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This paper reports non-intrusive partial discharge (PD) investigations on aeronautic and electric vehicle motors fed by inverter drive under variable environmental conditions. A representative test procedure and experimental setup based on operating aeronautic conditions are essential to ensure the accuracy and reliability of PD test on aircraft systems to make informed decisions on insulation system design choice. The aim of this paper is to demonstrate the feasibility of PD test of the insulation system on a different type of motor under such conditions, both electrically and environmentally. To do so, a study of the pressure influence on the frequency spectrum of discharges was carried out. This analysis defines the ability of the non-intrusive measurement system to detect PDs in equipment operating at low pressure. This paper also presents some tests on an industrial test bench to validate the ability of the non-intrusive test method and the associated numerical signal processing to detect PD in motors fed by PWM voltage. Then, an analysis is carried out on a motor to find out which voltage magnitude trigger PD events. The study helps to realize the benefits of using an inverter based test method to find the limits of the insulation system. It is shown that a representative insulation system performance picture could be drawn experimentally and used to enhance insulation design and manufacturing choices. The paper concludes with an analysis of results and thoughts about future work regarding advanced test procedure.

Voltage inverters based on the pulse width modulation are widely used for applications that require controlling rotation speed. The devices used today to create pulse width modulation are Silicon (Si) IGBTs. The use of IGBTs enables to generate rising edges of tens of kV /µs, and to reach switching frequencies around 20 kHz. These improvements have helped to reduce switching losses and motor torque ripple. On the other hand, the reliability of motors has declined dramatically. The causes of motor failures may be due to different phenomena, but one of the main ageing mechanisms is the erosion of the different insulation materials induced by Partial Discharges (PD). For high voltage, high power and/or high frequency applications, silicon carbide (SiC) based components will in most of the case replace the current silicon-based components. If some works have already been achieved for on-line PD detection in low voltage motors fed by inverters using Si-IGBT technology, works are now needed when SiC-based components are used. For motors fed by low voltage, PDs mainly occur during the voltage edge. It is therefore necessary to discriminate them from the noise induced by switchings. The use of high pass filters proved its effectiveness for IGBTs but the use of SiC MOSFET will result in an increase of switching speed and consequently an increase of the noise frequency. For such conditions, it may be difficult to differentiate partial discharges from noise. This paper presents a study on the partial discharge inception voltage, on the ability to detect partial discharges and on the voltage stresses in motors supplied by SiC-MOSFET and Si-IGBT inverters. These results are discussed and possible strategies are proposed.

The problematics of ageing in the Electrical Insulation Systems (EIS), especially in machines fed by adjustable speed drives, have been studied in numerous scientific publications, and even more with the introduction of wide-band gaps materials such as SiC. These fast-switching components induce over-voltages, which allow partial discharges to incept and lead to an erosion of the insulation materials. Various ageing mechanisms exist and depend on multiple parameters, but the influence of voltage slope, and therefore rise time, is a controversial subject which could require some further examination. Thus, it may be interesting to determine if these parameters have a direct impact on the ageing of EIS or if they only contribute to it indirectly, while their own effect would be less significant. To clarify this point, accelerated tests were performed and aimed at the comparison between the ageing of samples supplied by sinusoidal and square-wave stresses. The amplitude and frequency of the signals were the same, with a duty cycle of 50% in order to study the influence of the voltage slope only. Several levels of stress and frequencies were selected for the analysis and with additional purpose of reduction of tests duration. Lifetimes of samples were recorded to determine if there were any differences and to what extent.

In aeronautics, the concept of the “more electrical aircraft” emerged during the recent years thanks to the evolution of power electronics, the increase of power density, which has considerably spread the use of power converters for Adjustable Speed Drive (ASD) applications. In parallel, due to the power demand, increasing the voltage of the on-board network has been mandatory. Last but not least, some of these equipments work in depressurized areas of the aircraft. All these conditions put together made possible the existence of Partial Discharges (PD) in systems not designed to endure them. One of the main questions to address is the development of an approach for PD detection in machines supposed to be PD free. Their detection under PWM is therefore a key issue in this new field of applications. Recent advances made in the related different topics i.e on line PD detection under PWM voltage on real industrial test benches will be presented and discussed regarding their consequences.

