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Proceedings ArticleDOI

Advanced Partial Discharge Testing of 540V Aeronautic Motors Fed by SiC Inverter under Altitude Conditions

19 Sep 2017-pp 1-17

TL;DR: It is shown that a representative insulation system performance diagram could be built experimentally and used to enhance insulation design and manufacturing choices to make informed decisions on insulation system design choice.
Abstract: 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.
Topics: Partial discharge (61%), Insulation system (57%), Test method (53%), Inverter (51%)

Summary (7 min read)

Jump to: [Background][Scope and Goal of the Work][Outline][An electrical discharge that only partially bridges the insulation between conductors. A transient gaseous ionization occurs in an insulation system when the electric stress exceeds a critical value,][Consequences of Partial Discharge][Partial Discharge in More Electrical Aircraft][Partial Discharge Inception Voltage][More Electrical Aircraft Paradigm][Key Role of Highly Integrated Power Electronics][High Speed High Voltage Power Amplifier][Analog to Digital Conversion][Analog High Pass-Filtering][Partial Discharge Sensors][Capacitive Sensor][Environmental Conditions][Rise Time and Overvoltage Measurement][Capacitive Sensor Study][Switching Noise Magnitude Evolution: Relation with Common Mode Current][Analogical Filters Performance][Noise Suppression Improvement][Electric Motors Description][Stator n°1: Laboratory Dummy Sample][Stator n°2: High Mechanical Integration Constraint Stator][Stator n°3: Low Cost Stator][General Purpose][PDIV of Experimental Set-Up][Stator n°1][Phase to ground][Phase to Phase][Stator n°2][Phase to Ground Tests][Stator Supplied by Three-Phase SiC Inverter at Atmospheric Pressure][Stator n°3][Phase to Ground][Coil-to-Coil Tests][Coil Configurations and Electric Stator Characteristics][Preventing PD in Turn-to-Turn Insulation][Preventing PD in Coil to Coil Insulation][Discussion about Winding Configuration Influence] and [Summary and Conclusions]

Background

  • Optimization of energy sources aboard aircraft and permanent improvements in more electric technologies are pushing the aeronautic industry to aim for the more electrical aircraft (MEA).
  • Power generation, distribution and conversion are easier because achieved than with traditional hydraulic systems needing large, heavy and maintenance intensive distribution system.
  • But, this shift towards MEA is not without consequences on the electrical stress the insulation system has to withstand.
  • Thus, with primary voltage increasing, power distribution architecture evolution and high power density power electronics, partial discharge (PD) is now a serious cause of concern for aircraft integrator, system designer and component manufacturer.
  • Once PDs are occurring regularly, degradation of the insulation system until premature failure of the aircraft system is irremediable.

Scope and Goal of the Work

  • This topic of interest has already been discussed by several key actors of the aerospace industry, research center such as US Air force laboratory or international academic actors.
  • Among key issues of aeronautic companies that has to be investigated electric motors in an electrically non-intrusive way and under representative aeronautic environment when fed by a silicon carbide (SiC) inverter drive will be addressed in this paper and will be the main contribution.
  • The aim of this paper is to demonstrate the feasibility of partial discharge test of conditions, both electrically and environmentally.
  • The study helps to limits of the insulation system under various pressure and electrical conditions.
  • But, as a whole, a key link in the testing chain was still missing.

Outline

  • In a second step, key features of more electrical aircraft will be recalled and how they relate to the innovative experimental set-up used here.
  • Then, its main characteristics will be presented and an analysis is made regarding the relation between time, dV/dt and overvoltage.
  • The impact of a SiC inverter drive on the non-intrusive detection and wavelet numerical processing will be presented as a mean to double-check partial discharge inception (PDIV) values.
  • Then, details of the 3 stator will be presented and will be followed by tests results and analysis.
  • Stator n°1 illustrates the potential consequences of undetected partial discharge on the insulation system and its consecutive failure.

An electrical discharge that only partially bridges the insulation between conductors. A transient gaseous ionization occurs in an insulation system when the electric stress exceeds a critical value,

  • And this ionization produces partial discharges.

Consequences of Partial Discharge

  • Partial discharge events have been known and studied for more than a century, starting with Paschen, Peek and Townsend among others.
  • Partial discharges are feared because they contribute to the degradation of the insulation system and lead to its premature failure [8] as will be shown in this paper.

