreases considerably with operating pressure. Although electrical discharges can be detected by different techniques, optical methods are very attractive due to their sensitivity and immunity to acoustic and electromagnetic noise typical of aeronautical environments. This work analyzes the UV-visible spectrum of corona discharges and electric arcs in the 10–100 kPa pressure range, which covers most of the aeronautical applications, due to the lack of experimental data for this pressure range. The data presented in this work are important to select the most suitable optical sensors to detect electrical discharges at an early stage, before significant damage occurs. This approach will help implement preventive maintenance plans and increase aircraft safety. The results presented in this paper can also be applied to other areas, such as monitoring of discharges in power lines, particularly those located in high-altitude regions.
Use of DSLR and Sonic Cameras to Detect and Locate High-Voltage Corona Discharges
Riba, J.-R.; Bas-Calopa, P. Sensors 2022, 22, 7250. https://doi.org/10.3390/s22197250
Corona discharges are a concern in high-voltage applications. It is of utmost importance to detect and locate the discharges at an early stage using simple methods for this purpose. This paper evaluates and compares the sensitivity of two methods for detecting and locating the source of discharges, which are based on a digital single-lens reflex (DSLR) camera and a portable wideband sonic camera incorporating a matrix of micro-electromechanical systems (MEMS) microphones. Both cameras can generate an image of the studied area where the discharge sites are identified. The study is carried out with different electrode geometries, 50 Hz alternating current (ac) and positive and negative direct current (dc) supplies, and the effect of the distance between the sensor and the discharge sites is also analyzed. The presented results show that the sonic camera enables fast, simple, and sensitive detection and localization of the source of corona discharges even at a very early stage in daylight conditions, regardless of the type of power supply, that is, ac or positive/negative dc, and at distance of several meters from the discharge source.
Low-pressure optical detection, location and quantification of electrical discharges in aircraft wiring systems
Riba, J.-R.; Bas-Calopa, P.; Ortega, J.A. Aerospace 2023, 10(1), 3. https://doi.org/10.3390/aerospace10010003
Strict regulations issued by international administrative bodies limit the CO2 equivalent emissions for new aircraft, while increasing efficiency requirements. To reach this goal, next generations of aircraft will use more electrical power than their predecessors, so distribution voltage levels will inevitably increase to limit the weight of the electrical wiring interconnect system (EWIS). However, such increased voltage levels generate higher electric stresses in insulation materials as well as in electric and electronic components; thus new failure modes triggered by electrical discharges will appear, their effects being aggravated by harsh environments typical of aircraft systems. The combined effect of higher electrical stresses, compact designs, and low-pressure operating conditions greatly intensifies the risks of premature insulation failure due to electrical discharge activity. This paper shows that by using image sensors, it is possible to detect, localize, and quantify the intensity of electrical discharges occurring in aircraft environments. Through experiments carried out in a low-pressure chamber using an image sensor, this work detects and determines the intensity of electrical discharges generated in electrical wires in their initial stage, long before major faults develop. This paper also shows that the intensity of the discharges calculated from the digital images obtained with the image sensor is directly proportional to the electrical energy involved in the discharge process and increases linearly with the applied voltage. Due to the difficulty of detecting these failure modes at a very early stage, this strategy could potentially facilitate predictive maintenance tasks while contributing to increased levels of aircraft safety.
Analyzing the effect of dynamic pressure drop on corona discharges for aircraft applications
Bas-Calopa, P.; Riba, J.-R.; Moreno-Eguilaz, M. Aerospace 2023, 10, 320. https://doi.org/10.3390/aerospace10030320
The combination of the low-pressure environment found in aircraft systems and the gradual electrification of aircraft increases the risk of electrical discharges occurrence. This is an undesirable situation that compromises aircraft safety and complicates maintenance operations. Experimental data are needed to understand this problem. However, most of the published studies are based on static pressure conditions, but aircraft systems are exposed to dynamic pressure conditions, especially during the climb and descent phases of flight. This paper analyzes the effect of dynamic pressure during the climb phase on the corona inception voltage because this phase experiences the worst pressure drop rate. The experimental evidence presented in this paper shows that within the analyzed pressure drop rate range, the dynamic pressure conditions do not have a significant effect on the corona inception value under typical conditions found in aircraft systems during the climb phase.