At the dawn of this new millennium, transportations facing a much greener approach, the main aircrafts manufacturers have to change their paradigms: to replace the combination of hydraulic, pneumatic, electrical and mechanical power by a « More » (and “All” in the future) Electrical Aircraft approach consisting in drastically increasing the power density of electrical power systems without compromising on reliability. The increasing demand for more on board electrical power has led to increase the voltage and/or to change its shape. Such an increase may lead, depending on many parameters related to the electrical characteristics of the power chain (power converter, voltage waveform (dV/dt, frequency, …), the cables length, the type of machine driven) or to the environment (pressure, temperature, relative humidity) to the Partial Discharges Ignition in systems which were not supposed (and have not been designed) to endure them. Partial Discharges are voltage-dependent electrical discharges in insulation, which : - do not lead to a direct breakdown of the system, - lead to a gradual deterioration of the insulating material and to its premature failure - is often defined as “the silent enemy One of the main questions to address is the development of an approach for PD detection in type I machines (according to EIC 60034-18-41) ie machines supposed to be PD free allowing the determination of their existence under very different electrical conditions (PWM) due to the wide nature of the embarked equipment and to the different possible natures of the discharges. Recent advances made in the related different topics i.e on line PD detection under PWM voltage, influence of the pressure, influence of the components types…will be presented and discussed regarding their consequences.

International audience; The present paper reports non-electrically intrusive partial discharge investigations on an aeronautic motor fed by SiC inverter drive under variable environmental conditions. A representative test procedure and experimental set-up based on operating aeronautic conditions are essential to ensure the accuracy and reliability of partial discharge test on aircraft systems to make informed decisions on insulation system design choice. The aim of this paper is to demonstrate the feasibility of partial discharge test of the insulation system on a typical aeronautic motor under such conditions, both electrically and environmentally. To do so, the paper will start by detailing the innovative experimental set-up to be used in the study. It mainly consists in a high-voltage (1000V) inverter drive using SiC components to provide fast rise time surges and associated with phase-by-phase surge filtering. A vacuum chamber is used to simulate altitude while the association of non-intrusive sensors and wavelet based signal processing provided partial discharge detection. Optical detection is also used to reinforce partial discharge inception level accuracy. Then, an analysis is carried out on a 540V motor to find out which combination of switching frequency, harness length, rise time by phase and voltage magnitude is the worst case scenario. The study helps to realize the benefits of using an inverter based test method to find the limits of the insulation system under various pressure and electrical conditions. It is shown that a representative insulation system performance diagram could be built experimentally and used to enhance insulation design and manufacturing choices. This paper will also review the ability of the non-intrusive test method and the associated numerical signal processing to detect partial discharge in a motor fed by fast-rise time surge and under different pressures. The paper concludes with an analysis of results and thoughts about future work regarding advanced test procedure.

International audience; The present paper reports on a study of non-electrically intrusive partial discharge investigations on an aeronautic motor. Relevancy, robustness and repeatability of partial discharge testing procedures, both on insulating materials characterization and on operating aeronautic equipment are essential to ensure reliability of the aircraft systems. The aim of this paper is to be the very first step of defining such procedures and the associated test equipments. To do so, the paper will start by providing an understanding of partial discharge phenomena and will review typical more electrical aircrafts architectures and their key characteristics causing partial discharge risk to increase. The impact of harness length, high performance power electronics and increase of voltage level on insulation system is demonstrated. Then, an analysis is conducted from motor design point of view to find out which test procedures are relevant to each insulation system performance both at atmospheric pressure and reduced pressure. The study helps to realize the benefits of using multiple test samples and procedures to assess insulation system performance levels through the design process of the motor. It is shown that a good agreement is find out between the stator and representative samples. This paper will also review the ability of the non-intrusive test method used to detect partial discharge with a full scope of voltage signal from AC to impulse voltage and under different pressure. The paper is concluded with analysis of results and thoughts about future work regarding motor design taking into account partial discharge risk and evolution of proposed procedures.