Partial Discharge in More Electrical Aircraft

  • Since this variation is non-linear with pressure, it is assumed that no simple scale factor could be applied to predict partial discharge inception voltage from results at atmospheric pressure.
  • It is thus mandatory to carry out test across the whole range of pressure.

Partial Discharge Inception Voltage

  • The lowest voltage at which continuous partial discharges (PDs) permissible background noise) occur as the applied voltage is including the rate at which the voltage is increased as well as the previous history of the voltage applied to the winding or component thereof PDIV could be expressed either at RMS or peak voltage depending on the applied voltage during test.
  • During partial discharge test of equipment, PDIV is usually a representation of the insulation system quality.
  • In other words, it partial discharge occurs.
  • It is thus of a critical importance to that tests are robust, easy to reproduce and relevant for the foreseen application.
  • Have dramatic consequence on its reliability, leading to short-circuits creating electrical arcs.

More Electrical Aircraft Paradigm

  • The MEA approach underlines the use of electrical system for non-propulsive application such as environmental control systems.
  • Other applications such as electrical taxiing or anti-icing are also aircraft has no on-engine hydraulic power generation and bleed air.

Key Role of Highly Integrated Power Electronics

  • A key enabler of such development is the breakthrough in high power density, high voltage and reliable silicon-based power semiconductor switching device such as insulated gate bipolar transistor (IGBT).
  • It is expected that state-of-the-art switching device such as Silicon Carbide (SiC) or Gallium Nitride (GaN) will dramatically improve inverter drive, converters, motor controller and other semiconductor.
  • The evolution of power electronics towards fast switching in the primary voltage is putting even more stress on motor insulation system [9, 10, 11, 12].
  • The combination of harness length, fast rise time is creation overvoltage at motor terminals and an uneven voltage distribution is found on coils increasing electrical stress on the turn-to-turn insulation system.
  • The following experimental set-up aims to recreate such electrical stresses.

High Speed High Voltage Power Amplifier

  • 10kV peak and a maximum of 40mA RMS current with a bandwidth tested such as AC at various frequency, square bipolar with adaptable duty cycle, frequency and other point-per-point signals.
  • An inverter drive has been designed at IRT Saint Exupéry to recreate voltage, two 15kW 500V ElektroAutomatic DC power supplies are in series with the mid-point grounded, the total DC bus voltage could remotely be varied from ± 10V to ± 500V.
  • The inverter drive consists in three 1700V SiC Cree power modules delivering fast rise times on each phase with driver boards accepting Matlab-Simulink model could be used to control the inverter drive thanks to the use of an OPAL-RT real time calculator.
  • Switching frequency, carrier frequency and modulation factor could easily be per phase (enable and command) allowing the use of the inverter as a High Voltage Measurements Voltage level are monitored using a Testec TT-SI 9010A (1/1000.

Analog to Digital Conversion

  • Data are displayed and recorded using a Keysight DSOS204A oscilloscope with a sampling rate of 20GSa/s and numerical bandwidth numerically, the high resolution mode (12 bits) is used instead of the peak detect mode at the higher sampling frequency available.

Analog High Pass-Filtering

  • When performing measurement using non-intrusive sensor, it is usual remove noise coming from inverter drive switches or power have been used in the following experiments.

Partial Discharge Sensors

  • Technological research at IRT Saint-Exupéry are focused on non-intrusive sensors.
  • These sensors and associated method have both electric motor in automotive [2] and aeronautic test benches [5].

Capacitive Sensor

  • The non-intrusive sensor used to detect partial discharge is taking sensor behavior in the next part.
  • This sensor has already been used in numerous study, particularly [2] and [6].

Environmental Conditions

  • All the tests have been carried out within a grounded vacuum chamber, acting as a faraday chamber, connected to a vacuum pump.

Rise Time and Overvoltage Measurement

  • Time dependent rise time and overvoltage analysis has been carried out while feeding a three phase electric.
  • Measurements were probe between the DC- and the output of the power module.
  • Table 1 details the used operating point.
  • Typical SiC inverter behavior could be observed on both rise time and overvoltage which is both are current dependent.
  • As a result, the electrical stress created by the combination of dV/dt and overvoltage is time dependant.

Capacitive Sensor Study

  • Impulses are transduced into voltage variations through the capacitance between the copper wire and oscilloscope impedance.
  • Due to its small geometry, achieving good contact and adequate holding on the 3D printed pliers to ensure good contact regardless of the cable gauge and vibrations Sensor sensitivity can therefore be increased simply by improving the coupling capacitance value.
  • This is achieved by increasing the contact surface by putting copper tape on the surface of the power cable to control the interacting area and thus the value of the induced capacity ( ).
  • It is important to note that this sensor is sensitive to the dynamic of the partial discharge compared to the "standards" sensors, which are only sensitive to the amplitude of the discharge.

Switching Noise Magnitude Evolution: Relation with Common Mode Current

  • When performing non-intrusive PD detection, periodic pulses numeric, it is important to track how maximum switching noise is evolving with DC bus voltage.
  • Each of these switching is intrusive sensor.
  • This source of noise collected by the sensor is dependent of the common mode capacitance of the whole set-up value.
  • Whereas the common mode capacitance is decreased when stator frame is will be low when the stator frame is grounded, as it is usually the case in aeronautic applications.
  • The sensitivity of the measurement of PD pulse high frequency current will thus be function of the sample common mode capacitance, detection capacitance and the spread of frequency content between switching common mode current and partial discharge current.

Analogical Filters Performance

  • Since the sensor is sensitive to quick changes in current, any phenomenon that induces this type of variation can cause a sensor response.
  • When seeking to detect PDs in equipment supplied by inverter using PWM., a key challenge is to distinguish the raw signal with respect to electromagnetic noise induced by fast switching inverters.
  • The magnitude of the signal associated with partial discharges generally has an amplitude of several tens of mV, while the magnitude of the noise signal is on the order of several hundred mV and depends on the voltage magnitude as has been demonstrated previously.
  • A study was carried increased capacitance.
  • It can be seen in that the noise increases with the amplitude of This is explained by the fact that the dV / dt is not only dependent on the amplitude of the voltage but also the switched current.

Noise Suppression Improvement

  • In aeronautical environments, some equipment operates under pressure and temperature conditions that can vary greatly.
  • Signal reconstructed by CWT (red) at atmospheric pressure Moreover this method sets all the wavelet transform 21].
  • This method has real no longer required to remove noise in signals.
  • It should be noted that although PDIV could be determined with this method, no calibration or PD pulse shape analysis could be carried out at the moment with the proposed algorithm.

Electric Motors Description

  • In order to validate their detection method and to make the best use of their test bench based on the SiC technology, three low voltage stators chosen of designed.
  • The table below summarizes some of their properties.
  • These are stators of three-phases Permanent Magnet Synchronous Motor (PMSM), they are designed to be powered with Pulse Width Modulation (PWM) inverters.

Stator n°1: Laboratory Dummy Sample

  • The design of this stator has been extensively detailed in [6] are tables regarding insulation and electric design are recalled below (Tables 5, 6, 7).
  • The two terminals of each of his three phases are accessible.
  • This allows to test each phase separately.
  • It is very important to highlight that the stator is not impregnated and that it has been rewound before starting the test campaign to ensure a PD free previous history.

Stator n°2: High Mechanical Integration Constraint Stator

  • Pressure (VPI process), this allows the varnish to penetrate as much as possible within the windings.
  • Its end-windings are mechanically compressed to optimize the axial length of the machine ( ).
  • The neutral point is not accessible so the evaluation of the PDIV of each phase alone (turn to turn PDIV) is not possible.
  • Therefore, only the star-connected case will be tested.
  • Due to non-disclosure agreement with their industrial partners, insulation and electrical design details could not be provided for stator n°2 except that this is a three phases motor with four parallel coils per phase.

Stator n°3: Low Cost Stator

  • Unlike the other two stators, this stator is cooled by air.
  • The insertion of its coil is automated, this allows a more reproducible winding but end-windings are not compressed and are insulated by relatively thick tapes.
  • It is also varnished using dipped impregnation instead of vacuum pressure impregnation as shown in Each of its three phases (U, V and W) is composed of four coils (U1, U2, U3, U4, V1, V2, V3, V4 and W1, W2, W3, W4).
  • This stator is designed for electric traction application under atmospheric conditions.

General Purpose

  • Both 100mbars and atmospheric pressure except for stator n°3.
  • The purpose of these tests is to investigate the PDIV under SiC inverter drive electrical stress compared to typical AC tests usually carried out.
  • On one hand, AC tests are used to determine the PDIV between phases (if neutral point is disconnected), and between phases and stator frame.
  • On the other hand, SiC inverter tests will be used to determine PDIV in a more realistic approach with fast rime time impulse compared to aeronautic standard (>5V/µs).

PDIV of Experimental Set-Up

  • Before starting any investigation, PDIV of the experimental set-up Table 8).