International audience; In forecoming “more electrical aircrafts”, aircrafts will become more compact and light, as hydraulic, pneumatic or mechanical systems will be replaced by electrical ones. The network voltage is expected to increase far above Paschen’s minimum, thus increasing the risk of partial discharges. These discharges, known as silent enemies, may affect the reliability of the system. Moreover, some electrical equipments are located in unpressurized area and their operating conditions (temperature, pressure) may change in a large range. These environmental parameters (and their cycling) have an influence on discharge inception voltage and may even modify its nature. This paper deals with the influence of the pressure on partial discharges and especially on the modification of partial discharges spectra with pressure. Twisted pairs of enamel wires were subjected to repetitive square voltage waveform and sinusoidal voltage at various pressures.

International audience; In forecoming “more electrical aircrafts”, aircrafts will become more compact and lighter. Hydraulic, pneumatic or mechanical systems will be replaced by electrical ones thus leading to an increased demand of electric power. The network voltage is expected to increase far above Paschen’s minimum, thus increasing the risk of partial discharges. Furthermore the use of inverter drives will be generalized and PD detection on square voltage powered equipments will become a mandatory challenge. The purpose of this study is to propose a method to denoise partial discharge signals embedded in the electromagnetic noise induced by switchings. This denoising is performed using the wavelet decomposition.

International audience; This paper presents the recent advances made in the field of Partial Discharges detection and analysis in the field of aeronautics. More particularly, it intends to present the influence of the voltage waveform on the type of detection method, the role of the assembly process on the PD Inception Voltage and finally an on line PD detection under PWM voltage. The influence of the pressure on the type and nature of the discharges is also discussed.

This paper deals with Partial Discharge (PD) detection in a twisted pair fed by a bipolar square shape voltage using a non-intrusive sensor. These discharges are hardly detected, yet harmful, in such an environment and it may be caused by the nature of the discharge itself. Thus, the aim of this work is to investigate the nature of the discharge using an intensified CCD camera to follow the temporal evolution of the light distribution on a controlled sample.

This paper deals with partial discharge (PD) measurements in twisted pair fed, in parallel, by a PWM inverter driving an electric motor. PD detection is carried out while the motor is running using a non-intrusive antenna sensor. Data are randomly acquired while the powertrain is running. Then, two alternative numerical signal processing methods based on energy spectral density are proposed to classify signals with or without PDs. The first method uses spectral features chosen by human experts. The second method automatically derives optimum features by using linear discriminant analysis.

This paper deals with partial discharge measurements in twisted pair fed by a PWM inverter. Measurements are carried out using antenna sensors. Both D-Dot sensor and self-made sensors are compared when it comes to detect partial discharge in a PWM environment. High-pass filter performance is tested as well with these sensors. Finally, a innovative noise suppression method is demonstrated using two identical antenna sensors. This method could be a useful and simple mean to improve signal to noise ratio before signal processing.

This paper deals with partial discharge measurements in twisted pair fed by a PWM inverter. Measurements are carried out using antenna sensors. Both D-Dot sensor and self-made sensors are compared when it comes to detect partial discharge in a PWM environment. High-pass filter performance is tested as well with these sensors. Finally, a blind source separation method is presented.

The voltage level aboard new aircraft generations has grown from 115V AC to 230V AC . This has given rise to a new HVDC +/- 270V instead of +270V. The Adjustable Speed Drives (ASD) aboard more electrical aircraft are currently fed by fast switching PWM IGBT converters which rise time and fall time are higher than 50ns. To improve the converters power density, the very fast Wide Bandgap semiconductor technologies (Silicon Carbide) are currently under evaluation; their switching rise time and fall time could be lower than 20ns. This paper, by using industrial ASD fed by 540Vdc, initially addresses an experimental investigations analysis of motor overvoltages according to: inverters technologies (IGBT and SiC), harness length and harness shielding. Then, investigations on the Partial Discharges Inception Voltage (PDIV) are carried out on primary components of Electrical Insulation System (EIS) type 1 at atmospheric and reduced pressures, according to several parameters: magnet wire (MW) diameter, MW grade, polyimide insulating paper thickness. The paper concludes with a discussion of the different results and thoughts about overvoltages and partial discharges challenges.