Stator n°1

  • Stator n°1 has been designed at IRT Saint-Exupery to represent a typical aeronautic electric motor insulation system.

Phase to ground

  • Grounded to test the slot insulation only.
  • Then each phase is tested separately in respect to the stator frame.
  • Tests are performed with 50 Table 9) Results are similar with their previous technical report [6], showing that even a complete rewound of the electric motor lead to stable between phases could be noted suggesting that slot insulation is balanced in all slots.

Phase to Phase

  • The phase to phase insulation is made with the same material as the slot insulation (insulating paper).
  • Results (Table 15) are consistent with this observation and should lead to better phase-to-phase insulation performance, although PDIV value are also more widely distributed.
  • Another possible cause for this better performance is the concentric windings.

Stator n°2

  • Stator n°2 is also an aeronautic electric motor with the neutral point star connected meaning only few tests are possible both in AC and possible.

Phase to Ground Tests

  • A typical phase to ground insulation test is made on all phases at the Phase to ground insulation performance is better than for stator n°1 which presents similar insulation characteristics except for test for the VPI varnishing process.
  • It is believed that the VPI process helps most of air gaps.

Stator Supplied by Three-Phase SiC Inverter at Atmospheric Pressure

  • The electric stator is tested at low pressure (100mbars).
  • It can be seen on that the discharge appears at 641 Vpeak at 100 mbar for the maximum voltage.
  • Any insulation could trigger a This PD location is not characteristics of any insulation on the contrary to the previous case.
  • Other parasitic signals of lower amplitude at 100 mbar could be observed and are labelled as residual noise.
  • Detection with high-pass test and numerical signal processing.

Stator n°3

  • Stator n°3 is only tested at atmospheric pressure.

Phase to Ground

  • In table 14, PDIV values for each phase are more widely distributed regarding stator n°3 than for both previous stators which is phase-to-ground insulation performance.
  • Lowest phase to ground PDIV for stator n°3 is very similar to stator n°1 average phase to ground PDIV value.

Coil-to-Coil Tests

  • Since 12 coils are available, each one is tested relatively to each other within each phase.
  • This is not a conventional test since these coils are supposed to be connected in parallel within each phase and should coils of the same phase are in close vicinity to each other and the magnet wire and varnish is the only insulation and it could lead to a fairly low PDIV if the start of one coil is close to the end of the other.
  • Or coils are wide away meaning that PDIV should be very high compared to other insulation.
  • Phase U presents the lowest coil to coil insulation of all phase at This weakness obviously does not appears with AC test because all coils are at the same voltage.
  • This may be explain by the fact that this motor has already be tested numerous time regarding partial discharge level with an inverter.

Coil Configurations and Electric Stator Characteristics

  • Take advantage of having access to its 12 coils and connect them to • ) • ) • ).
  • In terms of functional performance, the number of turns per phase ), therefore the base b b represents the speed from which the consequently the current consumed by the motor.
  • In the nominal case when all phases are star-connected, the PDIV could not be determined which is consistent with the fact that the most stressing case is when only one phase is tested.
  • When comparing results with coils results for phases V and W one could observe that it is likely that phase V presents a turn-to turn PD whereas phase W presents a coil-to coil PD.
  • This is due to the fact that the current supplied is lower and the tendency of SiC switch to produce faster dV/dt under low current, the applied electrical stress regarding turn insulation is thus higher.

Preventing PD in Turn-to-Turn Insulation

  • The critical area of insulation for phase V is the turn-to-turn insulation of coil 2 (named blue/yellow).
  • It thus seems interesting to change the coil connection to try to reduce the electrical stress applied to it.
  • The weakest coil V2 was connected in series to coil V4 which does not present turn-to-turn PD.
  • It can be seen in that the electrical stress applied to the turn-to-turn critical area has been decreased because PD are no longer observed at coil V2 PDIV.

Preventing PD in Coil to Coil Insulation

  • Coil insulation between W1 ( yellow) and W4 .
  • The authors can see in that the electrical stress decreased because there is not any PD at the voltage previously observed.
  • As before, voltage is now divided between coils in series which, in turn, reduce the coil to coil stress.
  • Bus voltage has been increased up to 970VDC without observing any PD signals.

Discussion about Winding Configuration Influence

  • Using results from coil-to-coil and impulse tests, the advantage of the same insulation system.
  • What could have been expected from a simple voltage distribution analysis on coils have been tested experimentally on a typical electric stator.
  • This holds true for this segregating coils and coils of few turns which does not prevent Although these conclusions could not be directly extended on any enhanced PDIV performance on other electric motor even without knowing a priori of all insulation in the motor.
  • Obviously, this better PDIV performance come at a cost regarding electromechanical torque and speed.

Summary and Conclusions

  • This paper illustrates with stator n°2 the robustness of non-intrusive detection method at low pressure under SiC impulse voltage.
  • Both PDIV with a better signal to noise ratio for the latter.
  • The experimental set-up consisting in a three phases SiC inverter drive and a vacuum chamber is able to reproduce any PWM waveform on a wide range of electric stator both at atmospheric pressure and at low altitude.
  • The failure of stator n°1 illustrates the destructive potential of non-detected partial discharge.
  • This study showed how, without any knowledge of PDIV of each similar insulation system and identical electromechanical performance to evaluate insulation performance.

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Content maybe subject to copyright    Report

To cite this version : Billard, Thibaut and Abadie, Cédric and Taghia, Bouazza
Advanced partial discharge testing of 540V aeronautic motor fed by SiC
inverter under altitude conditions. (2017) In: SAE 2017 AeroTech Congress &
Exhibition, 26 September 2017
- 28 September 2017 (Fort Worth, United
States). (Unpublished)
Open Archive TOULOUSE Archive Ouverte (OATAO)
OATAO is an open access repository that collects the work of Toulouse researchers and
makes it freely available over the web where possible.
This is an author-deposited version published in : http://oatao.univ-toulouse.fr/
Eprints ID : 18282
To link to this article: DOI: 10.4271/2017-01-2029
URL : http://dx.doi.org/10.4271/2017-01-2029
Any
pository
administrator:
staff-oatao@listes-diff.inp-toulouse.fr

Introduction
Background
Optimization of energy sources aboard aircraft and permanent
improvements in more electric technologies are pushing the
aeronautic industry to aim for the more electrical aircraft (MEA).
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power generation, distribution and conversion are easier because
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achieved than with traditional hydraulic systems needing large, heavy
and maintenance intensive distribution system.
But, this shift towards MEA is not without consequences on the
electrical stress the insulation system has to withstand. Thus, with
primary voltage increasing, power distribution architecture evolution
and high power density power electronics, partial discharge (PD) is
now a serious cause of concern for aircraft integrator, system designer
and component manufacturer. Once PDs are occurring regularly,
degradation of the insulation system until premature failure of the
aircraft system is irremediable.
Scope and Goal of the Work
This topic of interest has already been discussed by several key actors
of the aerospace industry, research center such as US Air force
laboratory or international academic actors. All acknowledge that PD
risk in a harsh aeronautic environment where pressure, temperature
and humidity variation, electrical stress created by inverter and
harness length and weight increase. [1, 2, 3, 4]
Among key issues of aeronautic companies that has to be investigated
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electric motors in an electrically non-intrusive way and under
representative aeronautic environment when fed by a silicon carbide
(SiC) inverter drive will be addressed in this paper and will be the
main contribution.
Advanced Partial Discharge Testing of 540V Aeronautic
Motors Fed by SiC Inverter under Altitude Conditions
Thibaut BILLARD, Cedric Abadie, and Bouazza Taghia
IRT Saint-Exupery
CITATION: %,//$5'7$EDGLH&DQG7DJKLD%$GYDQFHG3DUWLDO'LVFKDUJH7HVWLQJRI9$HURQDXWLF0RWRUV)HGE\6L&
Inverter under Altitude Conditions," SAE Technical Paper 2017-01-2029, 2017, doi:10.4271/2017-01-2029.
Abstract
The present paper reports non-electrically intrusive partial discharge
investigations on aeronautic and electric vehicle motors 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
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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. A vacuum chamber is used to simulate altitude while the
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¿OWHULQJDQGZDYHOHW
based signal processing provided partial discharge detection.
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voltage magnitude trigger partial discharge events. The study helps to
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limits of the insulation system under various pressure and electrical
conditions. It is shown that a representative insulation system
performance picture could be drawn 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
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and thoughts about future work regarding advanced test procedure.