The development of power electronics in recent years has led to increase power density and to decrease pulse width modulation (PWM) voltage inverter cost. These developments have expanded the use of power converters for variable speed drive applications which enabled the development of the concept of "more electric aircraft". This concept consists in replacing one of energy carriers (pneumatic or hydraulic) with electrical energy. However, the deployment of electrical energy has increased the onboard voltage, which leads to premature aging of onboard electrical equipment. The shape of the PWM voltage consists of pulse trains. With the application of these pulses, the voltage is no longer homogeneously distributed along the coil. In this case, large differences in potential between the strands are present. In addition, another important parameter derived from the winding type motor used in industry. The random winding is the most common technique for low voltage motors due to its lower cost. The risk generated by this type of winding is that the first and the last turns of the first coil can be facing one another. In this case, up to 80% of the voltage will be supported by a few tens of microns of enamel, and existing insulation systems are not designed to withstand such severe constraints. The use of long cable connecting the inverter to the motor can also cause significant overvoltage at the motor terminals. This phenomenon is explained by the fact that the cable behaves as a transmission line to which the motor coils is not adapted in terms of impedance. In addition, these large potential differences associated with low pressures in the depressurized areas of the aircraft, may cause the occurrence of partial discharge. Partial discharges are electrical discharges that short-circuited partially the gap between two conductors. There are many detection methods well known under AC and DC voltage, however, in the case of the detection under PWM like voltage in low-voltage motors, the detection is much more complex. Partial discharge signals are embedded in the electromagnetic noise generated by the switching. The aim of this thesis is to develop a detection method and filtering method enabling a non-intrusive and an "on-line" partial discharges detection in the aeronautical field in order to qualify the electrical insulation systems used in aircraft.; L'évolution de l'électronique de puissance ces dernières années a entraîné une augmentation de la densité de puissance et une diminution du coût des onduleurs de tension à modulation de largeur d'impulsion (MLI). Ces évolutions ont répandu l'utilisation de convertisseurs de puissance pour les applications de variateurs de vitesse ce qui a permis le développement du concept d' " avion plus électrique ". Ce concept consiste à remplacer un des vecteurs énergétiques (pneumatique ou hydraulique) par l'énergie électrique. Cependant, le développement du réseau électrique a entraîné une augmentation de la tension embarquée, ce qui a conduit à un vieillissement prématuré des équipements électriques embarqués. La forme de tension appliquée, appelée "modulation de largeur d'impulsion" (MLI), est constituée de trains d'impulsions. Avec l'application de ces impulsions, la tension n'est plus distribuée de manière homogène le long du bobinage. Dans ce cas, on pourra observer d'importantes différences de potentiel entre les spires d'une même phase voire entre deux phases du bobinage. En outre, un autre paramètre important provient du type d'enroulement des moteurs utilisés par l'industrie. L'enroulement aléatoire est la technique de bobinage la plus courante pour les moteurs basses tensions car cette méthode présente un faible coût. Le risque induit par ce type d'enroulement est que la première et une des dernières spires de la première bobine peuvent être proches l'une de l'autre. Dans ce cas, jusqu'à 80% de la tension sera supportée par quelques dizaines de microns d'émail, et les systèmes d'isolation existants ne sont pas dimensionnés pour résister à de telles contraintes. L'utilisation de longs câbles reliant l'onduleur au moteur peut aussi provoquer des surtensions importantes aux bornes du moteur. Ce phénomène s'explique par le fait que le câble se comporte comme une ligne de transmission qui n'est pas adaptée en termes d'impédance au bobinage du moteur. De plus, ces importantes différences de potentiel associées à de faibles pressions, présentes dans les zones dépressurisées de l'aéronef, peuvent entraîner l'apparition de décharges partielles. Les décharges partielles sont des décharges électriques qui court-circuitent partiellement l'intervalle entre deux conducteurs. Il existe de nombreuses méthodes de détection bien connues pour les tensions AC et DC, cependant, la détection sous tension de type MLI dans des moteurs basse tension est beaucoup plus complexe. Les signaux de décharge partielle sont en effet intégrés dans le bruit électromagnétique généré par la commutation. Le but de cette thèse est donc de développer un procédé de détection et un procédé de filtrage permettant une détection non intrusive et en fonctionnement (on-line) des décharges partielles dans le domaine aéronautique afin de qualifier les systèmes d'isolation électrique utilisés dans les aéronefs.