Indeed, it has been recently demonstrated that on-line PD detection
on electric motors fed by inverter drive proves to be possible using
non-intrusive sensors. A broad range of operating electric motors
have been tested on industrial test benches under nominal conditions
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detection method [5]. Moreover, a previous analysis illustrated the
gains of carrying out a detailed and progressive analysis of the
insulation system both under AC and impulse voltage from twisted
pair sample to a complete stator [6]. But, as a whole, a key link in the
testing chain was still missing. So, in order to make one step further,
a unique and new testing mean has been designed at IRT Saint-
Exupéry and will be used in this paper. It is a highly customizable
three phases SiC inverter drive with a high voltage DC bus of 1kV.
The aim of this experimental set-up is thus to help electric motor
designer evaluate the quality of the insulation system under harsh
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operating conditions. The three kind of PD tests conditions (simple
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thus complementary and give the full picture of the insulation system.
Outline
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system will be recalled. In a second step, key features of more
electrical aircraft will be recalled and how they relate to the
innovative experimental set-up used here. Then, its main
characteristics will be presented and an analysis is made regarding
the relation between time, dV/dt and overvoltage.
The impact of a SiC inverter drive on the non-intrusive detection
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and wavelet numerical processing will be presented as a mean to
double-check partial discharge inception (PDIV) values.
Then, details of the 3 stator will be presented and will be followed by
tests results and analysis. Stator n°1 illustrates the potential
consequences of undetected partial discharge on the insulation system
and its consecutive failure. Stator n°2 illustrates the performance of
the whole experimental set-up both at atmospheric and low pressure.
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discussion is followed by details of future work.
Partial Discharge Basics
What is a Partial Discharge? IEEE Definition
$FFRUGLQJWR,(((VWDQGDUGGH¿QLWLRQ>7] a partial discharge is:
An electrical discharge that only partially bridges the insulation
between conductors. A transient gaseous ionization occurs in an
insulation system when the electric stress exceeds a critical value,
and this ionization produces partial discharges.
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opening time 30s [6]
Consequences of Partial Discharge
Partial discharge events have been known and studied for more than a
century, starting with Paschen, Peek and Townsend among others.
Partial discharges are feared because they contribute to the
degradation of the insulation system and lead to its premature failure
[8] as will be shown in this paper.
Partial Discharge in More Electrical Aircraft
With the recent increase in voltage from 115 V AC to 230 V AC or
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Moreover, it is known from Paschen curve that partial discharge risk
is highly linked to pressure level. Since this variation is non-linear
with pressure, it is assumed that no simple scale factor could be
applied to predict partial discharge inception voltage from results at
atmospheric pressure. Indeed, it is impossible to state a priori that the
weakest insulation point test at atmospheric pressure is also the
weakest insulation point at low pressure so that a scale factor is a
sound hypothesis. It is thus mandatory to carry out test across the
whole range of pressure.
Partial Discharge Inception Voltage
According to IEEE Standard [7], PDIV is
The lowest voltage at which continuous partial discharges (PDs)
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permissible background noise) occur as the applied voltage is
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including the rate at which the voltage is increased as well as the
previous history of the voltage applied to the winding or
component thereof
PDIV could be expressed either at RMS or peak voltage depending
on the applied voltage during test.

During partial discharge test of equipment, PDIV is usually a
representation of the insulation system quality. In other words, it
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partial discharge occurs.
It is thus of a critical importance to that tests are robust, easy to
reproduce and relevant for the foreseen application. It is also
important to have an accurate PDIV measurement method that could
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simple material characterization test at atmospheric pressure, to an
operating system in a low pressure environment.
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have dramatic consequence on its reliability, leading to short-circuits
creating electrical arcs. Safe level of target PDIV should be set in order
to ensure equipment are PD free during operational life of the system.
More Electrical Aircraft Paradigm
The MEA approach underlines the use of electrical system for
non-propulsive application such as environmental control systems
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Other applications such as electrical taxiing or anti-icing are also
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aircraft has no on-engine hydraulic power generation and bleed air
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Key Role of Highly Integrated Power Electronics
A key enabler of such development is the breakthrough in high power
density, high voltage and reliable silicon-based power semiconductor
switching device such as insulated gate bipolar transistor (IGBT).
It is expected that state-of-the-art switching device such as Silicon
Carbide (SiC) or Gallium Nitride (GaN) will dramatically improve
inverter drive, converters, motor controller and other semiconductor
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The evolution of power electronics towards fast switching in the
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primary voltage is putting even more stress on motor insulation
system [9, 10, 11, 12]
The combination of harness length, fast rise time is creation
overvoltage at motor terminals and an uneven voltage distribution is
found on coils increasing electrical stress on the turn-to-turn
insulation system. The following experimental set-up aims to recreate
such electrical stresses
Experimental Set-Up
Power Supplies
High Speed High Voltage Power Amplifier
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10kV peak and a maximum of 40mA RMS current with a bandwidth
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tested such as AC at various frequency, square bipolar with adaptable
duty cycle, frequency and other point-per-point signals.
High Voltage SiC Inverter Drive
An inverter drive has been designed at IRT Saint Exupéry to recreate
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voltage, two 15kW 500V ElektroAutomatic DC power supplies are in
series with the mid-point grounded, the total DC bus voltage could
remotely be varied from ± 10V to ± 500V.
The inverter drive consists in three 1700V SiC Cree power modules
delivering fast rise times on each phase with driver boards accepting
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Matlab-Simulink model could be used to control the inverter drive
thanks to the use of an OPAL-RT real time calculator. Switching
frequency, carrier frequency and modulation factor could easily be
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per phase (enable and command) allowing the use of the inverter as a
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High Voltage Measurements
Voltage level are monitored using a Testec TT-SI 9010A (1/1000
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Signal Acquisition
Analog to Digital Conversion
Data are displayed and recorded using a Keysight DSOS204A
oscilloscope with a sampling rate of 20GSa/s and numerical bandwidth
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numerically, the high resolution mode (12 bits) is used instead of the
peak detect mode at the higher sampling frequency available.
Analog High Pass-Filtering
When performing measurement using non-intrusive sensor, it is usual
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remove noise coming from inverter drive switches or power
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have been used in the following experiments
Partial Discharge Sensors
Technological research at IRT Saint-Exupéry are focused on
non-intrusive sensors. These sensors and associated method have
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both electric motor in automotive [2] and aeronautic test benches [5].
Capacitive Sensor
The non-intrusive sensor used to detect partial discharge is taking
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sensor behavior in the next part. This sensor has already been used in
numerous study, particularly [2] and [6].

Environmental Conditions
All the tests have been carried out within a grounded vacuum
chamber, acting as a faraday chamber, connected to a vacuum pump.
The system is currently able to regulate pressure from atmospheric to
20mbars with an accuracy of +/- 5 mbars.
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Table 1. Inverter drive operating point
Rise Time and Overvoltage Measurement
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time dependent rise time and overvoltage analysis has been carried
out while feeding a three phase electric. Measurements were
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probe between the DC- and the output of the power module. Table 1
details the used operating point.
In IEC 60034-18-41 standard [13], stress magnitude categories are
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nominal DC bus voltage. It is thus interesting to track the time
dependent evolution of this parameters to check when the electrical
stress is the most severe.
Typical SiC inverter behavior could be observed on both rise time
and overvoltage which is both are current dependent. Although
current was not monitored during measurement, the time dependency
and periodicity could be observed on rise time which is maximum at
current polarity reversal while minimum when current is at his
highest value. On the contrary, overvoltage is maximum when current
is at its maximum while overvoltage is minimum at current polarity
reversal. As a result, the electrical stress created by the combination
of dV/dt and overvoltage is time dependant.
These phenomena could be explained by the very nature of SiC
switch, current magnitude, grid resistor and other power electronics
characteristics. In essence, dV/dt is maximum for low current turn-on
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shown on )LJ for falling edge in red.
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phase could be observed by small perturbations on overvoltage.
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Citations
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Journal ArticleDOI
TL;DR: It is shown that a representative insulation system performance picture could be drawn experimentally and used to enhance insulation design and manufacturing choices and to demonstrate the feasibility of PD test of the insulation system on a different type of motor under such conditions, both electrically and environmentally.
Abstract: 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.

18 citations


Cites result from "Advanced Partial Discharge Testing ..."

  • ...The results presented in this paper are part of a larger study [21]....

    [...]


Journal ArticleDOI
Bouazza Taghia1, Bernardo Cougo, Hubert Piquet1, David Malec1  +2 moreInstitutions (1)
TL;DR: A fast and accurate modeling methodology is proposed to predict transient overvoltage in Adjustable Speed Drives and the impact of SiC inverter technology on overvoltages at motor terminals is analyzed.
Abstract: Key points in the development of More Electrical Aircraft (MEA) are currently DC power distribution in higher voltage levels (540 V) and the use of disruptive technology such as Wide BandGap (WBG) semiconductors in power inverters. Using WBG components (SiC and GaN) increases the power converter mass density. However, fast switching of WBG components (tens of kV/s) induces voltage transient overshoots due to parasitic elements within the inverter. In addition, propagation and reflection phenomena along the harness connected to this inverter, even for small lengths, cause a significant voltage overshoot across the loads. Such overvoltage in Adjustable Speed Drives (ASD: association of inverter, harness and motor) supplied by the new HVDC 540 V aeronautical network could be fatal for the Electrical Insulation System (EIS). This paper proposes a fast and accurate modeling methodology to predict transient overvoltage; it allows us to analyze the impact of SiC inverter technology on overvoltage at motor terminals.