The development of power electronics in recent years has led to increase power density and to decrease pulse width modulation (PWM) voltage inverter cost. These developments have expanded the use of power converters for variable speed drive applications which enabled the development of the concept of "more electric aircraft". This concept consists in replacing one of energy carriers (pneumatic or hydraulic) with electrical energy. However, the deployment of electrical energy has increased the onboard voltage, which leads to premature aging of onboard electrical equipment. The shape of the PWM voltage consists of pulse trains. With the application of these pulses, the voltage is no longer homogeneously distributed along the coil. In this case, large differences in potential between the strands are present. In addition, another important parameter derived from the winding type motor used in industry. The random winding is the most common technique for low voltage motors due to its lower cost. The risk generated by this type of winding is that the first and the last turns of the first coil can be facing one another. In this case, up to 80% of the voltage will be supported by a few tens of microns of enamel, and existing insulation systems are not designed to withstand such severe constraints. The use of long cable connecting the inverter to the motor can also cause significant overvoltage at the motor terminals. This phenomenon is explained by the fact that the cable behaves as a transmission line to which the motor coils is not adapted in terms of impedance. In addition, these large potential differences associated with low pressures in the depressurized areas of the aircraft, may cause the occurrence of partial discharge. Partial discharges are electrical discharges that short-circuited partially the gap between two conductors. There are many detection methods well known under AC and DC voltage, however, in the case of the detection under PWM like voltage in low-voltage motors, the detection is much more complex. Partial discharge signals are embedded in the electromagnetic noise generated by the switching. The aim of this thesis is to develop a detection method and filtering method enabling a non-intrusive and an "on-line" partial discharges detection in the aeronautical field in order to qualify the electrical insulation systems used in aircraft.; L'évolution de l'électronique de puissance ces dernières années a entraîné une augmentation de la densité de puissance et une diminution du coût des onduleurs de tension à modulation de largeur d'impulsion (MLI). Ces évolutions ont répandu l'utilisation de convertisseurs de puissance pour les applications de variateurs de vitesse ce qui a permis le développement du concept d' " avion plus électrique ". Ce concept consiste à remplacer un des vecteurs énergétiques (pneumatique ou hydraulique) par l'énergie électrique. Cependant, le développement du réseau électrique a entraîné une augmentation de la tension embarquée, ce qui a conduit à un vieillissement prématuré des équipements électriques embarqués. La forme de tension appliquée, appelée "modulation de largeur d'impulsion" (MLI), est constituée de trains d'impulsions. Avec l'application de ces impulsions, la tension n'est plus distribuée de manière homogène le long du bobinage. Dans ce cas, on pourra observer d'importantes différences de potentiel entre les spires d'une même phase voire entre deux phases du bobinage. En outre, un autre paramètre important provient du type d'enroulement des moteurs utilisés par l'industrie. L'enroulement aléatoire est la technique de bobinage la plus courante pour les moteurs basses tensions car cette méthode présente un faible coût. Le risque induit par ce type d'enroulement est que la première et une des dernières spires de la première bobine peuvent être proches l'une de l'autre. Dans ce cas, jusqu'à 80% de la tension sera supportée par quelques dizaines de microns d'émail, et les systèmes d'isolation existants ne sont pas dimensionnés pour résister à de telles contraintes. L'utilisation de longs câbles reliant l'onduleur au moteur peut aussi provoquer des surtensions importantes aux bornes du moteur. Ce phénomène s'explique par le fait que le câble se comporte comme une ligne de transmission qui n'est pas adaptée en termes d'impédance au bobinage du moteur. De plus, ces importantes différences de potentiel associées à de faibles pressions, présentes dans les zones dépressurisées de l'aéronef, peuvent entraîner l'apparition de décharges partielles. Les décharges partielles sont des décharges électriques qui court-circuitent partiellement l'intervalle entre deux conducteurs. Il existe de nombreuses méthodes de détection bien connues pour les tensions AC et DC, cependant, la détection sous tension de type MLI dans des moteurs basse tension est beaucoup plus complexe. Les signaux de décharge partielle sont en effet intégrés dans le bruit électromagnétique généré par la commutation. Le but de cette thèse est donc de développer un procédé de détection et un procédé de filtrage permettant une détection non intrusive et en fonctionnement (on-line) des décharges partielles dans le domaine aéronautique afin de qualifier les systèmes d'isolation électrique utilisés dans les aéronefs.