8 citations


Cites background from "Advanced Partial Discharge Testing ..."

  • ...Its lifetime can be reduced by partial discharges and breakdown [7]....

    [...]


Proceedings ArticleDOI
24 Jun 2020
TL;DR: A particle swarm optimization algorithm is applied to automatically find the optimal parameters for an accurate behavioral model of an automotive grade SiC MOSFET that properly fits the datasheet curves.
Abstract: Power device modeling plays an important role at the design stage of power conversions systems, especially in the automotive and aircraft sectors. In this context, it is important to obtain in short time an accurate model that account for the mutual interaction of thermal and electrical quantities. The behavioral model is the best approach because it consists of a set of equations that emulates the device behavior at terminals level and can be easily implemented in a SPICE simulation tool, largely adopted both in industrial and academic contexts. The major issue of the behavioral model is to choose the equations parameters such that the simulations results fit the measurement data. In this paper, this problem is tackled by means of a particle swarm optimization algorithm. It is applied to automatically find the optimal parameters for an accurate behavioral model of an automotive grade SiC MOSFET that properly fits the datasheet curves. The comparison between the waveforms obtained by experimental tests and the SPICE simulations in a double test has confirmed the accuracy of the model.

3 citations


Cites background from "Advanced Partial Discharge Testing ..."

  • ...The SiC MOSFET is a suitable device also in this context where high efficiency, high power density and high reliability are fundamental [21]-[23]....

    [...]


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Abstract: The latest advances in electric and electronic aircraft technologies from the point of view of an "all-electric" aircraft are presented herein. Specifically, we describe the concept of a "more electric aircraft" (MEA), which involves removing the need for on-engine hydraulic power generation and bleed air off-takes, and the increasing use of power electronics in the starter/generation system of the main engine. Removal of the engine hydraulic pumps requires fully-operative electrical power actuators and mastery of the flight control architecture. The paper presents a general overview of the electrical power generation system and electric drives for the MEA, with special regard to the flight controls. Some discussion regarding the interconnection of nodes and safety of buses and protocols in distributed systems is also presented

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Abstract: Medium and high voltage power cables are widely used in the electrical industry with substantial growth over the last 20-30 years ago, particular in the use of XLPE insulated systems. Ageing of the cable insulation is becoming an increasing problem that requires development of reliable methods for on-line condition assessment. For insulation condition assessment of MV and HV cables, partial discharge (PD) monitoring is one of the most effective techniques. However on-site and on-line PD measurements are affected by electromagnetic interference (EMI) that makes sensitive PD detection very difficult, if not impossible. This paper describes implementation of wavelet transform techniques to reject noise from on-line partial discharge measurements on cables. A new wavelet threshold determination method is proposed with the technique. With implementation of this novel de-noising method, PD measurement sensitivity has been greatly improved. In addition, a full AC cycle data recovery can be achieved instead of focusing only on recovering individual PD pulses. Other wavelet threshold de-noising methods are discussed and examined under a noisy environment to compare their performance with the new method proposed here. The method described here has been found to be superior to the other wavelet-based methods

200 citations


Proceedings ArticleDOI
Xavier Roboam1Institutions (1)
27 Jun 2011
TL;DR: The main trends and future challenges of electrical networks embedded in “more electrical aircraft” especially in the fields of industrial electronics and energy conversion are described, including reversible and hybrid HVDC networks including new storage devices.
Abstract: This paper describes the main trends and future challenges of electrical networks embedded in “more electrical aircraft” especially in the fields of industrial electronics and energy conversion. In the first part, the current context and new standards are put forward, emphasizing the main evolutions on aircraft architectures, from AC fixed frequency networks, variable frequency to “Bleedless” architectures. The main characteristics of more electrical aircraft are discussed, especially in terms of power management rationalization, maintenance, health monitoring capacity, etc. The second part deals with the new trends and challenges of “more and more” electrical aircraft linked with power integration and new architecture with HVDC standard. Recent methodological orientations towards “Integrated Optimal Design” are discussed with representative examples. Finally, new trends towards reversible and hybrid HVDC networks including new storage devices are also emphasized.

117 citations



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